A 10-year-old boy presents with haematuria, hypertension, and periorbital oedema 2 weeks after a streptococcal throat infection. Electron microscopy of the renal biopsy shows large subepithelial electron-dense deposits described as 'humps'. Which complement pathway is primarily activated in this condition?

• A Alternative pathway via C3 nephritic factor
• B Lectin pathway via mannan-binding lectin
• C Terminal pathway only, without C3 consumption
• D Classical pathway via IgG/IgM immune complexes ✓

Explanation

Post-streptococcal glomerulonephritis (PSGN) is mediated by deposition of immune complexes (streptococcal antigens + antibodies) in the subepithelial space, activating the classical complement pathway; serum C3 is typically low while C1q and C4 may be mildly reduced. The large subepithelial 'humps' on EM are pathognomonic. The alternative pathway and C3 nephritic factor are characteristic of MPGN type II (dense deposit disease). The lectin pathway is not the primary mechanism in PSGN.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.