Experimental glomerular lesions induced by chronic immune complex formation. I. Formation and elimination of the immune complex (relationship between the immune status and the glomerular changes)

Induction of membranous nephropathy in rabbits by administration of an exogenous cationic antigen

We examined the role of antigenic electrical charge as a determinant of glomerular immune complex localization in the rabbit. Serum sickness nephritis was induced in groups of New Zealand white rabbits by daily 25-mg intravenous injections of bovine serum albumin (BSA) chemically modified to be cationic (pI > 9.5) or more anionic (pI, 3.5-4.6); an additional group received unmodified native BSA (pI, 4.5-5.1). Factors known to influence immune complex localization, e.g., molecular size of the administered antigen and resulting circulating immune complexes, immunogenicity, and disappearance time from the circulation were examined and found to be similar for both anionic and cationic BSA. Charge modification did increase the nonimmune clearance of cationic and anionic BSA compared with native BSA. Injected cationic BSA was shown in paired label experiments to bind directly to glomeruli compared with native BSA. The renal lesion produced by cationic BSA was markedly different from that found in rabbits given anionic or native BSA. Animals receiving cationic BSA uniformly developed generalized diffuse granular capillary wall deposits of IgG, C3, and BSA detected after 2 wk of injections and increasing until death at 6 wk. Qualitatively similar deposits were produced by the administration of low doses of cationic BSA of only 1 or 10 mg/d. In contrast, the injection of both anionic and native BSA resulted in mesangial deposits at 2 and 4 wk with capillary wall deposits appearing by 6 wk. Ultrastructural examination of animals receiving cationic BSA revealed pure, extensive formation of dense deposits along the lamina rara externa of the glomerular basement membrane whereas such deposits were absent or rare in animals injected with the anionic or native BSA. Albuminuria was significantly greater at 6 wk in the groups receiving cationic BSA with a mean of 280 mg/24 h compared with 53 mg/24 h in the combined groups injected with anionic or native BSA. Blood urea nitrogen values were similar in all groups at 2 and 4 wk but higher in the animals receiving cationic BSA at 6 wk. These experiments describe the reproducible induction of epimembranous immune deposits by administration of an exogenous cationic antigen. They suggest that antigenic charge can play an important role in the pathogenesis of membranous nephropathy by permitting direct glomerular binding of an antigen and predisposing to in situ immune complex formation.

Experimental glomerular lesions induced by chronic immune complex formation. II. Pathomorphological analysis

Eleven rabbits were given bovine serum albumin i.v., in daily doses of 25 mg. Renal biopsy was performed on the 30th, 60th and 100th day of treatment and the specimens were subjected to light-, electron-microscopic and immunofluorescent studies, so as to follow up the dynamics of the glomerular process. Proteinuria and the serum creatinine and BUN levels were also measured. By the 100th day of treatment mesangioproliferative glomerulopathy had developed in 7, membranoproliferative glomerulopathy in 3 cases and membraneous glomerulopathy in 1 case. On the 30th day of treatment exudative glomerulopathy was demonstrable in the majority of the cases (in 9 animals). It is suggested that the earliest stage of the various glomerulopathies, regardless of their type, is marked by exudative lesions. The heaviest proteinuria was found in membraneous and membranoproliferative glomerulopathies. Changes in the serum creatinine and BUN levels indicative of a deteriorating renal function were noted in the membranoproliferative cases. The results are correlated with clinical observations of human glomerulopathies.