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 1ymphocytes. 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.