The Immune System &
Topics in Medicine and Biology
Summer Ventures in Science & Math
Instructor: Willson Kwok
July 14, 2006
The body has a system of defenses known as the immune system. The immune system
has many parts that work together to protect the body against viruses, bacteria, micro-organisms,
parasites, and other foreign bodies. Lymphatic organs and leukocytes each have their own role in
fighting off invaders of the body. There are two types of leukocytes: phagocytes, which ingest
and destroy foreign matter, and lymphocytes, which consist of B-cells and T-cells that regulate
the two immune responses: cellular and humoral. When problems arise with the immune system
because of non-self/self recognition breakdown, allergies, and excessive response, disorders
arise. This paper also discusses Lupus, an autoimmune disorder, which affects all parts of the
body. In Lupus, the immune system loses its ability to tell the difference between foreign
substances (antigens) and its own cells and tissues, making it a serious and life-threatening
Introduction to the System:
The immune system is a complex and intricate network of many organs and cells that
work together in combination to defend the body against infection, disease, and foreign
substances. It can be stimulated in specific ways to fight specific health challenges, which
includes fighting off millions of bacteria, microbes, viruses, toxins, cancer cells, and parasites.
The organs of the immune system, which are spread throughout the entire body, are called the
lymphatic organs (Wikipedia Immune System, 2006).
The Human Body’s Lines of General Defense:
There are three lines of defense for the human body. The first line of defense consists of
surface membrane barriers such as the skin. The skin, which has an acidic pH, is a passive
physical barrier to foreign materials such as bacteria and viruses. The skin glands secrete
chemicals to inhibit bacterial growth and organisms that live on the skin’s surface are unable to
penetrate through. Moreover mucous membranes in the respiratory, digestive, reproductive, and
urinary tracts secrete mucus to form an additional barrier. The mucus in the digestive and
respiratory pathways traps micro-organisms while the mucosa of the stomach produces
hydrochloric acid (HCl) and has protein-digesting enzymes (Farabee, 2001).
The second line of defense is the inflammatory response, which is triggered when body
tissues are injured. There are four cardinal signs of inflammation: redness, heat, swelling, and
pain, which result in a chain of events that lead to defense and healing. The inflammatory
response helps prevent the spread of infectious and harmful agents, it removes cell debris and
pathogens, and helps set the stage for body repair (Marieb, 2003).
The third line of defense is a specific response known as the immune system. It is antigen
specific, which means it recognizes and acts against particular foreign substances. In addition it
is system and is not restricted to the initial infection site, and has memory, which aids in a
stronger attack on previously encountered pathogens (Marieb, 2001).
Parts of the Immune System:
Throughout the entire human body, the parts of the immune system each have their own
role. The bone marrow is the site of origin for all the cells of the immune system including red
blood cells, white cells (neutrophils, lymphocytes), and platelets, which are formed and then
released into circulation. These cells form through a process called hematopoiesis, where bone
marrow-derived stem cells differentiate into either mature cells or into precursors of cells that
migrate out of the bone marrow to continue their maturation elsewhere. In the thorax, the
thymus gland is responsible for the maturation of new lymphoid cells before they are released
into the bloodstream. This maturation process allows T cells to develop self tolerance and the
white cells to develop specialized functions.
The small bean-shaped structures known as the lymph nodes filter particulate matter and
micro-organisms, and produce antibodies to destroy invading organisms and abnormal cells. The
defense cells within the lymph nodes are macrophages, which engulf and destroy foreign
substances, and lymphocytes, which provide an immune response to antigens (Cann, 2005). The
spleen in the upper left section of the abdomen consists of two components which filter blood,
destroys worn out blood cells, forms blood cells in the fetus, acts a blood reservoir, and removes
abnormal cells from circulation: the red pulp and the white pulp. The red pulp houses a complex
system of blood vessels, designed to remove old or damage blood cells from circulation. The
white pulp, which contains T cells, B cells and accessory cells, has the role of mounting
immunological responses to antigens within the blood. Another important part of the immune
system is Gut Associated Lymphoid Tissue, which includes tonsils, adenoids (Waldeyer’s ring),
Peyer’s patches, lymphoid aggregates in the appendix and large intestine, lymphoid tissue in the
stomach, small lymphoid aggregates in the esophagus, diffusely distributed lymphoid cells and
plasma cells in the lamina propria of the gut. The tonsils are small masses of lymphoid tissue in
the back of the throat around the pharynx. They act as a filter to trap and remove bacteria and
foreign intruders that cause infection. Peyer’s patches in the walls of the small intestine capture
and destroy bacteria. They facilitate the generation of an immune response within the mucosal
membrane, where B cell precursors and memory cells are stimulated by antigens (Cann, 2005).
