Autoreactive B cell responses to RNA-related antigens due to TLR7 gene duplication

Metabolic and immunological responses of male and female new Zealand Greenshell™ mussels (Perna canaliculus) infected with Vibrio sp

Massive mortalities due to pathogens are routinely reported in bivalve cultivation that have significant economic consequences for the global aquaculture industry. However, host-pathogen interactions and infection mechanisms that mediate these interactions are poorly understood. In addition, gender-specific immunological responses have been reported for some species, but the reasons for such differences have not been elucidated. In this study, we used a GC/MS-based metabolomics platform and flow cytometry approach to characterize metabolic and immunological responses in haemolymph of male and female mussels (Perna canaliculus) experimentally infected with Vibrio sp. Sex-based differences in immunological responses were identified, with male mussels displaying higher mortality, oxidative stress and apoptosis after pathogen exposure. However, central metabolic processes appeared to be similar between sexes at 24 h post injection with Vibrio sp. DO1. Significant alterations in relative levels of 37 metabolites were detected between infected and uninfected mussels. These metabolites are involved in major perturbations on the host's innate immune system. In addition, there were alterations of seven metabolites in profiles of mussels sampled on the second day and mussels that survived six days after exposure. These metabolites include itaconic acid, isoleucine, phenylalanine, creatinine, malonic acid, glutaric acid and hydroxyproline. Among these, itaconic acid has the potential to be an important biomarker for Vibrio sp. DO1 infection. These findings provide new insights on the mechanistic relationship between a bivalve host and a pathogenic bacterium and highlight the need to consider host sex as a biological variable in future immunological studies.

Epistatic Interactions Between Mutations of Deoxyribonuclease 1-Like 3 and the Inhibitory Fc Gamma Receptor IIB Result in Very Early and Massive Autoantibodies Against Double-Stranded DNA

Autoantibodies against double-stranded DNA (anti-dsDNA) are a hallmark of systemic lupus erythematosus (SLE). It is well documented that anti-dsDNA reactive B lymphocytes are normally controlled by immune self-tolerance mechanisms operating at several levels. The evolution of high levels of IgG anti-dsDNA in SLE is dependent on somatic hypermutation and clonal selection, presumably in germinal centers from non-autoreactive B cells. Twin studies as well as genetic studies in mice indicate a very strong genetic contribution for the development of anti-dsDNA as well as SLE. Only few single gene defects with a monogenic Mendelian inheritance have been described so far that are directly responsible for the development of anti-dsDNA and SLE. Recently, among other mutations, rare null-alleles for the deoxyribonuclease 1 like 3 (DNASE1L3) and the Fc gamma receptor IIB (FCGR2B) have been described in SLE patients and genetic mouse models. Here, we demonstrate that double Dnase1l3- and FcgR2b-deficient mice in the C57BL/6 background exhibit a very early and massive IgG anti-dsDNA production. Already at 10 weeks of age, autoantibody production in double-deficient mice exceeds autoantibody levels of diseased 9-month-old NZB/W mice, a long established multigenic SLE mouse model. In single gene-deficient mice, autoantibody levels were moderately elevated at early age of the mice. Premature autoantibody production was accompanied by a spontaneous hyperactivation of germinal centers, early expansions of T follicular helper cells, and elevated plasmablasts in the spleen. Anti-dsDNA hybridomas generated from double-deficient mice show significantly elevated numbers of arginines in the CDR3 regions of the heavy-chain as well as clonal expansions and diversification of B cell clones with moderate numbers of somatic mutations. Our findings show a strong epistatic interaction of two SLE-alleles which prevent early and high-level anti-dsDNA autoantibody production. Both genes apparently synergize to keep in check excessive germinal center reactions evolving into IgG anti-dsDNA antibody producing B cells.

New application of anti-TLR monoclonal antibodies: detection, inhibition and protection

Monoclonal antibody (mAb) is an essential tool for the analysis in various fields of biology. In the field of innate immunology, mAbs have been established and used for the study of Toll-like receptors (TLRs), a family of pathogen sensors that induces cytokine production and activate immune responses. TLRs play the role as a frontline of protection against pathogens, whereas excessive activation of TLRs has been implicated in a variety of infectious diseases and inflammatory diseases. For example, TLR7 and TLR9 sense not only pathogen-derived nucleic acids, but also self-derived nucleic acids in noninfectious inflammatory diseases such as systemic lupus erythematosus (SLE) or hepatitis. Consequently, it is important to clarify the molecular mechanisms of TLRs for therapeutic intervention in these diseases. For analysis of the molecular mechanisms of TLRs, mAbs to nucleic acid-sensing TLRs were developed recently. These mAbs revealed that TLR7 and TLR9 are localized also in the plasma membrane, while TLR7 and TLR9 were thought to be localized in endosomes and lysosomes. Among these mAbs, antagonistic mAbs to TLR7 or TLR9 are able to inhibit in vitro responses to synthetic ligands. Furthermore, antagonistic mAbs mitigate inflammatory disorders caused by TLR7 or TLR9 in mice. These results suggest that antagonistic mAbs to nucleic acid-sensing TLRs are a promising tool for therapeutic intervention in inflammatory disorders caused by excessive activation of nucleic acid-sensing TLRs. Here, we summarize the molecular mechanisms of TLRs and recent progresses in the trials targeting TLRs with mAbs to control inflammatory diseases.

Plasmacytoid dendritic cell heterogeneity is defined by CXCL10 expression following TLR7 stimulation

Plasmacytoid dendritic cells (pDCs) play a critical role in bridging the innate and adaptive immune systems. pDCs are specialized type I interferon (IFN) producers, which has implicated them as initiators of autoimmune pathogenesis. However, little is known about the downstream effectors of type I IFN signaling that amplify autoimmune responses. Here, we have used a chemokine reporter mouse to determine the CXCR3 ligand responses in DCs subsets. Following TLR7 stimulation, conventional type 1 and type 2 DCs (cDC1 and cDC2, respectively) uniformly upregulate CXCL10. By contrast, the proportion of chemokine positive pDCs was significantly less, and stable CXCL10⁺ and CXCL10^- populations could be distinguished. CXCL9 expression was induced in all cDC1s, in half of the cDC2 but not by pDCs. The requirement for IFNAR signaling for chemokine reporter expression was interrogated by receptor blocking and deficiency and shown to be critical for CXCR3 ligand expression in Flt3-ligand-derived DCs. Chemokine-producing potential was not concordant with the previously identified markers of pDC heterogeneity. Finally, we show that CXCL10⁺ and CXCL10^- populations are transcriptionally distinct, expressing unique transcriptional regulators, IFN signaling molecules, chemokines, cytokines, and cell surface markers. This work highlights CXCL10 as a downstream effector of type I IFN signaling and suggests a division of labor in pDCs subtypes that likely impacts their function as effectors of viral responses and as drivers of inflammation.

