Given the dramatic accumulation of Tfh cells in our STAT5 mutants, the capacity of Tfh cells to promote autoimmunity, and recent work showing that STAT5 can suppress Tfh differentiation (Ballesteros-Tato et al., 2012; Johnston et al., 2012), we conclude that exaggerated Tfh responses factor heavily in the autoantibody responses and attendant kidney pathology seen in Stat5b-deficient mice. The gene discussed is STAT5A; the disease is Autoimmunity.