The Cells of the Immune System and their Function:
There are many different types of cells in the immune system that work together to
protect the human body. The two main classes of lymphocytes are B cells and T cells, which
originate from the hemocytoblasts in the red bone marrow. B lymphocytes mature in the bone
marrow, while T lymphocytes mature in the thymus. B lymphocytes play a large role in the
humoral immune response and function to produce antibodies in response to foreign proteins
such as bacteria, viruses, and tumor cells. Antibodies are specialized proteins that specifically
recognize and bind to one particular protein. Antibody production and binding to a foreign
substance or antigen is critical as a means of communicating with other cells to engulf, kill or
remove that substance from the body. B-cells differentiate to form plasma cells and memory
cells. The plasma cells secrete antibodies which help destroy antigens by binding to them and the
memory cells produce antibodies to provide immunity to a familiar antigen. There are three
different types of T-cells: helper T-cells, suppressor T-cells, and killer T-cells. Helper T-cells
(CD4+) activate B-cells that produce antibodies; suppressor T-cells slow down and inhibit B-
cells and T-cells from generating an immune response; and cytotoxic (CD8+) aka Killer T-cells
recognize and kill virus-infected cells without communicating with other lymphoid organs.
Helper T-cells aid the cellular and humoral immune
responses by supplying cytokines.
Killer T-cells that are activated by
CD4+ T-cells secretions kill their viral-infected targets more effectively. B-cells make up
10-20%, helper T-cells make up 68-75%, and killer T-cells make up
5-10% of lymphocytes (Purves, 2001).
In addition to B-cells and T-cells, there are monocytes, macrophages, dendritic cells, and
granulocytes. These cells are known as phagocytes because they engulf and ingest foreign bodies
and harmful micro-organisms while absorbing waste materials in the bloodstream and tissues.
Monocytes make up to 1-6% of white blood cells; their function is to circulate in the
bloodstream, migrate to other tissues, and differentiate into macrophages. Macrophages, which
are phagocytic cells, can be found in a variety of tissues. They play an important role in
regulating immune responses because they collect and ingest foreign materials and present the
antigens to B-cells and T-cells. Along with activating the immune response, they engulf and
digest micro-organisms along with releasing cytokines to activate T-cells. Another type of cells
is a dendritic cell, which can be found in the structural components of lymphoid organs i.e.
thymus, lymph nodes, and spleen. They capture antigens and transport them to the lymphoid
organs, but little is known about these cells due to the difficulty in isolating them (NIAID, 2003).
There is another group of white blood cells known as granulocytes or polymorphonuclear
leukocytes. There are three cell types that compose granulocytes: neutrophils, eosinophils, and
basophils. Their overall role is to remove bacteria and parasites by engulfing these foreign
materials and using powerful enzymes to wear them down. Neutrophils, making up 50-70% of
white blood cells, respond to inflammation by moving from the blood to the site of
inflammation, where they phagocytize debris and pathogens. Another type of cell that makes up
1-3% of white blood cells is an eosinophil. They migrate from the blood to other tissues and kill
antibody-coated parasites. Basophils are the third and smallest group of granulocytes that make
up less than 1% of white blood cells. Basophils secrete histamine, several proteoglycans, lipid
mediators like leukotrienes, and several cytokines, all which contribute to inflammation and an
allergic response (Linnemeyer, 1993).
