EXPRESSION OF DOPAMINE-RECEPTORS IN IMMUNE ORGANS AND CIRCULATING IMMUNE CELLS

The existence of dopamine (DA) D-1- and D-2-like receptors in the rat and pigeon thymus and in human peripheral blood lymphocytes was invest igated. The selective D-1-like antagonist [H-3]-SCH 23390 was used as a ligand of DA D-1-like receptors (D-1 and D-5 sites). Pharmacological analysis suggests that binding of [H-3]-SCH 23390 to sections of thym us and to human peripheral blood lymphocytes belongs mainly to the dop amine D-5 receptor subtype. Light microscope autoradiography, performe d in sections of rat and pigeon thymus, revealed that these receptors are located primarily in the cortical layer. DA D-2-like receptors (D- 2, D-3 and D-4 sites) were studied in sections of rat thymus and in pe ripheral blood lymphocytes by using the putative DA D-3 receptor agoni st [H-3]-7-OH-DPAT as a ligand. Both rat and pigeon thymus and human p eripheral blood lymphocytes express a putative DA D-3 receptor. These data are in agreement with recent molecular biology studies performed in human peripheral blood lymphocytes. The demonstration of different subtypes of DA receptors in a primary immune organ such as the thymus and in circulating immune cells supports the hypothesis of an involvem ent of DA in the control of immune function.