CD163 and rheumatoid arthritis: Consistent with our hypothesis that MSC-sEVs could mitigate the severity of RA by enhancing M2 macrophage polarization, we observed that the reduced disease severity in MSC-sEV treatment was concomitant with reduced pro-inflammatory CD86+ cells M1 macrophages in the synovium, and increased CD163+ anti-inflammatory M2 macrophages in the synovial lining.