For example, D1R antagonist suppresses the severity of CIA [28]; dopamine released by dendritic cells causes aggravation of synovial inflammation of RA [29]; D2R expression level on B lymphocytes negatively correlates with RA activity [30]; D3R-positive mast cells in the synovial fluid show a declining trend with the increased disease activity in RA patients [31]; and D3R expressed on mast cells alleviates inflammation in CIA [32]. This evidence concerns the gene DRD1 and rheumatoid arthritis.