We have previously shown in inbred strains of mice which naturally develop systemic lupus erythematosus that kidney C3, C2, C4 and factor B gene expression increases coincidently with the occurrence of glomerulonephritis, suggesting that local tissue complement gene expression could contribute to the pathogenesis of immune complex injury. In this study, we investigated the synthesis of complement proteins in glomerular epithelial cells (GECs) and its regulation. Using biosynthetic labelling, immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we demonstrated that GECs synthesized Clr, Cls, Cl inhibitor, C3, C2 and factor B. Interferon-γ induced increases in the synthesis of all these proteins. Both factor B and C3 proteins were increased following addition of either IL-1β, IL-6 or TNF-α to GEC cultures; however, these cytokines did not increase either C2, Clr, Cls or Cl-inhibitor biosynthesis. Lipopolysaccharide affected the biosynthesis of these proteins in a similar way. A semiquantitative analysis of the mRNA expression of some of these proteins by reverse-transcriptase polymerase chain reaction showed that these cytokine effects were pretranslational as there was enhancement of factor B mRNA expression by IL-1 TNF-α, IFN-γ, IL-6 and endotoxin, but only IFN-γ enhanced Cl-inhibitor and C4 mRNA expression. These results may be of significance in the immunopathogenesis of glomerulonephritis, where it is likely that local complement production in GECs is independently regulated by cytokines, derived from resident glomerular mesangial cells or infiltrating monocyte/macrophages and T cells.

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