Periodontal disease, Porphyromonas gingivalis, and rheumatoid arthritis: what triggers autoimmunity and clinical disease?

The RNA landscape of the human commensal Segatella copri reveals a small RNA essential for gut colonization

The bacterium Segatella copri is a prevalent member of the human gut microbiota associated with health and disease states. However, the intrinsic factors that determine its ability to colonize the gut effectively remain largely unknown. By extensive transcriptome mapping of S. copri and examining human-derived samples, we discover a small RNA, which we name Segatella RNA colonization factor (SrcF), and show that SrcF is essential for S. copri gut colonization in gnotobiotic mice. SrcF regulates genes involved in nutrient acquisition, and complex carbohydrates, particularly fructans, control its expression. Furthermore, SrcF expression is strongly influenced by human microbiome composition and by the breakdown of fructans by cohabitating commensals, suggesting that the breakdown of complex carbohydrates mediates interspecies signaling among commensals beyond its established function in generating energy. Together, this study highlights the contribution of a small RNA as a critical regulator in gut colonization.

In Vitro and In Vivo Anti-Inflammatory Properties of the Hydroethanolic Extract of the Roots of Vernonia guineensis (Asteraceae)

In traditional Cameroonian medicine, to relieve many inflammations, parts of Vernonia guineensis, are very widely used. This study considered the evaluation of acute toxicity and anti-inflammatory properties of the hydroethanolic extract of the roots of Vernonia guineensis. In an acute toxicity study, 250, 2500, and 5000 mg/kg were administered orally to mice in a single dose, and general behavior, adverse effects, and mortality were monitored. In vitro and in vivo anti-inflammatory tests were performed, and then histological, serum, hematological, and oxidative stress parameters have been evaluated. In an acute toxicity, all groups revealed neither mortality nor any significant alteration in behavior; only drowsiness, sedation, and lethargy were observed at 5000 mg/kg. For in vitro tests, the extract inhibited anti-inflammatory activity. In the formalin test, at 250 mg/kg, the extract inhibited edema with a percentage of 56.41% (4^th hour) in an acute treatment and 74.44% (10^th day). Joint edema was reduced by 67.24% (24^th hour) in a single treatment and by 74.25% (7^th day) in repeated treatment. The extract caused an increase in red blood cell, hemoglobin, and serum protein levels and reduced the white blood cells as well as the activities of alkaline phosphatase and alanine aminotransferase. The extract modulated oxidative stress parameters in the brain, spinal cord, liver, and kidneys. The extract protected the joint by reducing the bone and cartilage erosion. The present work highlights the anti-inflammatory, antioxidant, and antianemic properties of the hydroethanolic extract of the roots of Vernonia guineensis, which supports its empirical use in traditional medicine for the treatment of inflammatory pathologies.

Clonal IgA and IgG autoantibodies from individuals at risk for rheumatoid arthritis identify an arthritogenic strain of Subdoligranulum

The mucosal origins hypothesis of rheumatoid arthritis (RA) proposes a central role for mucosal immune responses in the initiation or perpetuation of the systemic autoimmunity that occurs with disease. However, the connection between the mucosa and systemic autoimmunity in RA remains unclear. Using dual immunoglobulin A (IgA) and IgG family plasmablast-derived monoclonal autoantibodies obtained from peripheral blood of individuals at risk for RA, we identified cross-reactivity between RA-relevant autoantigens and bacterial taxa in the closely related families Lachnospiraceae and Ruminococcaceae. After generating bacterial isolates within the Lachnospiraceae/Ruminococcaceae genus Subdoligranulum from the feces of an individual, we confirmed monoclonal antibody binding and CD4⁺ T cell activation in individuals with RA compared to control individuals. In addition, when Subdoligranulum isolate 7 but not isolate 1 colonized germ-free mice, it stimulated T_H17 cell expansion, serum RA-relevant IgG autoantibodies, and joint swelling reminiscent of early RA, with histopathology characterized by antibody deposition and complement activation. Systemic immune responses were likely due to mucosal invasion along with the generation of colon-isolated lymphoid follicles driving increased fecal and serum IgA by isolate 7, because B and CD4⁺ T cell depletion not only halted intestinal immune responses but also eliminated detectable clinical disease. In aggregate, these findings demonstrate a mechanism of RA pathogenesis through which a specific intestinal strain of bacteria can drive systemic autoantibody generation and joint-centered antibody deposition and immune activation.

