Complex sex-biased antibody responses: Estrogen receptors bind estrogen response elements centered within immunoglobulin heavy chain gene enhancers.

Nuclear hormone receptors including the estrogen receptor (ERα) and the retinoic acid receptor regulate a plethora of biological functions including reproduction, circulation, and immunity. To understand how estrogen and other nuclear hormones influence antibody production, we characterized total serum antibody isotypes in female and male mice of C57BL/6J, BALB/cJ, and C3H/HeJ mouse strains. Antibody levels were higher in females compared to males in all strains and there was a female preference for IgG2b production. Sex -biased patterns were influenced by vitamin levels, and by antigen-specificity toward influenza virus or pneumococcus antigens. To help explain sex-biases, we examined the direct effects of estrogen on immunoglobulin heavy chain sterile transcript production among purified, LPS-stimulated B cells. Supplemental estrogen in B cell cultures significantly increased immunoglobulin heavy chain sterile transcripts. Chromatin immunoprecipitation analyses of activated B cells identified significant ERα binding to estrogen response elements (ERE) centered within enhancer elements of the immunoglobulin heavy chain locus, including the Eμ enhancer and hypersensitive site 1,2 (HS1,2) in the 3' regulatory region. The ERE in HS1,2 was conserved across animal species, and in humans marked a site of polymorphism associated with the estrogen-augmented autoimmune disease, lupus. Taken together, results highlight: (i) important targets of ERα in regulatory regions of the immunoglobulin heavy chain locus that influence antibody production, and (ii) the complexity of mechanisms by which estrogen instructs sex-biased antibody production profiles.