Expression of preproenkephalin mRNA and production and secretion of enkephalins by human thymocytes

Human thymocytes were tested for the capacity to express the preproenkephalin (PPE) gene and for production of the end product metenkephalin (MENK). It is shown here for the first time that the cytokines IL-2, IL-4, IL-6, and TGF-β are capable of inducing PPE mRNA expression. Moreover, a culture of thymocytes with the cytokines results in intracellular expression of MENK as determined by immunohistochemistry. Thymocytes do not secrete detectable amounts of MENK, however, but only the larger MENK-containing peptides or proteins. Cytokines IL-1β and IL-10 increase the expression of PPE mRNA in 50% of the thymuses tested, whereas IFN-γ does not induce changes in PPE mRNA expression.