Clonal IgA and IgG autoantibodies from individuals at risk for rheumatoid arthritis identify an arthritogenic strain of Subdoligranulum

The mucosal origins hypothesis of rheumatoid arthritis (RA) proposes a central role for mucosal immune responses in the initiation or perpetuation of the systemic autoimmunity that occurs with disease. However, the connection between the mucosa and systemic autoimmunity in RA remains unclear. Using dual immunoglobulin A (IgA) and IgG family plasmablast-derived monoclonal autoantibodies obtained from peripheral blood of individuals at risk for RA, we identified cross-reactivity between RA-relevant autoantigens and bacterial taxa in the closely related families Lachnospiraceae and Ruminococcaceae. After generating bacterial isolates within the Lachnospiraceae/Ruminococcaceae genus Subdoligranulum from the feces of an individual, we confirmed monoclonal antibody binding and CD4⁺ T cell activation in individuals with RA compared to control individuals. In addition, when Subdoligranulum isolate 7 but not isolate 1 colonized germ-free mice, it stimulated T_H17 cell expansion, serum RA-relevant IgG autoantibodies, and joint swelling reminiscent of early RA, with histopathology characterized by antibody deposition and complement activation. Systemic immune responses were likely due to mucosal invasion along with the generation of colon-isolated lymphoid follicles driving increased fecal and serum IgA by isolate 7, because B and CD4⁺ T cell depletion not only halted intestinal immune responses but also eliminated detectable clinical disease. In aggregate, these findings demonstrate a mechanism of RA pathogenesis through which a specific intestinal strain of bacteria can drive systemic autoantibody generation and joint-centered antibody deposition and immune activation.

Cortisol Promotes Surface Translocation of Porphyromonas gingivalis

Studies are showing that the stress hormone cortisol can reach high levels in the gingival sulcus and induce shifts in the metatranscriptome of the oral microbiome. Interestingly, it has also been shown that cortisol can influence expression levels of Type IX Secretion System (T9SS) genes involved in gliding motility in bacteria belonging to the phylum Bacteroidota. The objective of this study was to determine if cortisol impacts gene expression and surface translocation of Porphyromonas gingivalis strain W50. To conduct these experiments, P. gingivalis was stabbed to the bottom of soft agar plates containing varying cortisol concentrations (0 μM, 0.13 μM, 1.3 μM, and 13 μM), and surface translocation on the subsurface was observed after 48 h of incubation. The results show that when grown with certain nutrients, i.e., in rich medium with the addition of sheep blood, lactate, or pyruvate, cortisol promotes migration of P. gingivalis in a concentration-dependent manner. To begin to examine the underlying mechanisms, quantitative PCR was used to evaluate differential expression of genes when P. gingivalis was exposed to cortisol. In particular, we focused on differential expression of T9SS-associated genes, including mfa5, since it was previously shown that Mfa5 is required for cell movement and cell-to-cell interactions. The data show that mfa5 is significantly up-regulated in the presence of cortisol. Moreover, an mfa5 deletion mutant showed less surface translocation compared to the wild-type P. gingivalis in the presence of cortisol, and the defects of the mfa5 deletion mutant were restored by complementation. Overall, cortisol can stimulate P. gingivalis surface translocation and this coincides with higher expression levels of T9SS-associated genes, which are known to be essential to gliding motility. Our findings support a high possibility that the stress hormone cortisol from the host can promote surface translocation and potentially virulence of P. gingivalis.

The Relationship Between Porphyromonas Gingivalis and Rheumatoid Arthritis: A Meta-Analysis

Rheumatoid arthritis (RA) is a systematical autoimmune disease, characterized by chronic synovial joint inflammation and hurt. Porphyromonas gingivalis(P. gingivalis) can cause life-threatening inflammatory immune responses in humans when the host pathogenic clearance machinery is disordered. Some epidemiological studies have reported that P. gingivalis exposure would increase the prevalence of RA. However, the results remain inconsistent. Therefore, a meta-analysis was done to systematically analyze the relationship between P. gingivalis exposure and the prevalence of rheumatoid arthritis. Database including Cochrane Library, Web of Science, PubMed, and EMBASE were searched for published epidemiological articles assessed the relationship between P. gingivalis and RA. Obtained studies were screened based on the predefined inclusion and exclusion criteria. The overall Odds Ratios (ORs) of incorporated articles were pooled by random-effect model with STATA 15.1 software. The literature search returned a total of 2057 studies. After exclusion, 28 articles were included and analyzed. The pooled ORs showed a significant increase in the risk of RA in individuals with P. gingivalis exposure (OR = 1.86; 95% CI: 1.43-2.43). Subgroup analysis revealed that pooled ORs from populations located in Europe (OR = 2.17; 95% CI: 1.46-3.22) and North America (OR = 2.50; 95% CI: 1.23-5.08) were significantly higher than that from population in Asia (OR = 1.11; 95% CI: 1.03-1.20). Substantial heterogeneity was observed but did not significantly influence the overall outcome. In conclusion, our results indicated P. gingivalis exposure was a risk factor in RA. Prompt diagnosis and management decisions on P. gingivalis antimicrobial therapy would prevent rheumatoid arthritis development and progression.

Role of the gut microbiome in multiple sclerosis: From etiology to therapeutics

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS that affects around one million people in the United States. Predisposition or protection from this disease is linked with both genetic and environmental factors. In recent years, gut microbiome has emerged as an important environmental factor in the pathobiology of MS. The gut microbiome supports various physiologic functions, including the development and maintenance of the host immune system, the perturbation of which is known as dysbiosis and has been linked with multiple diseases including MS. We and others have shown that people with MS (PwMS) have gut dysbiosis that is characterized by specific gut bacteria being enriched or depleted. Consequently, there is an emphasis on determining the mechanism(s) through which gut bacteria and/or their metabolites alter the course of MS through their ability to provide protection, predispose individuals, or promote disease progression. Improving our understanding of these mechanisms will allow us to harness the enormous potential of the gut microbiome as a diagnostic and/or therapeutic agent. In this chapter, we will discuss current advances in microbiome research in the context of MS, including a review of specific bacteria that are currently linked with this disease, potential mechanisms of disease pathogenesis, and the utility of microbiome-based therapy for PwMS.

