Background/Purpose: Epidemiological data suggests that females of child-bearing age are more resistant to infectious disease.  The sex hormone estrogen (E2) is present at elevated levels in this population and has been shown to influence immune cell function by regulating the expression of multiple genes through binding of estrogen receptors (ER) α and β.  Systemic lupus erythematosus (SLE) is a multi-organ auto-inflammatory disease predominantly affecting child-bearing age females.  We hypothesize that estrogenic effects could establish a heightened immune-activation state, which would have a survival advantage in the defense against infection, but may have deleterious effects when it comes to autoimmune development.

Methods: Human peripheral blood mononuclear cells (PBMCs) were stimulated with β-estradiol (E2) and/or BOOSTRIX® immunogen to measure cellular proliferation and cytokine expression.  RNA was isolated from whole blood of healthy individuals and SLE patients.  PBMCs, human hematopoietic cell lines, and primary monocyte derived macrophages (MDMs) were treated with a physiological dose of testosterone, E2, and/or toll-like receptor (TLR) agonists to look at gene expression by Western blotting and real time-RT-PCR.  Furthermore, E2 was injected subcutaneously into wild-type mice and lymphoid tissue was collected for real time-RT-PCR analysis to measure TLR8 expression.  Additionally, siRNA was used to target ERα or IFNα.  EMSAs were performed with putative ERα-binding sites defined by ChIP-seq analysis and nuclear extracts or recombinant ERα protein.

Results: Cellular proliferation and cytokine production were most significantly enhanced with E2 treatment in female PBMCs challenged with immunogen.  TLR8 was identified to be over-expressed in whole blood of SLE patients and its ex vivo expression was induced in PBMCs by estrogen, but not by testosterone.  E2-induced TLR8 expression was also observed in mouse lymphoid tissue in vivo.  Furthermore, both estrogen and TLR agonist stimulated the expression of endosomal TLRs, but not TLR4, which is cell membrane-associated.  Female sex-biased expression of TLR8 was demonstrated in human PBMCs when stimulated with both agonist and estrogen simultaneously.  Moreover, siRNA targeting ERα blocked E2-mediated TLR8 expression, while siRNA against IFNα had no effect.  EMSA analysis suggested that E2 enhanced ERα binding to an ER response element 25 kb downstream from the 3’ end of the TLR8 gene.

Conclusion:

We find that the expression of TLR8 is positively regulated by estrogen and that TLR8 is over-expressed in SLE patients. We propose that estrogen-induced up-regulation of TLR8 expression is mediated directly through ERα, but not IFNα.  In conjunction with the TLR8 autocrine feedback loop, estrogen lowers the inflammation threshold, which could promote an inflammatory state contributing to higher SLE incidence among women.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/estrogen-modulates-the-expression-of-endosome-associated-toll-like-receptor-8-through-estrogen-receptor-%ce%b1-which-may-contribute-to-sex-bias-in-systemic-lupus-erythematosus/