T-cell subpopulations express a different pattern of dopaminergic markers in intra-and extra-thymic compartments

An involvement of dopamine in regulation of the immune function has been assessed and dopaminergic system has been found widely represented in thymus. Nevertheless detail on the characterization of dopaminergic system in assisting thymocytes development and lymphocytes mature physiology are still lacking. The present study was designed to characterize dopamine plasma membrane transporter (DAT), vesicular dopamine transporters (VMAT)-1 and -2, and dopamine D1-like and D2-like receptors in rat thymocytes, splenocytes and peripheral blood mononuclear cells. Western blot and RT-PCR analyses, performed on these cells, showed an expression of dopamine transporters and receptors during thymocyte development (when of CD4 and CD8 markers are differently expressed). Furthermore FACS analysis, indicates that DAT and dopamine D1-like receptors are expressed at high levels in thymocytes, splenocytes, and peripheral lymphocytes. The percentage of CD4⁺ CD8⁺ (double-positive) thymocytes expressing dopaminergic markers was significantly higher compared to the percentage of double-negative ones. The percentage of CD8⁺ single positive cells expressing dopaminergic markers was significantly higher than that of CD4⁺ cells. The results suggest that the dopaminergic system plays a role in the thymus microenvironment during T-cell development. The more pronounced expression of dopaminergic markers in CD8⁺ subsets suggests that dopamine plays a role in development of cytotoxic T-cells. Our findings indicate dopaminergic system to have a role during the maturation and selection of lymphocytes, and support its involvement in the active phases of immune response.