Serotonin 2A receptor attenuates psoriatic inflammation by suppressing IL-23 secretion in monocyte-derived Langerhans cells.

Anecdotal evidence has suggested an association between psychiatric drugs and psoriasis, but consensus is absent due to contradicting reports, and the mechanism remains poorly defined. Here, we investigate the function of serotonin 2A receptor (HTR2A), a receptor commonly targeted by psychiatric drugs, in regulating psoriasis. HTR2A antagonistic drugs worsen psoriatic outcome, and HTR2A modulation reduces psoriatic inflammation. Using the Imiquimod-induced psoriasiform model, HTR2A-deficient mice manifest exacerbated inflammation. Hematopoietic cells, particularly monocyte-derived Langerhans cells (moLC), are involved in this phenotype. Mechanistically, the exacerbated inflammation is due to increased interleukin-23 (IL-23) secretion, and HTR2A suppresses this by inhibiting activation of the non-canonical NFκB pathway. Serotonin is the putative agonist modulating HTR2A, attenuating psoriatic inflammation. Lastly, our findings in mice are also validated clinically. Our data demonstrate that serotonin modulates HTR2A, attenuating psoriatic inflammation by suppressing IL-23 secretion via inhibiting the non-canonical NFκB pathway in moLCs.