TACI deletion protects against progressive murine lupus nephritis induced by BAFF overexpression

B cells are known to promote the pathogenesis of systemic lupus erythematosus (SLE) via the production of pathogenic anti-nuclear antibodies. However, the signals required for autoreactive B cell activation and the immune mechanisms whereby B cells impact lupus nephritis pathology remain poorly understood. The B cell survival cytokine B cell activating factor of the TNF Family (BAFF) has been implicated in the pathogenesis of SLE and lupus nephritis in both animal models and human clinical studies. Although the BAFF receptor has been predicted to be the primary BAFF family receptor responsible for BAFF-driven humoral autoimmunity, in the current study we identify a critical role for signals downstream of Transmembrane Activator and CAML Interactor (TACI) in BAFF-dependent lupus nephritis. Whereas transgenic mice overexpressing BAFF develop progressive membranoproliferative glomerulonephritis, albuminuria and renal dysfunction, TACI deletion in BAFF-transgenic mice provided long-term (about 1 year) protection from renal disease. Surprisingly, disease protection in this context was not explained by complete loss of glomerular immune complex deposits. Rather, TACI deletion specifically reduced endocapillary, but not mesangial, immune deposits. Notably, although excess BAFF promoted widespread breaks in B cell tolerance, BAFF-transgenic antibodies were enriched for RNA- relative to DNA-associated autoantigen reactivity. These RNA-associated autoantibody specificities were specifically reduced by TACI or Toll-like receptor 7 deletion. Thus, our study provides important insights into the autoantibody specificities driving proliferative lupus nephritis, and suggests that TACI inhibition may be novel and effective treatment strategy in lupus nephritis.

Fas ligand promotes an inducible TLR-dependent model of cutaneous lupus-like inflammation

Toll-like receptors TLR7 and TLR9 are both implicated in the activation of autoreactive B cells and other cell types associated with systemic lupus erythematosus (SLE) pathogenesis. However, Tlr9-/- autoimmune-prone strains paradoxically develop more severe disease. We have now leveraged the negative regulatory role of TLR9 to develop an inducible rapid-onset murine model of systemic autoimmunity that depends on T cell detection of a membrane-bound OVA fusion protein expressed by MHC class II+ cells, expression of TLR7, expression of the type I IFN receptor, and loss of expression of TLR9. These mice are distinguished by a high frequency of OVA-specific Tbet+, IFN-γ+, and FasL-expressing Th1 cells as well as autoantibody-producing B cells. Unexpectedly, contrary to what occurs in most models of SLE, they also developed skin lesions that are very similar to those of human cutaneous lupus erythematosus (CLE) as far as clinical appearance, histological changes, and gene expression. FasL was a key effector mechanism in the skin, as the transfer of FasL-deficient DO11gld T cells completely failed to elicit overt skin lesions. FasL was also upregulated in human CLE biopsies. Overall, our model provides a relevant system for exploring the pathophysiology of CLE as well as the negative regulatory role of TLR9.

The Confluence of Sex Hormones and Aging on Immunity

The immune systems of post-pubescent males and females differ significantly with profound consequences to health and disease. In many cases, sex-specific differences in the immune responses of young adults are also apparent in aged men and women. Moreover, as in young adults, aged women develop several late-adult onset autoimmune conditions more frequently than do men, while aged men continue to develop many cancers to a greater extent than aged women. However, sex differences in the immune systems of aged individuals have not been extensively investigated and data addressing the effectiveness of vaccinations and immunotherapies in aged men and women are scarce. In this review, we evaluate age- and sex hormone-related changes to innate and adaptive immunity, with consideration about how this impacts age- and sex-associated changes in the incidence and pathogenesis of autoimmunity and cancer as well as the efficacy of vaccination and cancer immunotherapy. We conclude that future preclinical and clinical studies should consider age and sex to better understand the ways in which these characteristics intersect with immune function and the resulting consequences for autoimmunity, cancer, and therapeutic interventions.

Accelerated model of lupus autoimmunity and vasculopathy driven by toll-like receptor 7/9 imbalance

Objectives

Activation of endosomal toll-like receptor (TLR)7 or TLR9 has been proposed as a critical step for the initiation and development of SLE. Traditional spontaneous lupus models normally introduce multiple risk alleles, thereby adding additional confounding factors. In the induced lupus models, the role of TLR9 remains unclear. In the present study, we explored the role of an imbalance between TLR7 and TLR9 pathways in the pathogenesis of lupus and its associated vasculopathy using the imiquimod model in TLR9 KO/B6 background.

Methods

Wild type (WT) and Tlr9^-/- mice were epicutaneously treated with imiquimod cream 5% on both ears three times per week for indicated times. At euthanasia, mice were analysed for organ involvement, endothelium-dependent vasorelaxation, serum autoantibodies, and innate and adaptive immune responses.

Results

Compared with the lupus-like phenotype that develops in imiquimod-treated WT mice, Tlr9^-/- mice exposed to imiquimod have increased severity of autoimmunity features and inflammatory phenotype that develops at earlier stages. These abnormalities are characterised by enhanced TLR7 expression and immune activation, increased immune complex deposition, Th1 T cells and dendritic cell kidney infiltration and significant impairments in endothelial function. Modulation of TLR7 expression was observed in the Tlr9^-/- mice.

Conclusions

These findings further underscore the protective role of TLR9 in TLR7-driven autoimmunity and also in the development of vasculopathy, further strengthening the importance of tightly manipulating TLRs in putative therapeutic strategies. This study provides a new model of accelerated lupus phenotype driven by danger-associated molecular patterns.

SOCS1 and SOCS3 Target IRF7 Degradation To Suppress TLR7-Mediated Type I IFN Production of Human Plasmacytoid Dendritic Cells

Type I IFN production of plasmacytoid dendritic cells (pDCs) triggered by TLR-signaling is an essential part of antiviral responses and autoimmune reactions. Although it was well-documented that members of the cytokine signaling (SOCS) family regulate TLR-signaling, the mechanism of how SOCS proteins regulate TLR7-mediated type I IFN production has not been elucidated yet. In this article, we show that TLR7 activation in human pDCs induced the expression of SOCS1 and SOCS3. SOCS1 and SOCS3 strongly suppressed TLR7-mediated type I IFN production. Furthermore, we demonstrated that SOCS1- and SOCS3-bound IFN regulatory factor 7, a pivotal transcription factor of the TLR7 pathway, through the SH2 domain to promote its proteasomal degradation by lysine 48-linked polyubiquitination. Together, our results demonstrate that SOCS1/3-mediated degradation of IFN regulatory factor 7 directly regulates TLR7 signaling and type I IFN production in pDCs. This mechanism might be targeted by therapeutic approaches to either enhance type I IFN production in antiviral treatment or decrease type I IFN production in the treatment of autoimmune diseases.

