Human Th17- and IgG3-associated autoimmunity induced by a translocating gut pathobiont.

Extraintestinal autoimmune diseases are multifactorial with translocating gut pathobionts implicated as instigators and perpetuators in mice. However, the microbial contributions to autoimmunity in humans remain largely unclear, including whether specific pathological human adaptive immune responses are triggered by such pathobionts. We show here that the translocating pathobiont Enterococcus gallinarum induces human IFNγ + Th17 differentiation and IgG3 subclass switch of anti- E. gallinarum RNA and correlating anti-human RNA autoantibody responses in patients with systemic lupus erythematosus and autoimmune hepatitis. Human Th17 induction by E. gallinarum is cell-contact dependent and involves TLR8-mediated human monocyte activation. In murine gnotobiotic lupus models, E. gallinarum translocation triggers IgG3 anti-RNA autoantibody titers that correlate with renal autoimmune pathophysiology and with disease activity in patients. Overall, we define cellular mechanisms of how a translocating pathobiont induces human T- and B-cell-dependent autoimmune responses, providing a framework for developing host- and microbiota-derived biomarkers and targeted therapies in extraintestinal autoimmune diseases. One Sentence Summary: Translocating pathobiont Enterococcus gallinarum promotes human Th17 and IgG3 autoantibody responses linked to disease activity in autoimmune patients.

Translocating Lactobacillus torments tumors via tryptophan catabolism.

Variability in the efficacy of immune checkpoint inhibitors in cancer patients is associated with the human gut microbiota. However, detailed mechanisms are unclear. In this issue of Cell, Bender et al. uncovered that a probiotic Lactobacillus strain translocates into murine tumors to enhance immunotherapy via the tryptophan metabolite indole-3-aldehyde (I3A).

Research article network analysis of polymicrobial chronic wound infections in Masanga, Sierra Leone.

BACKGROUND: Chronic wounds are frequently colonized or infected with multiple bacterial or fungal species, which can both promote or inhibit each other. Network analyses are helpful to understand the interplay of these species in polymicrobial infections. Our aim was to analyse the network of bacterial and fungal species in chronic wounds. METHODS: Swabs (n = 163) from chronic wound infections (Masanga, Sierra Leone, 2019-2020) were screened for bacterial and fungal species using non-selective agars. Some of these wounds were suspected but not confirmed Buruli ulcer. Species identification was done with MALDI-TOF mass spectrometry. Network analysis was performed to investigate co-occurrence of different species within one patient. All species with n ≥ 10 isolates were taken into account. RESULTS: Of the 163 patients, 156 had a positive wound culture (median of three different species per patient; range 1-7). Pseudomonas aeruginosa (n = 75) was the dominating species with frequent co-detections of Klebsiella pneumoniae (21 cases; OR = 1.36, 95%CI: 0.63-2.96, p = 0.47), Staphylococcus aureus (14 cases; OR = 1.06, 95%CI: 0.44-2.55, p = 1) and Proteus mirabilis (13 cases; OR = 0.84, 95%CI: 0.35-1.99, p = 0.69). CONCLUSION: The culturome of chronic wounds in Sierra Leonean patients is highly diverse and characterized by the co-occurrence of P. aeruginosa, K. pneumoniae and S. aureus.

Supporting the differential diagnosis of connective tissue diseases with neurological involvement by blood and cerebrospinal fluid flow cytometry.

OBJECTIVE: Neurological manifestations of autoimmune connective tissue diseases (CTD) are poorly understood and difficult to diagnose. We here aimed to address this shortcoming by studying immune cell compositions in CTD patients with and without neurological manifestation. METHODS: Using flow cytometry, we retrospectively investigated paired cerebrospinal fluid (CSF) and blood samples of 28 CTD patients without neurological manifestation, 38 CTD patients with neurological manifestation (N-CTD), 38 non-inflammatory controls, and 38 multiple sclerosis (MS) patients, a paradigmatic primary neuroinflammatory disease. RESULTS: We detected an expansion of plasma cells in the blood of both N-CTD and CTD compared to non-inflammatory controls and MS. Blood plasma cells alone distinguished the clinically similar entities N-CTD and MS with high discriminatory performance (AUC: 0.81). Classical blood monocytes indicated higher disease activity in systemic lupus erythematosus (SLE) patients. Surprisingly, immune cells in the CSF did not differ significantly between N-CTD and CTD, while CD4+ T cells and the CD4+/CD8+ ratio were elevated in the blood of N-CTD compared to CTD. Several B cell-associated parameters partially overlapped in the CSF in MS and N-CTD. We built a machine learning model that distinguished N-CTD from MS with high discriminatory power using either blood or CSF. CONCLUSION: We here find that blood flow cytometry alone surprisingly suffices to distinguish CTD with neurological manifestations from clinically similar entities, suggesting that a rapid blood test could support clinicians in the differential diagnosis of N-CTD.

