A tuberculin skin test becomes positive with induration peaking 48 to 72 hours after intradermal injection of purified protein derivative. This reaction is best classified as which immunologic process?
- A Type I hypersensitivity mediated by IgE and mast cells
- B Type III hypersensitivity due to immune complex deposition
- C Delayed type hypersensitivity mediated by CD4+ Th1 effector memory T cells ✓
- D Antibody dependent cytotoxicity mediated by NK cells
Correct answer: C. Delayed type hypersensitivity mediated by CD4+ Th1 effector memory T cells
Explanation
The Mantoux reaction is the prototype of delayed type (type IV) hypersensitivity. Previously sensitized CD4+ Th1 memory cells recognize antigen presented by dermal APCs and secrete IFN-gamma and TNF, recruiting macrophages over 24 to 72 hours to produce induration. IgE reactions appear within minutes, ruling out option A, and immune complex (Arthus) reactions peak at 4 to 10 hours with a hemorrhagic edematous morphology, distinguishing them from the delayed cellular infiltrate seen here.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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