Influence of methionine-enkephalin on interleukin-2 production and interleukin-2 receptor expression

Influences of methionine enkephalin (met-enk) on delayed hypersensitivity (DH) against 2,4-dinitrofluoro-benzene (DNFB) and interleukin-2 (IL-2) production of mouse lymphocytes were examined. Met-enk enhanced the DH response to ear challenge when mice were treated with met-enk beginning at the same time as cpicutaneous sensitization with DNFB but not after being sensitized. When met-enk (10 nmol.L-1-100 mumol.L-1) was included in Con A-stimulated lymphocyte cultures, the IL-2 production increased in a concentration-dependent manner. Furthermore, in vivo treatment with met-enk also increased IL-2 production of splenocytes, and the enhancement of IL-2 production was parallel to that of lymphocyte proliferation. However, met-enk 10 nmol.L-1 had no effect on IL-2 receptor expression on thymocytes, splenocytes, and gut-associated lymphocytes. The data suggested that the stimulative effect of met-enk on lymphocytes may be mediated through the increase of IL-2, but not through the IL-2 receptor expression.