HRH4 and Arthritis: The mechanisms that H4R antagonist controls arthritis are reduction of pro-inflammatory cytokines and mediators, nuclear factor NF-κB, MMP-3, and a pro-inflammatory receptor, glucocorticoid-induced TNFR-related protein, while H4R antagonist increases number of blood CD4+ CD25+ FOXP3+ Treg cells, and the expression of interleukin (IL)-10 and transforming growth factor-β29, 30.