Suppression of humoral immune responses by synthetic C3a peptides.

Synthetic oligopeptides based on the COOH-terminal sequence of native human C3a were examined for the ability to suppress antigen-specific and polyclonal antibody responses. The synthetic peptides were found to qualitatively mimic the suppressive actions of human C3a, but proved to be less active on a molar basis. Comparison of the activity of the peptides with native C3a indicates that the most potent peptide is C3a 57-77 with C3a 65-77, C3a 70-77, C3a[Ala 71,72]70-77, and C3a 73-77 being less active, respectively. These results indicate that the region of the C3a molecule responsible for immunosuppression is located in the COOH region.