The composition of the lung microbiome differs between patients with dermatomyositis and rheumatoid arthritis associated with interstitial lung disease

Dermatomyositis and rheumatoid arthritis are inflammatory diseases that affect the skeletal muscles and joints, respectively. A common systemic complication of these diseases is interstitial lung disease (ILD), which leads to a poor prognosis and increased mortality. However, the mechanism for the initiation and development of ILD in patients with dermatomyositis is currently unknown. In the present study, we used 16S rRNA high‐throughput sequencing to profile the bacterial community composition of bronchoalveolar lavage fluid of patients with dermatomyositis associated with ILD (DM‐ILD; shortened to DM below), rheumatoid arthritis associated with ILD (RA‐ILD; shortened to RA below) and healthy controls (N) aiming to understand the differences in their lung microbiota and to predict gene function. We found that there were more operational taxonomic units (OTUs) in the lung microbiota of both RA and DM compared to N, although there was no significant difference in the number of OTUs between RA and DM. Similarly, the diversity in alphaproteobacteria differed between RA and DM compared to N, but not between RA and DM. The lung microbiota of RA, DM and N was mainly comprised of five phyla: Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria and Fusobacteria, with 10 dominant genera. Despite the similarity in microbiota composition, we also identified 41 OTUs of lung microbiota that differed among RA, DM and N. Additionally, linear discriminant analysis effect size and linear discriminant analysis genus scores confirmed that 31 microbial biomarkers were clearly distinguished among RA, DM and N. The functional and metabolic alterations of the lung microbiota among RA, DM and N were predicted using picrust, and differentially abundant KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways were identified. Research on the lung microbiota of patients with DM and RA may open new opportunities for developing biomarkers to identify high‐risk patients.

Exploring the Oral Microbiome in Rheumatic Diseases, State of Art and Future Prospective in Personalized Medicine with an AI Approach

The oral microbiome is receiving growing interest from the scientific community, as the mouth is the gateway for numerous potential etiopathogenetic factors in different diseases. In addition, the progression of niches from the mouth to the gut, defined as "oral-gut microbiome axis", affects several pathologies, as rheumatic diseases. Notably, rheumatic disorders (RDs) are conditions causing chronic, often intermittent pain affecting the joints or connective tissue. In this review, we examine evidence which supports a role for the oral microbiome in the etiology and progression of various RDs, including rheumatoid arthritis (RA), Sjogren's syndrome (SS), and systemic lupus erythematosus (SLE). In addition, we address the most recent studies endorsing the oral microbiome as promising diagnostic biomarkers for RDs. Lastly, we introduce the concepts of artificial intelligence (AI), in particular, machine learning (ML) and their general application for understanding the link between oral microbiota and rheumatic diseases, speculating the application of a possible AI approach-based that can be applied to personalized medicine in the future.

The Emerging World of Microbiome in Autoimmune Disorders: Opportunities and Challenges

Trillions of commensal bacteria colonizing humans (microbiome) have emerged as essential player(s) in human health. The alteration of the same has been linked with diseases including autoimmune disorders such as multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, and ankylosing spondylitis. Gut bacteria are separated from the host through a physical barrier such as skin or gut epithelial lining. However, the perturbation in the healthy bacterial community (gut dysbiosis) can compromise gut barrier integrity, resulting in translocation of bacterial contents across the epithelial barrier (leaky gut). Bacterial contents such as lipopolysaccharide and bacterial antigens can induce a systemic inflammatory environment through activation and induction of immune cells. The biggest question in the field is whether inflammation causes gut dysbiosis or dysbiosis leads to disease induction or propagation, i.e., it is inside out or outside in or both. In this review, we first discuss the microbiome profiling studies in various autoimmune disorders, followed by a discussion of potential mechanisms through which microbiome is involved in the pathobiology of diseases. A better understanding of the role of the microbiome in health and disease will help us harness the power of commensal bacteria for the development of novel therapeutic agents to treat autoimmune disorders.

