There is some evidence for a nongenomic signaling role for ER in SLE; treatment of SLE patient‐derived peripheral blood mononuclear cells (PBMCs) with 17β‐estradiol induced a mitogen‐activated protein kinase (MAPK)‐dependent increase in IL‐21 expression in these cells [120]. This evidence concerns the gene IL21 and systemic lupus erythematosus.