An update on lupus animal models

PURPOSE OF REVIEW

The complexity and heterogeneity of the clinical presentation in systemic lupus of erythematosus (SLE), combined to the inherent limitations of clinical research, have made it difficult to investigate the cause of this disease directly in patients. Various mouse models have been developed to dissect the cellular and genetic mechanisms of SLE, as well as to identify therapeutic targets and to screen treatments. The purpose of this review is to summarize the major spontaneous and induced mouse models of SLE and to provide an update on the major advances they have contributed to the field.

RECENT FINDINGS

Mouse models of SLE have continued to contribute to understand the cellular, signaling and metabolic mechanisms contributing to the disease and how targeting these pathways can provide therapeutic targets. Whenever possible, we discuss the advantage of using one model over the others to test a specific hypothesis.

SUMMARY

Spontaneous and induced models of lupus models are useful tools for the study of the cause of the disease, identify therapeutic targets and screen treatments in preclinical studies. Each model shares specific subsets of attributes with the disease observed in humans, which provides investigators a tool to tailor to their specific needs.

IgM and IgD B cell receptors differentially respond to endogenous antigens and control B cell fate

Naive B cells co-express two BCR isotypes, IgM and IgD, with identical antigen-binding domains but distinct constant regions. IgM but not IgD is downregulated on autoreactive B cells. Because these isotypes are presumed to be redundant, it is unknown how this could impose tolerance. We introduced the Nur77-eGFP reporter of BCR signaling into mice that express each BCR isotype alone. Despite signaling strongly in vitro, IgD is less sensitive than IgM to endogenous antigen in vivo and developmental fate decisions are skewed accordingly. IgD-only Lyn^-/- B cells cannot generate autoantibodies and short-lived plasma cells (SLPCs) in vivo, a fate thought to be driven by intense BCR signaling induced by endogenous antigens. Similarly, IgD-only B cells generate normal germinal center, but impaired IgG1⁺ SLPC responses to T-dependent immunization. We propose a role for IgD in maintaining the quiescence of autoreactive B cells and restricting their differentiation into autoantibody secreting cells.

Toll-like receptors 7 and 9 in myasthenia gravis thymus: amplifiers of autoimmunity?

Pathogen infections and dysregulated Toll-like receptor (TLR)-mediated innate immune responses are suspected to play key roles in autoimmunity. Among TLRs, TLR7 and TLR9 have been implicated in several autoimmune conditions, mainly because of their ability to promote abnormal B cell activation and survival. Recently, we provided evidence of Epstein-Barr virus (EBV) persistence and reactivation in the thymus of myasthenia gravis (MG) patients, suggesting an involvement of EBV in the intrathymic pathogenesis of the disease. Considerable data highlight the existence of pathogenic crosstalk among EBV, TLR7, and TLR9: EBV elicits TLR7/9 signaling, which in turn can enhance B cell dysfunction and autoimmunity. In this article, after a brief summary of data demonstrating TLR activation in MG thymus, we provide an overview on the contribution of TLR7 and TLR9 to autoimmune diseases and discuss our recent findings indicating a pivotal role for these two receptors, along with EBV, in driving, perpetuating, and/or amplifying intrathymic B cell dysregulation and autoimmune responses in MG. Development of therapeutic approaches targeting TLR7 and TLR9 signaling could be a novel strategy for treating the chronic inflammatory autoimmune process in myasthenia gravis.

Bruton's Tyrosine Kinase, a Component of B Cell Signaling Pathways, Has Multiple Roles in the Pathogenesis of Lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the loss of adaptive immune tolerance to nucleic acid-containing antigens. The resulting autoantibodies form immune complexes that promote inflammation and tissue damage. Defining the signals that drive pathogenic autoantibody production is an important step in the development of more targeted therapeutic approaches for lupus, which is currently treated primarily with non-specific immunosuppression. Here, we review the contribution of Bruton’s tyrosine kinase (Btk), a component of B and myeloid cell signaling pathways, to disease in murine lupus models. Both gain- and loss-of-function genetic studies have revealed that Btk plays multiple roles in the production of autoantibodies. These include promoting the activation, plasma cell differentiation, and class switching of autoreactive B cells. Small molecule inhibitors of Btk are effective at reducing autoantibody levels, B cell activation, and kidney damage in several lupus models. These studies suggest that Btk may promote end-organ damage both by facilitating the production of autoantibodies and by mediating the inflammatory response of myeloid cells to these immune complexes. While Btk has not been associated with SLE in GWAS studies, SLE B cells display signaling defects in components both upstream and downstream of Btk consistent with enhanced activation of Btk signaling pathways. Taken together, these observations indicate that limiting Btk activity is critical for maintaining B cell tolerance and preventing the development of autoimmune disease. Btk inhibitors, generally well-tolerated and approved to treat B cell malignancy, may thus be a useful therapeutic approach for SLE.

Radiation- and Age-Associated Changes in Peripheral Blood Dendritic Cell Populations among Aging Atomic Bomb Survivors in Japan

Previous immunological studies in atomic bomb survivors have suggested that radiation exposure leads to long-lasting changes, similar to immunological aging observed in T-cell-adaptive immunity. However, to our knowledge, late effects of radiation on dendritic cells (DCs), the key coordinators for activation and differentiation of T cells, have not yet been investigated in humans. In the current study, we hypothesized that numerical and functional decreases would be observed in relationship to radiation dose in circulating conventional DCs (cDCs) and plasmacytoid DCs (pDCs) among 229 Japanese A-bomb survivors. Overall, the evidence did not support this hypothesis, with no overall changes in DCs or functional changes observed with radiation dose. Multivariable regression analysis for radiation dose, age and gender effects revealed that total DC counts as well as subpopulation counts decreased in relationship to increasing age. Further analyses revealed that in women, absolute numbers of pDCs showed significant decreases with radiation dose. A hierarchical clustering analysis of gene expression profiles in DCs after Toll-like receptor stimulation in vitro identified two clusters of participants that differed in age-associated expression levels of genes involved in antigen presentation and cytokine/chemokine production in cDCs. These results suggest that DC counts decrease and expression levels of gene clusters change with age. More than 60 years after radiation exposure, we also observed changes in pDC counts associated with radiation, but only among women.

Spontaneous germinal centers and autoimmunity

Germinal centers (GCs) are dynamic microenvironments that form in the secondary lymphoid organs and generate somatically mutated high-affinity antibodies necessary to establish an effective humoral immune response. Tight regulation of GC responses is critical for maintaining self-tolerance. GCs can arise in the absence of purposeful immunization or overt infection (called spontaneous GCs, Spt-GCs). In autoimmune-prone mice and patients with autoimmune disease, aberrant regulation of Spt-GCs is thought to promote the development of somatically mutated pathogenic autoantibodies and the subsequent development of autoimmunity. The mechanisms that control the formation of Spt-GCs and promote systemic autoimmune diseases remain an open question and the focus of ongoing studies. Here, we discuss the most current studies on the role of Spt-GCs in autoimmunity.

