The synovial microenvironment in RA is a complex milieu characterized by the concomitant upregulation of multiple chemokines, including CCL5 (a ligand for CCR5) and CXCL12 (a ligand for CXCR4), which are critically involved in leukocyte recruitment and synovitis [32, 34, 35]. Here, CXCR4 is linked to rheumatoid arthritis.