Expression of alpha-AR subtypes in T lymphocytes and role of the alpha-ARs in mediating modulation of T cell function

Previous work in our laboratory has shown that alpha-adrenoreceptors (alpha-ARs) and beta-ARs exist on lymphocytes from functional profile, and that the receptors mediate the regulation of lymphocyte function by catecholamines. In the present study, we directly examined the expression of alpha-AR subtypes, alpha(1)-AR and alpha(2)-AR mRNAs, in T lymphocytes and explored the roles of the alpha-AR subtypes and intracellular signal transduction mechanisms linked to the receptors in mediating the modulation of T lymphocyte function.

T lymphocytes from mesenteric lymph nodes of rats were purified by using a nylon wool column. Reverse transcription polymerase chain reaction was used to detect the expression of alpha(1)-AR and alpha(2)-AR mRNAs in the freshly isolated T cells and the mitogen concanavalin A (Con A)-activated lymphocytes. Colorimetric methylthiazoletetrazolium assay was employed to measure lymphocyte proliferation induced by Con A. Interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) levels in the Con A-stimulated lymphocyte culture supernatants were examined by enzyme-linked immunosorbent assay.

T cells expressed both alpha(1)-AR and alpha(2)-AR mRNAs. The expression of both alpha(1)-AR and alpha(2)-AR mRNAs was significantly higher in the Con A-activated lymphocytes than in the resting lymphocytes. Phenylephrine, a selective alpha(1)-AR agonist, had no evident effect on lymphocyte proliferation nor on IFN-gamma and IL-4 production induced by Con A. However, the selective alpha(2)-AR agonist clonidine attenuated Con A-induced lymphocyte proliferation as well as IFN-gamma and IL-4 production. The inhibited lymphocyte proliferation and IFN-gamma and IL-4 production by clonidine were blocked by yohimbine, an alpha(2)-AR antagonist. Either phospholipase C inhibitor U-73122 or protein kinase C inhibitor chelerythrine partially prevented the suppressive effect of clonidine on Con A-stimulated lymphocyte proliferation and IL-4 production.

T lymphocytes express both alpha(1)-ARs and alpha(2)-ARs, but only the alpha(2)-ARs participate in the suppressive modulation of lymphocyte proliferation and cytokine production in vitro. The inhibitory effect of alpha(2)-AR stimulation on lymphocyte function is partially mediated via the phospholipase C-protein kinase C pathway.