Lupus nephritis progression in FcγRIIB-/-yaa mice is associated with early development of glomerular electron dense deposits and loss of renal DNase I in severe disease

FcγRIIB^-/-yaa mice develop severe lupus glomerulonephritis due to lack of an inhibitory immune cell receptor combined with a Y-chromosome linked autoimmune accelerator mutation. In the present study, we have investigated nephritis development and progression in FcγRIIB^-/-yaa mice to find shared features with NZB/NZW F1 lupus prone mice and human disease. We sacrificed 25 male FcγRIIB^-/-yaa mice at various disease stages, and grouped them according to activity and chronicity indices for lupus nephritis. Glomerular morphology and localization of electron dense deposits containing IgG were further determined by immune electron microscopy. Renal DNase I and pro-inflammatory cytokine mRNA levels were measured by real-time quantitative PCR. DNase I protein levels was assessed by immunohistochemistry and zymography. Our results demonstrate early development of electron dense deposits containing IgG in FcγRIIB^-/-yaa mice, before detectable levels of serum anti-dsDNA antibodies. Similar to NZB/NZW F1, electron dense deposits in FcγRIIB^-/-yaa progressed from being confined to the mesangium in the early stage of lupus nephritis to be present also in capillary glomerular basement membranes. In the advanced stage of lupus nephritis, renal DNase I was lost on both transcriptional and protein levels, which has previously been shown in NZB/NZW F1 mice and in human disease. Although lupus nephritis appears on different genetic backgrounds, our findings suggest similar processes when comparing different murine models and human lupus nephritis.

The sexist behaviour of immune checkpoint inhibitors in cancer therapy?

BACKGROUND

Immune checkpoint inhibitors, targeting the molecules CTLA-4, PD-1 and PD-L1, showed efficacy against several type of cancers and are currently used in clinical practice. An important biological variable that influences innate and adaptive immunity is the sex, acting through genetic, hormonal and environmental factors. The overall differences between sexes could be crucial to evaluate the response to ICIs.

MATERIALS AND METHODS

We performed a meta-analysis of Phase II-III Clinical Trials published up to June 2017 in which anti-CTLA-4, anti-PD-1 and anti-PD-L1 were studied. We extracted the OS and PFS HR differentiated by sex from subgroups analysis of each trial. We analyzed the three classes of drugs separately.

RESULTS

We selected 36 Phase II-III Clinical Trials, 9 of which reported results for OS and 6 for PFS. We analyzed 2 Clinical Trials for OS with anti-CTLA-4, including 1178 patients, observing a benefit for males vs females (HR 0.65, 95% CI 0.55-0.77 vs HR 0.79, 95% CI 0.65-0.96, p 0.078).Not statistically significant results were observed with anti-PD-1 neither for OS (males vs females: HR 0.72, 95% CI 0.64-0.83 vs HR 0.81, 95% CI 0.70-0.94, p 0.285) neither for PFS (males vs females: HR 0.66, 95% CI 0.52-0.82 vs HR 0.85, 95% CI 0.66-1.09, p 0.158). We cannot perform a meta-analysis for anti-PD-L1 due to the lack of data.

CONCLUSIONS

Different mechanisms could be involved in sex differences with regard to immunotherapy. These differences could be relevant to identify immunological targets in order to draw studies exploring novel combinations of immunotherapy agents.

Enhanced IFN-α production is associated with increased TLR7 retention in the lysosomes of palasmacytoid dendritic cells in systemic lupus erythematosus

Background

Interferon-α (IFN-α) is increased and plays an important role in the pathogenesis of systemic lupus erythematosus (SLE). Plasmacytoid dendritic cells (pDCs) are the main producer of IFN-α, but their IFN-α producing capacity has been shown to be unchanged or reduced when stimulated with a Toll-like receptor 9 (TLR9) agonist in patients with SLE compared to in healthy individuals. In this study, we investigated the IFN-α-producing capacity of lupus pDCs under different stimulation.

Methods

pDCs from patients with SLE and healthy controls (HC) were stimulated with TLR9 or TLR7 agonist, and their IFN-α producing capacity was examined by intracellular cytokine staining and flow cytometry. The correlation of IFN-α-producing capacity with serum IFN-α levels and disease activity was assessed. The effect of in vitro IFN-α exposure on IFN-α production by pDCs was examined. Localization of TLR7 in cellular compartments in pDCs was investigated.

Results

The IFN-α producing capacity of pDCs was reduced after TLR9 stimulation, but increased when stimulated with a TLR7 agonist in SLE compared to in HC. IFN-α production by pDCs upon TLR9 stimulation was reduced and the percentage of IFN-α⁺pDC was inversely correlated with disease activity and serum IFN-α levels. However, the TLR7 agonist-induced IFN-α producing capacity of lupus pDCs was enhanced and correlated with disease activity and serum IFN-α. Exposure to IFN-α enhanced IFN-α production of TLR7-stimulated pDCs, but reduced that of pDCs activated with a TLR9 agonist. TLR7 localization was increased in late endosome/lysosome compartments in pDCs from SLE patients.

Conclusions

These findings indicate that enhanced TLR7 responses of lupus pDCs, owing to TLR7 retention in late endosome/lysosome and exposure to IFN-α, are associated with the pathogenesis of SLE.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1441-7) contains supplementary material, which is available to authorized users.

Loss of Xist RNA from the inactive X during B cell development is restored in a dynamic YY1-dependent two-step process in activated B cells

X-chromosome inactivation (XCI) in female lymphocytes is uniquely regulated, as the inactive X (Xi) chromosome lacks localized Xist RNA and heterochromatin modifications. Epigenetic profiling reveals that Xist RNA is lost from the Xi at the pro-B cell stage and that additional heterochromatic modifications are gradually lost during B cell development. Activation of mature B cells restores Xist RNA and heterochromatin to the Xi in a dynamic two-step process that differs in timing and pattern, depending on the method of B cell stimulation. Finally, we find that DNA binding domain of YY1 is necessary for XCI in activated B cells, as ex-vivo YY1 deletion results in loss of Xi heterochromatin marks and up-regulation of X-linked genes. Ectopic expression of the YY1 zinc finger domain is sufficient to restore Xist RNA localization during B cell activation. Together, our results indicate that Xist RNA localization is critical for maintaining XCI in female lymphocytes, and that chromatin changes on the Xi during B cell development and the dynamic nature of YY1-dependent XCI maintenance in mature B cells predisposes X-linked immunity genes to reactivation.

