Microbiology

To isolate/eliminate pathogens

Hypersensitivity

Autoimmunity

An immune response to an environmental agent (allergen)

Allergy

Type I: immediate or anaphylactic

Type II: antibody-dependent cytotoxic

Type III: immune-complex

Type IV: delayed or cell-mediated

Immediate-type or anaphylactic hypersensitivity:

Fast! Occurs 5-30 minutes after exposure

Immediate-type or anaphylactic hypersensitivity:

inhaled: hay fever, pet dander, mold spores, dust mites

injected: bee sting allergies, vaccines, drugs

ingested: food, orally administered drugs (penicillin)

Anaphylactic reactions:

1. initial allergen exposure induces IgE production

2. IgE "sensitizes" mast cell by attaching its FC region (leg of Ab) to mast cell surface receptor (IgE normally is not on mast cells.

3. subsequent allergen exposure

4. Fc receptors cross linked

5. degranulaltion of histamine and/or leukotriens (highly inflammatory)

Antibody-dependent cytotoxic hypersensitivity:

Ab combines with host cell--death by complement activation or phagocytosis

Antibody-dependent cytotoxic hypersensitivity:

blood group incompatibility

Rh factors in pregnancy

Immune-complex hypersensitivity:

Small particulate Ab-Ag combination (called immune complex)

• This complex can stimulate the rest of the immune system
• -results in surrounding host cell/tissue destruction
• -serum sickness

• example:
• -Snake venom

Delayed or Cell-mediated hypersensitivity:

Occurs ~24-72 hours after Ag exposure

• example:
• -TB skin test
• -Poison ivy

An immune response to self proteins

• Immune cells that attack the host (self) are removed during fetal development
• -called clonal deletion

Autoimmunity is loss of self tolerance

Cytotoxic autoimmune reactions

Immune complex autoimmune reactions

Cell-mediated autoimmune reactions

Antibodies react to cell-surface Ag

No cytotoxic destruction of host cells

• examples:
• -Myasthenia gravis (muscle weakness)--make Ab against Ach receptors and the receptors get destroyed
• -Graves' disease (overactive thyroid)

Immune complexes are deposited on host cells

• examples:
• -Systemic lupus erythematosus--autoimmune response is directed at autoantigens present in almost all host cells. Inflammatory reaction = cell/tissue destruction. Trigger factors remain unknown
• -Rheumatoid arthritis--joint infiltration with immune cells. Eventually, immune cells release proteinases and collagenases that damage cartilage, ligaments, and tendons.

Mediated by T cells (no antibodies)

• examples:
• -Multiple sclerosis--immune response to myelin basic protein. Infiltration of immune cells in CNS. Create T cells that attack myelin sheath.
• -Insulin-dependent diabetes mellitus--selective destruction of insulin producing cells in the pancreas. AKA type I diabetes (juvenile-onset). Attacks insulin-making cells--> B cells.