Histamine H4 receptor optimizes TR cell frequency and facilitates anti-inflammatory responses within the CNS

摘要

Histamine (HA) is a biogenic amine that mediates multiple physiological processes including immunomodulatory effects in allergic and inflammatory reactions, and also plays a key regulatory role in experimental allergic encephalomyelitis (EAE), the autoimmune model of multiple sclerosis (MS). The pleiotropic effects of HA are mediated by four G protein-coupled receptors: Hrh1/H1R, Hrh2/H2R, Hrh3/H3R, and Hrh4/H4R. H4R expression is primarily restricted to hematopoietic cells, and its role in autoimmune inflammatory demyelinating disease of the CNS has not been studied. In this report we show that, compared to wild type (WT) mice, animals with a disrupted Hrh4 (H4RKO) develop more severe myelin oligodendrocyte glycoprotein 35–55 (MOG35-55) peptide-induced EAE. Mechanistically, we also show that H4R plays a role in determining the frequency of T regulatory (TR) cells in secondary lymphoid tissues, and regulates TR cell chemotaxis and suppressor activity. Moreover, the lack of H4R leads to an impairment of an anti-inflammatory response due to fewer TR cells in the CNS during the acute phase of the disease and an increase in the proportion of Th17 cells.