Isolation of modified ubiquitin as a neutrophil chemotaxis inhibitor from uremic patients.

Uremic toxins are factors that accumulate in the serum and peritoneal cavity of uremic patients. They are responsible for a variety of functional disturbances and also contribute to the increased risk of infection by interfering with essential functions of the unspecific immune response. From the peritoneal effluent of peritoneal dialysis (PD) patients, a peptide was isolated by applying three different chromatographic methods. This peptide inhibits the chemotactic movement of polymorphonuclear leukocytes (PMNL) in an in vitro assay in a concentration-dependent, nonreversible manner, and therefore belongs to the group of uremic toxins. Amino acid sequencing showed that the isolated peptide has the same amino terminal sequence as ubiquitin. The peptide also reacted with anti-ubiquitin antibodies in a Western blot experiment, but had a more acidic isoelectric point than ubiquitin. By using affinity chromatography, anti-ubiquitin antibody binding fractions were isolated from all PD and hemodialysis (HD) patients investigated. These fractions contained the same acidic band and also significantly inhibited PMNL chemotaxis. Ubiquitin per se had no effect on PMNL chemotaxis. Therefore, it is concluded that from PD and HD patients a modified form of ubiquitin was isolated, and this modification was responsible for its inhibitory effect.