Fas or FasL deficiency in mice (Fas receptor mutation lpr mice and FasL deficiency gld mice) causes accumulation of TCRαβ+CD3+B220+CD4−CD8− double negative (DN) T cells and systemic lupus erythematosus like autoimmune disease, which indicated Fas/FasL pathway plays an important role in T cell negative selection in thymus (41, 42). The gene discussed is FAS; the disease is autoimmune disease.