Methionine-enkephalin stimulates in vitro proliferation of human peripheral lymphocytes via δ-opioid receptors

Abstract

The influence of methionine-enkephalin (Met-Enk) on in vitro proliferation of human peripheral lymphocytes was investigated. Met-Enk, in the concentration range 10 −12 to 10 −4 M enhanced the proliferative response to suboptimal concentrations of concanavalin A of human peripheral lymphocytes and to cells in the absence of mitogen. The response was donor-dependent characterizing most but not all individuals tested. The response to Met-Enk in the absence of mitogen was not influenced by the presence of fetal calf serum; similar levels of enhancement were seen in cultures supplemented with 10% autologous serum. Enhancement of proliferation was blocked in a concentration-dependent manner by both naloxone and the δ specific antagonist ICI-174864. The sensitivity to the antagonistic influence of ICI-174864 suggests strongly that the stimulatory influence of Met-Enk on human lymphocyte proliferation in the absence of mitogen is mediated via the δ-opioid receptor.