Gut Microbiota Perturbations in Reactive Arthritis and Postinfectious Spondyloarthritis

The Current and Future of Biomarkers of Immune Related Adverse Events

With their groundbreaking clinical responses, immune checkpoint inhibitors (ICIs) have ushered in a new chapter in cancer therapeutics. However, they are often associated with life-threatening or organ-threatening autoimmune/autoinflammatory phenomena, collectively termed immune-related adverse events (irAEs). In this review, we will first describe the mechanisms of action of ICIs as well as irAEs. Next, we will review biomarkers for predicting the development of irAEs or stratifying risks.

16s RNA-based metagenomics reveal previously unreported gut microbiota associated with reactive arthritis and undifferentiated peripheral spondyloarthritis

OBJECTIVES

Reactive arthritis (ReA) provides a unique opportunity to comprehend how a mucosal infection leads to inflammatory arthritis at a distant site without the apparent invasion of the pathogen. Unfortunately, conventional stool cultures after ReA provide limited information, and there is a dearth of metagenomic studies in ReA. The objective of this study was to identify gut microbiota associated with the development of ReA.

METHODS

Patients with ReA or undifferentiated peripheral spondyloarthritis (UpSpA) were included if they presented within 4 weeks of the onset of the current episode of arthritis. Metagenomic DNA was extracted from the stools of these patients and of 36 age- and sex-similar controls. Sequencing and analysis were done using a standard 16S ribosomal pipeline.

RESULTS

Of 55 patients, there was no difference between the gut microbiota of postdiarrheal ReA (n = 20) and of upSpA (n = 35). Comparing the gut microbiota of patients vs healthy controls, the patients had significantly higher alpha and beta diversity measures. After stringency filters, Proteobacteria had high abundance while Firmicutes had lesser as compared with the controls. Six families were overexpressed in patients, while another five were overexpressed in controls. Sixteen genera and 18 species were significantly different between patients and controls. At the species level there was strong association of Staphylococcus aureus, Clostridium septicum Klebsiella pneumoniae, Escherichia coli, Empedobacter brevis, Roseburia hominis, Bacillus velezensis and Crassaminicella with ReA.

CONCLUSION

The microbiota of classical gut-associated ReA and upSpA is similar. Patients have higher diversities in their gut microbiota compared with healthy controls. Both known and previously unreported species associated with ReA/upSpA were identified.

The role of the gastrointestinal microbiome on rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis and reactive arthritis: A systematic review

BACKGROUND

There is an increasing body of literature observing a state of dysbiosis in the gut microbiome in different autoimmune conditions including inflammatory arthritis. It is unknown whether the microbiome can be a biomarker for prognostication purposes or for stratification of treatment strategies. This review aims to evaluate the existing evidence on the association between the microbiome and inflammatory arthritis, including rheumatoid arthritis (RA), psoriatic arthritis (PsA) and ankylosing spondylitis (AS) and reactive arthritis (ReA) population groups.

METHODS

This systematic review was performed based on methods from the Cochrane guidelines and reported based on PRISMA criteria. Studies exploring the microbiome of patients with RA, AS, PsA or ReA compared with controls via 16s rRNA or shotgun sequencing were evaluated. The outcomes of interest include alpha and beta diversity, abundance or depletion of organisms and functional analysis. Literature up to August 2024 was retrieved searching the databases PubMed, Medline, ScienceDirect, Scopus, Web of Science, Cochrane, EMBASE and CINAHL. All references were systematically evaluated by two reviewers. Quality of the studies were evaluated by the Newcastle-Ottawa Scale.

FINDINGS

The review yielded 25,794 search results, of which 53 studies were included for the RA group, 34 studies for the AS group, 6 studies for the PsA group and 2 studies for the ReA group. Reduced diversity has been observed in disease groups and in patients with higher disease activity.

INTERPRETATION

There are limited longitudinal studies on the role of the microbiome in inflammatory arthritis, in particular PsA. Existing cross-sectional studies suggest altered microbiome in disease states compared with controls. Further studies are required to understand the utility of the microbiome as a biomarker to better understand prognosis and tailor treatments.

