Glomerular Diseases USMLE Step 1 Practice Question

A 13-year-old boy presents with periorbital and lower extremity edema. Vital signs reveal BP 142/88 mmHg, HR 88/min, RR 18/min, and Temp 37.2°C. Urinalysis shows hematuria and proteinuria (3.2 g/day). Serum creatinine is 1.8 mg/dL (baseline 0.8), with low C3 (45 mg/dL) and normal C4 levels. Renal biopsy demonstrates electron-dense ribbon-like intramembranous deposits on electron microscopy. He denies recent streptococcal infection. Which mechanism most likely explains his glomerulonephritis?