CXCL13 and systemic lupus erythematosus: Circulating levels of CXCL13 (C-X-C motif chemokine 13), a chemokine known to attract B cells, are elevated, correlate with disease activity, severity and treatment response in patients with SLE, Sjögren’s syndrome, rheumatoid arthritis and ANCA-associated vasculitides (21–26).