Microbiome research in autoimmune and immune-mediated inflammatory diseases: lessons, advances and unmet needs

The increasing prevalence of autoimmune and immune-mediated diseases (AIMDs) underscores the need to understand environmental factors that contribute to their pathogenesis, with the microbiome emerging as a key player. Despite significant advancements in understanding how the microbiome influences physiological and inflammatory responses, translating these findings into clinical practice remains challenging. This viewpoint reviews the progress and obstacles in microbiome research related to AIMDs, examining molecular techniques that enhance our understanding of microbial contributions to disease. We discuss significant discoveries linking specific taxa and metabolites to diseases such as rheumatoid arthritis, systemic lupus erythematosus and spondyloarthritis, highlighting the role of gut dysbiosis and host-microbiome interactions. Furthermore, we explore the potential of microbiome-based therapeutics, including faecal microbiota transplantation and pharmacomicrobiomics, while addressing the challenges of identifying robust microbial targets. We advocate for integrative, transdisease studies and emphasise the need for diverse cohort research to generalise findings across populations. Understanding the microbiome's role in AIMDs will pave the way for personalised medicine and innovative therapeutic strategies.

The role of tumor types in immune-related adverse events

Immune checkpoint inhibitors (ICIs) are monoclonal antibodies that block inhibitors of T cell activation and function. With the widespread use of ICIs in cancer therapy, immune-related adverse events (irAEs) have gradually emerged as urgent clinical issues. Tumors not only exhibit high heterogeneity, and their response to ICIs varies, with "hot" tumors showing better anti-tumor effects but also a higher susceptibility to irAEs. The manifestation of irAEs displays a tumor-heterogeneous pattern, correlating with the tumor type in terms of the affected organs, incidence, median onset time, and severity. Understanding the mechanisms underlying the pathogenic patterns of irAEs can provide novel insights into the prevention and management of irAEs, guide the development of biomarkers, and contribute to a deeper understanding of the toxicological characteristics of ICIs. In this review, we explore the impact of tumor type on the therapeutic efficacy of ICIs and further elucidate how these tumor types influence the occurrence of irAEs. Finally, we assess key candidate biomarkers and their relevance to proposed irAE mechanisms. This paper also outlines management strategies for patients with various types of tumors, based on their disease patterns.

Gut microbiome and orthopaedic health: Bridging the divide between digestion and bone integrity

The gut microbiome, a complex ecosystem of microorganisms in the digestive tract, has emerged as a critical factor in human health, influencing metabolic, immune, and neurological functions. This review explores the connection between the gut microbiome and orthopedic health, examining how gut microbes impact bone density, joint integrity, and skeletal health. It highlights mechanisms linking gut dysbiosis to inflammation in conditions such as rheumatoid arthritis and osteoarthritis, suggesting microbiome modulation as a potential therapeutic strategy. Key findings include the microbiome's role in bone metabolism through hormone regulation and production of short-chain fatty acids, crucial for mineral absorption. The review also considers the effects of diet, probiotics, and fecal microbiota transplantation on gut microbiome composition and their implications for orthopedic health. While promising, challenges in translating microbiome research into clinical practice persist, necessitating further exploration and ethical consideration of microbiome-based therapies. This interdisciplinary research aims to link digestive health with musculoskeletal integrity, offering new insights into the prevention and management of bone and joint diseases.

Causal relationship between gut microbiota and ankylosing spondylitis and potential mediating role of inflammatory cytokines: A mendelian randomization study

Associations between gut microbiota and ankylosing spondylitis have been discovered in previous studies, but whether these associations reflect a causal relationship remains inconclusive. Aiming to reveal the bidirectional causal associations between gut microbiota and ankylosing spondylitis, we utilized publicly available genome wide association study summary data for 211 gut microbiota (GM) taxa and ankylosing spondylitis (AS) to conduct two sample mendelian randomization analyses. Mediation analysis was performed to explore mediating inflammatory cytokines. We found that genetically predicted higher abundance of Lactobacillaceae family, Rikenellaceae family and Howardella genus had suggestive associations with decreased risk of ankylosing spondylitis while genetic proxied higher abundance of Actinobacteria class and Ruminococcaceae_NK4A214_group genus was associated with increased risk of ankylosing spondylitis. IL23 and IFN-γ were potential mediating cytokines for GM dysbiosis, especially for Actinobacteria class, leading to AS. Our study provided a new exploration direction for the treatment of AS. Lactobacillaceae family, Rikenellaceae family, Howardella genus, Actinobacteria class and Ruminococcaceae_NK4A214_group genus are expected to become new therapeutic targets and monitoring indicators for AS.