Types of Immunity:
There are four different types of immunity: natural passive immunity, acquired passive
immunity, natural active immunity, and acquired active immunity. Natural passive
immunity is where antibodies produced by one individual are passed into another individual i.e.
from a mother to her baby. In this type of hereditary immunity, antibodies from a mother cross
the placenta and enter her fetus so that they can protect the baby for the first six months of its
life, until its own immune system is functional. Passive immunity can also be transferred from a
mother’s first milk because the baby’s intestines absorb antibodies. A second type of passive
immunity is acquired from vaccines i.e. rabies and tetanus, where antibodies made in one
individual are injected into another individual’s blood. It is not permanent and only lasts for a
temporary period of time.
Just as there are two types of passive immunities, there are two active forms. The
first is natural active immunity, in which a person who has suffered a disease and its symptoms
becomes immune to it. It is also known as a secondary response, where B-Cells fire off
antibodies to combat a recognized antigen. The body makes its own antibodies the first time it is
exposed to the infectious agent, and the memory cells that were formed the first time are able to
manufacture mass amounts of antibodies when the same antigen presents itself again. An
example of this is chicken pox, because after the infectious antigen presents itself once, the body
is immune to it, and it generally persists for life. The last type of immunity is acquired active
immunity, where a vaccine i.e. polio (small amounts of antigen) is injected in an individual. This
small dose guarantees that the individual will not contract that disease and will produce
antibodies against the antigen.
The Immune Responses:
There are two types of immune responses in the human body: cellular (controlled by
T-cells) and humoral (regulated by B cells and their antibodies). The cellular or cell-mediated
response does not involve antibodies, and instead involves the activation of macrophages and
killer T-cells, the production of antigen-specific cytotoxic T-cells, and the release of various
cytokines in response to an antigen. In this immune response antigens must be presented to an
immunocompetent T- cell by macrophages. The T- cell must recognize if it is non-self or self,
an important function of the immune system. After antigen binding, clones form as with B cells,
but different classes of cells are produced. The cytotoxic T-cells specialize in killing infected
cells by inserting a toxic chemical called perforin. The helper T-cells recruit other cells to fight
the invaders and interact directly with B cells. The suppressor T-cells release chemicals to
suppress T-cell and B-cell activity, and are like the off switch for the immune response in order
to prevent uncontrolled activity (Marieb, 2003).
The humoral immune response is regulated by B-cells and the antibodies they produce.
Some of the digested antigens are displayed on the surfaces of the macrophages and provide
other cells of the immune system with an opportunity to recognize the invader and become
activated. In this process known as antigen presentation, the macrophage selects helper T-cells
and B-cells which have membrane receptors that are complementary in shape to the antigens
exposed. This selection process is known as clonal selection (Millar, 2003). The humoral
response pathway diagram (Figure 5) shows that in the humoral immune response, B
lymphocytes with specific receptors bind to a specific antigen. This binding activates the
lymphocyte to undergo clonal selection, where a large number of clones are produced (primary
humoral response). Most B cells become plasma cells, which produce antibodies to destroy
antigens, although some B cells become long-lived memory cells (secondary humoral response).
The following chart on the next page shows the two types immunities and the process
B-cells and T-cells undergo to emit an immune response (Millar, 2003).
In many cases, the immune system fails. An impaired immune system is called
immunocompromise and can leave the body vulnerable to various viral, bacterial, or fungal
opportunistic infections. Causes of immune deficiency can include various illnesses such as
viruses, chronic illness, or immune system illnesses i.e. AIDS. Other types of immune disorders
involve an over-active immune response. There are several different classes of diseases from an
excessive response by the immune system:
1. Allergies - a true allergy to a substance or food is caused by the immune response.
2. Asthma - caused by an allergic reaction affecting the airway passages.
3. Anaphylaxis - an extremely dangerous over-reaction that can lead to shock
4. Autoimmune diseases - a group of more than 100 diseases where the body's own immune
system gets confused and starts to attack good body cells.
