CD4 and systemic lupus erythematosus: Because of the lpr mutation in the Fas gene, for many years, LPR mice have been used to study lupus because they reproduce most of the classic and severe symptoms observed in patients with SLE in the short term (3–4 months): glomerulonephritis, circulating antibodies against nuclear antigens, central nervous system inflammation, skin rash, and an aberrant accumulation of inflammatory CD4 and DN T cells (33).