PTPN2 links colonic and joint inflammation in experimental autoimmune arthritis

Loss-of-function variants of protein tyrosine phosphatase non-receptor type 2 (PTPN2) enhance risk of inflammatory bowel disease and rheumatoid arthritis; however, whether the association between PTPN2 and autoimmune arthritis depends on gut inflammation is unknown. Here we demonstrate that induction of subclinical intestinal inflammation exacerbates development of autoimmune arthritis in SKG mice. Ptpn2-haploinsufficient SKG mice — modeling human carriers of disease-associated variants of PTPN2 — displayed enhanced colitis-induced arthritis and joint accumulation of Tregs expressing RAR-related orphan receptor γT (RORγt) — a gut-enriched Treg subset that can undergo conversion into FoxP3^–IL-17⁺ arthritogenic exTregs. SKG colonic Tregs underwent higher conversion into arthritogenic exTregs when compared with peripheral Tregs, which was exacerbated by haploinsufficiency of Ptpn2. Ptpn2 haploinsufficiency led to selective joint accumulation of RORγt-expressing Tregs expressing the colonic marker G protein–coupled receptor 15 (GPR15) in arthritic mice and selectively enhanced conversion of GPR15⁺ Tregs into exTregs in vitro and in vivo. Inducible Treg-specific haploinsufficiency of Ptpn2 enhanced colitis-induced SKG arthritis and led to specific joint accumulation of GPR15⁺ exTregs. Our data validate the SKG model for studies at the interface between intestinal and joint inflammation and suggest that arthritogenic variants of PTPN2 amplify the link between gut inflammation and arthritis through conversion of colonic Tregs into exTregs.

Loss of protein tyrosine phosphatase non-receptor type 2 amplifies the link between gut and joint inflammation through conversion of colonic Tregs into arthritogenic exTregs.

Relationship between periodontitis and rheumatoid arthritis in Vietnamese patients

Objective: This study aimed to survey periodontal status of Vietnamese patients with rheumatoid arthritis (RA) and investigates the association between periodontitis and RA in these patients.Materials and methods: We conducted a cross-sectional descriptive study on 150 RA patients and another 150 patients with osteoarthritis (OA). RA was evaluated using the DAS28 disease activity score based on C-reactive protein levels (DAS28-CRP), disease activity classification, and serum levels of RA biomarkers. Periodontal status was determined using periodontal indices.Results: The proportion of periodontitis cases in the RA group was significantly higher than the OA group (67 and 28%, respectively). The rate of severe periodontitis observed in the RA group was also significantly higher than that in the OA group (22.7 and 8%, respectively). RA patients with periodontitis had higher DAS28-CRP scores, disease activity levels, ACPA positivity and higher serum levels of CRP and ACPAs. Periodontitis is associated with an increased risk for RA (odds ratio [OR]: 5.14, 95% confidence interval [CI]: 3.14 - 8.41) and with higher disease activity classification (OR: 2.7, 95% CI: 1.14 - 6.42).Conclusions: Vietnamese RA patients often presented with a more serious periodontal condition than OA patients. We observed an association between periodontal disease (PD) status and clinic symptoms and biochemical/immunological characteristics of RA.

Porphyromonas: A neglected potential key genus in human microbiomes

Anaerobes form a large part of microbial communities, and have begun to be specifically studied in both healthy and pathologic contexts. Porphyromonas is one of the top ten anaerobic taxa in the microbiome (anaerobiome) in healthy subjects. However, to date, most studies focused on the deleterious role of P. gingivalis, the most widely described species. Interestingly, targeted metagenomics reveals Porphyromonas other than gingivalis (POTG), highlighting other species such as P. catoniae or P. pasteri as potential biomarkers in disease progression or pathogen colonization susceptibility. From the sparse data, it appears that the Porphyromonas genus may also be a relevant target of investigation in several pulmonary diseases. Moreover, deciphering cutaneous, gastric and oral microbiomes hint that Porphyromonas may be a genus of interest in non-pulmonary diseases. This review aims to summarize the major data on POTG and to report their impact on the various human microbiomes in different clinical states.

Chronic diarrhoea and risk of rheumatoid arthritis: findings from the French E3N-EPIC Cohort Study

Objectives

To assess the relationship between gastrointestinal disorders and the risk of further development of RA.

Methods

The Etude Epidémiologique auprès des femmes de la Mutuelle générale de l’Education Nationale-European Prospective Investigation into Cancer and Nutrition Study is a French prospective cohort including 98 995 healthy women since 1990. Participants completed mailed questionnaires on their lifestyles and health-related information. Gastrointestinal disorders were assessed in the third questionnaire (sent in 1993). Hazard ratios and 95% CIs for incident RA were estimated using Cox proportional hazards regression models with age as the time scale. Models were age adjusted, and then additionally adjusted for known risk factors of RA such as smoking, and for potential cofounders.

Results

Among 65 424 women, 530 validated incident RA cases were diagnosed after a mean (s.d.) of 11.7 (5.9) years after study baseline. In comparison with no gastrointestinal disorder, chronic diarrhoea was associated with an increased risk of developing RA during follow-up (hazard ratio = 1.70, 95% CI 1.13, 2.58), independently of dysthyroidism or dietary habits. The association was stronger among ever-smokers (hazard ratio = 2.21, 95% CI 1.32, 3.70). There was no association between RA risk and constipation or alternating diarrhoea/constipation.

Conclusion

Chronic diarrhoea was associated with an increased risk of subsequent RA development, particularly among ever-smokers. These data fit with the mucosal origin hypothesis of RA, where interaction between intestinal dysbiosis and smoking could occur at an early stage to promote emergence of autoimmunity, followed years later by clinical disease.