In the case of autoimmune diseases like multiple sclerosis, systemic lupus erythematosus, and
some forms of arthritis and diabetes, the process of self/non-self recognition breaks down, and
the immune system attacks its own cells (Wikipedia Immune System, 2006).
Lupus is an autoimmune disease that affects your immune system. Autoimmune
diseases are illnesses which occur when the body’s tissues are attacked by its own immune
system. It may also be called Systemic Lupus Erythematosus or (SLE). Usually your immune
system tries to fight off infections by killing germs, but in Lupus it makes the mistake of
attacking its healthy cells instead. Lupus can affect any part of an individual’s body from their
joints, kidneys, skin, all the way to their heart and lungs. The body’s immune system normally
makes proteins called antibodies to protect
the body against viruses, bacteria and other foreign materials. These foreign materials
are called antigens. In an autoimmune disorder such as lupus, the immune system loses its ability
to tell the difference between foreign substances (antigens) and its own cells and tissues. The
immune system then makes antibodies directed against “self.” These antibodies, called
“auto-antibodies,” react with the “self” antigens to form immune complexes. The immune
complexes build up in the tissues and cause inflammation, injury to tissues, and pain. In some
people, Lupus’s effects are not as prevalent as it is in others. A few will only be affected in the
joints and skin, but others will be affected in the heart and lungs. Lupus is usually a slow
processing disease that has symptoms, which just come and go, but sometimes it becomes life
threatening and can become very dangerous about deadly. Lupus can be thought of as a self
allergy that attacks its own cells and tissues, which causes inflammation, pain, swelling, and
possible organ damage. Patients with lupus produce abnormal antibodies in their blood that
target tissues within their own body rather than foreign infectious agents. Lupus can cause
disease of the skin, heart, lungs, kidneys, joints, and nervous system. When only the skin is
involved, the condition is called systemic lupus erythematosus (SLE).
Lupus is one of America’s
least recognized diseases but is one
of its major diseases. More people
in America have lupus than any other
disease like anemia, multiple
sclerosis, or even cystic fibrosis. It
is one of the most prevailing diseases
in America, but it is very
unnoticeable. However, while lupus
is widespread, awareness and
accurate knowledge about it lags
behind many other illnesses.
Lupus is on the rise, and scientists don't know exactly why. A recent report from the
Centers for Disease Control and Prevention (CDC) revealed a 60 to 70 percent rise in lupus
deaths between the years of 1979 and 1998. Each year during the study phase, death rates were
more than five times higher for women than for men, and more than three times higher for
African Americans than for Caucasians. The LFA market research data show that between
1,400,000 and 2,000,000 people reported to have been diagnosed with lupus. Lupus is more
common in women especially in Latino, Asian, and Native American. Women take over 90
percent of the lupus disease population. Lupus is the leading cause of kidney disease, stroke,
and premature cardiovascular disease in women of childbearing years. Regrettably, statistics
show that 5 percent of children born to lupus-diagnosed mothers will eventually develop the
There are several forms of lupus. The first one, which is also the most common type of
lupus is Systemic Lupus Erythematosus (SLE).
SLE can affect a magnificent amount of parts of the body like joints, skin, kidneys, blood
vessels, nervous system, heart, blood, brain, and the lungs. This type of lupus is found in teens
and adults from the ages ranging from 15 to 44.
Even though SLE happens between these ages it could show early or late symptoms as well.
SLE is an elaborate disorder affecting a diminutive young population and shares resemblances
with the HIV infection. The etiology of SLE is not known. It can occur at all ages, but is more
common in young women. It is also a disease with many manifestations. The immune
complex deposition in many tissues leads to the manifestations of the disease. Immune
complexes can be deposited in glomeruli, skin, lungs, synovium, mesothelium, and other places.
Many SLE patients develop renal complications (Eustice, 2006).
Discoid lupus erythematosus (DLE) is a second type of lupus which affects just the skin.
