A 40-year-old male presents with edema and oliguria for 1 week. BP 160/100 mmHg, urinary protein 2g/24h, urinary RBCs 20-30/HP, serum creatinine 600 μmol/L, circulating immune complexes (CIC) (+). Renal pathology: Light microscopy shows 11 glomeruli, partial capillary narrowing, 6 cellular crescents, 3 fibrous crescents. IgG and C3 show granular deposition along capillary walls and mesangium. The diagnosis is: