C5AR1 and rheumatoid arthritis: Furthermore, given that previous studies have identified CD88(+) and CD88(−) MC subsets in SM, skin, and lung [31,38,39], and elevated levels of CD88(+) MC in the SM of individuals with RA compared to OA [31], we additionally compared NMU/NMUR in CD88(+) and CD88(−) MC-RFs.