Females are predisposed to develop various autoimmune disorders, and the genetic basis for this susceptibility is the X-chromosome. X-linked genes are dosage compensated between sexes by X-chromosome Inactivation (XCI) during embryogenesis and maintained into adulthood. Here we show that the chromatin of the inactive X loses epigenetic modifications during B cell lineage development. We found that female mature B cells, which are the pathogenic cells in autoimmunity, have a dynamic two-step mechanism of maintaining XCI during stimulation. The transcription factor YY1, which regulates DNA looping during V(D)J recombination in B cells, is necessary for relocalizing Xist RNA back to the inactive X in activated B cells. YY1 deletion ex vivo in mature B cells impairs heterochromatin mark enrichment on the inactive X, and results in increased X-linked gene expression. We demonstrate that the DNA binding domain of YY1 is sufficient for localizing Xist RNA to the inactive X during B cell stimulation. Our study indicates that Xist RNA localization is critical for maintaining XCI in female lymphocytes. We propose that chromatin changes on the Xi during B cell development and the dynamic nature of YY1-dependent XCI maintenance in mature B cells predisposes X-linked immunity genes to reactivation.

Human Immunodeficiency Virus 1 and Type I Interferons-Where Sex Makes a Difference

The human immunodeficiency virus (HIV)-1 epidemic continues to represent a global health problem that is over-proportionally affecting women from sub-Saharan Africa. Besides social and environmental factors, the modulation of immunological pathways by sex hormones and gene dosage effects of X chromosomal-encoded genes have been suggested to lead to differential outcomes in HIV-1 disease. Women present with lower HIV-1 loads early in infection. However, the progression to AIDS for the same level of viremia is faster in women than in men. Type I interferons (IFNs) play a prominent role in the control of HIV-1 transmission and replication. Continuous stimulation of type I IFNs in chronic viral infections can lead to increased levels of immune activation, which can be higher in HIV-1-infected women than in men. A role of steroid hormone signaling in regulating viral replication has been postulated, which might further account for sex differences observed in HIV-1 infections. Here, we review recent findings and current knowledge on sex-specific differences in HIV-1 infections.

Innate Immune Receptors as Competitive Determinants of Cell Fate

Infections can cause a multitude of stresses on the host and microbe. To detect potential infections, the mammalian immune system utilizes several families of pattern recognition receptors, which survey the intracellular and extracellular environments for microbial products. Members of each receptor family induce antimicrobial effector responses, which include inflammatory cytokine or interferon expression, downregulation of protein synthesis, or host cell death. In this review, we discuss the benefits of each of these innate immune responses. We highlight how non-infectious bacteria and viruses typically activate a single family of receptors, which results in a predictable host response. Infections with virulent pathogens, in contrast, may activate receptors from distinct families. As each receptor family may induce responses that antagonize or synergize with the activities of another family, cell fate decisions during pathogenic encounters are unpredictable. Understanding the antagonistic antimicrobial activities of the innate immune system should provide insight into how cell fate decisions are made during infections and potentially during other environmental stresses.

The multiple pathways to autoimmunity

Efforts to understand autoimmunity have been pursued relentlessly for several decades. It has become apparent that the immune system evolved multiple mechanisms for controlling self-reactivity, and defects in one or more of these mechanisms can lead to a breakdown of tolerance. Among the multitude of lesions associated with disease, the most common seem to affect peripheral tolerance rather than central tolerance. The initial trigger for both systemic autoimmune disorders and organ-specific autoimmune disorders probably involves the recognition of self or foreign molecules, especially nucleic acids, by innate sensors. Such recognition, in turn, triggers inflammatory responses and the engagement of previously quiescent autoreactive T cells and B cells. Here we summarize the most prominent autoimmune pathways and identify key issues that require resolution for full understanding of pathogenic autoimmunity.

The Immune System in Obesity: Developing Paradigms Amidst Inconvenient Truths

PURPOSE OF REVIEW

Adipose tissue (AT) houses both innate and adaptive immune systems that are crucial for preserving AT function and metabolic homeostasis. In this review, we summarize recent information regarding progression of obesity-associated AT inflammation and insulin resistance. We additionally consider alterations in AT distribution and the immune system in males vs. females and among different racial populations.

RECENT FINDINGS

Innate and adaptive immune cell-derived inflammation drives insulin resistance both locally and systemically. However, new evidence also suggests that the immune system is equally vital for adipocyte differentiation and protection from ectopic lipid deposition. Furthermore, roles of anti-inflammatory immune cells such as regulatory T cells, "M2-like" macrophages, eosinophils, and mast cells are being explored, primarily due to promise of immunotherapeutic applications. Both immune responses and AT distribution are strongly influenced by factors like sex and race, which have been largely underappreciated in the field of metabolically-associated inflammation, or meta-flammation. More studies are required to recognize factors that switch inflammation from controlled to uncontrolled in obesity-associated pathogenesis and to integrate the combined effects of meta-flammation and immunometabolism. It is critical to recognize that the AT-associated immune system can be alternately beneficial and destructive; therefore, simply blocking immune responses early in obesity may not be the best clinical approach. The dearth of information on gender and race-associated disparities in metabolism, AT distribution, and the immune system suggest that a greater understanding of such differences will be critical to develop personalized treatments for obesity and the associated metabolic dysfunction.

Sex-specific regulation of immune responses by PPARs

The prevalence of autoimmune, infectious and metabolic diseases is different for men and women owing to the respective ability of their immune systems to respond to self and foreign antigens. Although several factors, including hormones and the X-chromosome, have been suggested to contribute to such sex-specific immune responses, the underlying factors remain poorly defined. Recent studies using peroxisome proliferator-activated receptor (PPAR) ligands and knockout mice have identified sex-dimorphic expression of PPARs, and have shown that the inhibitory functions of PPAR in T cells are substantially affected by the sex hormones. In this review, we consider the sex-specific differences in PPARs and summarize the diverse PPAR-mediated, sex-specific properties of effector T-cell responses, such as T-cell activation, survival and differentiation, as well as their involvement in T-cell-related autoimmune diseases, including colitis, graft-versus-host disease and experimental autoimmune encephalomyelitis. Understanding PPAR-mediated sex differences in immune responses will provide more precise insights into the roles of PPARs in effector T cells.

Diagnosis and management of the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy complications in the presence of persistent antiphospholipid antibodies (APLA). Laboratory diagnosis of APLA depends upon the detection of a lupus anticoagulant, which prolongs phospholipid-dependent anticoagulation tests, and/or anticardiolipin (aCL) and anti-β2-glycoprotein-1 (β2GPI) antibodies. APLA are primarily directed toward phospholipid binding proteins. Pathophysiologic mechanisms underlying thrombosis and pregnancy loss in APS include APLA induced cellular activation, inhibition of natural anticoagulant and fibrinolytic systems, and complement activation, among others. There is a high rate of recurrent thrombosis in APS, especially in triple positive patients (patients with lupus anticoagulant, aCL and anti-β2GPI antibodies), and indefinite anticoagulation with a vitamin K antagonist is the standard of care for thrombotic APS. There is currently insufficient evidence to recommend the routine use of direct oral anticoagulants (DOAC) in thrombotic APS. Aspirin with low molecular weight or unfractionated heparin may reduce the incidence of pregnancy loss in obstetric APS. Recent insights into the pathogenesis of APS have led to the identification of new potential therapeutic interventions, including anti-inflammatory and immunomodulatory therapies. Additional research is needed to better understand the effects of APLA on activation of signaling pathways in vascular cells, to identify more predictive biomarkers that define patients at greatest risk for a first or recurrent APLA-related clinical event, and to determine the safety and efficacy of DOACs and novel anti-inflammatory and immune-modulatory therapies for refractory APS.

