CD19 and rheumatoid arthritis: In summary, the levels of CXCL12, CXCL13 and CCL19 in synovial fluid of RA patients were significantly higher as compared to RA sera and OA SF, and were positively associated with the proportions of CD19+CD24hiCD27+ B cells in RA SF, suggesting that CXCL12, CXCL13, and CCL19 promote the increase of SF CD19+CD24hiCD27+ B cells in RA patients.