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18. ch 17_343-360_ BODY DEFENSES_ IMMUNITY_ AND VACCINES Powered By Docstoc
					346   ✦   CHAPTER SEVENTEEN

C    hapter 5 presents a rather frightening list of harmful
     organisms that surround us in our environment. For-
tunately, most of us survive contact with these invaders
                                                                   Finally, an individual’s condition, or predisposition,
                                                               to infection is also important. Disease organisms are
                                                               around us all the time. Why does a person only occasion-
and even become more resistant to disease in the process.      ally get a cold, flu, or other infection? Part of the answer
The job of protecting us from these harmful agents be-         lies in the person’s condition, as influenced by general
longs in part to certain blood cells and to the lymphatic      physical and emotional health, nutrition, living habits,
system, which together make up our immune system.              and age.
    The immune system is part of our general body de-
                                                               Checkpoint 17-1 What are some factors that influence the oc-
fenses against disease. Some of these defenses are non-        currence of infection?
specific; that is, they are effective against any harmful
agent that enters the body. Other defenses are referred to
as specific; that is, they act only against a certain agent
and no others.                                                 ◗ Nonspecific Defenses
                                                               The features that protect the body against disease are usu-
                                                               ally considered as successive “lines of defense,” beginning
◗ Why Do Infections Occur?                                     with the relatively simple or outer barriers and proceed-
Although the body is constantly exposed to pathogenic          ing through progressively more complicated responses
invasion, many conditions determine whether an infec-          until the ultimate defense mechanism—immunity—is
tion will actually occur. Pathogens have a decided prefer-     reached.
ence for certain body tissues and must have access to
these tissues. Some viruses attack only nervous tissue.        Chemical and Mechanical Barriers
The poliovirus, for example, may be inhaled or swallowed       Part of the first line of defense against invaders is the skin,
in large numbers and therefore may come into direct con-       which serves as a mechanical barrier as long as it remains
tact with the mucous membranes lining the respiratory          intact. A serious danger to burn victims, for example, is
and digestive tracts, yet it causes no apparent disorder of    the risk of infection as a result of skin destruction.
these tissues. In contrast, the viruses that cause influenza        The mucous membranes that line the passageways
and the common cold do attack these mucous mem-                leading into the body also act as barriers, trapping foreign
branes. HIV, the virus that causes AIDS, attacks a certain     material in their sticky secretions. The cilia in membranes
type of T cell (lymphocyte), which has surface receptors       in the upper respiratory tract help to sweep impurities
for the virus.                                                 out of the body.
    The portal of entry is an important condition influ-            Body secretions, such as tears, perspiration, and
encing the occurrence of infection. The respiratory tract      saliva, wash away microorganisms and may contain acids,
is a common entrance route for pathogens. Other impor-         enzymes, or other chemicals that destroy invaders. Diges-
tant avenues of entry include the digestive system and the     tive juices destroy many ingested bacteria and their tox-
tubes that open into the urinary and reproductive sys-         ins.
tems. Any break in the skin or in a mucous membrane al-             Certain reflexes aid in the removal of pathogens.
lows organisms such as staphylococci easy access to            Sneezing and coughing, for instance, tend to remove for-
deeper tissues and may lead to infection, whereas unbro-       eign matter, including microorganisms, from the upper
ken skin or mucous membranes are usually not affected.         respiratory tract. Vomiting and diarrhea are ways in
    The virulence (VIR-u-lens) of an organism, or the or-      which toxins and bacteria may be expelled.
ganism’s power to overcome its host’s defenses, is another
important factor. Virulence has two aspects: one may be         Checkpoint 17-2 What tissues constitute the first line of de-
thought of as “aggressiveness,” or invasive power; the          fense against the invasion of pathogens?
other is the organism’s ability to produce toxins (poi-
sons) that damage the body. Different organisms vary in        Phagocytosis
virulence. The virulence of a specific organism also can
change; the influenza virus, for example, can be more          Phagocytosis is part of the second line of defense against
dangerous in some years than in others. Organisms may          invaders. In the process of phagocytosis, white blood cells
gain virulence as they pass from one infected host to an-      take in and destroy waste and foreign material (see Fig.
other.                                                         13-6 in Chapter 13). Neutrophils and macrophages are
    The dose (number) of pathogens that invade the body        the main phagocytic white blood cells. Neutrophils are a
also is a determining factor in whether or not an infection    type of granular leukocyte. Macrophages are derived from
develops. Even if the virulence of a particular organism       monocytes, a type of agranular leukocyte. Both types of
happens to be low, infection may occur if a large number       cells travel in the blood to infection sites. Some of the
enter the body.                                                macrophages remain fixed in the tissues, for example, in
                                                                      BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 347

the skin, liver, lungs, lymphoid tissue, and bone marrow,           enlarged and tender, a sign that they are performing their
to fight infection and remove debris.                               protective function by working overtime to produce
                                                                    phagocytic cells that “clean” the lymph flowing through
Natural Killer Cells                                                them.
The natural killer (NK) cell is a type of lymphocyte dif-
ferent from those active in specific immunity, which are
described later. NK cells can recognize body cells with ab-         An increase in body temperature above the normal range
normal membranes, such as tumor cells and cells infected            can be a sign that body defenses are at work. When
with virus, and, as their name indicates, can destroy them          phagocytes are exposed to infecting organisms, they re-
on contact. NK cells are found in the lymph nodes,                  lease substances that raise body temperature. Fever
spleen, bone marrow, and blood. They destroy abnormal               boosts the immune system in several ways. It stimulates
cells by secreting a protein that breaks down the cell              phagocytes, increases metabolism, and decreases certain
membrane, but the way in which they find their targets is           organisms’ ability to multiply.
not yet completely understood.                                          A common misperception is that fever is a dangerous
                                                                    symptom that should always be eliminated. Control of
Inflammation                                                        fever in itself does little to alter the course of an illness.
                                                                    Healthcare workers, however, should always be alert to
Inflammation is the body’s effort to get rid of anything
                                                                    fever development as a possible sign of a serious disorder
that irritates it or, if this is not possible, to limit the harm-
                                                                    and should recognize that an increased metabolic rate
ful effects of the irritant. Inflammation can occur as a
                                                                    may have adverse effects on the hearts of weak patients.
result of any irritant, not only microorganisms. Friction,
fire, chemicals, x-rays, and cuts or blows all can be clas-
sified as irritants. If irritation is caused by pathogenic in-
vasion, the resulting inflammation is termed an infection.          Certain cells infected with a virus release a substance that
With the entrance of pathogens and their subsequent                 prevents nearby cells from producing more virus. This
multiplication, a whole series of defensive processes be-           substance was first found in cells infected with influenza
gins. This inflammatory reaction is accompanied by four             virus, and it was called interferon because it “interferes”
classic symptoms: heat, redness, swelling, and pain, as de-         with multiplication and spread of the virus. Interferon is       17
scribed below.                                                      now known to be a group of substances. Each is abbrevi-
     When tissues are injured, histamine (HIS-tah-mene)             ated IFN with a Greek letter, alpha ( ), beta ( ), or
and other substances are released from the damaged cells,           gamma ( ) to indicate the category of interferon and ad-
causing the small blood vessels to dilate (widen). More             ditional letters or numbers to indicate more specific
blood then flows into the area, resulting in heat, redness,         types, such as 2a or 1b.
and swelling.                                                            Pure interferons are now available in adequate quan-
     With the increased blood flow come a vast number of            tities for treatment because they are produced by genetic
leukocytes. Then a new phenomenon occurs: the walls of              engineering in microorganisms. They are used to treat
the tiny blood vessels become “coarsened” in texture (as            certain viral infections, such as hepatitis. Interferons are
does a piece of cloth when it is stretched). Blood flow             also of interest because they act nonspecifically on cells of
slows down, and the leukocytes move through these al-               the immune system. They have been used with varying
tered walls and into the tissue, where they can reach the           success to boost the immune response in the treatment of
irritant directly. Fluid from the blood plasma also leaks           malignancies, such as melanoma, leukemia, and Kaposi
out of the vessels into the tissues and begins to clot.             sarcoma, a cancer associated with AIDS. Interestingly, in-
     When this response occurs in a local area, it helps            terferon is used to treat the autoimmune disorder mul-
prevent the spread of the foreign agent. The mixture of             tiple sclerosis (MS), because it stimulates cells that de-
leukocytes and fluid, the inflammatory exudate, causes              press the immune response.
pressure on the nerve endings, which combined with the
increased amount of blood in the vessels, causes the pain           Checkpoint 17-3 What are some nonspecific factors that help
of inflammation.                                                    to control infection?
     As the phagocytes do their work, large numbers of
them are destroyed, so that eventually the area becomes
filled with dead leukocytes. The mixture of exudate, liv-           ◗ Immunity
ing and dead white blood cells, pathogens, and destroyed
tissue cells is pus.                                                Immunity is the final line of defense against disease. Im-
     Meanwhile, the lymphatic vessels begin to drain fluid          munity to disease can be defined as an individual’s power
from the inflamed area and carry it toward the lymph                to resist or overcome the effects of a particular disease
nodes for filtration. The regional lymph nodes become               agent or its harmful products. In a broader sense, the im-

