It is known that BXSB.Yaa disease requires IL‐21 and Th cells, in particular ICOS‐expressing Tfh cells that produce IL‐21, and are critical for the development of SLE‐like disease in BXSB mice (Chu et al, 1996; Bubier et al, 2007, 2009; Li et al, 2011). The gene discussed is IL21; the disease is systemic lupus erythematosus.