Evolving concepts of host-pathobiont interactions in autoimmunity.

Autoimmune diseases are complex, multifactorial diseases with a polygenic trait and diverse environmental factors that contribute to triggering and exacerbating each disorder. The human microbiome is increasingly implicated in the multistep pathogenesis of autoimmune diseases. We summarize here the latest developments in the field of how the microbiota interacts with the host on a cellular and molecular level. We review how pathobionts evolve within the gut of autoimmune-prone hosts to translocate to secondary lymphoid tissues. On mucosal sites and in non-gut tissues, pathobionts trigger autoimmune pathways through various mechanisms, including cross-reactivity with autoantigens and secretion of metabolites that alter immune functions. A better understanding of these mechanisms will hasten the development of unconventional therapeutic approaches for autoimmune diseases.

Subdoligranulum chews up joints: how a gut pathobiont can instigate arthritis.

The microbiota has been implicated in triggering certain autoimmune diseases. In rheumatoid arthritis (RA), the 'mucosal origins' hypothesis suggests that such a trigger can instigate systemic autoimmune responses that lead to synovial inflammation. Chriswell et al. recently identified a human gut commensal bound by monoclonal autoantibodies and eliciting autoantibody-mediated, transferable arthritis in gnotobiotic mouse models.

Within-host evolution of a gut pathobiont facilitates liver translocation.

Gut commensal bacteria with the ability to translocate across the intestinal barrier can drive the development of diverse immune-mediated diseases1-4. However, the key factors that dictate bacterial translocation remain unclear. Recent studies have revealed that gut microbiota strains can adapt and evolve throughout the lifetime of the host5-9, raising the possibility that changes in individual commensal bacteria themselves over time may affect their propensity to elicit inflammatory disease. Here we show that within-host evolution of the model gut pathobiont Enterococcus gallinarum facilitates bacterial translocation and initiation of inflammation. Using a combination of in vivo experimental evolution and comparative genomics, we found that E. gallinarum diverges into independent lineages adapted to colonize either luminal or mucosal niches in the gut. Compared with ancestral and luminal E. gallinarum, mucosally adapted strains evade detection and clearance by the immune system, exhibit increased translocation to and survival within the mesenteric lymph nodes and liver, and induce increased intestinal and hepatic inflammation. Mechanistically, these changes in bacterial behaviour are associated with non-synonymous mutations or insertion-deletions in defined regulatory genes in E. gallinarum, altered microbial gene expression programs and remodelled cell wall structures. Lactobacillus reuteri also exhibited broadly similar patterns of divergent evolution and enhanced immune evasion in a monocolonization-based model of within-host evolution. Overall, these studies define within-host evolution as a critical regulator of commensal pathogenicity that provides a unique source of stochasticity in the development and progression of microbiota-driven disease.

[The role of the microbiome in lupus and antiphospholipid syndrome]. / Die Rolle des Mikrobioms bei Lupus und Antiphospholipidsyndrom.

Systemic lupus erythematosus (SLE) and antiphospholipid syndrome are related, systemic autoimmune diseases of unclear etiology. Genetically predisposing factors are known; however, these alone cannot be decisive for the onset and severity of these diseases. This article explains the role of the bacterial microbiome in the origin and progression of these rheumatic diseases. The most recent knowledge in the field of microbiome research based on animal experimental approaches, patient cohorts and human samples is summarized. Various commensal bacteria that promote autoimmunity, so-called pathobionts, which originate from the gut, the skin and the oral cavity, are described. Additionally, their different mechanisms of action are described: Enterococcus gallinarum and Limosilactobacillus reuteri induce adaptive autoimmunity and innate type I interferon pathways via translocation from the small intestine to the liver and spleen; Bacteroides thetaiotaomicron, Actinomyces massiliensis, Pseudopropionibacterium propionicum, Corynebacterium amycolatum, Ruminococcus gnavus and Roseburia intestinalis lead to the formation of pathogenic T­cell and autoantibody responses via the cross-reactivity with autoantigens (Ro60, dsDNA and ß2 glycoprotein I). Finally, potential future treatment approaches are also discussed, such as immunization against certain pathobionts or the targeted modulation of the microbiome via dietary approaches, which can successfully reduce autoimmune pathologies in animal models.

