B6.MRL/lpr and NZBW/F1 mice are universal lupus animal models5, 6 and both showed decreased frequency of Treg cells or of absolute cell numbers in spleen; however, we found that the B6.MRL/lpr mice but not the NZBW/F1 mice showed an increased frequency of NKG2D+CD4+ T cells in our experimental period (Fig. 2B). Here, KLRK1 is linked to systemic lupus erythematosus.