Patients with DLE could also get sores in the mouth and throat. Discoid lupus erythematosus is
a chronic skin condition characterized by inflammation and scarring type skin lesions which
occur on the ears, face, scalp and sometimes on other parts of the body. These lesions develop
as a swollen growth with, scaling and a warty like form. The center areas may appear lighter in
color encircled by an area darker than the normal skin. When wounds occur in hairy areas such
as the scalp, permanent scarring and hair loss can occur. A small percentage of patients with
discoid lupus can develop disease of the internal organs which can make the person sick. Not
many but a few people with DLE get SLE. It is not known for sure if a DLE person will get
SLE. DLE does not affect the organs as SLE does, even though there are a small percentage of
people who get DLE have organ failure. The cause of this type is unknown and it is said that
this condition tends to run in families; females outnumber males with this condition 3 to 1. In
some patients with discoid lupus erythematosus, sunlight may make the lesions come out
The next type of lupus is Neonatal Lupus Erythematosus (NLE). Neonatal lupus occurs in
babies. If a woman gets pregnant and she has SLE or any other immune system disorders then
the baby could be born with neonatal lupus. Neonatal is a rare type of lupus. In most of the
cases neonatal lupus does not need to be treated. In those cases neonatal lupus disappears
impulsively in a few weeks, leaving nothing behind. With a simple blood test you will be able
to tell which women will deliver a child with neonatal lupus. Many of the children born with
neonatal lupus are born to mothers who don’t have SLE. Some of the babies who are born with
this disease could have a serious or even sometimes minor heart defect, though most of the time
it is serious. Once a baby is born with this heart defect it stays permanent and cannot be cured
but treated with a pacemaker (Eustice, 2006).
The very last type of lupus is the Drug-Induced Lupus Erythematosus (DILE); it is
related to drug prescriptions. This type of lupus is related to a reaction from some sort of
prescription medications. This type of lupus will not show right away after you had a reaction
to medicine it would have to take months or even years before the first symptoms show and then
when you quit taking those medications it would take days, weeks, months, or even years for the
symptoms to go away. Lupus-inducing drugs are normally those used to treat chronic diseases.
The list includes medicines used to treat: Heart disease, Thyroid disease, Hypertension,
Neuropsychiatric disorders, and certain anti-inflammatory agents and antibiotics. At least 38
drugs recently used can cause DILE. However, most cases have been associated with these
three drugs: Procainamide (Pronestyl), Hydralazine (Apresoline), Quinidine (Quinaglute). The
risk for developing lupus-like disease from any of the other 35 drugs is very low; with some
drugs only one or two cases have been reported. For the high-risk drugs such as procainamide
and hydralazine, only 5 to 20 percent of people treated for one to two years at currently used
doses will develop drug-induced lupus. With most of the other drugs, the risk is less than 1
percent that those taking the medication will develop DILE. Some studies show that Caucasians
are more likely to develop this than African Americans. Usually DILE occurs in males over the
age of 50, because they have a higher chance of developing chronic diseases that require this
type of continuous medication procainamide or quinidine is prescribed for cardiac arrhythmias,
and hydralazine is prescribed for hypertension. Obviously men over 50 have both or one of
these (Eustice, 2006).
Lupus is a disease whose cause is still unknown, even if it is starting to become one of
the major diseases in Americans. It is thought that there is no single cause for any type of lupus
but a combination of many things. These include genetic, environmental, and maybe hormonal
factors that work together to make this immune disorder come alive. People cannot catch lupus
from a person when they sneeze or even when they breath on you because lupus is not
contagious, but is known to run in the family. Some of the environmental factors that may
trigger the disease are: infections, antibiotics (especially those in the sulfa and penicillin groups),
ultraviolet light, extreme stress, and certain drugs (What causes lupus?, 1996).
Lupus is often called a "woman's disease" despite the fact that many men are affected.
Lupus can occur at any age, and in either sex, although it occurs 10 to15 times more frequently
among adult females than among adult males. The symptoms of the disease are the same in
men and women. People of African, American Indian, and Asian origin are thought to develop
the disease more frequently than Caucasian women, but the studies that led to this result are
small and need validation. Hormonal factors may explain why lupus occurs more frequently in
females than in males. The increase of disease symptoms before menstrual periods and/or
during pregnancy support the belief that hormones, particularly estrogen, may be involved.
