FAS and systemic lupus erythematosus: Massive accumulation of DNT has been observed in lpr mice, and the origin and function of lpr DNT have been widely debated.32, 33, 34, 35 Based on our results here, we suggest that at least some of the accumulated DNT in lpr mice might be converted from activated CD4+ T cells because of immune system losses of Fas-mediated apoptosis and that they could serve as an immune regulator in this lupus model.