Nonspecific Immune Defenses
Unbroken skin with antimicrobial peptides called defensins, plus lysozyme, a
bacteriocidal enzyme found on the skin.
Bleeding, running nose, cough, abundant vaginal secretions.
Acidity of stomach, cilia in lungs.
Normal bacterial flora of gut, mouth, vagina, etc.
Filtering of lymph in lymph nodes.
Phagocytic cells (especially macrophages) in lungs, vagina, uterus, liver. These have
"Toll-like receptors" on their surfaces that recognize "pathogen-associated
molecular patterns" like bacterial flagella and double-stranded viral RNA.
Natural killer cells, a type of lymphocyte that punches holes in cancer cells and cells
infected with viruses, some bacteria, and some fungi.
Complement, a series of proteins that make holes in the membranes of invading
pathogens, make them easier to phagocytize, and attract white blood cells.
Interferon, a cytokine that that helps cells resist viral attack.
Tumor necrosis factors, cytokines that initiate inflammation responses and fever as
well as attack tumors.
The inflammation response, including:
a) increased blood flow to a damaged area and increased permeability of capillaries
due to release of histamine from damaged tissues;
b)action of complement;
c) attraction of phagocytic macrophages and neutrophils.
For systemic infections, fever. This retards the growth of pathogens, increases the
activity of defensive cells, and sequesters iron in the liver.
Cytokine - a general name for a molecule (usually a glycoprotein) that stimulates cells to divide or
become active. Interferon and interleukins are cytokines.
Specific immune defenses - immune mechanisms that mount a very vigorous attack against a particular
invader. Specific immune defenses involve either antibodies, killer T cells, or complement.
Specificity - ability to attack only a certain invader.
Diversity - ability to attack a wide (perhaps infinite) variety of invaders.
Danger recognition - ability to ignore harmless foreign molecules and respond to those that pose a threat,
usually because they cause tissue damage.
Memory - ability to attack an invader even more quickly and forcefully the second time it appears, even if
this is years later.
Self/nonself recognition - ability to mount attacks against invaders while not attacking the body's own
tissues. This ability is lost in autoimmune diseases.