Expression of dopamine receptors in immune organs and circulating immune cells

The existence of dopamine (DA) D1- and D2-like receptors in the rat and pigeon thymus and in human peripheral blood lymphocytes was investigated. The selective D1-like antagonist [3H]-SCH 23390 was used as a ligand of DA D1-like receptors (D1 and D5 sites). Pharmacological analysis suggests that binding of [3H]-SCH 23390 to sections of thymus and to human peripheral blood lymphocytes belongs mainly to the dopamine D5 receptor subtype. Light microscope autoradiography, performed in sections of rat and pigeon thymus, revealed that these receptors are located primarily in the cortical layer. DA D2-like receptors (D2, D3 and D4 sites) were studied in sections of rat thymus and in peripheral blood lymphocytes by using the putative DA D3 receptor agonist [3H]-7-OH-DPAT as a ligand. Both rat and pigeon thymus and human peripheral blood lymphocytes express a putative DA D3 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 involvement of DA in the control of immune function.