CXCR4 and rheumatoid arthritis: The correlation among four effective biomarkers (CCL5, CXCR4, GZMA, and CD8A) and 10 significantly differential immune cells (M1 macrophages, Tfh cells, memory activated CD4+ T cells, plasma cells, regulatory T cells, activated dendritic cells, activated NK cells, memory resting CD4+ T cells, resting mast cells, and activated mast cells) were analyzed in RA synovial tissues.