Chapter 16 Innate Immunity: Nonspecific
Defenses of the Host
Immunity or resistance is the body’s ability to ward off disease from microbes and
protect our selves from environmental agents(pollens, drugs, foods and chemicals).
Susceptibility is the body’s vulnerability to diseases and lack of immunity.
Overview of the Body’s Defenses
First Line of Defense (Innate/Nonspecific Immunity)
Second Line of Defense (Innate/Nonspecific Immunity)
Natural Killer Cells
White Blood Cells (Phagocytic)
Third Line of Defense (Adaptive/Acquired Immunity)
The Concept of Immunity
Innate (nonspecific) immunity refers to the defenses present at birth such as skin and
Adaptive (specific) immunity refers to the defenses that have specific microbial
recognition that acts against the microbes when the first line of defense is breached, such
as T and B cells and antibodies.
First Line of Defense
1. Skin (Intact)
Epidermis is the outer, thinner portion directly in contact with the external
o Top layer sheds periodically to remove microbes
o Contains keratin as protective protein.
Dermis is the inner and thicker portion consisting of connective tissues.
Keratin is the protective protein of the epidermis layer.
2. Mucous Membranes and other physical factors
Consist of epithelial and underlying connective tissue layers such as respiratory
and gastrointestinal tracts.
Less protection than skin but nonetheless inhibit microbial entrance
Mucus is a thick viscous fluid secreted by mucous membrane to lubricate tracts.
Treponema pallidum survives in mucus and can penetrate the membranes.
Lacrimal apparatus (lacrimal glands, tears, canals, ducts) wash away keep
microorganisms from settling on the eyes.
Saliva produce by salivary glands dilutes microorganism, wash them away from
teeths and mucous membranes of the mouth
Nose hairs filters inhaled microorganisms
Cillia in the lower respiratory tract help propels out toward the throat (ciliary
escalator) microorganisms that have become trapped.
Epiglottis that covers the larynx (voice box) during swallowing prevents
microorganisms from entering the lower respiratory tract.
Urine cleanse urethra
Vaginal secretions move microorganisms out.
Defecation and vomiting expel microbes
3. Normal Microbiota
Normal Microbiota are opportunistic microorganisms that inhabit the body and
helps ward off and do not cause disease under normal conditions.
Normal microbiota in the vagina secrete acidic substance to prevent Candida
albicans from causing vaginitis
Escherichia coli secretes bacteriocins that inhibit the growth of Salmonella and
Oily substance produce by sebaceous glands of the skin to form protective film on
the skin surface and to prevent hair from drying and becoming brittle.
2. Low pH (3 and 5)
Caused by secretions of lactic acid and fatty acid prevents growth of many
Contains in the perspiration breaks down cells walls of gram-positive bacteria and
to lesser extent gram-negative bacteria.
4. Gastric Juice (pH 1.2-3.0)
Gastric juice which is a mixture of hydrochloric acid, enzymes and mucus
produced by stomach glands destroy bacteria and their toxins.
Exception is Clostridium botulinum and Staphylococcus aureus.
Helicobacter pylori neutralizes stomach acid and grow to cause ulcers and
Second Line of Defense
Leukocytes (White Blood Cells)
Granulocytes have large granules in their cytoplasm that can be seen under a light
Stains a pale lilac with a mixture of acidic and basic dyes and consist of 2 to 5
Phagocytic, motile, active in the initial stages of infection.
Have the ability to leave the blood, enter an infected tissue and destroy microbes
and foreign particles.
Stains blue-purple with the basic dye methylene blue
Release substances such as histamine that is important in inflammation and
Stain orange or red with the basic dye eosin.
Phagocytic and have the ability to leave the blood.
Produce toxic proteins against certain parasites such as helminthes.
Have granules but are not visible under a light microscope.
Are not phagocytic until they leave the blood and mature into macrophage and
become the best phagocyte in the tissue.
3rd line of defense
Play a key role in the adaptive immunity.
Natural killer cells
Phagocytosis is the ingestion of microorganisms and other particles by a cell.
Phagocytes are collective cells that perform phagocytosis.
Phagocytes are activated by cytokines, lipid A and lipopolysaccharides (LPS).
The Mechanisms of Phagocytosis
1. Chemotaxis and adherence of microbe to phagocyte
Microbe surface attaches to the plasma membrane of the phagocyte.
2. Ingestion of microbe by phagocyte
Pseudopods engulf the microbe
3. Formation of a phagosome
Phagosome surrounds the microbe.
4. Formation of phagolysosome
Fusion of phagososome and lysosome.
5. Digestion of ingested microbe by enzymes.
6. Formation of residual body containing indigestible material.
7. Discharge of waste materials.
Defensive response triggered by damage to the body’s tissue.
It is characterized by redness, pain, heat, swelling and loss of function.
Accute inflammation is an intense and short lasting inflammation. Example:
response to boil.
Chronic inflammation is a less intense but long lasting inflammation. Example:
response to tuberculosis.
Process of Inflammation (3 Stages)
1. Vasodilation and increased permeability of blood vessels.
Vasodilation is the dilation of blood vessels that increase blood flow to the
damage tissue causing erythema (redness) and head associated inflammation.
Increased permeability allows fluid to move from blood into tissue spaces causing
Histamine is a chemical substance released by damaged cells in response to injury
and the causative agent of vasodilation and increased permeability.
Abscess is the focus of infection consisting of localized collection of pus, dead
cells and body fluids in a cavity as a cause of the breakdown of body tissues.
2. Phagocyte Migration and Phagocytosis.
Margination is the sticking process of neutrophils and monocytes to the inner
surface endothelium of blood vessels.
3. Tissue Repair
Stroma is the supporting connective tissue that causes scar for example in the case
of major tissue damage.
Parenchyma is the functioning part of the tissue that can repair minor tissue
damage with no visible signs.
Fever is an abnormally high body temperature. (above 37 deg Cel or 98.6 deg F)
Hypothalamus is the thermostat of the body (Microorganism releases LPS
Phagocyte release interleukin-1hypothalamus releases prostaglandin
reset hypothalamus thermotat)
Shivering and chill is a sign of that body temperature is increasing.
Crisis is the phase of the fever when the body temperature is falling.
1. The Complement System
Complement system is a defensive system consisting of over 30 proteins
produced by the liver and found circulating in the blood serum.
Proteins of the complement system destroy microbes by cytolysis, inflammation,
phagocytosis, and prevent excessive damage to host tissues.
Interferons (IFNs) are antiviral proteins and host-specific produced by certain
cells such as lymphocytes and macrophages to prevent viral multiplication.
Transferrins are iron-binding proteins found in the blood, milk, saliva, and tears
that inhibit the growth of bacteria by reducing the available amount of iron.
4. Antimicrobial Peptides
Consist of dozen amino acids produce my mucous membrane cells and
phagocytes that binds to microbial plasma membranes to cause lysis.