Malignant T Cell Activation by a Bacillus Species Isolated from Cutaneous T-Cell Lymphoma Lesions.

Cutaneous T-cell lymphoma (CTCL) is a life-debilitating malignancy of lymphocytes homing to the skin. Although CTCL is thought to arise from a combination of genetic, epigenetic, and environmental factors, specific triggers are unclear. The skin is colonized by a unique microbiota and is heavily influenced by its interactions. We hypothesized that adaptive immune responses to skin commensals lead to clonal T-cell proliferation and transformation in the appropriate genetic background. We therefore collected lesional and nonlesional skin microbiota from patients with CTCL to study T cell interactions using skin T cell explants and peripheral, skin-homing CD4+ T cells. By various methods, we identified Bacillus safensis in CTCL lesions, a rare human commensal in healthy skin, and showed that it can induce malignant T cell activation and cytokine secretion. Taken together, our data suggest microbial triggers in the skin microbiota of patients with CTCL as potential instigators of tumorigenesis.

Skin Deep: The Role of the Microbiota in Cutaneous Autoimmunity.

The skin microbiota is thought to possibly contribute to the pathogenesis of skin autoimmune diseases. The gut microbiota affects systemically the development and function of the immune system, thereby potentially influencing cutaneous autoimmunity as well. In this paper, we review the role of the gut and skin microbiota in cutaneous autoimmune diseases. Besides direct inflammatory effects at the skin barrier, microbiota may contribute to the pathogenesis of skin autoimmune diseases by metabolites, recall immune cell responses, and permeation of antigens to the subepidermal space. Skin and gut barrier dysfunction may represent a common pathophysiologic process allowing microbiota or its particles to promote autoimmune diseases at barrier surfaces.

[Still's syndrome-similarities and differences between the juvenile and adult forms]. / Morbus Still ­ Ähnlichkeiten und Differenzen zwischen juveniler und adulter Form.

Still's syndrome includes systemic juvenile idiopathic arthritis (sJIA) and the adult form of Still's disease (adult-onset Still's disease, AOSD). Except for age, there are many similarities between sJIA and AOSD. A biphasic disease model is currently put forth. At disease onset, autoinflammation predominates, which is caused by dysregulation of the innate immune system. Later on, the disease can progress to a chronic-articular form, which is predominantly mediated by the adaptive immune system and is consequently due to autoimmunity. The "window-of-opportunity" hypothesis is based on this biphasic model and supports the assumption that an early, targeted therapy with cytokine blockade can prevent disease progression to chronic destructive arthritis. Macrophage activation syndrome (MAS) is a serious complication of the so-called cytokine storm during the systemic phase of the disease. Clinically, there are many similarities between sJIA and AOSD. Recurrent fever, a fleeting, salmon-colored rash, and arthralgia/arthritis are common signs and symptoms of both sJIA and AOSD. The few differences are mainly related to the therapies and their side effects in children versus adults. In addition, the contribution of genetics to pathogenesis is more pronounced in sJIA compared to AOSD, but there are also smooth transitions in this respect and both diseases are heavily influenced by exogenous factors such as microbial triggers. Future research aspects could include additional investigation of these triggers such as viruses, bacteria, or dysbiosis of the human microbiome.

Efficacy of therapeutic fasting and plant-based diet in patients with rheumatoid arthritis (NutriFast): study protocol for a randomised controlled clinical trial.

BACKGROUND: Previous studies have shown beneficial effects of therapeutic fasting and plant-based dietary interventions on disease activity in patients with rheumatoid arthritis (RA) for a duration of up to 1 year. To date, the effects of such interventions on the gut microbiome and on modern diagnostic markers in patients with RA have not been studied. This trial aims to investigate the clinical effects of therapeutic fasting and a plant-based diet in patients with RA, additionally considering current immunological diagnostic tools and microbiome analyses. METHODS/DESIGN: This trial is an open-label, single-centre, randomised, controlled, parallel-group clinical trial. We will randomly assign 84 patients with RA under a stable standard therapy to either (1) therapeutic fasting followed by a plant-based dietary intervention or (2) to a conventional nutritional counselling focusing on an anti-inflammatory dietary pattern according to the recommendations of the Deutsche Gesellschaft für Ernährung (German society for nutrition). Primary outcome parameter is the group difference from baseline to 12 weeks on the Health Assessment Questionnaire (HAQ). Other secondary outcomes include established clinical criteria for disease activity and treatment response in RA (Disease Activity Score 28, Simple Disease Activity Index, ACR-Response Criteria), changes in self-reported health and physical functional ability, mood, stress, quality of life, dietary behaviour via 3-day food records and a modified Food Frequency Questionnaire, body composition, changes in the gut microbiome, metabolomics and cytometric parameters. Outcomes will be assessed at baseline and day 7, after 6 weeks, 12 weeks and after 6 months. ETHICS AND DISSEMINATION: Ethical approval to process and analyse data, and to publish the results was obtained through the institutional review board of Charité-Universitätsmedizin Berlin. Results of this trial will be disseminated through peer-reviewed publications and scientific presentations. TRIAL REGISTRATION NUMBER: NCT03856190.

