BIO 250
R. Donham
Immune System
Overview
I. Nonspecific Defenses
II. Specific Defenses
III. Disfunction
I. Nonspecific Defenses
a. First Line of Defense: innate and nonspecific. Skin, mucus membranes, hair in ears and
nose, acid in stomach, lysozyme (in tears, nasal mucus, saliva), resident microorganisms
(normal flora), etc.
b. Second Line of Defense: innate and nonspecific. Complement proteins (punch holes in
bacteria, trigger inflammation, provide handles), Interferons (cause neighboring cells to
release antiviral proteins), phagocytes (white blood cells that engulf and destroy pathogens),
natural killer cells (kill virally infected or cancerous cells), inflammation.
i. Inflammation: redness, pain, heat, swelling. Injurymast cell and basophil
degranulation releases histamine. Histamine dilates capillaries so that blood plasma is
released, as well as complement proteins, phagocytes and cytokines (fever).
II. Specific Defenses
a. Third Line of Defense: acquired (needs to be upregulated), specific (recognizes a particular
antigen), immunological memory
i. B Lymphocytes are involved in humoral immunity.
1. When a particular antigen binds to a BCR (B cell receptor), it triggers that
particular cell to undergo clonal expansion. It produces plasma cells (which
produce antibodies) as well as memory cells.
a. Antibodies: proteins that have specific antigen binding sites. When
bound, and antibody can stimulate the complement system, inflammation,
recruitment of other WBC’s, act as opsonins, etc.
ii. T Lymphocytes are involved in cellular immunity.
1. Helper T Cells: activated when bind to MHC II (antigen system found on antigen
presenting cells) and presented antigen.
a. Undergoes clonal expansion, produces many cytokines. Cytokines work
with the humoral immune system to increase clonal expansion of the B
cells.
2. Cytotoxic T Cells: activated when bind to MHC I (antigen system found on any
nucleated cell) and viral or cancer antigen
a. Undergo clonal expansion, produce perforin enzymes (punch holes in
cells) and granzymes (trigger apoptosis in infected or cancerous cell).
iii. Memory allows vaccines to work. The vaccine triggers the 3rd line of defense and
memory cells last for months to life.
III. Disfunctions:
i. Allergies: overactive immune response, results from sensitization (repeated exposure)
ii. HIV/AIDS: virus attacks Helper T Cells, and victims succumb to opportunistic
infections