Immunosuppressive activity of C-terminal fragments of tachykinins

The immunosuppressive activity of three pentapeptides related to the C-terminal fragments of tachykinins was investigated using the PFC (plaque forming cell) test. The peptides were of the general structure Phe-X-Gly-Leu-Met-NH2, with Tyr, Val and Ile in X position, respectively. The results were compared with those obtained previously for the substance P (SP) C-terminal pentapeptide. It was found that peptides containing aromatic residues in X position were more potent immunosuppressors than peptides containing aliphatic residues in the same position. The results also suggest that in mammalian organisms substance SP may be involved in immunomodulation which is rather not the case with other mammalian tachykinins (neurokinin A and neurokinin B).