Organ System Pathology USMLE Step 1 Practice Question

A 13-year-old boy presents with periorbital edema, hematuria, and declining renal function. Vital signs show BP 145/92 mmHg, HR 88 bpm, RR 16, temperature 37.2°C, SpO2 98%. Serum creatinine is 1.8 mg/dL (elevated), C3 is low at 35 mg/dL, but C4 is normal at 18 mg/dL. Urinalysis shows 3+ protein. Renal biopsy demonstrates dense ribbon-like intramembranous electron-dense deposits on electron microscopy. No respiratory involvement is noted. Which mechanism most likely explains this disease?