A 34-year-old man presents with chronic sinusitis, hemoptysis, and rapidly rising creatinine. Urinalysis shows red cell casts. Cytoplasmic staining (c-ANCA) pattern is seen on indirect immunofluorescence of ethanol-fixed neutrophils. The specific antigen recognized by this antibody is:

• A Proteinase 3 ✓
• B Myeloperoxidase
• C NC1 domain of the alpha 3 chain of type IV collagen
• D Elastase

Explanation

Granulomatosis with polyangiitis (Wegener granulomatosis) is characteristically associated with c-ANCA directed against proteinase 3, a serine protease in neutrophil azurophilic granules. Perinuclear staining (p-ANCA) with antimyeloperoxidase antibodies instead points toward microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis. Antibodies against the NC1 domain of the alpha 3 chain of type IV collagen define anti-GBM disease, a separate entity that can also cause pulmonary hemorrhage and crescentic glomerulonephritis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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