Bisphenol A Does Not Mimic Estrogen in the Promotion of the In Vitro Response of Murine Dendritic Cells to Toll-Like Receptor Ligands.

Sex hormones affect immune responses and might promote autoimmunity. Endocrine disrupting chemicals such as bisphenol A (BPA) may mimic their immune effects. Conventional dendritic cells (cDCs) are pivotal initiators of immune responses upon activation by danger signals coming from pathogens or distressed tissues through triggering of the Toll-like receptors (TLRs). We generated in vitro murine cDCs in the absence of estrogens and measured the effects of exogenously added estrogen or BPA on their differentiation and activation by the TLR ligands LPS and CpG. Estrogen enhanced the differentiation of GM-CSF-dependent cDCs from bone marrow precursors in vitro, and the selective estrogen receptor modulators (SERMs) tamoxifen and fulvestrant blocked these effects. Moreover, estrogen augmented the upregulation of costimulatory molecules and proinflammatory cytokines (IL-12p70 and TNFα) upon stimulation by TLR9 ligand CpG, while the response to LPS was less estrogen-dependent. These effects are partially explained by an estrogen-dependent regulation of TLR9 expression. BPA did not promote cDC differentiation nor activation upon TLR stimulation. Our results suggest that estrogen promotes immune responses by increasing DC activation, with a preferential effect on TLR9 over TLR4 stimulation, and highlight the influence of estrogens in DC cultures, while BPA does not mimic estrogen in the DC functions that we tested.

Poly(ADP-ribose) polymerase-1 regulates the progression of autoimmune nephritis in males by inducing necrotic cell death and modulating inflammation.

Necrotic lesions and necrotic cell death characterize severe autoimmune nephritides, and contribute to local inflammation and to progression of the disease. Poly(ADP-ribose) polymerase-1 (PARP-1), a DNA repair enzyme, is involved in the induction of necrosis and is a key player in the acute and chronic inflammation. Therefore, we hypothesized that PARP-1 controls the severity of nephritis by mediating the induction of necrosis in the kidney. We used lupus and anti-glomerular basement membrane models of nephritis to determine the effects of PARP-1 on the inflammatory response in the kidney. We show in this study that PARP-1 is indeed activated during the course of glomerulonephritis. We also show that the absence of PARP-1 or its pharmacological inhibition results in milder nephritis, with lower blood urea nitrogen levels, reduced necrotic lesions, and higher survival rates. The relevance of PARP-1 showed a strong male sex specificity, and treatment of male mice with 17beta-estradiol prolonged their survival during the course of nephritis. PARP-1 also regulated TNF-alpha expression and up-regulation of adhesion molecules, further supporting a role of PARP-1 in the inflammatory process within the kidney. Our results demonstrate that PARP-1 activation and consequent necrotic cell death play an important role in the pathogenesis of male nephritis, and suggest that PARP-1 can be a novel therapeutic target in glomerulonephritis.

IL-4 suppresses dendritic cell response to type I interferons.

Cytokines play an important role in modulating the development and function of dendritic cells (DCs). Type I IFNs activate DCs and drive anti-viral responses, whereas IL-4 is the prototype of a Th2 cytokine. Evidence suggests that type I IFNs and IL-4 influence each other to modulate DC functions. We found that two type I IFNs, IFN-alpha and IFN-beta, stimulated a similar costimulatory profile in myeloid resting DCs. IL-4 suppressed the response of myeloid DCs to both type I IFNs in vitro and in vivo by impairing the up-regulation of MHC and costimulatory molecules and the production of cytokines, such as IL-6 and IL-15, and anti-viral genes, such as Mx-1, upon type I IFN stimulation. In dissecting the mechanism underlying this inhibition, we characterized the positive feedback loop that is triggered by IFN-alpha in primary DCs and found that IL-4 inhibited the initial phosphorylation of STAT1 and STAT2 (the transducers of signaling downstream of IFN-alpha and -beta receptors (IFNARs)) and reduced the up-regulation of genes involved in the amplification of the IFN response such as IRF-7, STAT1, STAT2, IFN-beta, and the IFNARs in vitro and in vivo. Therefore, IL-4 renders myeloid DCs less responsive to paracrine type I IFNs and less potent in sustaining the autocrine positive loop that normally amplifies the effects of type I IFNs. This inhibition could explain the increased susceptibility to viral infections observed during Th2-inducing parasitoses.

Abnormal costimulatory phenotype and function of dendritic cells before and after the onset of severe murine lupus.

We analyzed the activation and function of dendritic cells (DCs) in the spleens of diseased, lupus-prone NZM2410 and NZB-W/F1 mice and age-matched BALB/c and C57BL/6 control mice. Lupus DCs showed an altered ex vivo costimulatory profile, with a significant increase in the expression of CD40, decreased expression of CD80 and CD54, and normal expression of CD86. DCs from young lupus-prone NZM2410 mice, before the development of the disease, expressed normal levels of CD80 and CD86 but already overexpressed CD40. The increase in CD40-positive cells was specific for DCs and involved the subset of myeloid and CD8alpha+ DCs before disease onset, with a small involvement of plasmacytoid DCs in diseased mice. In vitro data from bone marrow-derived DCs and splenic myeloid DCs suggest that the overexpression of CD40 is not due to a primary alteration of CD40 regulation in DCs but rather to an extrinsic stimulus. Our analyses suggest that the defect of CD80 in NZM2410 and NZB-W/F1 mice, which closely resembles the costimulatory defect found in DCs from humans with systemic lupus erythematosus, is linked to the autoimmune disease. The increase in CD40 may instead participate in disease pathogenesis, being present months before any sign of autoimmunity, and its downregulation should be explored as an alternative to treatment with anti-CD40 ligand in lupus.