Synthetic C3a analogs as specific inhibitors of C3a activity.

Various C3a-related C-terminal synthetic oligopeptides were investigated for their ability to induce a release of serotonin from guinea pig platelets. The results confirm earlier findings that expression of biological C3a activity requires the four to five C-terminal amino acids of the C3a primary structure and underlines the essential role of the C-terminal arginine. Besides their ability to induce a specific release reaction, these peptides--after short incubation with the platelets--lead to a specific desensitization of the cells for C3a or C3a-related stimuli. Expression of this inhibitory activity required concentrations of the peptides more than 100-fold lower than those that were necessary to induce secretion. The possibility of using C3a analogs as specific inhibitors for C3a offers a valuable tool for in vivo studies of biological C3a activity.