A peptide isolated from a patient on continuous ambulatory peritoneal dialysis has homology to ubiquitin and inhibits the chemotactic response of polymorphonuclear leukocytes.

Susceptibility to bacterial infections in the peritoneal cavity is a serious problem for peritoneal dialysis patients. Uremic toxins are among the causes of the diminished function of polymorphonuclear leuckocytes (PMNLs), cells of the local immune defense. We isolated from the peritoneal dialysis effluent of a uremic patient, a peptide that inhibits PMNL chemotaxis in a concentration-dependent manner. The amino terminus of this factor is identical to that of ubiquitin. The peptide shows the same size as ubiquitin on SDS-polyacrylamide gels, but has a more acidic isoelectric point than intact ubiquitin, which has no effect on PMNL chemotaxis. We conclude that we have isolated a modified form of ubiquitin and that this modification is responsible for its inhibiting effect on PMNL chemotaxis.