| α-Melanocyte-stimulating hormone (MSH) is a tridecapeptide that is derived from the precursor molecule pro-opiomelanocortin. Besides being a pigmentary hormone α-MSH also plays a crucial role in the regulation of immune and inflammatory reactions. α-MSH can reduce endotoxin-induced liver or brain inflammation, decline the mortality of endotoxic shock mice, suppress sensitization and elicitation of contact hypersensitivity as well as induce hapten-specific tolerance in mice. All these effects of α-MSH are mediated via melanocortin receptors (MCRs). Up to date, five subtypes of MCRs (MC1-R～MC5-R) have been found. MCRs were broadly distributed in many kinds of tissues and cells including immune cells such as monocytes/macrophages, neutrophils and B cells. MCRs were found in so many types of cells and the biological activities mediated by MCRS were investigated systemly. But the reports about MCRs expression on T lymphocytes, which are very important cells in immune responses, have not been found yet. It is unknown whether and what type(s) of MCRS are expressed on human T lymphocytes. The purpose of the first part in the present study was to examine whether there are specific MCRs for α-MSH expressed on human T cells. Radioligand competition and equilibrium-binding assays were performed using ?51-labeled NDP-MSH as a tracer. The results showed that a number of cL-MSH binding sites were detectable on Jurkat cells , which are immortal human T lymphocytes. Upon FACS analysis and immunofluorescence methods using specific goat-polyclonal antibodies against MC1 ～5R, T lymphocytes from normal human PBMC expressed proteins for five subtypes of MCRs. Following these tests, RT-PCR using MC1-, MC2-, MC3-, MC4-, MC5-R specific primer pairs were performed. PCR-products specific for MC1-, MC2-, MC3-, MC4-, MC5-R with the expected length were detectable in Jurkat and Molt-4 cells. So, the expression of MC1～5R by T cells was testified both in protein and gene level. In addition, it was found that all five types of MCRs were expressed on both CD4+ and CD8+T cells, but the number of each subtype of MCRs is unequal on different subtypes of T cells. In order to further investigate whether α-MSH can affect the functions of human T lymphocytes directly via binding specific MCR, we selected Jurkat cells as a target and investigated the effects of ct.α-MSH on the cells proliferation, the production of IL-2 and the expression of CD molecules of PHA-induced Jurkat cells. The results showed that α-MSH (1O-10mol/L～10-7mol/L) inhibited the production of JL-2 in dose-dependent "U-shape" , and these effects could be converted partly by pre-treated with the antibodies against MC1～5R respectively. Similar situations occurred in cell proliferation and the expression of CD2, CD3, CD25, CD28 and CD45 on PHA-induced Jurkat cells. The effect of α-MSH on the DNA-binding activity of NFAT, which plays a critical role in the production of IL-2, was investigated using EMSA. The DNA-binding activity of NEAT was inhibited by α-MSH at different concentration and may be one of the signal transduction mechanisms of the down-regulation effects of α-MSH on IL-2 production. According to the anti-inflammatory effects of a-MSH and the results in the first part, we infer that ct-MSH could inhibit the occurrence and the development of autoimmune diseases, which are mediated chiefly by T lymphocytes. Experimental allergic encephalomyelitis (EAE) is mediated mainly by CD4+T lymphoc...
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