Inhibition of Toll-Like Receptor Signaling as a Promising Therapy for Inflammatory Diseases: A Journey from Molecular to Nano Therapeutics

The recognition of invading pathogens and endogenous molecules from damaged tissues by toll-like receptors (TLRs) triggers protective self-defense mechanisms. However, excessive TLR activation disrupts the immune homeostasis by sustained pro-inflammatory cytokines and chemokines production and consequently contributes to the development of many inflammatory and autoimmune diseases, such as systemic lupus erythematosus (SLE), infection-associated sepsis, atherosclerosis, and asthma. Therefore, inhibitors/antagonists targeting TLR signals may be beneficial to treat these disorders. In this article, we first briefly summarize the pathophysiological role of TLRs in the inflammatory diseases. We then focus on reviewing the current knowledge in both preclinical and clinical studies of various TLR antagonists/inhibitors for the prevention and treatment of inflammatory diseases. These compounds range from conventional small molecules to therapeutic biologics and nanodevices. In particular, nanodevices are emerging as a new class of potent TLR inhibitors for their unique properties in desired bio-distribution, sustained circulation, and preferred pharmacodynamic and pharmacokinetic profiles. More interestingly, the inhibitory activity of these nanodevices can be regulated through precise nano-functionalization, making them the next generation therapeutics or “nano-drugs.” Although, significant efforts have been made in developing different kinds of new TLR inhibitors/antagonists, only limited numbers of them have undergone clinical trials, and none have been approved for clinical uses to date. Nevertheless, these findings and continuous studies of TLR inhibition highlight the pharmacological regulation of TLR signaling, especially on multiple TLR pathways, as future promising therapeutic strategy for various inflammatory and autoimmune diseases.

Associations of Autoimmunity, Immunodeficiency, Lymphomagenesis, and Gut Microbiota in Mice with Knockins for a Pathogenic Autoantibody

A number of mouse strains transgenic for B-cell receptors specific for nucleic acids or other autoantigens have been generated to understand how autoreactive B cells are regulated in normal and autoimmune mice. Previous studies of nonautoimmune C57BL/6 mice heterozygous for both the IgH and IgL knockins of the polyreactive autoantibody, 564, produced high levels of autoantibodies in a largely Toll-like receptor 7-dependent manner. Herein, we describe studies of mice homozygous for the knockins that also expressed high levels of autoantibodies but, unlike the heterozygotes, exhibited a high incidence of mature B-cell lymphomas and enhanced susceptibility to bacterial infections. Microarray analyses and serological studies suggested that lymphomagenesis might be related to chronic B-cell activation promoted by IL-21. Strikingly, mice treated continuously with antibiotic-supplemented water did not develop lymphomas or abscesses and exhibited less autoimmunity. This mouse model may help us understand the reasons for enhanced susceptibility to lymphoma development exhibited by humans with a variety of autoimmune diseases, such as Sjögren syndrome, systemic lupus erythematosus, and highly active rheumatoid arthritis.

TLR7/TLR9- and B Cell Receptor-Signaling Crosstalk: Promotion of Potentially Dangerous B Cells

B cells are capable of receptor-mediated responses to foreign antigens. Recognition of microbial-derived nucleic acid (NA) by toll-like receptors (TLRs) 7 and 9 in B cells has been substantiated. Endogenous NA released from damaged or dying cells can also be immunogenic in certain contexts and can incite aberrant activation of B cells. When TLR-driven B cell receptor (BCR)-activated B cells are not properly constrained, pathologic autoantibodies are produced. It is also clear that endosomal TLR7/TLR9 can operate in conjunction with BCR. In addition to BCR signaling, a balance between TLR7 and TLR9 is pivotal in the development of B cell autoreactivity. While TLR9 is important in normal memory B cell responses through BCR, TLR9 activation has been implicated in autoantibody production. Paradoxically, TLR9 also plays known protective roles against autoimmunity by directly and indirectly inhibiting TLR7-mediated autoantibody production. Herein, we summarize literature supporting mechanisms underpinning the promotion of pathological BCR-activated B cells by TLR7 and TLR9. We focus on the literature regarding known points of TLR7/TLR9 and BCR crosstalk. Data also suggest that the degree of TLR responsiveness relies on alterations of certain intrinsic B-cell signaling molecules and is also context specific. Because allogeneic hematopoietic stem cell transplantation is a high NA and B cell-activating factor environment, we conclude that B cell studies of synergistic TLR-BCR signaling in human diseases like chronic graft-versus-host disease are warranted. Further understanding of the distinct molecular pathways mediating TLR-BCR synergy will lead to the development of therapeutic strategies in autoimmune disease states.

Pathways leading to an immunological disease: systemic lupus erythematosus

SLE is a chronic autoimmune disease caused by perturbations of the immune system. The clinical presentation is heterogeneous, largely because of the multiple genetic and environmental factors that contribute to disease initiation and progression. Over the last 60 years, there have been a number of significant leaps in our understanding of the immunological mechanisms driving disease processes. We now know that multiple leucocyte subsets, together with inflammatory cytokines, chemokines and regulatory mediators that are normally involved in host protection from invading pathogens, contribute to the inflammatory events leading to tissue destruction and organ failure. In this broad overview, we discuss the main pathways involved in SLE and highlight new findings. We describe the immunological changes that characterize this form of autoimmunity. The major leucocytes that are essential for disease progression are discussed, together with key mediators that propagate the immune response and drive the inflammatory response in SLE.

Modelling clinical systemic lupus erythematosus: similarities, differences and success stories

Mouse models of SLE have been indispensable tools to study disease pathogenesis, to identify genetic susceptibility loci and targets for drug development, and for preclinical testing of novel therapeutics. Recent insights into immunological mechanisms of disease progression have boosted a revival in SLE drug development. Despite promising results in mouse studies, many novel drugs have failed to meet clinical end points. This is probably because of the complexity of the disease, which is driven by polygenic predisposition and diverse environmental factors, resulting in a heterogeneous clinical presentation. Each mouse model recapitulates limited aspects of lupus, especially in terms of the mechanism underlying disease progression. The main mouse models have been fairly successful for the evaluation of broad-acting immunosuppressants. However, the advent of targeted therapeutics calls for a selection of the most appropriate model(s) for testing and, ultimately, identification of patients who will be most likely to respond.

