Identification of the Polymorphonuclear Leukocyte C5a Receptor

The peptide C5a is thought to play an important role in the inflammatory response primarily through its action on the polymorphonuclear leukocyte (PMN). The receptor for C5a on human PMN has now been identified by affinity labeling. Cross-linking 125I-C5a to intact PMN with disuccinimidyl suberate produced a species that had a molecular mass on sodium dodecyl sulfate gels of 5.2 X 10(4) daltons. We believe this species represents a complex between C5a and its receptor for the following reasons. The band is eliminated if the cross-linking experiment is performed in the presence of a large excess of unlabeled C5a, but is unaffected by the presence of nonspecific protein or the chemotactic factors N-formyl-Met-Leu-Phe and leukotriene B4. The 5.2 X 10(4)-dalton species is not observed if the cross-linker is omitted. Finally, the dose-response curves for the inhibition of binding of 125I-C5a by unlabeled C5a and the inhibition of cross-linking are similar. Subtraction of the molecular mass of C5a from that of the complex gives a molecular mass for the binding moiety of the C5a receptor of 4.0 X 10(4) daltons.