ESR1 and systemic lupus erythematosus: Increased steady-state levels of ERα mRNA (Fig. 2A) protein (Fig. 2B and C) in splenic cells from (NZB × NZW) F1 female mice as compared to age-matched male mice and cooperation between the IFN and E2-signaling in cells to activate transcription of reporter genes (Fig. 6) prompted us to investigate whether the expression of E2 or IFN-responsive genes is differentially regulated between male and female (NZB × NZW) F1 lupus-prone mice.