CCL21 and rheumatoid arthritis: The CCL20/CCR6, CXCL12/CXCR4, and CXCL13/CXCR5 axes regulate B cell migration into RA SFs (130, 161, 162), whereas the CCL19/CCR7, CCL20/CCR6, CCL21/CCR7, and CXCL12/CXCR4 axes regulate B cell recruitment into the RA synovium (130, 131).