New analogs of the immunoregulatory PRP-pentapeptide.

To determine the role of consecutive amino acid residues in the immunoreactivity of the shortest active fragment of PRP, a series of analogs substituted by L-alanine in successive positions of the peptide chain was synthesized. The immunological investigations were carried out in several models: the immune response to T-cell dependent antigen, SRBC (in vivo and in vitro) and to T-cell independent antigen, PVP in vitro. The immunotropic action of the peptide was, in addition, verified with respect to thymocytes forming autologous rosettes. The results of these experiments revealed immunotropic activity (in all tests) of the analog containing alanine instead of proline in position 5 of PRP-pentapeptide.