Modulation of phagocytosis-associated respiratory burst by human cystatin C: Role of the N-terminal tetrapeptide LysProProArg

Abstract

Cystatin C, a cysteine protease inhibitor, has recently been suggested to be a potent regulator in inflammatory processes. Human cystatin C was isolated from the urine of one patient suffering from tubular disorders and was tested for its effects on two functions of human polymorphonuclear neutrophils (PMN): O 2 − release and phagocytosis. Slow-form or (des 1–4) cystatin C and fast-form or (des 1–8) cystatin C differed by the presence in (des 1–4) cystatin C only of the N-terminal tetrapeptide LysProProArg. Whereas (des 1–8) cystatin C did not seem to interfere with PMN functions at physiological concentrations, (des 1–4) cystatin C induced an inhibition of PMN phagocytosis-associated respiratory burst in response to opsonized zymosan particles. The inhibition may be attributed to the tetrapeptide LysProProArg which has been synthesized and shown to have the same inhibitor effects, at concentrations similar to those required for (des 1–4) cystatin C. These results support a potential role for cystatin C as a modulator during inflammation.