A previous study in RA showed that the CD4+ CTL existed in peripheral blood and synovium; upregulated chemokine receptor CX3CR1 could drive CD4+ CTLs to synovium due to the expression of CX3CR1 ligand, fractalkine (CX3CL1) in synoviocytes (46). The gene discussed is CX3CL1; the disease is rheumatoid arthritis.