On the other hand, in BWF1 mice, which spontaneously develop lupus, chronic administration of 17β-estradiol (E2) increased the secretion of anti-DNA and anti-Br-RBC IgM autoantibodies in B1 cells in vitro (147), highlighting the importance of this population in autoimmunity. This evidence concerns the gene CD40LG and systemic lupus erythematosus.