In the present study we investigated the effect of thyrotropin (TSH) on both the proliferative capacity and the natural killer (NK) cell activity of murine spleen lymphocytes. It was found that TSH at various concentrations significantly increased the proliferative response of mouse lymphocytes to both concanavalin A (Con A) and phytohemagglutinin (PHA). This increase was particularly evident when suboptimal concentrations of mitogens were used (40-50% increase). The administration to cell cultures of TSH alone could not induce a significant stimulation of proliferative capacity. In order to provide a better knowledge about the mechanism by which TSH improved the mitogen-induced lymphocyte proliferation, the effect of the pituitary hormone on lymphocytes directly stimulated with recombinant interleukin-2 (RIL-2), was examined. It was observed that there was a great increase in IL-2-induced lymphocyte proliferation by TSH. The improvement in proliferative capacity of lymphocytes was particularly evident by using suboptimal rIL-2 concentrations (25-30% increase). The studies carried out on the cytotoxic activity of NK cells showed that TSH was able to significantly increase the IL-2-induced NK cell activity without modifying the basal levels of cytotoxicity. The results support the immunoregulatory role of TSH and contribute towards understanding the mechanisms of interaction between neuroendocrine and immune systems.
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