Myelopeptide-1 blocks the T-suppressor activity.

The immunoregulatory properties of two myelopeptides (MPs) [Phe-Leu-Gly-Phe-Pro-Thr (MP-1) and Leu-Val-Val-Tyr-Pro-Trp (MP-2)] were studied. The antibody production-stimulating activity was determined in the culture of lymph node cells (LNC) obtained from mice on the 4th day of the secondary immune response to sheep red blood cells (SRBC). T suppressors were induced in mouse spleen cell (SC) culture by incubation with concanavalin A (Con A) for 48 h. Immune LNC were cultured alone or with T suppressors in the presence or absence of MPs. After cultivation, the immune response was estimated by enumeration of indirect antibody forming cells (AFC). MP-1, but not MP-2, increased the number of AFC and abolished Con A induction of T suppressors in SC suspensions. MP-1 also fully blocked and MP-2 only partly decreased the inhibitory effect of T suppressors in the culture of immune LNC. Immunoregulatory peptide MP-1 may participate in regulation of the antibody response and in development of some states of immunological tolerance.