Endogenous complement C3 synthesis in immune complex nephritis.

Human renal epithelial and mesangial cells have been shown to synthesise complement C3 in culture, but the relevance of this finding to the development of complement-mediated nephritis is uncertain. We investigated C3 gene expression in tissue biopsies that showed three main categories of renal injury. By semiquantitative polymerase chain reaction, biopsies from patients with immune-complex glomerulonephritis and those with cell-mediated interstitial nephritis showed increased C3 expression (p < 0.05), but biopsies from patients with non-immune glomerular injury did not. These findings suggest that local C3 production is enhanced in immune-mediated nephritis and are consistent with the hypothesis that locally synthesised complement components are involved in the pathogenesis of tissue injury.