mRNA expression of serotonin receptors in cells of the immune tissues of the rat

Serotonin (5-hydroxyrtyptamine, 5-HT) has been shown to play a role in immu noregulation; however, little is known about specific subtypes of 5-HT rece ptors involved in peripheral immunomodulation. In the present study we used RT-PCR methods to examine the mRNA expression of 5-HT receptors in the cel ls of lymphoid tissues of the rat. All 13 rat 5-HT receptor genes cloned so far were examined in ex vivo isolated spleen, thymus, and peripheral blood lymphocytes, as well as in mitogen-stimulated spleen cells. Positive signa ls were obtained for 5-HT1B, 5-HT1F, 5-HT2A, 5-HT2B, 5-HT6, and 5-HT7 recep tor mRNAs in all three compartments. Mitogen (ConA and PWM) stimulated cell s additionally expressed mRNA corresponding to the 5HT-3 receptor subtype. In contrast, 5-HT1A, 5-HT1D, 5-HT2C, 5-HT4, 5-HT5A, and 5-HT5B mRNAs were n ot detected in any of the examined cell populations. These results may be u seful as a starting point For future functional studies on immunomodulatory effects of 5-HT and may help to understand conflicting serotonergic effect s on immune functions as found in the literature. (C) 2000 Academic Press.