A 25-year-old man with recurrent episodes of gross hematuria following upper respiratory tract infections has IgA deposits in the mesangium on renal biopsy. Which complement pathway is primarily activated in this disease?

• A Alternative pathway activated by polymeric IgA ✓
• B Classical pathway via C1q binding
• C Lectin pathway via mannose-binding lectin
• D Terminal complement pathway only

Explanation

IgA nephropathy (Berger disease) involves mesangial deposition of polymeric IgA1, which activates the alternative complement pathway. Unlike IgG and IgM, IgA does not efficiently bind C1q and thus bypasses the classical pathway. Complement activation contributes to mesangial injury and proteinuria. The hallmark clinical feature is synpharyngitic hematuria, distinguishing it from post-streptococcal GN where hematuria is delayed 1–3 weeks.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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