In addition, synovial CXCL13-producing CD4+ T cells in RA are almost independent of cells expressing IFN-γ, IL-17, or FoxP3, indicating that the synovial PD-1hiCXCR5−CXCL13+ CD4 population is a distinct CD4 subset (5). Here, CXCL13 is linked to rheumatoid arthritis.