Estrogen modulation of endosome-associated toll-like receptor 8: An IFNα-independent mechanism of sex-bias in systemic lupus erythematosus

- Estrogen lowers the threshold of immune system activation.
- TLR8 is up-regulated in SLE and estrogen induces TLR8 and all other endosomal TLRs.
- Sex-biased TLR8 induction by estrogen and/or ligand is more robust in females in vitro.
- ERα, but not IFNα, mediates E2-induced up-regulation of TLR8.
- Therefore, TLR8 induction by estrogen and ligand could predispose females to SLE.

Females of child-bearing age are more resistant to infectious disease and have an increased risk of systemic lupus erythematosus (SLE). We hypothesized that estrogen-induced gene expression could establish an immunoactivated state which would render enhanced defense against infection, but may be deleterious in autoimmune development. Using peripheral blood mononuclear cells (PBMCs), we demonstrate enhanced responses with immunogen stimulation in the presence of 17β-estradiol (E2) and gene array analyses reveal toll-like receptor 8 (TLR8) as an E2-responsive candidate gene. TLR8 expression levels are up-regulated in SLE and PBMCs stimulated with TLR8 agonist display a female sex-biased, E2-sensitive response. Moreover, we identify a putative ERα-binding region near the TLR8 locus and blocking ERα expression significantly decreases E2-mediated TLR8 induction. Our findings characterize TLR8 as a novel estrogen target gene that can lower the inflammatory threshold and implicate an IFNα-independent inflammatory mechanism that could contribute to higher SLE incidence in women.