CCL21 and rheumatoid arthritis: For instance, the CXC-chemokines (CXCL5, CXCL8, CXCL9, CXCL10, CXCL12, CXCL13 and CXCL16), the CC-chemokines (CCL2, CCL3, CCL4, CCL5, CCL18, CCL19, CCL20, CCL21, CCL25), and the CX3C-chemokine CX3CL1 are increased in serum, synovial fluid, and synovial tissue of RA patients, compared with healthy controls (10), (11), (12), (13), (14), (15).