Micro & Immunology · single question
What is the mechanism of a Type IV hypersensitivity reaction?
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Correct answer: C. Delayed-type, cell-mediated hypersensitivity involving T lymphocytes
Type IV hypersensitivity (also called delayed-type hypersensitivity, DTH) is mediated by T lymphocytes (specifically CD4+ Th1 cells), not antibodies. It is called 'delayed' because the reaction typically occurs 48-72 hours after antigen exposure. Examples include contact dermatitis (e.g., latex allergy), tuberculin skin test reaction, and granulomatous reactions. Type I is IgE-mediated (anaphylaxis, atopy). Type II is antibody-dependent cytotoxicity. Type III is immune complex-mediated (e.g., serum sickness, SLE).
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