Heparin-induced thrombocytopenia type 2 (HIT) is a prothrombotic complication mediated by antibodies against which antigen?

• A Glycoprotein IIb-IIIa (integrin alphaIIb-beta3)
• B Phospholipid-beta2 glycoprotein I complex
• C Platelet factor 4 (PF4)-heparin complex ✓
• D Von Willebrand factor multimers

Explanation

HIT type 2 is caused by IgG antibodies against the complex of heparin and platelet factor 4 (PF4), a cationic platelet alpha-granule chemokine. The antibody-antigen complexes bind platelet FcgammaRIIA receptors, causing platelet activation, aggregation, and consumption (thrombocytopenia), while simultaneously activating monocytes and endothelial cells to generate tissue factor and thrombin, creating a paradoxical hypercoagulable, thrombotic state despite thrombocytopenia. Anti-beta2-GPI antibodies cause antiphospholipid syndrome. Anti-GPIIb-IIIa antibodies cause immune thrombocytopenia.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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