C5a anaphylatoxin as a product of complement activation up‐regulates the complement inhibitory factor H in rat Kupffer cells

Open Access
Publisher Website
Google Scholar
Abstract
The 155‐kDa complement regulator factor H (FH) is the predominant soluble regulatory protein of the complement system. It acts as a cofactor for the factor I‐mediated conversion of the component C3b to iC3b, competes with factor B for a binding site on C3b and C3(H2O) and promotes the dissociation of the C3bBb complex. The primary site of synthesis is the liver, i.e. FH‐specific mRNA and protein were identified in both hepatocytes (HC) and Kupffer cells (KC). Previous studies in rat primary HC and KC had shown that the proinflammatory cytokine IFN‐γ influences the balance between activation and inhibition of the complement system through up‐regulation of the inhibitory FH. In this study we show that C5a, as a product of complement activation, stimulates the expression of FH‐specific mRNA and protein in KC and thus induces a negative feedback. Quantitative‐competitive RT‐PCR showed an approximate threefold C5a‐induced up‐regulation of FH. ELISA analyses revealed a corresponding increase in FH protein in the supernatants of KC. The up‐regulation of FH was completely inhibited by the C5a‐blocking monoclonal antibody 6‐9F. Furthermore, an involvement of LPS and IFN‐γ was excluded, which strongly indicates a direct effect of C5a on the expression of FH in KC.