mune system will recognize any foreign material and at-               Some members of a given group have a more highly
tempt to rid the body of it, as occurs in tissue transplan-       developed individual immunity to specific diseases. For
tation from one individual to another. Immunity is a se-          example, some people are prone to cold sores (fever blis-
lective process; that is, immunity to one disease does not        ters) caused by herpes virus, whereas others have never
necessarily cause immunity to another. This selective             shown signs of this type of infection. Newspapers and
characteristic is called specificity (spes-ih-FIS-ih-te).         magazines sometimes feature the advice of an elderly per-
    There are two main categories of immunity:                    son who is asked to give his or her secret for living to a
                                                                  ripe old age. Some elderly people may say that they lived
◗   Inborn immunity is inherited along with other charac-         a carefully regulated life with the right amount of rest, ex-
    teristics in a person’s genes.                                ercise, and work, whereas others may boast of drinking
◗   Acquired immunity develops after birth. Acquired im-          alcohol, smoking, not exercising, and other kinds of un-
    munity may be obtained by natural or artificial means;        healthy behavior. However, it is possible that the latter
    in addition, acquired immunity may be either active or        group resisted infection and maintained health despite
    passive.                                                      their habits, rather than because of them, thanks to in-
                                                                  herited resistance factors.
    Figure 17-1 summarizes the different types of immu-
nity. Refer to this diagram as we investigate each category       Acquired Immunity
in turn.
                                                                  Unlike inborn immunity, which is due to inherited fac-
                                                                  tors, acquired immunity develops during a person’s life-
Inborn Immunity                                                   time as that person encounters various specific harmful
Both humans and animals have what is called a species             agents.
immunity to many of each other’s diseases. Although cer-              If the following description of the immune system
tain diseases found in animals may be transmitted to hu-          seems complex, bear in mind that from infancy on, your
mans, many infections, such as chicken cholera, hog               immune system is able to protect you from millions of
cholera, distemper, and other animal diseases, do not af-         foreign substances, even synthetic substances not found
fect human beings. However, the constitutional differ-            in nature. All the while, the system is kept in check, so
ences that make human beings immune to these disorders            that it does not usually overreact to produce allergies or
also make them susceptible to others that do not affect           mistakenly attack and damage your own body tissues.
different species. Such infections as measles, scarlet fever
and diphtheria do not appear to affect animals who come           Checkpoint 17-4 What is the difference between inborn and
                                                                  acquired immunity?
in contact with infected humans.

                                                                                     Antigens An antigen (AN-te-jen)
                        Immunity                                                     (Ag) is any foreign substance that en-
                                                                                     ters the body and induces an immune
                                                                                     response. (The word is formed from
     Inborn                                   Acquired                               antibody       gen because an antigen
                                                                                     stimulates production of antibody.)
     Species                                                                         Most antigens are large protein mole-
    Individual                                                                       cules, but carbohydrates and some
                                                                                     lipids may act as antigens. Antigens
                                Natural                        Artificial            may be found on the surface of patho-
                                                                                     genic organisms, on the surface of red
                                                                                     blood cells and tissue cells, on pollens,
                                                                                     in toxins, and in foods. The critical
                                                                                     feature of any substance described as
                       Active           Passive          Active        Passive       an antigen is that it stimulates the ac-
                                                                                     tivity of certain lymphocytes classified
                     Contact with      Placenta       Vaccine:    Immune             as T or B cells.
                     the disease      Mother's milk     Killed     serum
                                                     Attenuated                      T Cells Both T and B cells come from
                                                       Toxoid                        hematopoietic (blood-forming) stem
                                                     Component                       cells in bone marrow, as do all blood
                                                  Recombinant DNA                    cells. The T and B cells differ, how-
                                                                                     ever, in their development and their
                        Figure 17-1    Types of immunity.                            method of action. Some of the imma-
                                                                       BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 349

