Enkephalins as immunomodulators.

The protective effects of methionine enkephalin as well as leucine enkephalin were studied in BDF1 mice inoculated with 1 X 10(4) and 1 X 10(2) cells of L1210 murine leukemia. Significant increases in number of survivors were observed in mice treated with enkephalins. Methionine enkephalin in the presence of PHA was found to stimulate lymphocyte blastogenesis at concentrations of 1 mg/ml to 10(-8) mg/ml. In the case of leucine enkephalin, concentrations of 1 mg/ml to 10(-10) mg/ml stimulated blastogenesis. Stimulation of blastogenesis was seen at PHA dilutions of 1:100, 1:250, 1:750, with both methionine enkephalin and leucine enkephalin. The results are discussed in terms of immunomodulation. It is proposed that endogenous enkephalins play a neuroendocrine role between the central nervous system and the immune system and are direct immunostimulants.