Is there a bidirectional association between rheumatoid arthritis and periodontitis? A systematic review and meta-analysis

BACKGROUND

Several lines of evidence suggest a bi-directional association between Rheumatoid Arthritis (RA) and Periodontitis (PD). Our aim was to systematically appraise the evidence on the association between RA and PD in terms of clinical and laboratory outcomes.

METHODS

An electronic search of several databases (PubMed, EMBASE, MEDLINE, LILACS, CINHL, Scopus, Web of Science, The Cochrane Library, OpenGrey and Google Scholar) was conducted up to March 2019 (PROSPERO CRD42018107817) by two independent reviewers. Observational studies included in the review were quality-appraised using the Newcastle-Ottawa Scale (NOS) tool. Random effects models were used for quantitative analyses.

RESULTS

A total of 8 case-control studies were identified after the final search of 1491 titles. Following quality assessment, 2 studies were excluded due to the high risk of bias, while the remaining 6 were further analysed. Meta-analyses revealed no substantial effect of RA on the Probing Pocket Depth (PPD) and Clinical Attachment Level (CAL) of patients with PD when compared to controls but high degree of study heterogeneity was found. To the contrary, PD was associated with substantially worse RA disease activity as assessed by an increase in the DAS28 score of 0.74 (0.25-1.24, 95%CI, p < 0.001).

CONCLUSION

There is consistent evidence suggesting that PD is associated with worse RA clinical activity as assessed by DAS28 scores whereas, RA patients do not have worsen PD clinical outcomes.

Synthesis of ppGpp impacts type IX secretion and biofilm matrix formation in Porphyromonas gingivalis

In order to persist, bacteria need to adjust their physiological state in response to external and internal cues. External stimuli are often referred to as stressors. The stringent response, mediated by the alarmone (p)ppGpp, is central to the stress response in many bacteria; yet, there is limited knowledge regarding the role of (p)ppGpp signaling in bacteria belonging to the phylum Bacteroidetes. Like its counterparts in the gut (e.g., Bacteroides thetaiotaomicron and Bacteroides fragilis), Porphyromonas gingivalis persists in close association with its human host. Given the potential for numerous perturbations in the oral cavity, and the fact that P. gingivalis can enter and replicate within host cells, we hypothesized that (p)ppGpp is a key signaling molecule for stress adaptation and persistence. Here, we show that accumulation of ppGpp in P. gingivalis is governed by two homologous enzymes, designated Rel, and RshB, and that ppGpp signaling affects growth rate, survival, biofilm formation, production of outer membrane vesicles, and expression of genes encoding type IX secretion structural and cargo proteins. Overall, our findings provide a potential mechanism by which biofilm formation and virulence of P. gingivalis are integrated via ppGpp signaling, a regulatory mechanism central to bacterial survival in dynamic environments.

Microbiota-mediated mucosal inflammation in arthritis

Mucosal surfaces are a unique symbiotic environment between a host and a vast and diverse ecology of microbes. These microbes have great immunomodulatory potential with respect to the host organism. Indeed, the mucosal immune system strikes a delicate balance between tolerance of commensal organisms and overt inflammation to ward off pathogens. Disruptions of the microbial ecology at mucosal surfaces has been described in a vast number of different human disease processes including many forms of arthritis, and the resulting implications are still being understood to their fullest. Herein, we review the current state of knowledge in microbe-host interactions as it relates to the development of arthritis through bacterial translocation, bacterial metabolite production, education of the immune response, and molecular mimicry.

The role of microbiome in rheumatoid arthritis treatment

Rheumatoid arthritis (RA) is an autoimmune disorder with multifactorial etiology; both genetic and environmental factors are known to be involved in pathogenesis. Treatment with disease-modifying antirheumatic drugs (DMARDs) plays an essential role in controlling disease progression and symptoms. DMARDs have immunomodulatory properties and suppress immune response by interfering in various pro-inflammatory pathways. Recent evidence has shown that the gut microbiota directly and indirectly modulates the host immune system. RA has been associated with dysbiosis of the gut microbiota. Patients with RA treated with DMARDs show partial restoration of eubiotic gut microbiome. Hence, it is essential to understand the impact of DMARDs on the microbial composition and its consequent influences on the host immune system to identify novel therapies for RA. In this review, we discuss the importance of antirheumatic-drug-induced host microbiota modulations and possible probiotics that can generate eubiosis.