Current Approaches to Prevent or Reverse Microbiome Dysbiosis in Chronic Inflammatory Rheumatic Diseases

Advances in knowledge of the microbiome and its relationship with the immune system have led to a better understanding of the pathogenesis of chronic inflammatory rheumatic diseases (CIRD). Indeed, the microbiome dysbiosis now occupies a particular place with implications for the determinism and clinical expression of CIRD, as well as the therapeutic response of affected patients. Several approaches exist to limit the impact of the microbiome during CIRD. This review aimed to present current strategies to prevent or reverse microbiome dysbiosis based on existing knowledge, in order to provide practical information to healthcare professionals treating patients suffering from CIRD.

The Current and Future of Biomarkers of Immune Related Adverse Events

With their groundbreaking clinical responses, immune checkpoint inhibitors (ICIs) have ushered in a new chapter in cancer therapeutics. However, they are often associated with life-threatening or organ-threatening autoimmune/autoinflammatory phenomena, collectively termed immune-related adverse events (irAEs). In this review, we will first describe the mechanisms of action of ICIs as well as irAEs. Next, we will review biomarkers for predicting the development of irAEs or stratifying risks.

Role of the Gut Microbiota in Osteoarthritis, Rheumatoid Arthritis, and Spondylarthritis: An Update on the Gut-Joint Axis

Dysregulation of the gut microbiota and their metabolites is involved in the pathogenic process of intestinal diseases, and several pieces of evidence within the current literature have also highlighted a possible connection between the gut microbiota and the unfolding of inflammatory pathologies of the joints. This dysregulation is defined as the "gut-joint axis" and is based on the joint-gut interaction. It is widely recognized that the microbiota of the gut produce a variety of compounds, including enzymes, short-chain fatty acids, and metabolites. As a consequence, these proinflammatory compounds that bacteria produce, such as that of lipopolysaccharide, move from the "leaky gut" to the bloodstream, thereby leading to systemic inflammation which then reaches the joints, with consequences such as osteoarthritis, rheumatoid arthritis, and spondylarthritis. In this state-of-the-art research, the authors describe the connections between gut dysbiosis and osteoarthritis, rheumatoid arthritis, and spondylarthritis. Moreover, the diagnostic tools, outcome measures, and treatment options are elucidated. There is accumulating proof suggesting that the microbiota of the gut play an important part not only in immune-mediated, metabolic, and neurological illnesses but also in inflammatory joints. According to the authors, future studies should concentrate on developing innovative microbiota-targeted treatments and their effects on joint pathology as well as on organizing screening protocols to predict the onset of inflammatory joint disease based on gut dysbiosis.

ExpLOring the role of the intestinal MiCrobiome in InflammATory bowel disease-AssocIated SpONdylarthritis (LOCATION-IBD)

Background

Inflammatory Bowel Disease (IBD)-associated arthritis is a frequent and potentially debilitating complication of IBD, that can affect those with or without active intestinal disease, and is often difficult to treat. The microbiome is known to play a role in IBD development and has been shown to be associated with inflammatory arthritis without concomitant IBD, but its role in IBD-associated arthritis is still unexplored. Further, disease localization is associated with development of IBD-associated arthritis, and stool compositional profiles are predictive of disease localization, yet mucosal location-specific microbiomes have not been well characterized. To address this gap in understanding, we designed a study (LOCATION-IBD) to characterize the mucosa-associated intestinal microbiome and metabolome in IBD-associated arthritis.

Methods

Adults with an established diagnosis of IBD undergoing clinical colonoscopy between May of 2021 and February of 2023 were invited to participate in this study; those interested in participation who met inclusion criteria were enrolled. Prior to enrollment, participants were stratified into those with or without IBD-associated arthritis. All participants were interviewed and had clinical and demographic data collected, and 97.8% completed clinical colonoscopy with biopsy collection.

Results and conclusion

A total of 182 participants, 53 with confirmed IBD-associated arthritis, were enrolled in this study, resulting in 1151 biopsies obtained for microbiome and metabolome analysis (median 6, mean 6.3 per participant). Clinical and demographic data obtained from the study population will be analyzed with microbiome and metabolome data obtained from biopsies, with the goal of better understanding the mechanisms underpinning the host-microbiome relationship associated the development of IBD-associated arthritis.

