The presence of CD138-expressing αβ T cells has been reported in Fas and FasL mutant mouse strains (C3H gld, μMT/lpr, and B6/lpr mice) manifesting lupus-like disease, but the physiological significance of CD138-expressing T cells in lupus pathogenesis remains unexplored (24, 25). Here, FAS is linked to systemic lupus erythematosus.