IL21 and rheumatoid arthritis: Recent reports in RA patients following treatment with filgotinib have shown significant reductions in markers important for B cell chemotaxis [chemokine (C-X-C motif) ligand 13, CXCL13]; activation and survival (BAFF); regulatory function (IL-10) and germinal center and plasma cell differentiation (IL-2, IL-5, IL-7, and IL-21) (226).