Reactive Arthritis in Children: Case Report, Narrative Review and Proposed Therapy

Reactive arthritis is an acute inflammatory aseptic arthritis that is preceded by an infectious process in genetically predisposed individuals. It has been associated with gastrointestinal or genitourinary infection. Reactive arthritis is rare in children. In this review, we present two index cases that need biologic treatment followed by a thorough review of reactive arthritis in children and adolescents with proposed treatment algorithm.

Chronic cold environment regulates rheumatoid arthritis through modulation of gut microbiota-derived bile acids

The pathologies of many diseases are influenced by environmental temperature. As early as the classical Roman age, people believed that exposure to cold weather was bad for rheumatoid arthritis (RA). However, there is no direct evidence supporting this notion, and the molecular mechanisms of the effects of chronic cold exposure on RA remain unknown. Here, in a temperature-conditioned environment, we found that chronic cold exposure aggravates collagen-induced arthritis (CIA) by increasing ankle swelling, bone erosion, and cytokine levels in rats. Furthermore, in chronic cold-exposed CIA rats, gut microbiota dysbiosis was identified, including a decrease in the differential relative abundance of the families Lachnospiraceae and Ruminococcaceae. We also found that an antibiotic cocktail suppressed arthritis severity under cold conditions. Notably, the fecal microbiota transplantation (FMT) results showed that transplantation of cold-adapted microbiota partly recapitulated the microbiota signature in the respective donor rats and phenocopied the cold-induced effects on CIA rats. In addition, cold exposure disturbed bile acid profiles, in particular decreasing gut microbiota-derived taurohyodeoxycholic acid (THDCA) levels. The perturbation of bile acids was also associated with activation of the TGR5-cAMP-PKA axis and NLRP3 inflammasome. Oral THDCA supplementation mitigated the arthritis exacerbation induced by chronic cold exposure. Our findings identify an important role of aberrant gut microbiota-derived bile acids in cold exposure-related RA, highlighting potential opportunities to treat cold-related RA by manipulating the gut microbiota and/or supplementing with THDCA.

Identification of gut microbiota dysbiosis in bullous pemphigoid under different disease activity

Bullous pemphigoid (BP) is a severe autoimmune blistering disease affecting patients' quality of life. Gut microbiota (GM) dysbiosis have been investigated to be associated with multiple autoimmune diseases. However, the relationship between GM and BP onset and remission remains to be established by a systematic study. We conducted a study that enrolled 24 patients with BP onset (BP group), 24 patients under remission stage (BP-R group) and 24 healthy controls (HC group). We applied 16S rRNA sequencing on faecal samples and revealed a separation of the microbiota structure. At the family level, Lachnospiraceae, Prevotellaceae and Veillonellaceae were more abundant in the HC and BP-R groups, while Bacteroidaceae, Ruminococcaceae and Enterobacteriaceae were more abundant in the BP group. Bugbase analysis revealed the potentially pathogenic bacteria had an increasing trend in the BP group compared with the HC group and this variation vanished in the BP-R group. At the amplicon sequence variants (ASV) level, Bacteroides ovatus (ASV40) and Veillonella dispar (ASV140) significantly decreased, while Prevotella copri (ASV54) increased in the BP group compared to the HC and BP-R groups. The HC group and BP-R group shared similar abundance. Furthermore, by correlation analysis, we investigated key ASVs correlated with clinical parameters and found some discriminate biomarkers between the BP and BP-R groups. Our study established a dynamic GM profile in BP patients under different disease activity, providing a new direction to understand the role of GM in BP pathogenesis and therapeutic effects.

Manifestation and staging of arthropathy in cystic fibrosis. Defining different stages of cystic fibrosis arthropathy using ultrasound imaging and clinical scoring

BACKGROUND

The true prevalence of cystic fibrosis arthropathy (CFA) remains unclear and may be significantly higher than previously reported. In recent studies, joint symptoms have been reported in up to 30% of adults with CF. This underlines the importance of CFA as a rising and clinically relevant co-morbidity. A clear definition of CFA is yet missing and its pathogenesis remains unclear. We investigated the clinical manifestation of CFA particularly via ultrasound (US) examination to define and implement a staging for clinical assessment.

