Expression Of Dopamine Receptors In T Lymphocytes And Role Of The Receptors In Mediating The Regulation Of T Cell Function

Objectives: With the increasing studies on neural-endocrine-immune interaction, lymphocytes have been shown to haveα- andβ-adrenoreceptors and the receptors participate in mediating the regulation of immune cell function. However, although some reports have demonstrated that dopamine (DA) receptors exist in lymphocytes, which DA receptor subtypes are on the T lymphocytes and what roles of the DA receptor subtypes in mediating the modulation of T cell function are less known. Thus, in the present study, on the one hand we provided the further evidence for the expressions of two subtypes of DA receptors, D1-like receptors (including D1 and D5 receptors) and D2-like receptors (including D2, D3 and D4 receptors), in T lymphocytes, and on the other hand we explored the roles of D1-like and D2-like receptors in mediating the modulation of T cell function and signal transduction molecules involved in the modulation in order to extend the comprehension of neural-endocrine-immune regulatory network. Methods: Lymphocytes were separated from the mesenteric lymph nodes of mice. T cells were purified by using a nylon wool column. The purity of the T lymphocytes purified was determined by flow cytometric assay. Reverse transcription-polymerase chain reaction (RT-PCR) was used to measure the expression of each subtype of DA receptor mRNA in the purified T cells. The lymphocytes from the mesenteric lymph nodes of mice were incubated with concanavalin A (Con A) and treated with selective D1-like receptor agonist (SKF38393) and antagonist (SCH23390), or with selective D2-like receptor agonist (quinpirole) and antagonist (haloperidol) for 48 h. Colorimetric assay of methylthiazol tetrazolium bromide (MTT) was employed to measure the proliferative response of the lymphocytes to Con A. Cytometric bead array was used to examine the levels of cytokines interferon-γ(IFN-γ), tumor necrosis factor (TNF) and interleukin-4 (IL-4) in the supernatants of the Con A-stimulated lymphocyte cultures. The content of cAMP in the Con A-activated lymphocytes was measured by 125I-cAMP radioimmunoassay. Results: The percentage of purified T lymphocytes (CD3+) in the mesenteric lymph node cells was 93.8±0.53%, which was significantly higher than 74.1±0.95% of T cells that were not purified. The purified T lymphocytes expressed the all subtypes of DA receptor mRNA, including D1 and D5 of D1-like receptors, as well as D2, D3 and D4 of D2-like receptors. After the lymphocytes were treated with D1-like receptor agonist SKF38393 (10-9 to 10-5 M), the proliferative response of the lymphocytes to Con A did not exhibit an evident change. Similarly, the production of TNF and IL-4 by the con A-stimulated lymphocytes that were treated with SKF38393(10-8 M)did not show remarkable change, but the IFN-γproduction by the lymphocytes treated with SKF38393 was notably lower than that of SKF38393-untreated lymphocytes. D1-like receptor antagonist SCH23390 (10-7 M) blocked the inhibitory effect of agonist SKF38393 on the IFN-γproduction by the Con A-stimulated lymphocytes. The content of cAMP in the Con A-activated lymphocytes did not exhibit a notable change no matter what treatments were used with D1-like receptor agonist and antagonist. However, the treatment of lymphocytes with D2-like receptor agonist quinpirole(10-9 to 10-5 M)led to a dramatic attenuation in the proliferative response of the lymphocytes to Con A. D2-like receptor antagonist haloperidol ( 10-10 to 10-7 M ) represented a concentration-dependent blockage of the suppressive effect of quinpirole on the Con A-induced lymphocyte proliferation. Furthermore, quinpirole (10-8 M) reduced the production of IFN-γand TNF, but increased the IL-4 production by the Con A-stimulated lymphocytes. Haloperidol (10-7 M) blocked the quinpirole-induced decrease in IFN-γand TNF levels and the increase in IL-4 production. The cAMP content in the lymphocytes was found decreased after the lymphocytes were treated with quinpirole (10-8 and 10-7 M), and haloperidol (10-8 and 10-7 M) blocked the decrease in cAMP content induced by quinpirole. Conclusions: T lymphocytes can express all the subtypes of DA receptors, including D1 and D5 receptors (i.e., D1-like receptors) and D2, D3, and D4 receptors (i.e., D2-like receptors). Of DA D1-like and D2-like receptors, D2-like receptors are more important in mediating the modulation of T cell function. The activation of D2-like receptors results in an inhibition of T cell proliferation, a decrease in IFN-γand TNF production and an increase in IL-4 level. The immunomodulation mediated by D2-like receptors may be performed by the second messenger cAMP in lymphocytes.