Epithelial secretion of C3 promotes colonization of the upper urinary tract by Escherichia coli.

To assess the role of complement in renal infection, we studied a model of Escherichia coli-induced pyelonephritis in mice deficient in complement components C3 and C4. Renal infection occurred less frequently in C3- and C4-deficient mice compared with wild-type mice. In vitro, renal epithelial cells internalized fewer bacteria in the absence of C3 or in the presence of blockade of C3 bound to the bacteria. Moreover, upregulation of epithelial C3 production by stimulation with lipopolysaccharide enhanced bacterial internalization. Here we provide evidence that uropathogenic E. coli might use host C3 to invade the renal epithelium and that local complement production is sufficient for the bacteria to achieve this effect.