C5 neoepitopes appearing during activation.

After activation of serum complement, a neoantigen was reported to appear on a 54,000-dalton fragment of C5. On the other hand, a monoclonal antibody (MoAb), No. 568, revealed that an epitope on the beta-chain of C5 became masked after the formation of SC5b-9 complex. Murine MoAbs were obtained to human C5a-des-Arg. Some of them are specific only to C5a-des-Arg but not to C5a or C5. Using these MoAbs, a sandwich immunoassay was devised for detection and measurement of C5a-des-Arg. The neoepitopes for these MoAbs were analyzed by their reactivities to synthetic peptide derivatives of human and porcine C5a, and the structural changes of C5a were suggested to occur after the removal of the carboxyl terminal arginine residue.