The enhancement of T cell proliferation by L-dopa is mediated peripherally and does not involve interleukin-2

Although several recent studies suggest that dopamine may have a significant role in the regulation of immune cell function, the mechanisms involved remain unclear. We undertook this study to clarify the actions of dopamine in vivo on lymphocyte proliferation and to determine whether such effects are mediated by alterations in interleukin-2 (IL-2) production and/or IL-2 receptor (IL-2R) expression. Administration of the dopamine precursor, L-dopa, for 5 days to BALB/c mice significantly increased Concanavalin A (ConA)-induced proliferation of lymphocytes. This effect was blocked by treatment with dopamine receptor antagonists as well as a peripheral dopamine synthesis inhibitor, suggesting a peripheral action of dopamine. L-dopa treatment had no effect on IL-2 production or IL-2R expression, indicating that the effects of dopamine on lymphocyte proliferation are not indirectly mediated by alterations in the IL-2 system.