OBJECTIVES: We have previously reported that dopamine D2-like receptors including D2, D3 and D4 receptors are more important in mediating modulation of T cells than dopamine D1-like receptors (D1 and D5 receptors). Here we aimed to clarify the role of D2-like receptors in regulation of differentiation and function of T lymphocyte subsets, including helper T (Th)1, Th2, Th17 and regulatory T (Treg) cells.
METHODS: Lymphocytes, separated from the mesenteric lymph nodes of mice, were stimulated with concanavalin A (Con A) and treated with the D2-like receptor agonist quinpirole or the antagonist haloperidol. Expression of lymphocyte cytokines and transcription factors and dopamine D2, D3 and D4 receptors were measured by real-time quantitative polymerase chain reaction and Western blot assay. Meanwhile, cAMP and phosphorylated cAMP-response element-binding (CREB) levels in the lymphocytes were examined by enzyme-linked immunosorbent assay and Western blot assay, respectively.
RESULTS: Activation of D2-like receptors with the agonist quinpirole upregulated the expression of Th2- and Treg-specific transcription factors and cytokines in Con A-activated lymphocytes, but downregulated the expression of Th1- and Th17-specific transcription factors and cytokines. Simultaneously, quinpirole increased dopamine D3 and D4 receptor expression, but did not alter D2 receptor expression. However, quinpirole reduced both cAMP and phosphorylated CREB levels in Con A-activated lymphocytes. All these quinpirole effects were blocked by haloperidol, an antagonist of D2-like receptors.
CONCLUSIONS: D2-like receptors, principally dopamine D3 and D4 receptors, promote differentiation and function of T lymphocytes towards anti-inflammatory T cell subsets by a negative link to cAMP-CREB pathway....