In the MRL/MpJ-Fas lpr murine model of lupus, a subset ofCD162lowCXCR4+ T cells, localized in extra-follicular sites,has been shown to mediate IgG production through IL-21 and CD40L.CD162lowCXCR4+ T cells are abundant in other autoimmune murinemodels and can exhibit either a follicular or an extra-follicular phenotype (60). Here, IL21 is linked to systemic lupus erythematosus.