Inflammatory arthritis disrupts gut resolution mechanisms, promoting barrier breakdown by Porphyromonas gingivalis

Rheumatoid arthritis is linked with altered host immune responses and severe joint destruction. Recent evidence suggests that loss of gut homeostasis and barrier breach by pathobionts, including Porphyromonas gingivalis, may influence disease severity. The mechanism(s) leading to altered gut homeostasis and barrier breakdown in inflammatory arthritis are poorly understood. In the present study, we found a significant reduction in intestinal concentrations of several proresolving mediators during inflammatory arthritis, including downregulation of the gut-protective mediator resolvin D5n-3 DPA (RvD5n-3 DPA). This was linked with increased metabolism of RvD5n-3 DPA to its inactive 17-oxo metabolite. We also found downregulation of IL-10 expression in the gut of arthritic mice that was coupled with a reduction in IL-10 and IL-10 receptor (IL-10R) in lamina propria macrophages. These changes were linked with a decrease in the number of mucus-producing goblet cells and tight junction molecule expression in the intestinal epithelium of arthritic mice when compared with naive mice. P. gingivalis inoculation further downregulated intestinal RvD5n-3 DPA and Il-10 levels and the expression of gut tight junction proteins. RvD5n-3 DPA, but not its metabolite 17-oxo-RvD5n-3 DPA, increased the expression of both IL-10 and IL-10R in macrophages via the upregulation of the aryl hydrocarbon receptor agonist l-kynurenine. Administration of RvD5n-3 DPA to arthritic P. gingivalis-inoculated mice increased intestinal Il-10 expression, restored gut barrier function, and reduced joint inflammation. Together, these findings uncover mechanisms in the pathogenesis of rheumatoid arthritis, where disruption of the gut RvD5n-3 DPA-IL-10 axis weakens the gut barrier, which becomes permissive to the pathogenic actions of the pathobiont P. gingivalis.

Modulation of autoimmune arthritis by environmental 'hygiene' and commensal microbiota

Observations in patients with autoimmune diseases and studies in animal models of autoimmunity have revealed that external environmental factors including exposure to microbes and the state of the host gut microbiota can influence susceptibility to autoimmunity and subsequent disease development. Mechanisms underlying these outcomes continue to be elucidated. These include deviation of the cytokine response and imbalance between pathogenic versus regulatory T cell subsets. Furthermore, specific commensal organisms are associated with enhanced severity of arthritis in susceptible individuals, while exposure to certain microbes or helminths can afford protection against this disease. In addition, the role of metabolites (e.g., short-chain fatty acids, tryptophan catabolites), produced either by the microbes themselves or from their action on dietary products, in modulation of arthritis is increasingly being realized. In this context, re-setting of the microbial dysbiosis in RA using prebiotics, probiotics, or fecal microbial transplant is emerging as a promising approach for the prevention and treatment of arthritis. It is hoped that advances in defining the interplay between gut microbiota, dietary products, and bioactive metabolites would help in the development of therapeutic regimen customized for the needs of individual patients in the near future.

Microbiota in T-cell homeostasis and inflammatory diseases

The etiology of disease pathogenesis can be largely explained by genetic variations and several types of environmental factors. In genetically disease-susceptible individuals, subsequent environmental triggers may induce disease development. The human body is colonized by complex commensal microbes that have co-evolved with the host immune system. With the adaptation to modern lifestyles, its composition has changed depending on host genetics, changes in diet, overuse of antibiotics against infection and elimination of natural enemies through the strengthening of sanitation. In particular, commensal microbiota is necessary in the development, induction and function of T cells to maintain host immune homeostasis. Alterations in the compositional diversity and abundance levels of microbiota, known as dysbiosis, can trigger several types of autoimmune and inflammatory diseases through the imbalance of T-cell subpopulations, such as Th1, Th2, Th17 and Treg cells. Recently, emerging evidence has identified that dysbiosis is involved in the progression of rheumatoid arthritis, type 1 and 2 diabetic mellitus, and asthma, together with dysregulated T-cell subpopulations. In this review, we will focus on understanding the complicated microbiota-T-cell axis between homeostatic and pathogenic conditions and elucidate important insights for the development of novel targets for disease therapy.

Evidence of the Immune Relevance of Prevotella copri, a Gut Microbe, in Patients With Rheumatoid Arthritis

OBJECTIVE

Prevotella copri, an intestinal microbe, may overexpand in stool samples from patients with new-onset rheumatoid arthritis (RA), but it is not yet clear whether the organism has immune relevance in RA pathogenesis.

METHODS

HLA-DR-presented peptides (T cell epitopes) from P copri were sought directly in the patients' synovial tissue or peripheral blood mononuclear cell (PBMC) samples using tandem mass spectrometry. The antigenicity of peptides or their source proteins was examined in samples from the RA patients or comparison groups. T cell reactivity was determined by enzyme-linked immunospot assay; antibody responses were measured by enzyme-linked immunosorbent assay, and cytokine/chemokine determinations were made by bead-based assays. Serum and synovial fluid samples were examined for 16S ribosomal DNA for P copri using nested polymerase chain reaction analysis.

RESULTS

In PBMCs, we identified an HLA-DR-presented peptide from a 27-kd protein of P copri (Pc-p27), which stimulated Th1 responses in 42% of patients with new-onset RA. In both new-onset RA patients and chronic RA patients, 1 subgroup had IgA antibody responses to either Pc-p27 or the whole organism, which correlated with Th17 cytokine responses and frequent anti-citrullinated protein antibodies (ACPAs). The other subgroup had IgG P copri antibodies, which were associated with Prevotella DNA in synovial fluid, P copri-specific Th1 responses, and less frequent ACPAs. In contrast, P copri antibody responses were rarely found in patients with other rheumatic diseases or in healthy controls.

