EFFECT OF MET-ENKEPHALIN ON THE PROLIFERATIVE RESPONSE OF EQUINE PERIPHERAL-BLOOD MONONUCLEAR-CELLS AND PURIFIED T-LYMPHOCYTES

Enkephalins (ENK) are synthesized by neurons, glia, diverse carcinomas and various cells of the immune system. Work in other species indicat es that exercise affects plasma concentrations of ENK. Various studies suggest that this may result in altered resistance to disease and pro gression of existing diseases. The present study was performed in orde r to determine whether Met-ENK may regulate the proliferative response of equine peripheral blood mononuclear cells (PBMCs) or isolated T ce lls. Quadruplicate aliquots of PBMCs from two geldings (G), T cells fr om one gelding (G) and PBMCs from one adult mare (M) were incubated wi th suboptimal concentrations of the T cell mitogen phytohemagglutinin (PHA), in the presence or absence of 10(-5), 10(-7), 10(-9) and 10(-11 ) M Met-ENK. Treatments were added at the beginning of culture and the incorporation of H-3-thymidine was measured on day 3. The 10(-5) M EN K treatment inhibited mitogen-induced proliferation of PBMCs from G wh ereas the PHA response of G PBMCs was stimulated by 10(-11) M ENK trea tments. For cells collected from M, PHA-blastogenesis was significantl y reduced by 10(-5), 10(-9) and 10(-11) M ENK treatments. There was no stimulatory effect of ENK on PHA-responsiveness of PBMCs from M. The PHA-stimulated response of T cells was enhanced by 10(-7) and 10(-9) M ENK treatments. Lower and higher ENK concentrations had no effect on the proliferation of T cells. Results from this experiment suggest tha t physiological to superphysiological concentrations of ENK may effect the non-specific proliferative response of equine immune cells. Wheth er endogenous enkephalins act to modify the resistance of horses to va rious infectious diseases requires further study.