Host-microbiota interactions in immune-mediated diseases.

Host-microbiota interactions are fundamental for the development of the immune system. Drastic changes in modern environments and lifestyles have led to an imbalance of this evolutionarily ancient process, coinciding with a steep rise in immune-mediated diseases such as autoimmune, allergic and chronic inflammatory disorders. There is an urgent need to better understand these diseases in the context of mucosal and skin microbiota. This Review discusses the mechanisms of how the microbiota contributes to the predisposition, initiation and perpetuation of immune-mediated diseases in the context of a genetically prone host. It is timely owing to the wealth of new studies that recently contributed to this field, ranging from metagenomic studies in humans and mechanistic studies of host-microorganism interactions in gnotobiotic models and in vitro systems, to molecular mechanisms with broader implications across immune-mediated diseases. We focus on the general principles, such as breaches in immune tolerance and barriers, leading to the promotion of immune-mediated diseases by gut, oral and skin microbiota. Lastly, the therapeutic avenues that either target the microbiota, the barrier surfaces or the host immune system to restore tolerance and homeostasis will be explored.

Friend or foe? Lactobacillus in the context of autoimmune disease.

Over the last decade, the interplay between the gut microbiota, the consortium of intestinal microbes that colonizes intestinal mucosal barriers, and its host immune system has been increasingly better understood. Disruption of the delicate balance between beneficial and pathogenic commensals, known as dysbiosis, contributes to a variety of chronic immunologic and metabolic diseases. Complicating this paradigm are bacterial strains that can operate paradoxically both as instigators and attenuators of inflammatory responses, depending on host background. Here, we review the role of several strains in the genus Lactobacillus within the context of autoimmune and other chronic disorders with a predominant focus on L. reuteri. While strains within this species have been shown to provide immune health benefits, they have also been demonstrated to act as a pathobiont in autoimmune-prone hosts. Beneficial functions in healthy hosts include competing with pathogenic microbes, promoting regulatory T cell development, and protecting the integrity of the gut barrier. On the other hand, certain strains can also break through a dysfunctional gut barrier, colonize internal tissues such as the spleen or liver and promote inflammatory responses in host tissues that lead to autoimmune disease. This review summarizes the manifold roles that these commensals play in the context of health and disease.

Mechanisms and consequences of gut commensal translocation in chronic diseases.

Humans and other mammalian hosts have evolved mechanisms to control the bacteria colonizing their mucosal barriers to prevent invasion. While the breach of barriers by bacteria typically leads to overt infection, increasing evidence supports a role for translocation of commensal bacteria across an impaired gut barrier to extraintestinal sites in the pathogenesis of autoimmune and other chronic, non-infectious diseases. Whether gut commensal translocation is a cause or consequence of the disease is incompletely defined. Here we discuss factors that lead to translocation of live bacteria across the gut barrier. We expand upon our recently published demonstration that translocation of the gut pathobiont Enterococcus gallinarum can induce autoimmunity in susceptible hosts and postulate on the role of Enterococcus species as instigators of chronic, non-infectious diseases.

Pathogenic Autoreactive T and B Cells Cross-React with Mimotopes Expressed by a Common Human Gut Commensal to Trigger Autoimmunity.

Given the immense antigenic load present in the microbiome, we hypothesized that microbiota mimotopes can be a persistent trigger in human autoimmunity via cross-reactivity. Using antiphospholipid syndrome (APS) as a model, we demonstrate cross-reactivity between non-orthologous mimotopes expressed by a common human gut commensal, Roseburia intestinalis (R. int), and T and B cell autoepitopes in the APS autoantigen ß2-glycoprotein I (ß2GPI). Autoantigen-reactive CD4+ memory T cell clones and an APS-derived, pathogenic monoclonal antibody cross-reacted with R. int mimotopes. Core-sequence-dependent anti-R. int mimotope IgG titers were significantly elevated in APS patients and correlated with anti-ß2GPI IgG autoantibodies. R. int immunization of mice induced ß2GPI-specific lymphocytes and autoantibodies. Oral gavage of susceptible mice with R. int induced anti-human ß2GPI autoantibodies and autoimmune pathologies. Together, these data support a role for non-orthologous commensal-host cross-reactivity in the development and persistence of autoimmunity in APS, which may apply more broadly to human autoimmune disease.

