CD4 and systemic lupus erythematosus: We show that female SLE patients have increased plasma levels of estradiol (Figure 4) and that incubation of CD4+ Tregs with 17β-estradiol (at physiological levels) either maintains or decreases FoxP3 expression in females with SLE, in contrast to inducing a significant increase in CD4+ Treg in healthy females (Figures 5, 6).