Xue L, et al. - This study was undertaken to determine if dopamine D3 receptor (D3R) on synovial mast cells (MCs) was linked to levels of reactive oxygen species (ROS) in rheumatoid arthritis (RA) patients. According to disease activity DAS28 scores, 73 patients with RA were split into three groups. In RA patients, D3R-positive MCs in the synovial fluid exhibited a declining trend with the increased disease activity DAS28 score. A negative association was found between D3R-positive MC numbers in the synovial fluid and disease severity DAS28 score of RA patients. Results indicate that D3R on MCs might be involved in ROS-mediated pathogenesis of RA.