ture stem cells migrate to the thymus and become T cells,            cytic vesicles (Fig. 17-2). They then insert fragments of
which constitute about 80% of the lymphocytes in the cir-            the foreign antigen into their plasma membrane. The for-
culating blood. While in the thymus, these T lymphocytes             eign antigens are displayed on the macrophage’s surface
multiply and become capable of combining with specific               in combination with antigens that a T cell can recognize
foreign antigens, at which time they are described as sen-           as belonging to the “self.” Self antigens are known as
sitized. These thymus-derived cells produce an immunity              MHC (major histocompatibility complex) antigens be-
that is said to be cell-mediated immunity.                           cause of their importance in cross-matching for tissue
    There are several types of T cells, each with different          transplantation. They are also known as HLAs (human
functions. The different types of T cells and some of their          leukocyte antigens), because white blood cells are used in
functions are as follows:                                            testing tissues for compatibility. Macrophages and other
                                                                     cells that present antigens to T cells are known as APCs
◗   Cytotoxic T cells (Tc) destroy foreign cells directly.           (antigen-presenting cells).
◗   Helper T cells (Th)release substances known as inter-                For a T cell to react with a foreign antigen, that anti-
    leukins (in-ter-LU-kinz) (IL) that stimulate other lym-          gen must be presented to the T cell along with the MHC
    phocytes and macrophages and thereby assist in the de-           proteins. A special receptor on the T cell must bind with
    struction of foreign cells. (These substances are so             both the MHC protein and the foreign antigen fragment
    named because they act between white blood cells).               (see Fig. 17-2). The activated Th then produces inter-
    There are several subtypes of these helper T cells, one          leukins (ILs), which stimulate other leukocytes, such as
    of which is infected and destroyed by the AIDS virus             B cells. There are many different types of interleukins,
    (HIV). The HIV-targeted T cells have a special surface           and they participate at different points in the immune re-
    receptor (CD4) to which the virus attaches.                      sponse. They are produced by white cells and also by fi-
◗   Regulatory T cells (Treg) suppress the immune re-                broblasts (cells in connective tissue that produce fibers)
    sponse in order to prevent overactivity. These T cells           and by epithelial cells. Because ILs stimulate the cells ac-
    may inhibit or destroy active lymphocytes.                       tive in immunity, they are used medically to boost the im-
◗   Memory T cells remember an antigen and start a rapid             mune system.
    response if that antigen is contacted again.
                                                                      Checkpoint 17-5 What is an antigen?
    The T cell portion of the immune system is generally
responsible for defense against cancer cells, certain                                                                                 17
                                                                     Checkpoint 17-6 List four types of T cells.
viruses, and other pathogens that grow within cells (in-
tracellular parasites), as well as for the rejection of tissue
transplanted from another person.                                    B Cells and Antibodies An antibody (Ab), also
                                                                     known as an immunoglobulin (Ig), is a substance pro-
The Role of Macrophages Macrophages are phago-                       duced in response to an antigen. Antibodies are manufac-
cytic white blood cells derived from monocytes (their                tured by B cells (B lymphocytes), another type of lym-
name means “big eater”). They act as processing centers              phocyte active in the immune system. These cells must
for foreign antigens. They ingest foreign proteins, such as          mature in the fetal liver or in lymphoid tissue before be-
disease organisms, and break them down within phago-                 coming active in the blood.

Foreign antigen                                                  T cell receptor     Helper T cell
        MHC protein
                                                       Antigen fragment                                        Activated helper
               Lysosome        Phagocytic vesicle                                                              T cell


 1 Macrophage ingests                                            2 Macrophage presents                     3 Activated T cell
   foreign antigen                                                 antigen fragment with                     produces interleukin,
                                                                   MHC proteins to                           which stimulates
                                                                   helper T cell                             other leukocytes

Figure 17-2 Activation of a helper T cell by a macrophage (antigen-presenting cell). ZOOMING IN ✦ What is contained in
the lysosome that joins the phagocytic vesicle?

                                                                                        Box 17-1 provides further information
                                                                                        about the different types of antibodies.
                                                                                            Some antibodies produced by B
                                                                                        cells remain in the blood to give long-
                                                                                        term immunity. In addition, some of
                           B cell with specific antigen receptor                        the activated B cells do not become
                                                                                        plasma cells but, like certain T cells,
                                                                                        become memory cells. On repeated
                                                        B cell binds to antigen         contact with an antigen, these cells are
                                                                                        ready to produce antibodies immedi-
                                                                                        ately. Because of this “immunologic
                                                                                        memory,” one is usually immune to a
                                           Activated                                    childhood disease after having it.
                                            B cell
                                                                                         Checkpoint 17-7 What is an antibody?

                                                                                         Checkpoint 17-8 What type of cells pro-
                                                                                         duce antibodies?

                                                                                        The Antigen–Antibody
                                                               B                        Reaction
                                                             memory                     The antibody that is produced in re-
                                                                                        sponse to a specific antigen, such as a
                          Plasma                                                        bacterial cell or a toxin, has a shape
                           cells                                                        that matches some part of that antigen,
                                                                                        much in the same way that the shape
                                                                                        of a key matches the shape of its lock.
                                                                                        The antibody can bind specifically to
                                                                                        the antigen that caused its production
                                                                                        and thereby destroy or inactivate it.
                                                                                        Antigen–antibody interactions are il-
                                                                                        lustrated and their protective effects
                                                                                        are described in Table 17-1.

                                                                                        Complement The destruction of
                                            Antibodies                                   foreign cells sometimes requires the en-
Figure 17-3 Activation of B cells. The B cell combines with a specific antigen. The      zymatic activity of a group of nonspe-
cell divides to form plasma cells, which produce antibodies. Some of the cells develop   cific proteins in the blood, together
into memory cells, which protect against reinfection. ZOOMING IN ✦ What two types        called complement. Complement pro-
of cells develop from activated B cells?                                                 teins are always present in the blood, but
                                                                                         they must be activated by antigen–
                                                                                         antibody complexes or by foreign cell
     B cells have surface receptors that bind with a specific       surfaces. Complement is so named because it assists with
type of antigen (Fig. 17-3). Exposure to the antigen stim-          immune reactions. Some of the actions of complement are:
ulates the cells to multiply rapidly and produce large
                                                                    ◗ It coats foreign cells to help phagocytes recognize and
numbers (clones) of plasma cells. Plasma cells produce
                                                                       engulf them.
antibodies against the original antigen and release these
                                                                    ◗ It destroys cells by forming complexes that punch holes
antibodies into the blood, providing the form of immu-
                                                                       in plasma membranes.
nity described as humoral immunity (the term humoral
                                                                    ◗ It promotes inflammation by increasing capillary per-
refers to body fluids).
     Humoral immunity generally protects against circulating
                                                                    ◗ It attracts phagocytes to an area of inflammation.
antigens and bacteria that grow outside the cells (extracellu-
lar pathogens). All antibodies are contained in a portion of          Checkpoint 17-9 What is complement?
the blood plasma called the gamma globulin fraction.
                                                                        BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 351

  Box 17-1     A Closer Look

   Antibodies: A Protein Army That Fights Disease

  A   ntibodies are proteins secreted by plasma cells (activated
      B cells) in response to specific antigens. They are all con-
  tained in a fraction of the blood plasma known as gamma
                                                                     immunoglobulins that vary in molecular size and in function
                                                                     (see below). Studies of these antibody fractions can be helpful
                                                                     in making a diagnosis. For example, high levels of IgM anti-
  globulin. Because the plasma contains other globulins as well,     bodies, because they are the first to be produced in an immune
  antibodies have become known as immunoglobulins (Ig). Im-          response, indicate a recent infection.
  munologic studies have shown that there are several classes of

                         IgG             75%             Found in the blood, lymph, and intestines
                                                         Enhances phagocytosis, neutralizes toxins, and
                                                            activates complement
                                                         Crosses the placenta and confers passive
                                                            immunity from mother to fetus
                         IgA             15%             Found in glandular secretions such as sweat,
                                                            tears, saliva, mucus, and digestive juices
                                                         Provides local protection in mucous membranes
                                                            against bacteria and viruses
                                                         Also found in breast milk, providing passive
                                                            immunity to newborn
                         IgM             5–10%           Found in the blood and lymph
                                                         The first antibody to be secreted after infection
                                                         Stimulates agglutination and activates complement
                         IgD                1%           Located on the surface of B cells                                             17
                         IgE                0.1%         Located on basophils
                                                         Active in allergic reactions and parasitic

