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Passive Heymann nephritis is an experimental rat model of human membranous nephropathy induced by injection of antisera against crude renal cortical fractions such as Fx1A or rat tubular microvilli. This results in the formation of subepithelial immune deposits, the activation of the C5b-9 membrane attack complex of complement, and severe proteinuria. While the formation of immune deposits is attributed to in situ immune complex formation with antibodies specific for the gp330-Heymann nephritis antigenic complex (HNAC), activation of complement and proteinuria appear to be caused by at least one additional antibody species present in anti-Fx1A sera. We have separated by affinity absorption polyspecific antisera against Fx1A and rat microvilli into one IgG fraction directed specifically against microvillar proteins (anti-Fx1A-prot) and another IgG fraction specific for glycolipids (ant-Fx1A-lip) of tubular microvilli. When injected into rats, the anti-Fx1A-prot fraction induced immune deposits but failed to activate complement or produce proteinuria, similar to results obtained with affinity-purified anti-gp330 IgG. When the antibodies of the anti-Fx1A-lip fraction were injected alone they did not bind to glomeruli. By contrast, when the IgGs specific for the Fx1A-prot fraction (or for gp330-HNAC) were combined with those directed against the Fx1A-lip glycolipid preparation, immune deposits were formed, in situ complement activation was observed, and also proteinuria was induced. It is concluded that within anti-Fx1A and anti-microvillar sera there are at least two IgG fractions of relevance for the development of PHN: one directed against the gp330-HNAC complex which is responsible for the development of immune deposits, and a second specific for glycolipid antigen(s) which activate(s) the complement cascade.

Systemic lupus erythematosus is a multifactorial systemic disease in which genetic, immunologic, hormonal, and environmental factors may contribute to disease pathogenesis. Bacterial products (eg, bacterial lipopolysaccharide [LPS]) induce a lupuslike disease in normal mice and trigger an early and accelerated form of lupus nephritis in NZB/W mice. To investigate whether the mechanism by which LPS accelerates nephritis in the NZB/W mice involves interference with processing of immune complexes (IC), we administered LPS to NZB/W mice for 5 weeks and probed the kinetics of removal, liver uptake, and organ localization of a subsaturating dose of radiolabeled IC (2.5 mg of bovine serum albumin-antibovine serum albumin). Control NZB/W mice received vehicle (saline) alone. In NZB/W exposed to LPS, features of polyclonal B-cell activation (PBA) were enhanced, anti-DNA antibodies were raised, and a proliferative glomerulonephritis developed that was associated with renal insufficiency and substantial proteinuria. This LPS-accelerated nephritis could not be attributed to altered complement concentration, to altered blood cell carrier function, to delayed removal of pathogenic (large-sized) ICs from the circulation, to impaired liver uptake of ICs, or to enhanced localization of ICs in kidney. The findings indicate that transformation of nephritis is probably the result of LPS-induced PBA, that defective processing of pathogenic IC is not a contributory factor to nephritis, and that mechanisms other than passive renal localization of circulating ICs must be operative.

Detailed immunopathologic studies of early or silent renal alterations in systemic lupus erythematosus have been sparse. The renal biopsies of 16 lupus patients with normal renal function, including 8 with hematuria and/or proteinuria of recent onset, and 8 without clinically detectable renal disease were investigated by light, immunofluorescence, and electron microscopy. Immunoglobulins, complement components, and electron-dense deposits were detected in glomeruli of all patients, regardless of morphologic appearance or lack of clinical evidence of renal involvement. Features of membranous glomerulonepritis were observed in 4 patients with substantial proteinuria. In the remaining 12 patients, including 3 with hematuria and 4 with slight proteinuria, either minimal glomerular alterations or features of mesangial proliferative glomerulonephritis were seen. Transformation of the original disease was demonstrated in 3 of 3 patients rebiopsied within 2 years. The significance of these findings is discussed in relation to a) the spectrum of clinical and immunopathologic alterations in lupus nephritis and b) transformation of the original disease.

Patients with progressive systemic sclerosis (PSS, scleroderma) exhibit a variety of immunologic abnormalities. To verify whether the renal vascular lesions of such patients might be mediated by an immunologic mechanism, kidney tissues of 16 patients with PSS were investigated by means of fluorescence, light, and electron microscopy; elution of tissue-bound antibody; and fixation of heterologous (guinea pig) complement. Controls consisted of 12 nonsclerodermatous patients with similar levels of hypertension with no evidence of associated immunologic abnormalities. Diffuse vascular deposits of immunoglobulins (predominantly IgM) and/or complement (predominantly Clq) were found in all 16 patients with PSS. These deposits were bound to the intima of intralobular and arcuate arteries which, by light microscopy, often exhibited typical fibromucinous alterations. Elution of antibody and heterologous complement fixation studies suggested that such reactants may represent the interaction of complement-fixing antibody and antigen. Electron microscopies studies demonstrated abundant fibrillar and ground substance material in the arterial intima but features of deposited (circulating) immune complexes were not found. By contrast, in the hypertensive (control) group, deposits of immunoglobulin (s) and/or complement were rare and, when present, were mostly confined to the arterioles. As judged by the results of elution and heterologous complement fixation, these arteriolar deposits appeared to represent trapped rather than specifically bound serum proteins. The possible signficance of these findings are discussed in relation to immunologic mechanisms which might be implicated in the pathogenesis of the renal vascular disease of PSS.

We investigated the effects of cyclophosphamide (Cy) on immunoreactants of plasma and kidney of mice with lupus nephritis. Cy therapy decreased plasma concentrations of IgG, but not the concentrations of anti-DNA antibodies, C3, and C1q reactive materials; in glomeruli deposits of immunoreactants were mesangial in location and decreased overall. Although Cy arrested the nephritis of NZB/W mice, the anti-DNA activity in the renal eluates was very low and comparable in untreated and in treated mice. Immune complex systems other than, or in addition to, DNA-anti-DNA are likely to play a role in the pathogenesis and course of murine lupus nephritis.