Serotonin 2A Receptor Attenuates Psoriatic Inflammation by Suppressing IL-23 Secretion in Monocyte-derived Langerhans cells

Serotonin and its receptor are known to play a role in regulating immune cells. However, how they affect an autoimmune disease like psoriasis is not well-established and the mechanism remains to be elucidated. Here, we investigated the role played by serotonin 2A receptor (HTR2A) in regulating psoriasis. HTR2A antagonistic drug worsens psoriatic outcome and HTR2A modulation reduced psoriatic inflammation. Using Imiquimod-induced psoriasiform inflammation model, HTR2A-deficient mice experienced exacerbated inflammation. Hematopoietic cells, particularly monocyte-derived Langerhans cells, were responsible for this exacerbated inflammation. Mechanistically, the exacerbated inflammation is due to increased interleukin-23 (IL-23) secretion and HTR2A suppresses it by inhibiting the activation of non-canonical NFkB pathway. Platelet-derived serotonin is the putative agonist modulating HTR2A attenuating psoriatic inflammation. Lastly, our findings in mice were also reproduced clinically. Thus, our data demonstrate platelet serotonin putatively modulates HTR2A attenuating psoriatic inflammation by suppressing IL-23 secretion via inhibiting non-canonical NFkB pathway in monocyte-derived Langerhans cells.