Targeting CD22 with the monoclonal antibody epratuzumab modulates human B-cell maturation and cytokine production in response to Toll-like receptor 7 (TLR7) and B-cell receptor (BCR) signaling

Background

Abnormal B-cell activation is implicated in the pathogenesis of autoimmune diseases, including systemic lupus erythematosus (SLE). The B-cell surface molecule CD22, which regulates activation through the B-cell receptor (BCR), is a potential target for inhibiting pathogenic B cells; however, the regulatory functions of CD22 remain poorly understood. In this study, we determined how targeting of CD22 with epratuzumab (Emab), a humanized anti-CD22 IgG1 monoclonal antibody, affects the activation of human B-cell subsets in response to Toll-like receptor 7 (TLR7) and BCR engagement.

Methods

B-cell subsets were isolated from human tonsils and stimulated with F(ab′)₂ anti-human IgM and/or the TLR7 agonist R848 in the presence of Emab or a human IgG1 isotype control. Changes in mRNA levels of genes associated with B-cell activation and differentiation were analyzed by quantitative PCR. Cytokine production was measured by ELISA. Cell proliferation, survival, and differentiation were assessed by flow cytometry.

Results

Pretreatment of phenotypically naïve CD19⁺CD10^–CD27^– cells with Emab led to a significant increase in IL-10 expression, and in some but not all patient samples to a reduction of IL-6 production in response to TLR7 stimulation alone or in combination with anti-IgM. Emab selectively inhibited the expression of PRDM1, the gene encoding B-lymphocyte-induced maturation protein 1 (Blimp-1) in activated CD10^–CD27^– B cells. CD10^–CD27^–IgD^– cells were highly responsive to stimulation through TLR7 as evidenced by the appearance of blasting CD27^hiCD38^hi cells. Emab significantly inhibited the activation and differentiation of CD10^–CD27^–IgD^– B cells into plasma cells.

Conclusions

Emab can both regulate cytokine expression and block Blimp1-dependent B-cell differentiation, although the effects of Emab may depend on the stage of B-cell development or activation. In addition, Emab inhibits the activation of CD27^–IgD^– tonsillar cells, which correspond to so-called double-negative memory B cells, known to be increased in SLE patients with more active disease. These data may be relevant to the therapeutic effect of Emab in vivo via modulation of the production of pro-inflammatory and anti-inflammatory cytokines by B cells. Because Blimp-1 is required by B cells to mature into antibody-producing cells, inhibition of Blimp1 may reduce autoantibody production.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1284-2) contains supplementary material, which is available to authorized users.

RIG-I-Like Receptors and Type I Interferonopathies

Type I interferon (IFN) production by the proper activation of nucleic acid sensors is essential for hosts to eliminate invading viruses. Among these sensors, RIG-I-like receptors (RLRs) are well-known viral RNA sensors in the cytoplasm that recognize the nonself signatures of viral RNAs to trigger IFN responses. Recent accumulating evidence has clarified that some specific and atypical self-RNAs also cause activation of RLRs independently of virus infection. Importantly, when RLR-activation by these RNAs or a conformational change via missense mutations is sustained, the resulting continuous production of type I IFN will lead to autoimmune disorders. We, herein, focus on autoimmune diseases caused by chronic activation of RLRs and discuss possible mechanisms of their onset.

Aging effects on T-bet expression in human B cell subsets

In order to compare human and mouse B cell subset markers, we evaluated T-bet expression in human B cell subsets from individuals of different ages. We found T-bet expressed in unstimulated memory more than naïve B cells, and more in young individuals. TLR7 stimulation up-regulated T-bet in all B cell subsets from young and elderly individuals, and more in the elderly. By fold-increase the best effect was seen in subsets of the elderly and especially in those that undergo class switch (naïve and IgM). We also evaluated CD11c expression, as T-bet+CD11c+ B cells are expanded in healthy elderly individuals and also in patients with autoimmunity. Similar to T-bet, CD11c expression was higher in memory than in naïve B cells, but no differences were observed between young and elderly individuals. After TLR7 stimulation, CD11c increases in all B cell subsets (especially in naïve and IgM) from the elderly.

Deficiency in IRAK4 activity attenuates manifestations of murine Lupus

Interleukin-1 receptor-associated kinase (IRAK) 4 mediates host defense against infections. As an active kinase, IRAK4 elicits full spectra of myeloid differentiation primary response protein (MyD) 88-dependent responses, while kinase-inactive IRAK4 induces a subset of cytokines and negative regulators whose expression is not regulated by mRNA stability. IRAK4 kinase activity is critical for resistance against Streptococcus pneumoniae, but its involvement in autoimmunity is incompletely understood. In this study, we determined the role of IRAK4 kinase activity in murine lupus. Lupus development in BXSB mice expressing the Y chromosome autoimmunity accelerator (Yaa) increased basal and Toll-like receptor (TLR) 4/7-induced phosphorylation of mitogen-activated protein kinases, p65 nuclear factor-κB (NF-κB), enhanced tumor necrosis factor (TNF)-α and C-C motif chemokine ligand (CCL) 5 gene expression in splenic macrophages, but decreased levels of Toll-interacting protein and IRAK-M, without affecting IRAK4 or IRAK1 expression. Mice harboring kinase-inactive IRAK4 on the lupus-prone Yaa background manifested blunted TLR signaling in macrophages and reduced glomerulonephritis, splenomegaly, serum anti-nuclear antibodies, numbers of splenic macrophages, total and TNF-α⁺ dendritic cells, activated T- and B-lymphocytes, and lower TNF-α expression in macrophages compared with lupus-prone mice with functional IRAK4. Thus, IRAK4 kinase activity contributes to murine lupus and could represent a new therapeutic target.

Regulatory T Cells in Systemic Sclerosis: a Comprehensive Review

Systemic sclerosis (SSc) is a chronic inflammatory disease with complex pathogenesis, based on the sophisticated interplay of injury to the vascular endothelium, exaggerated tissue regeneration and fibrosis, and extensive immune abnormalities. The role of regulatory T cells (Tregs) in the development of SSc has started being studied during the last decade with new aspects being disclosed continuously, in parallel with the better understanding of Tregs physiology. There is a general agreement in the medical literature regarding the decreased functional capacity of circulating Tregs in SSc. Some patients, particularly those with active disease, may have increased numbers of circulating Tregs, representing the inhibitory response of the immune system to its inappropriate activation or occurring as a compensatory move for Tregs' decreased suppressive ability. Decreased pool of circulating Tregs can be seen in other SSc patients, with even lower Treg percentages seen in patients with long-standing disease. Skin-resident Tregs are depleted in advanced SSc but can be active and have a role in earlier disease stages. In addition to diminished suppressive ability, Tregs can contribute to SSc evolution by their microenvironment-dependent transformation to pathogenic effector T cells of Th17 or Th2 lineages with respective pro-inflammatory or pro-fibrotic activity. The current data on the effects of existing treatment modalities, including autologous stem cell transplantation, on Tregs function in SSc, is controversial, not being sufficiently elaborated.

