Relationship of Proteinuria to Glomerular Basement Membrane Deposits in Serum-Sickness Glomerulonephritis in Rabbits

Fifteen rabbits were injected with one dose of 250 milligrams per kilogram of bovine serum albumin intravenously to induce acute serum sickness. The kidneys were removed from groups of five rabbits each at 10, 12 and 14 days after injection and examined by light, electron and immunofluorescent microscopy for evidence of immune complex glomerulonephritis. Urine was examined for protein when rabbits died. Glomerulonephritis was found in eight rabbits by light microscopy and in 10 rabbits by electron microscopy. Only one rabbit had positive immunofluorescence for immunologic components and only two rabbits had proteinuria. Hypercellularity was the primary change seen by light microscopy. Ultrastructural changes were numerous and various, and the major changes recognized were irregularity of the glomerular basement membrane, increased mesangial matrix, hypercellularity, endothelial hypertrophy, mesangial deposits, epithelial foot process fusion and mesangial circumferential interposition. Subepithelial humps were seen in only four rabbits; none of these rabbits had proteinuria. We concluded that increased permeability followed the deposition of immune complexes and development of ultrastructural lesions.