Naturally Acquired Immunity                                          infant for about 6 months, at which time the child’s own
                                                                     immune system begins to function. Nursing an infant can
Immunity may be acquired naturally through contact                   lengthen this protective period because of the presence of
with a specific disease organism, in which case, antibod-            specific antibodies in breast milk and colostrum (the first
ies manufactured by the infected person’s cells act against          breast secretion). These are the only known examples of
the infecting agent or its toxins. The infection that trig-          naturally acquired passive immunity.
gers the immunity may be so mild as to cause no symp-
toms (subclinical). Nevertheless, it stimulates the host’s            Checkpoint 17-10 What is the difference between the active
cells to produce an active immunity.                                  and passive forms of naturally acquired immunity?
    Each time a person is invaded by disease organisms,
his or her cells manufacture antibodies that provide im-
munity against the infection. Such immunity may last for
                                                                     Artificially Acquired Immunity
years, and in some cases for life. Because the host is ac-           A person who has not been exposed to repeated small
tively involved in the production of antibodies, this type           doses of a particular organism has no antibodies against
of immunity is called active immunity. See Box 17-2 for              that organism and may be defenseless against infection.
information on how stress affects the immune system.                 Therefore, medical personnel may use artificial measures
    Immunity also may be acquired naturally by the pas-              to cause a person’s immune system to manufacture anti-
sage of antibodies from a mother to her fetus through the            bodies. The administration of virulent pathogens obvi-
placenta. Because these antibodies come from an outside              ously would be dangerous. Instead, laboratory workers
source, this type of immunity is called passive immunity.            treat the harmful agent to reduce its virulence before it is
The antibodies obtained in this way do not last as long as           administered. In this way, the immune system is made to
actively produced antibodies, but they do help protect the           produce antibodies without causing a serious illness. This

                                                                                           protective process is known as vacci-
Table 17•1         Antigen-Antibody Interactions and Their                                 nation (vak-sin-A-shun), or immu-
                   Effects                                                                 nization, and the solution used is
 Interaction                             Effects                                           called a vaccine (vak-SENE). Ordinar-
                                                                                           ily, the administration of a vaccine is
 Prevention of attachment                A pathogen coated with antibody is                a preventive measure designed to pro-
                    Antibody               prevented from attaching to a cell.             vide protection in anticipation of inva-
                                                                                           sion by a certain disease organism.
                                                                                                Originally, the word vaccination
                                                                                           meant inoculation against smallpox.
 Clumping of antigen                     Antibodies can link antigens together,            (The term even comes from the Latin
                                           forming a cluster that phagocytes               word for cow, referring to cowpox,
                  Foreign cell
                                           can ingest.                                     which is used to vaccinate against
                                                                                           smallpox.) According to the World
                                                                                           Health Organization, however, small-
                                                                                           pox has now been eliminated as a
 Neutralization of toxins                Antibodies bind to toxin molecules to             result of widespread immunization
          Toxin                            prevent them from damaging cells.               programs. Mandatory vaccination has
                                                                                           been discontinued because the chance
                                                                                           of adverse side effects from the vaccine
                                                                                           is thought to be greater than the prob-
 Help with phagocytosis                  Phagocytes can attach more easily to              ability of contracting the disease.
           Foreign cell                    antigens that are coated with anti-                  All vaccines carry a risk of adverse
                              Antibody     body.                                           side effects and may be contraindicated
                                                                                           in some cases. People who are im-
                                                                                           munosuppressed, for example, should
                                                                                           not be given vaccines that contain live
                                                                                           virus. Also pregnant women should not
 Activation of complement                When complement attaches to anti-                 receive live virus vaccine because the
            Complement                    body on a cell surface, a series of              virus could cross the placenta and harm
            Antibody                      reactions begins that activates com-             the fetus.
            Foreign cell                  plement to destroy cells.
                                                                                           Types of Vaccines Vaccines can
 Activation of NK cells                  NK cells respond to antibody adhering             be made with live organisms or with
              NK cell                     to a cell surface and attack the cell.
                                                                                           organisms killed by heat or chemicals.
                                                                                           If live organisms are used, they must
              Foreign cell
                                                                                           be nonvirulent for humans, such as
                                                                                           the cowpox virus used for smallpox

Box 17-2           Clinical Perspectives

  Too Much Stress Makes The Immune System Sick

 T   he impact of stress on the immune system is the most
     wide-ranging and significant of its many effects on the
 body. Stressors such as trauma, infection, debilitating disease,
                                                                    ◗   inhibit histamine release from damaged tissues, thereby
                                                                        blocking inflammation and the arrival of phagocytic leuko-
 surgery, pain, extreme environmental conditions, and emo-          ◗   reduce phagocytosis in damaged tissues, thus preventing
 tional distress all hamper immune function. The mechanisms             antigen presentation to (and activation of) both killer T
 responsible for these changes are not yet fully understood. Sci-       cells and helper T cells.
 entists do know that stress causes the hypothalamus to pro-        ◗   inhibit interleukin secretion from helper T cells, thus pre-
 mote the release of ACTH from the anterior pituitary. This
                                                                        venting the immune system from mounting a coordinated
 hormone stimulates the adrenal cortex to release the hormone
 cortisol, which influences a person’s immediate ability to             response to infection.
 overcome any challenge, even stress itself. However, the ab-          Box 12-3, Stress: Mechanisms for Coping, suggests some
 normally high levels of cortisol that appear during periods of     strategies for reducing stress.
 intense stress can actually be harmful. Such levels can:
                                                                         BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 353

immunization, or they must be treated in the laboratory               their toxins. Because of whooping cough’s seriousness in
to weaken them as human pathogens. An organism weak-                  young infants, early inoculation with whooping cough, or
ened for use in vaccines is described as attenuated. In               pertussis (per-TUS-is), vaccine, is recommended. A new
some cases, just an antigenic component of the pathogen               form of the vaccine containing pertussis toxoid causes
is used as a vaccine. Another type of vaccine is made from            fewer adverse reactions than older types that contained
the toxin produced by a disease organism. The toxin is al-            heat-killed organisms. This acellular (aP) vaccine usually
tered with heat or chemicals to reduce its harmfulness,               is given in a mixture with diphtheria toxoid and tetanus
but it can still function as an antigen to induce immunity.           toxoid. The combination, referred to as DTaP, may be
Such an altered toxin is called a toxoid.                             given as early as the second month of life and should be
    The newest types of vaccines are produced from anti-              followed by additional injections at 4, 6, and 15 months
genic components of pathogens or by genetic engineering.              and again when the child enters day care, a school, or any
By techniques of recombinant DNA, the genes for specific              other environment in which he or she might be exposed
disease antigens are inserted into the genetic material of            to one of these contagious diseases. Diphtheria and
harmless organisms. The antigens produced by these or-                tetanus toxoid (Td) is given again at 11 to 12 years of age.
ganisms are extracted and purified and used for immuniza-             A tetanus booster is given when there is a disease risk and
tion. The hepatitis B vaccine is produced in this manner.             the last booster was administered more than 10 years
                                                                      prior to exposure.
Boosters In many cases, an active immunity acquired                       Routine inoculation against Haemophilus influenzae
by artificial (or even natural) means does not last a life-           type B (Hib) has nearly eliminated the life-threatening
time. Circulating antibodies can decline with time. To                meningitis caused by this organism among preschool chil-
help maintain a high titer (level) of antibodies in the               dren. Hib also causes pneumonia and recurrent ear infec-
blood, repeated inoculations, called booster shots, are ad-           tions in young children. Depending on the type used, the
ministered at intervals. The number of booster injections             vaccine is given in either two doses or three doses begin-
recommended varies with the disease and with an indi-                 ning at 2 months of age.
vidual’s environment or range of exposure. On occasion,                   Pneumococcal vaccine (PCV) protects against infec-
epidemics in high schools or colleges may prompt rec-                 tion with pneumococcus, an organism that can cause
ommendations for specific boosters. Table 17-2 lists the              pneumonia and meningitis. Four doses are given between
vaccines currently recommended in the United States for               the ages of 2 and 15 months.
childhood immunizations. The number and timing of
doses varies with the different vaccines.                             Examples of Viral Vaccines Intensive research on
                                                                           viruses has resulted in the development of vaccines for an
Examples of Bacterial Vaccines          Children are                       increasing number of viral diseases. The medical commu-
routinely immunized with vaccines against bacteria or                      nity has achieved spectacular results in eliminating po-
                                                                                               liomyelitis by the use of vaccines. The
                                                                                               first of these was an inactivated polio
Table 17•2 Childhood Immunizations*                                                            vaccine (IVP) developed by Dr. Jonas
                                                                                               Salk and made with killed poliovirus. A
  VACCINE            DISEASE(S)                         SCHEDULE                               more convenient oral vaccine (OPV),
                                                                                               made with live attenuated virus, was
  DTaP               Diphtheria, tetanus,               2, 4, 6, and 15–18 months
                        pertussis (whooping                Booster at 4–6 years                then developed by Dr. Albert Sabin.
                        cough)                             Diphtheria and tetanus              Both vaccine types are presently used
                                                           toxoid (Td) at 11–12 years          in worldwide immunization programs,
  Hib                Haemophilus influenza              2 and 4 months or 2, 4, and 6          but IPV is preferred for routine child-
                        type b (spinal                     months depending on type            hood immunizations. A series of three
                        meningitis)                        used
  PCV                Pneumococcus (pneu-                2, 4, 6, and 12–15 months              doses is given between 2 and 18
                        monia, meningitis)                                                     months, and a fourth dose is given be-
  MMR                Measles, mumps, rubella            15 months and 4–6 years                fore entry into school.
  HBV                Hepatitis B                        Birth, 1–2 months, 6–18                     MMR, made with live attenuated
                                                           months                              viruses, protects against measles
  Polio vaccine      Poliomyelitis                      2 and 4 months, 6–18 months,
    (IPV)                                                  and 4–6 years                       (rubeola), mumps, and rubella (Ger-
  Varicella          Chickenpox                         12–18 months                           man measles). Rubella is a very mild
                                                                                               disease, but it causes birth defects in a
  *Recommended by the Advisory Committee on Immunization Practices (,     developing fetus (see Table 2 in Ap-
  the American Academy of Pediatrics (, and the American Academy of Family         pendix 5). A first dose of MMR is
  Physicians ( Information available through the National Immunization Program   given at 15 months and a second be-
  website (
                                                                                               tween 4 and 6 years of age.

    Infants are now routinely immunized against hepati-          used in emergencies, that is, in situations in which there
tis B, receiving the first of three shots just after birth and   is no time to wait until an active immunity has developed.
two more before the age of 18 months. The vaccine is also
recommended for people at high risk of hepatitis B infec-        Preparation of Antisera Immune sera often are de-
tion, including healthcare workers, people on kidney             rived from animals, mainly horses. It has been found that
dialysis, people receiving blood clotting factors, injecting     the horse’s tissues produce large quantities of antibodies
drug users, and those with multiple sexual partners. A           in response to the injection of organisms or their toxins.
vaccine against hepatitis A virus is recommended for trav-       After repeated injections, the horse is bled according to
elers and others at high risk for infection.                     careful sterile technique; because of the animal’s size, it is
    A vaccine against chicken pox (varicella) has been           possible to remove large quantities of blood without caus-
available since 1995. Children who have not had the              ing injury. The blood is allowed to clot, and the serum is
disease by 1 year of age should be vaccinated. Although          removed and packaged in sterile containers.
chicken pox is usually a mild disease, it can cause en-              Injecting humans with serum derived from animals is
cephalitis, and infection in a pregnant woman can cause          not without its problems. The foreign proteins in animal
congenital malformation of the fetus. Because varicella is       sera may cause an often serious sensitivity reaction, called
the same virus that causes shingles, vaccination may pre-        serum sickness. To avoid this problem, human antibody
vent this late-life sequel.                                      in the form of gamma globulin may be used.
    A number of vaccines have been developed against in-
fluenza, which is caused by a variety of different viral         Checkpoint 17-13 What is an immune serum and when are im-
                                                                 mune sera used?
strains. Laboratories produce a new vaccine each year to
combat what they expect will be the most common
strains in the population. The elderly, the debilitated, and     Examples of Antisera Some immune sera contain anti-
children with certain risk factors, including asthma, heart      bodies, known as antitoxins, that neutralize toxins but
disease, sickle cell disease, HIV infection, and diabetes,       have no effect on the toxic organisms themselves. Certain
should be immunized yearly against influenza.                    antibodies act directly on pathogens, engulfing and de-
    The rabies vaccine is an exception to the rule that a        stroying them or preventing their continued reproduc-
vaccine should be given before invasion by a disease or-         tion. Some antisera are obtained from animal sources,
ganism. Rabies is a viral disease transmitted by the bite of     others from human sources. Examples of immune sera
wild animals such as raccoons, bats, foxes, and skunks.          are:
Mandatory vaccination of domestic animals has practi-
cally eliminated this source of rabies in some countries,        ◗   Diphtheria antitoxin, obtained from immunized horses.
including the United States, but worldwide, a variety of         ◗   Tetanus immune globulin, effective in preventing lock-
wild and domestic animals are host to the virus. There is            jaw (tetanus), which is often a complication of neg-
no cure for rabies; it is fatal in nearly all cases. The dis-        lected wounds. Because tetanus immune globulin is of
ease develops so slowly, however, that affected people               human origin, it carries less risk of adverse reactions
vaccinated after transmission of the organism still have             than do sera obtained from horses.
time to develop an active immunity. The vaccine may be           ◗   Immune globulin (human) is given to people exposed
given preventively to people who work with animals.                  to hepatitis A, measles, polio, or chickenpox. It is also
                                                                     given on a regular basis to people with congenital (pres-
Checkpoint 17-11 What are some bacterial diseases for which          ent at birth) immune deficiencies.
there are vaccines?                                              ◗   Hepatitis B immune globulin, used after hepatitis B ex-
                                                                     posure, is given principally to infants born to mothers
Checkpoint 17-12 What are some viral diseases for which              who have hepatitis.
there are vaccines?
                                                                 ◗   The immune globulin Rho(D) (trade name RhoGAM), a
                                                                     concentrated human antibody given to prevent an Rh-
Passive Immunization It takes several weeks to pro-                  negative mother from forming Rh antibodies. It is given
duce a naturally acquired active immunity and even                   during pregnancy if maternal antibodies develop and
longer to produce an artificial active immunity through              after the birth of an Rh-positive infant (or even after a
the administration of a vaccine. Therefore, a person who             miscarriage of a presumably Rh-positive fetus) (see
receives a large dose of virulent organisms and has no es-           Chapter 13). It is also given when Rh transfusion in-
tablished immunity to them is in great danger. To prevent            compatibilities occur.
illness, the person must quickly receive counteracting an-       ◗   Anti–snake bite sera, or antivenins (an-te-VEN-ins) are
tibodies from an outside source. This is accomplished                used to combat the effects of certain poisonous snake
through the administration of an immune serum, or an-                bites.
tiserum. The “ready-made” serum gives short-lived but            ◗   Botulism antitoxin, an antiserum from horses offers the
effective protection against the invaders in the form of an          best hope for botulism victims, although only if given
artificially acquired passive immunity. Immune sera are              early.
                                                                    BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 355