Disruption of Pathogenic Cellular Networks by IL-21 Blockade Leads to Disease Amelioration in Murine Lupus

Systemic lupus erythematosus (lupus) is characterized by autoantibody-mediated organ injury. Follicular Th (Tfh) cells orchestrate physiological germinal center (GC) B cell responses, whereas in lupus they promote aberrant GC responses with autoreactive memory B cell development and plasma cell-derived autoantibody production. IL-21, a Tfh cell-derived cytokine, provides instructional cues for GC B cell maturation, with disruption of IL-21 signaling representing a potential therapeutic strategy for autoantibody-driven diseases such as systemic lupus erythematosus. We used blockade of IL-21 to dissect the mechanisms by which this cytokine promotes autoimmunity in murine lupus. Treatment of lupus-prone B6.Sle1.Yaa mice with an anti-IL-21 blocking Ab reduced titers of autoantibodies, delayed progression of glomerulonephritis and diminished renal-infiltrating Tfh and Th1 cells, and improved overall survival. Therapy inhibited excessive accumulation of Tfh cells coexpressing IL-21 and IFN-γ, and suppressed their production of the latter cytokine, albeit while not affecting their frequency. Anti-IL-21 treatment also led to a reduction in GC B cells, CD138^hi plasmablasts, IFN-γ-dependent IgG2c production, and autoantibodies, indicating that Tfh cell-derived IL-21 is critical for pathological B cell cues in lupus. Normalization of GC responses was, in part, caused by uncoupling of Tfh-B cell interactions, as evidenced by reduced expression of CD40L on Tfh cells and reduced B cell proliferation in treated mice. Our work provides mechanistic insight into the contribution of IL-21 to the pathogenesis of murine lupus, while revealing the importance of T-B cellular cross-talk in mediating autoimmunity, demonstrating that its interruption impacts both cell types leading to disease amelioration.

Danger Signals and Graft-versus-host Disease: Current Understanding and Future Perspectives

Graft-versus-host response after allogeneic hematopoietic stem cell transplantation (allo-HCT) represents one of the most intense inflammatory responses observed in humans. Host conditioning facilitates engraftment of donor cells, but the tissue injury caused from it primes the critical first steps in the development of acute graft-versus-host disease (GVHD). Tissue injuries release pro-inflammatory cytokines (such as TNF-α, IL-1β, and IL-6) through widespread stimulation of pattern recognition receptors (PRRs) by the release of danger stimuli, such as damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs). DAMPs and PAMPs function as potent stimulators for host and donor-derived antigen presenting cells (APCs) that in turn activate and amplify the responses of alloreactive donor T cells. Emerging data also point towards a role for suppression of DAMP induced inflammation by the APCs and donor T cells in mitigating GVHD severity. In this review, we summarize the current understanding on the role of danger stimuli, such as the DAMPs and PAMPs, in GVHD.

Nucleic acid-sensing TLRs: trafficking and regulation

Toll-like receptors (TLRs) play an important role in innate immune responses against pathogenic microorganisms or tissue damage. Nucleic acid (NA)-sensing TLRs localize in intracellular vesicular compartments and recognize foreign-derived and host-derived nucleic acid ligands. Inappropriate activation of NA-sensing TLRs can cause pathogenic inflammation and autoimmunity. Multiple regulatory mechanisms exist to limit recognition of self-NAs. This review summarizes recent progress that has been made in understanding how NA-sensing TLRs are regulated via trafficking, proteolytic cleavage, as well as ligand processing and recognition.

Abnormal thymic maturation and lymphoproliferation in MRL-Fas lpr/lpr mice can be partially reversed by synthetic oligonucleotides: implications for systemic lupus erythematosus and autoimmune lymphoproliferative syndrome

MRL-Fas ^lpr/lpr mice represent an excellent animal model for studying non-malignant lymphoproliferation, regeneration and systemic autoimmunity. Retro-transposon insertion into the second intron of the pro-apoptotic Fas gene appears to be responsible for both lymphoproliferation and autoimmunity, while other genes are more likely to contribute to the regenerative healing characteristic of this mouse strain. Previous studies have shown that neonatal thymectomy can halt the development of abnormal lymphoproliferation. Whereas at four weeks of age primary and secondary lymphoid organs appear to be grossly intact, vigorous lymphoproliferation and autoantibody production subsequently ensues. This is first noticeable at six weeks of age, at which time lymph nodes, spleens and thymuses, but not the bone marrow, become infiltrated with abnormal B220⁺CD3⁺CD4^-CD8^- T cells. Around the same time, thymuses show a significant drop in CD4⁺CD8⁺double-positive T cells generating an abnormal ratio between double-positive and single-positive thymocytes. The objective of current study was to evaluate the effect of synthetic oligonucleotides-toll-like receptor antagonists on early lymphoid development in this strain of mice. Herein, we demonstrate the ability of synthetic oligonucleotides made with the nuclease-resistant phosphorothioate backbone to partially reverse abnormal lymphoproliferation and thymic involution in pre-diseased MRL-Fas ^lpr/lpr mice when administered intraperitoneally starting from week four of age. This curative effect of oligonucleotides was primary sequence/secondary oligonucleotide structure-independent, suggesting an effect through the toll-like receptor 7. A similar approach may potentially benefit patients with autoimmune lymphoproliferative syndrome who, like MRL-Fas ^lpr/lpr mice, carry a mutation in the Fas gene.

Sex differences in HIV-1-mediated immunopathology

PURPOSE OF REVIEW

The article reviews our current knowledge regarding the role of sex and sex hormones in regulating innate immune responses to viral infections, which may account for the described sex differences in immunity to HIV-1.

RECENT FINDINGS

Prominent sex differences exist in various infectious and autoimmune diseases. Biological mechanisms underlying these differences include the modulation of immunological pathways by sex hormones and gene dosage effects of immunomodulatory genes encoded by the X chromosome. During HIV-1 infections, women have been shown to present with lower viral load levels in primary infection, although their progression to AIDS is faster in comparison with men when accounting for viral load levels in chronic infection. HIV-1-infected women furthermore tend to have higher levels of immune activation and interferon-stimulated gene expression in comparison with men for the same viral load, which has been associated to innate sensing of HIV-1 by Toll-like receptor 7 and the consequent interferon-α production by plasmacytoid dendritic cells.

SUMMARY

Improvement in understanding the mechanisms associated with sex differences in HIV-1-mediated immunopathology will be critical to take sex differences into consideration when designing experimental and clinical studies in HIV-1-infected populations.

Sex and Gender Impact Immune Responses to Vaccines Among the Elderly

In response to the recommended vaccines in older-aged individuals, sex differences occur in response to those that protect against influenza, tetanus, pertussis, shingles, and pneumococcal infections. The efficacy of vaccines recommended for older-aged adults is consistently greater for females than for males. Gender differences as well as biological sex differences can influence vaccine uptake, responses, and outcome in older-aged individuals, which should influence guidelines, formulations, and dosage recommendations for vaccines in the elderly.