Bacterial lipopolysaccharide transforms mesangial into proliferative lupus nephritis without interfering with processing of pathogenic immune complexes in NZB/W mice

Abstract

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.