◗   Rabies antiserum, from humans or horses, is used with       Anaphylaxis Anaphylaxis (an-ah-fih-LAK-sis) is a se-
    the vaccine to treat victims of rabid animal bites.         vere, life-threatening allergic response in a sensitized indi-
                                                                vidual. (The term actually means excess “guarding,” in this
                                                                case, immune protection, from the Greek word phylaxis.)
◗ Disorders of the Immune System                                Any allergen can result in an anaphylactic response, but
                                                                common causes are drugs, insect venom, and foods. Symp-
Immune system disorders may result from overactivity or         toms appear within seconds to minutes after contact and
underactivity. Allergy and autoimmune diseases fall into        include breathing problems, swelling of the throat and
the first category; hereditary, infectious, and environ-        tongue, urticaria, edema, and decreased blood pressure
mental immune deficiency disease fall into the second.          with cardiovascular shock. Anaphylaxis is treated with in-
                                                                jectable epinephrine, antihistamine, administration of
Allergy                                                         oxygen, and plasma expanders to increase blood volume.
Allergy involves antigens and antibodies, and its chemi-        People subject to severe allergic reactions must avoid con-
cal processes are much like those of immunity. Allergy—         tact with known allergens. They should be sensitivity
a broader term for which is hypersensitivity—can be de-         tested before administration of a new drug and should also
fined informally as a tendency to react unfavorably to          carry injectable epinephrine and wear a medical bracelet
certain substances that are normally harmless to most           identifying their allergy.
    These reaction-producing substances are called aller-       Autoimmunity
gens (AL-er-jens), and like most antigens, they are usu-        The term autoimmunity refers to an abnormal reactivity
ally proteins. Examples of typical allergens are pollens,       to one’s own tissues. In autoimmunity, the immune sys-
house dust, animal dander (dander is the term for the           tem reacts to the body’s own antigens, described as “self,”
minute scales that are found on hairs and feathers), and        as if they were foreign antigens, or “nonself.” Normally,
certain food proteins. Many drugs can induce allergy, par-      the immune system learns before birth to ignore (toler-
ticularly aspirin, barbiturates, and antibiotics (especially    ate) the body’s own tissues by eliminating or inactivating
penicillin).                                                    those lymphocytes that will attack them. Some factors
    When a susceptible person’s tissues are repeatedly ex-      that might result in autoimmunity include:                         17
posed to an allergen—for example, exposure of the nasal
mucosa to pollens—those tissues become sensitized; that         ◗   A change in “self” proteins, as a result of disease, for ex-
is, antibodies are produced in them. When the next ex-
                                                                ◗   Loss of immune system control, as through loss of reg-
posure to the allergen occurs, there is an antigen–anti-
                                                                    ulatory T cell activity, for example.
body reaction. Normally, this type of reaction takes place
                                                                ◗   Cross-reaction of antibodies with “self” antigens. This
in the blood without harm, as in immunity. In allergy,
                                                                    reaction occurs in rheumatic fever, for example, when
however, the antigen–antibody reaction takes place
                                                                    antibodies to streptococci damage the valves of the
within the cells of the sensitized tissues, with results that
are disagreeable and sometimes dangerous. In the case of
the nasal mucosa that has become sensitized to pollen,              Autoimmunity is involved in a long list of diseases, in-
the allergic manifestation is hay fever, with symptoms          cluding rheumatoid arthritis, multiple sclerosis, lupus
much like those of the common cold.                             erythematosus, psoriasis, inflammatory bowel diseases,
    The antigen–antibody reaction in sensitive individu-        Graves disease, glomerulonephritis, and Type I diabetes.
als promotes the release of excessive histamine. Hista-         All of these diseases probably result to varying degrees
mine causes dilation and leaking from capillaries as well       from the interaction of individual genetic makeup with
as contraction of involuntary muscles (e.g., in the             environmental factors, including infections. Autoimmune
bronchi). Antihistamines are drugs that counteract hista-       diseases are three times more prevalent in women than in
mine and may be effective in treating the symptoms of           men, perhaps related to hormonal differences.
certain allergies. Sometimes, it is possible to desensitize         Autoimmunity is treated with drugs that suppress the
an allergic person by repeated intermittent injections of       immune system and with antibodies to lymphocytes. Pure
the offending allergen. Unfortunately, this form of pro-        antibodies, such as these, are prepared in the laboratory
                                                                and are known as monoclonal antibodies. A newer ap-
tection does not last long.
                                                                proach uses chemotherapy to destroy immune cells fol-
    Serum sickness is an example of an allergic manifes-
                                                                lowed by their replacement with healthy stem cells from
tation that may occur in response to various sera. People
                                                                bone marrow.
who are allergic to the proteins in serum from a horse or
some other animal show such symptoms as fever, vomit-
ing, joint pain, enlargement of the regional lymph nodes,
                                                                Immune Deficiency Diseases
and urticaria (ur-tih-KA-re-ah), also called hives. This        An immune deficiency is some type of failure of the im-
type of allergic reaction can be severe but is rarely fatal.    mune system. This failure may involve any part of the