CONCLUSION

Subgroups of RA patients have differential IgG or IgA immune reactivity with P copri, which appears to be specific for this disease. These observations provide evidence that P copri is immune-relevant in RA pathogenesis.

The lung microbiota in early rheumatoid arthritis and autoimmunity

BACKGROUND

Airway abnormalities and lung tissue citrullination are found in both rheumatoid arthritis (RA) patients and individuals at-risk for disease development. This suggests the possibility that the lung could be a site of autoimmunity generation in RA, perhaps in response to microbiota changes. We therefore sought to test whether the RA lung microbiome contains distinct taxonomic features associated with local and/or systemic autoimmunity.

METHODS

16S rRNA gene high-throughput sequencing was utilized to compare the bacterial community composition of bronchoalveolar lavage fluid (BAL) in patients with early, disease-modifying anti-rheumatic drugs (DMARD)-naïve RA, patients with lung sarcoidosis, and healthy control subjects. Samples were further assessed for the presence and levels of anti-citrullinated peptide antibodies (including fine specificities) in both BAL and serum.

RESULTS

The BAL microbiota of RA patients was significantly less diverse and abundant when compared to healthy controls, but similar to sarcoidosis patients. This distal airway dysbiosis was attributed to the reduced presence of several genus (i.e., Actynomyces and Burkhordelia) as well as reported periodontopathic taxa, including Treponema, Prevotella, and Porphyromonas. While multiple clades correlated with local and systemic levels of autoantibodies, the genus Pseudonocardia and various related OTUs were the only taxa overrepresented in RA BAL and correlated with higher disease activity and erosions.

CONCLUSIONS

Distal airway dysbiosis is present in untreated early RA and similar to that detected in sarcoidosis lung inflammation. This community perturbation, which correlates with local and systemic autoimmune/inflammatory changes, may potentially drive initiation of RA in a proportion of cases.

Microbiota at the crossroads of autoimmunity

Autoimmune diseases have a multifactorial etiology including genetic and environmental factors. Recently, there has been increased appreciation of the critical involvement of the microbiota in the pathogenesis of autoimmunity, although in many cases, the cause and the consequence are not easy to distinguish. Here, we suggest that many of the known cues affecting the function of the immune system, such as genetics, gender, pregnancy and diet, which are consequently involved in autoimmunity, exert their effects by influencing, at least in part, the microbiota composition and activity. This, in turn, modulates the immune response in a way that increases the risk for autoimmunity in predisposed individuals. We further discuss current microbiota-based therapies.

Periodontal disease and subgingival microbiota as contributors for rheumatoid arthritis pathogenesis: modifiable risk factors?

PURPOSE OF REVIEW

Since the early 1900s, the role of periodontal disease in the pathogenesis of rheumatoid arthritis has been a matter of intense research. The last decade has witnessed many advances supporting a link between periodontitis, the presence of specific bacterial species (i.e. Porphyromonas gingivalis) and their effects in immune response. This review will examine available evidence on the individuals.

RECENT FINDINGS

Epidemiological studies have stressed the commonalities shared by periodontal disease and rheumatoid arthritis. Many groups have focused their attention toward understanding the periodontal microbiota and its alterations in states of health and disease. The presence of circulating antibodies against periodontopathic bacteria and associated inflammatory response has been found in both rheumatoid arthritis (RA) patients and individuals at-risk for disease development. Most recently, the periodontal microbiota of smokers and patients with RA has been elucidated, revealing profound changes in the bacterial communities compared with those of healthy controls. This has led to several small clinical trials of progressive disease treatment as adjuvant for disease-modifying therapy in RA.

SUMMARY

Smoking and periodontal disease are emerging risk factors for the development of RA. Epidemiological, clinical, and basic research has further strengthened this association, pointing toward changes in the oral microbiota as possible contributors to systemic inflammation and arthritis.

Implications for eicosapentaenoic acid- and docosahexaenoic acid-derived resolvins as therapeutics for arthritis

Omega-3 polyunsaturated fatty acids are essential for health and are known to possess anti-inflammatory properties, improving cardiovascular health as well as benefiting inflammatory diseases. Indeed, dietary supplementation with omega-3 polyunsaturated fatty acids has proved efficacious in reducing joint pain, morning stiffness and nonsteroidal anti-inflammatory drugs usage in rheumatoid arthritis patients. However, the mechanisms by which omega-3 polyunsaturated fatty acids exert their beneficial effects have not been fully explored. Seminal discoveries by Serhan and colleagues have unveiled a novel class of bioactive lipid mediators that are enzymatically biosynthesized in vivo from omega-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), termed resolvins, protectins and maresins. These bioactive pro-resolving lipid mediators provide further rationale for the beneficial effects of fish-oil enriched diets. These endogenous lipid mediators are spatiotemporally biosynthesized to actively regulate resolution by acting on specific G protein-coupled receptors (GPCRs) to initiate anti-inflammatory and pro-resolving signals that terminate inflammation. In this review, we will discuss the mechanism of actions of these molecules, including their analgesic and bone-sparing properties making them ideal therapeutic agonists for the treatment of inflammatory diseases such as rheumatoid arthritis.

