Hypersensitivity reactions

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21st Century Complete Medical Guide to Allergy, Hay Fever, Hypersensitivity, Food, Latex, Dust Mite, Mold, and Pollen Allergies, and Allergic Reactions, ... for Patients and Physicians (CD-ROM)The Correct Answer is B


Hypersensitivity Type AB Complement effector cells Examples
Type I (immediate) IgE No Basophil, mast cell Anaphylaxis, hay fever, insect venom sensitivity, asthma
Type II (cytotoxic) IgG, IgM Yes PMN K cell Autoimmune hemolytic anemia. erythroblastosis fetalis, Goodpasture's syndrome
Type III (immune complex) IgG. IgM Yes PMN , M Serum sickness. SLE, R4, Glomeruloneplnritis, Arthritis
Type IV (delayed-cell mediated type ) None No CTL TH1, M Tuberculin test, poison ivy, contact dermatitis, transplant rejection.

Type I (immediate): Anaphylactic & atopic, Ag cross-links IgE on presensitized mast cells & basophils, triggering release of Vasoactive amines. Reaction develops rapidly after Ag exposure due to performed Ab.
Type II (cytotoxic): IgM, IgG bind to Ag on enemy cell. leading to lysis by complement or phagocytosis.
Type III (immune complex)
Immune complex: Ag-Ab complexes activate complement. which attracts neutrophils. neutrophils release lysosomal enzymes .
Serum sickness:An Immune complex disease in which Abs to the foreign proteins are produced (5 days). Immune complexes form & are deposited in membranes, where they fix complement, more common than Arthus reaction.

Arthus Reaction: A local subacute Ab mediated hypersensitivity reaction. Intradermal injection of Ag induces antibodies, which form Ag-Ab complexes in the skin Charaeterized by edema, necrosis, & activation of complement.

Type IV (delayed, cell mediated type): Sensitized T lymphocytes encounter antigen & then release lymphokines lead to macrophage activation.




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