The microbiome in systemic autoimmune disease: mechanistic insights from recent studies.

PURPOSE OF REVIEW: The resident bacterial communities and the host immune system have coevolved for millennia. However, recent changes in modern societies have disrupted this coevolutionary homeostasis and contributed to a rise in immune-mediated conditions. The purpose of this review is to provide an overview of recently elucidated mechanisms of how certain taxa within the bacterial microbiome propagate autoimmunity. RECENT FINDINGS: Interactions between the bacterial microbiome with innate and adaptive immune cells propagate autoreactivity, chronic inflammation, and tissue damage in susceptible hosts. These interactions contribute to autoimmune diseases such as rheumatoid arthritis or systemic lupus erythematosus, which are the focus of this review. Recent findings suggest that autoimmune manifestations in genetically susceptible individuals can arise through cross-reactivity with commensal orthologs of autoantigens or commensal-mediated posttranslational modification of autoantigens. Physiologic responses to gut, oral, or skin commensal bacteria can thus be misdirected toward such autoantigens in susceptible hosts. In addition, recent studies highlight that a breach of the gut barrier and translocation of commensal bacteria to non-gut organs can trigger several autoimmune pathways that can be prevented by commensal vaccination or dietary interventions. SUMMARY: Complex host-microbiota interactions contribute to systemic autoimmunity outside the gut. On a molecular level, posttranslational modification of, and cross-reactivity with, autoantigens represent mechanisms of how the microbiota mediates autoimmunity. On a cellular level, translocation of live gut bacteria across a dysfunctional gut barrier allows for direct interactions with immune and tissue cells, instigating autoimmunity systemically.

A Diet-Sensitive Commensal Lactobacillus Strain Mediates TLR7-Dependent Systemic Autoimmunity.

Western lifestyle is linked to autoimmune and metabolic diseases, driven by changes in diet and gut microbiota composition. Using Toll-like receptor 7 (TLR7)-dependent mouse models of systemic lupus erythematosus (SLE), we dissect dietary effects on the gut microbiota and find that Lactobacillus reuteri can drive autoimmunity but is ameliorated by dietary resistant starch (RS). Culture of internal organs and 16S rDNA sequencing revealed TLR7-dependent translocation of L. reuteri in mice and fecal enrichment of Lactobacillus in a subset of SLE patients. L. reuteri colonization worsened autoimmune manifestations under specific-pathogen-free and gnotobiotic conditions, notably increasing plasmacytoid dendritic cells (pDCs) and interferon signaling. However, RS suppressed the abundance and translocation of L. reuteri via short-chain fatty acids, which inhibited its growth. Additionally, RS decreased pDCs, interferon pathways, organ involvement, and mortality. Thus, RS exerts beneficial effects in lupus-prone hosts through suppressing a pathobiont that promotes interferon pathways implicated in the pathogenesis of human autoimmunity.

Commensal orthologs of the human autoantigen Ro60 as triggers of autoimmunity in lupus.

The earliest autoantibodies in lupus are directed against the RNA binding autoantigen Ro60, but the triggers against this evolutionarily conserved antigen remain elusive. We identified Ro60 orthologs in a subset of human skin, oral, and gut commensal bacterial species and confirmed the presence of these orthologs in patients with lupus and healthy controls. Thus, we hypothesized that commensal Ro60 orthologs may trigger autoimmunity via cross-reactivity in genetically susceptible individuals. Sera from human anti-Ro60-positive lupus patients immunoprecipitated commensal Ro60 ribonucleoproteins. Human Ro60 autoantigen-specific CD4 memory T cell clones from lupus patients were activated by skin and mucosal Ro60-containing bacteria, supporting T cell cross-reactivity in humans. Further, germ-free mice spontaneously initiated anti-human Ro60 T and B cell responses and developed glomerular immune complex deposits after monocolonization with a Ro60 ortholog-containing gut commensal, linking anti-Ro60 commensal responses in vivo with the production of human Ro60 autoantibodies and signs of autoimmunity. Together, these data support that colonization with autoantigen ortholog-producing commensal species may initiate and sustain chronic autoimmunity in genetically predisposed individuals. The concept of commensal ortholog cross-reactivity may apply more broadly to autoimmune diseases and lead to novel treatment approaches aimed at defined commensal species.