Growing evidence has suggested that Tfh cell may have a crucial role in the pathogenesis of SLE, as the aberrant expressions of Tfh cell-associated molecules, such as ICOS, SAP, PD-1 and IL-21, are all linked to autoantibody production and/or lupus-like disease in murine models [6]–[9]. Here, IL21 is linked to systemic lupus erythematosus.