ESR1 and systemic lupus erythematosus: Therefore, our observations that basal as well as IFN-induced levels of ERα were relatively higher in non lupus-prone (C57BL/6) as well as lupus-prone (NZB × NZW) F1 female mice as compared to the age and strain-matched males will require further work to determine whether other factors, such as promoter polymorphisms in the Esr1 gene, also contribute to differential expression of ERα in certain strains of mice.