system, such as T cells, B cells, or the thymus gland, and            tibodies. These cells produce an excess of a particular an-
it may vary in severity. Such disorders may be congenital             tibody, but the antibody is not effective. The disease
(present at birth) or may be acquired as a result of mal-             causes loss of resistance to infection, anemia, bone pain,
nutrition, infection, or treatment with x-rays or certain             and weakening of the bones, owing to production of a
drugs.                                                                factor that accelerates loss of bone tissue. High blood lev-
    The disease AIDS (acquired immunodeficiency syn-                  els of calcium and proteins secreted by the plasma cells
drome) is a devastating example of an infection that at-              often lead to kidney failure. Multiple myeloma is treated
tacks the immune system. It is caused by HIV (human im-               with chemotherapy. A new approach is high-dose
munodeficiency virus), which destroys the specific helper             chemotherapy combined with bone marrow transplants.
T cells that have a receptor (CD4) for the virus. Its first           Blood-forming stem cells in the bone marrow replace
appearance in the United States in the early 1980s was                cells killed by the chemotherapy. This treatment is ex-
among homosexual men and injecting drug users. It now                 pensive, and stem cell transplants in themselves are dan-
occurs worldwide in heterosexual populations of all ages.             gerous, but this combined treatment has improved sur-
AIDS is considered to be a pandemic, especially in sub-Sa-            vival rates.
haran Africa and in some parts of Asia. It is spread
through unprotected sexual activity and the use of con-               Checkpoint 17-14 What are some disorders of the immune sys-
taminated injection needles. It can also be transmitted
from a mother to her fetus. The testing of donated blood
has virtually eliminated the spread of AIDS through blood
transfusions.                                                         ◗ The Immune System and Cancer
    Diagnosis of HIV infection is based on the presence of
                                                                      Cancer cells differ slightly from normal body cells and
HIV antibodies, the virus, or viral components in the
                                                                      therefore the immune system should recognize them as
blood. The disease is monitored with CD4 T cell counts
                                                                      “nonself.” The fact that people with AIDS and other im-
and measurement of HIV RNA in the blood. (See Box 17-
                                                                      mune deficiencies develop cancer at a higher rate than
3 for information on the type of virus that causes AIDS.)
                                                                      normal suggests that this is true. Cancer cells probably
    Patients with AIDS succumb easily to disease, includ-
                                                                      form continuously in the body but normally are de-
ing rare diseases such as parasitic (Pneumocystis) pneu-
                                                                      stroyed by NK cells and the immune system, a process
monia and an especially malignant skin cancer, Kaposi
                                                                      called immune surveillance (sur-VAY-lans). As a person
(KAP-o-se) sarcoma.
                                                                      ages, cell-mediated immunity declines and cancer is more
    Drugs active against HIV stop viral growth at different
                                                                      likely to develop.
stages of replication. These drugs, often used in combina-
                                                                          Some efforts are being made to treat cancer by stimu-
tion, can slow the progress of AIDS, but so far, do not
                                                                      lating the patient’s immune system, a practice called im-
cure it. An obstacle to the development of a vaccine
                                                                      munotherapy. In one approach, T cells have been removed
against HIV is the tremendous variability of the virus.
                                                                      from the patient, activated with interleukin, and then rein-
                                                                      jected. This method has given some positive results, espe-
Multiple Myeloma                                                      cially in treatment of melanoma, a highly malignant form
Multiple myeloma is a cancer of the blood-forming cells               of skin cancer. In the future, a vaccine against cancer may
in bone marrow, mainly the plasma cells that produce an-              become a reality. Vaccines that target specific proteins

 Box 17-3      A Closer Look

   Retroviruses: Working Backward to Cause Disease

  H    IV, the virus that causes AIDS, belongs to a group of
       viruses that is unique in its method of reproduction. The
  group’s name, retroviruses, which means “backward viruses,”
                                                                     There, it may direct the formation of more viruses or lie dor-
                                                                     mant and undetected for long periods, even years, before being
                                                                     triggered to multiply and cause disease. Some retroviruses can
  refers to the way in which the viruses reverse the typical order   transform the DNA of the host cell and produce cancer. These
  of genetic action. Retroviruses have RNA instead of DNA as         viruses have been associated with leukemia in both humans
  their genetic material. Unlike other RNA viruses, however,         and animals and with other types of tumors in animals.
  they transcribe (copy) the RNA into DNA to reproduce inside           Some drugs that are used against retroviruses like HIV act
  the host. To accomplish this unusual feat, the virus has an en-    by inhibiting reverse transcriptase and interrupting the repli-
  zyme called reverse transcriptase.                                 cation cycle of the virus. The drug AZT is one such example.
     The DNA formed using reverse transcriptase enters the nu-       While drugs like AZT can slow the rate of HIV replication,
  cleus of the host cell and becomes part of the genetic material.   they do not cure or prevent HIV infection or AIDS.
                                                                         BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 357

produced by cancer cells have already been tested in a few            contain relatively few antigens that might cause trans-
forms of cancer.                                                      plant rejection in a recipient, the person receiving the
                                                                      part. (One exception to the need for careful cross-match-
                                                                      ing is corneal transplantation in the eye. Corneal proteins
◗ Transplantation and the                                             don’t enter the circulation to stimulate an immune re-
Rejection Syndrome                                                    sponse.)
                                                                          Because it is impossible to match all of a donor’s anti-
Transplantation is the grafting to a recipient of an organ            gens with those of the recipient, physicians give the re-
or tissue from an animal or other human to replace an in-             cipient drugs that will suppress an immune response to
jured or incompetent part of the body. Much experimen-                the transplanted tissue. These include drugs that suppress
tal work preceded transplantation surgery in humans.                  synthesis of nucleic acids, drugs or antibodies that inhibit
Tissues that have been transplanted include: bone mar-                lymphocytes, and adrenal glucocorticoid hormones, such
row, lymphoid tissue, skin, corneas, parathyroid glands,              as cortisol, that suppress immunity. These drugs cause a
ovaries, kidneys, lungs, heart, and liver.                            variety of adverse side effects, such as hypertension, kid-
    The natural tendency of every organism to destroy                 ney damage, and osteoporosis (glucocorticoids). Most
foreign substances, including tissues from another person             importantly, they reduce a patient’s ability to fight infec-
or any other animal, has been the most formidable obsta-              tion. Because T cells cause much of the reaction against
cle to complete success. This normal antigen–antibody                 the foreign material in transplants, scientists are trying to
reaction has, in this case, been called the rejection syn-            use drugs and antibodies to suppress the action of these
drome.                                                                lymphocytes without damaging the B cells. B cells pro-
    In all cases of transplantation or grafting, the tissues          duce circulating antibodies and are most important in
of the donor, the person donating the part, should be                 preventing infections. Success with transplantation will
typed in much the same way that blood is typed when a                 increase when methods are found to selectively suppress
transfusion is given. Blood type antigens are much fewer              the immune attack on transplants without destroying the
in number than tissue antigens; thus, the process of ob-              recipient’s ability to combat disease.
taining matching blood is much less involved than is the
                                                                       Checkpoint 17-15 What is the greatest obstacle to tissue trans-
process of obtaining matching tissues. Laboratories do                 plantation from one individual to another?
tissue typing in an effort to obtain donors whose tissues                                                                                 17

  Word Anatomy
Medical terms are built from standardized word parts (prefixes, roots, and suffixes). Learning the meanings of these parts can help you
remember words and interpret unfamiliar terms.

