CXCR4 and rheumatoid arthritis: Moreover, studies in patients with rheumatoid arthritis (RA) showed that fibroblast-like synoviocytes (FLS) constitutively express CCR2, CCR5, CXCR3,and CXCR4; in addition, stimulation with CCL2, CXCL12, CXCL9, and CXCL10 enhances FLS migration and proliferation (55, 56).