The gut microbiome in autoimmunity: Sex matters

Autoimmune diseases like rheumatoid arthritis are multifactorial in nature, requiring both genetic and environmental factors for onset. Increased predisposition of females to a wide range of autoimmune diseases points to a gender bias in the multifactorial etiology of these disorders. However, the existing evidence to date has not provided any conclusive mechanism of gender-bias beyond the role of hormones and sex chromosomes. The gut microbiome, which impacts the innate and adaptive branches of immunity, not only influences the development of autoimmune disorders but may interact with sex-hormones to modulate disease progression and sex-bias. Here, we review the current information on gender bias in autoimmunity and discuss the potential of microbiome-derived biomarkers to help unravel the complex interplay between genes, environment and hormones in rheumatoid arthritis.

Immunological hypoglycemia associated with insulin antibodies induced by exogenous insulin in 11 Chinese patients with diabetes

AIMS

To investigate the characteristics of immunological hypoglycemia associated with insulin antibodies (IAbs) induced by exogenous insulin in Chinese patients with diabetes.

METHODS

The clinical data of patients with immunological hypoglycemia due to IAbs were retrospectively analyzed by screening patients with diabetes discharged from West China Hospital from 2007 to 2013.

RESULTS

A total of 11 patients (eight men and three women) were identified. Insulin-C-peptide separation was found in all patients via insulin and C-peptide release test. Previous insulin use was ceased after admission and was switched to oral hypoglycemic agents (OHAs) (8/11), lifestyle modification only (2/11), or regular human insulin (1/11). Hypoglycemia was ameliorated after a median of 20 days (interquartile range [IQR], 11-40), while IAbs turned negative after a median of 17 months (IQR, 4-19), and serum immunoreactive insulin (IRI) levels dropped substantially after a median of 22 months (IQR, 9-32) in these cases.

CONCLUSIONS

In insulin-treated patients with unexpected and refractory hypoglycemia even after insulin therapy was gradually reduced or even withdrawn, IAbs induced by exogenous insulin should be considered, and insulin withdrawal might be promptly needed. The course of immunological hypoglycemia was benign and self-limited.

Prevention of rheumatic diseases: strategies, caveats, and future directions

Rheumatic diseases affect a significant portion of the population and lead to increased health care costs, disability, and premature mortality; effective preventive measures for these diseases could lead to substantial improvements in public health. Natural history studies show that for most rheumatic diseases there is a period of preclinical disease development during which abnormal biomarkers or other processes can be detected. These changes are useful to understand mechanisms of disease pathogenesis; in addition, they may be applied to estimate a personal risk of future disease while individuals are still relatively asymptomatic and ultimately be used to identify individuals who may be targeted for preventive interventions.

Association between periodontal disease and inflammatory arthritis reveals modulatory functions by melanocortin receptor type 3

Because there is clinical evidence for an association between periodontal disease and rheumatoid arthritis, it is important to develop suitable experimental models to explore pathogenic mechanisms and therapeutic opportunities. The K/BxN serum model of inflammatory arthritis was applied using distinct protocols, and modulation of joint disruption afforded by dexamethasone and calcitonin was established in comparison to the melanocortin (MC) receptor agonist DTrp(8)-γ-melanocyte stimulating hormone (MSH; DTrp). Wild-type and MC receptor type 3 (MC3)-null mice of different ages were also used. There was significant association between severity of joint disease, induced with distinct protocols and volumes of the arthritogenic K/BxN serum, and periodontal bone damage. Therapeutic treatment with 10 μg dexamethasone, 30 ng elcatonin, and 20 μg DTrp per mouse revealed unique and distinctive pharmacological properties, with only DTrp protecting both joint and periodontal tissue. Further analyses in nonarthritic animals revealed higher susceptibility to periodontal bone loss in Mc3r(-/-) compared with wild-type mice, with significant exacerbation at 14 weeks of age. These data reveal novel protective properties of endogenous MC3 on periodontal status in health and disease and indicate that MC3 activation could lead to the development of a new genus of anti-arthritic bone-sparing therapeutics.

Pathogenesis and prevention of rheumatic disease: focus on preclinical RA and SLE

Established and emerging data demonstrate that a 'preclinical' period of disease precedes the onset of clinical rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), as well as other autoimmune rheumatic diseases (ARDs).This preclinical stage of development of disease is characterized by abnormalities in disease-related biomarkers before the onset of the clinically apparent signs and symptoms. Numerous genetic and environmental risk factors for ARDs have also been identified, and many of these factors are likely to act before the clinical appearance of tissue injury to initiate and/or propagate autoimmunity and autoimmune disease. Thus, biomarkers representative of these autoimmune processes could potentially be used in conjunction with other clinical parameters during the preclinical period of ARDs to predict the future development of clinically apparent disease. This Review focuses on the preclinical stages of RA and SLE, as our current understanding of these diseases can be used to present an overall model of the development of ARDs that might ultimately be used to develop screening programmes and preventive strategies. Important considerations for the future development of such approaches, in particular, the issues that require additional research and how they might be addressed, are also discussed.