WORD PART                                MEANING                       EXAMPLE
Factors in the Occurrence of Infection
tox                                      poison                        A toxin is a substance that is poisonous.
Disorders of the Immune System
erg                                      work                          In cases of allergy, the immune system overworks.
ana-                                     excessive                     Anaphylaxis is a life-threatening condition that results from an
                                                                          excessive immune reaction.
myel/o                                   marrow                        Multiple myeloma is a cancer (-oma) of blood-forming cells in
                                                                          bone marrow.

I. Factors in the occurrence of infection                             II. Nonspecific defenses
A. Tissue preference of pathogen                                      A. Chemical and mechanical barriers
B. Portal of entry of pathogen                                           1. Skin
C. Virulence of pathogen                                                 2. Mucous membranes
   1. Invasive power                                                     3. Body secretions
   2. Production of toxins (poisons)                                     4. Reflexes—coughing, sneezing, vomiting, diarrhea
D. Dose (number) of pathogens                                         B. Phagocytosis—mainly by neutrophils and macrophages
E. Predisposition of host                                             C. Natural killer (NK) cells—attack tumor cells and virus-in-
                                                                         fected cells

D. Inflammation                                                         (2) Damages plasma membranes
E. Fever                                                                (3) Promotes inflammation
F. Interferon                                                           (4) Attracts phagocytes
   1. Substances released from virus-infected cells           D. Naturally acquired immunity
   2. Prevent virus production in nearby cells                   1. Active—acquired through contact with the disease
   3. Stimulate the immune response nonspecifically              2. Passive—acquired from antibodies obtained through
                                                                    placenta and mother’s milk
III. Immunity—specific defense against                        E. Artificially acquired immunity
     disease                                                     1. Active—immunization with vaccines
A. Inborn immunity                                                  a. Types: live (attenuated), killed, toxoid, recombinant
   1. Inherited                                                         DNA
   2. Types: species, individual                                    b. Boosters—keep antibody titers high
B. Acquired immunity—develops after birth                           c. Examples of bacterial vaccines
   1. Antigens—stimulate immune response by lymphocytes             d. Examples of viral vaccines
   2. T cells (T lymphocytes)                                    2. Passive—administration of immune serum (antiserum)
      a. Processed in thymus
      b. Types: cytotoxic, helper, regulatory, memory         IV. Disorders of the immune system
      c. Involved in cell-mediated immunity                   A. Allergy—hypersensitivity to normally harmless substances
   3. Macrophages                                                (allergens)
      a. Derived from monocytes                                  1. Anaphylaxis—severe, life-threatening allergic response
      b. Present antigen to T cells in combination with MHC   B. Autoimmunity—abnormal response to body’s own tissues
         (“self”) proteins                                    C. Immune deficiency disease—failure in the immune system
      c. Stimulate the release of interleukins (IL)              1. Congenital (present at birth)
   4. B cells (B lymphocytes)                                    2. Acquired (e.g., AIDS)
      a. Mature in lymphoid tissue                            D. Multiple myeloma—cancer of blood-forming cells in bone
      b. Develop into plasma cells                               marrow
         (1) Produce circulating antibodies
         (2) Antibodies counteract antigens                   V. The immune system and cancer
      c. Also develop into memory cells                       A. Immune surveillance—ability of immune system to find
      d. Involved in humoral immunity                            and destroy abnormal cells (e.g., cancer cells)
C. The antigen–antibody reaction                              B. Immunotherapy—stimulating the immune system to treat
   1. Shape of antibody matches shape of antigen                 cancer
   2. Results
      a. Prevention of attachment                             VII. Transplantation
      b. Clumping of antigen                                  A. Grafting of an organ or tissue to replace injured or incom-
      c. Neutralization of toxins                                petent part
      d. Help in phagocytosis                                 B. Requirements
      e. Activation of complement                                1. Tissue typing
      f. Activation of NK cells                                  2. Suppression of immune system
   3. Complement
      a. Group of proteins in blood
      b. Actions
         (1) Coats foreign cells

  Questions for Study and Review
Building Understanding
Fill in the blanks
1. The power of the organism to overcome its host’s de-       4. All antibodies are contained in a portion of the blood
fenses is called ______.                                      plasma termed the ______.
2. Heat, redness, swelling, and pain are classic signs of     5. Substances capable of inducing a hypersensitivity re-
______.                                                       action are called ______.
3. Any foreign substance that enters the body and in-
duces an immune response is called a(n)______.
                                                               BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 359

Match each numbered item with the most closely related lettered item.
___ 6. Destroy foreign cells directly.                                                            a.   regulatory T cells
___ 7. Release interleukins, which stimulate other cells to join the immune response.             b.   memory T cells
___ 8. Suppress the immune response in order to prevent overactivity.                             c.   cytotoxic T cells
___ 9. Remember an antigen and start a rapid response if the antigen is contacted again.          d.   B cells
___ 10. Manufacture antibodies when activated by antigens                                         e.   helper T cells
Multiple choice                                              17. What causes the symptoms of inflammation?
___ 11. All of the following are part of the first line of   18. Differentiate between the terms in each of the
         defense against invaders except                          following pairs:
         a. tears                                                 a. interferon and interleukin
         b. saliva                                                b. antibody and complement
         c. neutrophils                                           c. inborn immunity and acquired immunity
         d. skin                                                  d. cell-mediated immunity and humoral immunity
___ 12. Damaged cells release a vasodilator substance             e. active immunization and passive immunization
         called                                                   f. attenuated vaccine and toxoid
         a. interleukin                                      19. Describe the events that must occur for a T cell to
         b. interferon                                       react with a foreign antigen. Once activated, what do the
         c. histamine                                        T cells do?
         d. complement                                       20. What role do antibodies play in immunity? How are
___ 13. Which of the following cells mature in the           they produced? How do they work?
         thymus?                                             21. Compare and contrast the four types of acquired im-
         a. T cell                                           munity.
         b. B cell                                           22. What is an immune serum? Give examples. Define
         c. plasma cell                                      antitoxin.
         d. natural killer cell                              23. Define allergy. How is the process of allergy like that
___ 14. Sensitivity to animal-derived immune serum           of immunity, and how do they differ?
         may lead to a serious condition called              24. What is meant by rejection syndrome, and what is
         a. serum sickness                                   being done to offset this syndrome?                            17
         b. hay fever
         c. Kaposi sarcoma                                   Conceptual Thinking
         d. rejection syndrome                               25. While in the garden with his father Alek, a 4-year old
___ 15. An abnormal reactivity to one’s own tissues is       Caucasian boy was, in his own words, “kicked by a bee.”
         called                                              Shortly afterward, Alek developed hives near the affected
         a. allergy                                          area, which he began to scratch. About ten minutes later,
         b. autoimmunity                                     Alek’s father noticed that his son was wheezing. What is
         c. anaphylaxis                                      happening to Alek? Describe the inflammatory events
         d. rejection                                        that are occurring in his body. How should Alek’s father
Understanding Concepts                                       respond?
16. Describe four factors that influence the occurrence of   26. Why is HIV’s attack on helper T cells so devastating
infection.                                                   to the entire immune system?

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