T cells from SLE patients and lupus-prone mice have expanded T helper 1 (Th1), Th17, follicular, and extrafollicular helper T (Tfh and eTfh) cell subsets, which contribute to the inflammation and autoreactive antibody production through increased IFNγ, TNFα, IL-6, IL-17, and IL-21 secretion (3–7). Here, IL21 is linked to systemic lupus erythematosus.