However, the exact hormonal reason for the greater prevalence of lupus in women, and the cyclic
increase in symptoms, is unknown.
Although lupus can affect any part of the body, most people experience symptoms in
only a few organs. Since there is more than one type of lupus each type has its own symptoms.
95% Achy joints (arthralgia)
90% Fever over 100 degrees F (38
81% Prolonged or extreme fatigue
90% Arthritis (swollen joints)
74% Skin Rashes
50% Kidney Involvement
45% Pain in the chest on deep
42% Butterfly-shaped rash across the
cheeks and nose
27% Hair loss
17% Raynaud's phenomenon (fingers
turning white and/or blue in the
12% Mouth or nose ulcers
SLE type can present itself in very different ways regarding of the person’s body. About 80%
of people develop joint and muscle pain, skin
rashes, fatigue and a general feeling of being unwell. Often symptoms are worse before a
menstrual period and they are often thought to be just pre-menstrual tension. The most common
signs and symptoms are arthritis, fatigue, skin rashes, sun sensitivity, hair loss, kidneys,
depression, and some other symptoms. During a lupus flare-up the most common complaints
are of flu-like symptoms (with or without fever), fatigue, muscle and joint pains. Often
symptoms are reported to be worse before a menstrual period and they are often thought to be
just pre-menstrual tension. People with lupus can also have a variety of other symptoms
including high temperature, blood disorders, miscarriage, headaches, weight loss, chest pain and
abdominal pain. However, it is important to remember that the symptoms can vary greatly from
person to person. People with DLE tend to be quite sensitive to the sun. They are more likely to
get sunburn and the sun is likely to worsen their discoid lesions (Lahita, 2001).
Neonatal Lupus has few symptoms like skin rash, liver abnormalities, low blood
counts, and heart defects. Since it happens in babies given by the mom who is pregnant with the
baby the symptoms could be seen in the mom. Flares most often occur during the first or
second trimester, or during the two months immediately after delivery. Most of the flares tend
to be mild. Approximately 33 percent of lupus patients will have a decrease in platelet count
during pregnancy, and about 20 percent will have an increase in or new occurrence of protein in
the urine. It is important to distinguish the symptoms of a lupus flare from the normal body
changes that occur during pregnancy (Lockshin, 1994).
Treatments for lupus are not easy to find. There is no known cure for lupus so the
only option is to use home care. Home care for lupus generally involves taking prescribed
medications and using sunscreen whenever patients go outside because lupus patients are known
to be sensitive to the sun. For most of the symptoms, they can take medications because the
symptoms are from swelling or inflammation and there are medications for it. Some
medications are non-steroidal anti-inflammatory drugs (NSAIDS), which are often used to
moderate joint/muscle pain and inflammation in people who have minor SLE. This medication
comes in many different forms. Another kind of medicine is anti-malarial drugs, which are
medicines that are used to prevent or treat malaria, joint pain, skin rashes, and ulcers. Two
types of anti-malarials are hydroxychloroquine (Plaquenil) and chloroquine (Aralen). In
addition, there are corticosteroid hormones that are powerful drugs, which reduce inflammation
in various tissues of the body. This medication can be taken by mouth, by cream applied to the
skin, or by injection.
When a patient has a severe case of lupus and their major organs don’t function
properly, there is a treatment that is used known as Immunosuppressive agents/chemotherapy.
All of these drugs suppress the immune system to limit damage to the organs. Some examples
are azathioprine (Imuran) and cyclophosphamide (Cytoxan). For a patient without a known
diagnosis of lupus, the doctor will assess, but never likely provide a major diagnosis of lupus
unless there are clear and unmistakable features. Evaluation of chronic (not acute) diseases is
done in a medical office setting. However, certain tests to assess the possibility of organ
damage including some blood and urine tests, imaging studies, and heart tracings will allow the
doctors to assess an acute disease if someone with lupus seeks treatment in an emergency
department (Lahita, 2001).
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