ER expression was analyzed by qPCR only, due to the lack of reliable antibodies for analyzing protein expression by western blots or flow cytometry. Importantly, these assays were done in humanized mice, cell lines, or in vitro in activated primary cells, but have not been proved in freshly isolated DCs, monocytes, or macrophages in human ex vivo. Whether sex hormones have a direct or indirect NVP-BEZ235 effect on TLR signaling pathway in these immune cells is not clear as ERa expression impacts development of a number of different cell types. The effect of sex hormones on monocyte activation and TLR4 responsiveness can be mediated through an indirect or direct pathway. The direct pathway involves signaling through the sex hormone receptors such as ERa that either impact cytoplasmic kinase pathways or via ERa mediating gene transcription. The indirect pathway can be mediated by the sex hormones impacting gastrointestinal microbial product translocation or by impacting clearance of microbial products. The effects of estrogen on monocyte activation and TLR4 responses may also include modulation of TLR4 expression, TLR4 signaling pathways, LPS interaction cofactors, and levels of TLR4 ligands. As a consequence of enhanced monocyte activation and TLR4 responsiveness, women have overall higher levels of inflammatory markers and altered proportions of monocyte subsets compared to men. These sex differences in monocytes are further accentuated comparing SLE patients with female controls, and may partially account for sex bias in the prevalence of SLE disease. Consistent with our results, previous studies showed that patients with SLE have elevated monocyte number compared to controls, that monocytes from SLE patients spontaneously produce IL-6, and that LPS and TLR4 responses play a role in kidney damage in SLE. Moreover, plasma levels of sCD14, secreted by monocytes in response to LPS, are elevated, and the expression of membrane CD14 on monocytes are reduced in patients with SLE compared to controls. These studies are consistent with our results and indicate that monocytes are activated in vivo, produce pro-inflammatory cytokines, and contribute to chronic inflammation in SLE disease. Therefore, there may be a link between monocyte activation, TLR4 signaling pathway, monocyte maturation and differentiation, and SLE disease pathogenesis. In the current project, we first report that healthy women have roughly 3.5% higher percentage of non-classic monocytes and 9.1% lower percentage of classic monocytes compared to men. Furthermore, this subset of non-classic monocytes is expanded in sepsis patients, and also in SLE. This subset of monocytes is also a major source of pro-inflammatory cytokines induced in response to TLR7/8 ligands. In contrast, classic monocytes produce IL-10 in response to the TLR4 ligand LPS. Therefore an increase in the pro-inflammatory monocyte subset and a decreased classic monocyte subset may cooperate to drive elevated levels of persistent immune activation in women compared to men, and chronic inflammation in patients with SLE compared to controls. Treatments directed against TLR4 signaling down-stream pro-inflammatory cytokines are partially effective in SLE disease.