Enhancement of T lymphocyte proliferation and suppression of antibody producing cell formation by methionine-enkephalin.

Methionine-enkephalin (met-enk) 0.1-100 nmol/L significantly enhanced lymphocyte proliferation induced by T cell mitogens. On the other hand, the peptide markedly inhibited splenocyte blastogenesis induced by B cell mitogen lipopolysaccharides (LPS) and sheep red blood cell (SRBC)-driven plaque-forming cell (PFC) formation in vitro. Met-enk alone had no effect on immune responses. However, naloxone 50 nmol/L had also a stimulating effect on Con A-induced splenocyte proliferation. The similar results were also observed in vivo. The results also indicated that the enhancement of T cell function by met-enk was stronger in immunosuppressed mice than in the normal mice.