A 35-year-old woman develops jaundice and dark urine two weeks after starting a new medication. Smear shows spherocytes, reticulocytosis, and the direct antiglobulin test is strongly positive for IgG and C3b. Splenic macrophage destruction of antibody-coated red cells represents which type of hypersensitivity reaction?
- A Type I
- B Type III
- C Type II ✓
- D Type IV
Correct answer: C. Type II
Explanation
Warm antibody autoimmune hemolytic anemia is mediated by IgG antibodies coating red cells, leading to Fc receptor mediated phagocytosis by splenic macrophages, a classic type II antibody dependent cytotoxic hypersensitivity reaction. Type I involves IgE and mast cells, type III involves immune complex deposition, and type IV is T cell mediated delayed hypersensitivity. The positive direct Coombs test for IgG confirms antibody bound to the patient's own erythrocytes.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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