METHODS

In a prospective cohort study between March 2018 and February 2020 a total of 98 consecutively recruited, adult cystic fibrosis (CF) patients underwent joint-US examination according to a newly developed ultrasound score (US-CFA). A clinical assessment including rheumatological scores (DAS28, HAQ) has been conducted as well as a specially designed questionnaire. Investigation on clinical and microbiological data, as well as a comprehensive laboratory analysis, were carried out. Cluster analysis has been performed to detect patterns defining different CFA stages based on disease activity.

RESULTS

US imaging has shown a considerable incidence of mild to moderate effusion as sign of joint inflammation/(teno-)synovitis. K-means clustering was used to distinguish 3 different stages of CFA based on the intensity of the detected effusion. These stages showed a significant association with disease activity (DAS28, p = 0.0004) as well as with patient-reported symptoms such as total weeks of CFA per year (p = 0.004), acute CFA (p = 0.015), chronic CFA (p = 0.016), disease burden (p = 0.04). Based on the US-CFA, 16% of patients suffered from severe CFA (II), 51% from intermediate CFA (I) and 33% did not present detectable arthritis. Positive serology for Chlamydophilia pneumoniae (IgA, IgG) and Chlamydia trachomatis (IgA, IgG) significantly correlated with the US-CFA.

CONCLUSIONS

The results of this study show that a definition and categorization for the clinical manifestation of CFA can be described through US examination, which is able to detect disease activity concordant with the DAS28 as a validated clinical score on arthritis. Defining these stages will lead to a better understanding of the clinical phenotype of the disease and will optimize diagnosis, therapy and research on CFA in the future.

The Human Microbiome and Its Role in Musculoskeletal Disorders

Musculoskeletal diseases (MSDs) are characterized as injuries and illnesses that affect the musculoskeletal system. MSDs affect every population worldwide and are associated with substantial global burden. Variations in the makeup of the gut microbiota may be related to chronic MSDs. There is growing interest in exploring potential connections between chronic MSDs and variations in the composition of gut microbiota. The human microbiota is a complex community consisting of viruses, archaea, bacteria, and eukaryotes, both inside and outside of the human body. These microorganisms play crucial roles in influencing human physiology, impacting metabolic and immunological systems in health and disease. Different body areas host specific types of microorganisms, with facultative anaerobes dominating the gastrointestinal tract (able to thrive with or without oxygen), while strict aerobes prevail in the nasal cavity, respiratory tract, and skin surfaces (requiring oxygen for development). Together with the immune system, these bacteria have coevolved throughout time, forming complex biological relationships. Changes in the microbial ecology of the gut may have a big impact on health and can help illnesses develop. These changes are frequently impacted by lifestyle choices and underlying medical disorders. The potential for safety, expenses, and efficacy of microbiota-based medicines, even with occasional delivery, has attracted interest. They are, therefore, a desirable candidate for treating MSDs that are chronic and that may have variable progression patterns. As such, the following is a narrative review to address the role of the human microbiome as it relates to MSDs.

Alterations in the cutaneous microbiome of patients with psoriasis and psoriatic arthritis reveal similarities between non-lesional and lesional skin

OBJECTIVES

To investigate the cutaneous microbiome spanning the entire psoriatic disease spectrum, and to evaluate distinguishing features of psoriasis (PsO) and psoriatic arthritis (PsA).

METHODS

Skin swabs were collected from upper and lower extremities of healthy individuals and patients with PsO and PsA. Psoriatic patients contributed both lesional (L) and contralateral non-lesional (NL) samples. Microbiota were analysed using 16S rRNA sequencing.

RESULTS

Compared with healthy skin, alpha diversity in psoriatic NL and L skin was significantly reduced (p<0.05) and samples clustered separately in plots of beta diversity (p<0.05). Kocuria and Cutibacterium were enriched in healthy subjects, while Staphylococcus was enriched in psoriatic disease. Microbe-microbe association networks revealed a higher degree of similarity between psoriatic NL and L skin compared with healthy skin despite the absence of clinically evident inflammation. Moreover, the relative abundance of Corynebacterium was higher in NL PsA samples compared with NL PsO samples (p<0.05), potentially serving as a biomarker for disease progression.

CONCLUSIONS

These findings show differences in diversity, bacterial composition and microbe-microbe interactions between healthy and psoriatic skin, both L and NL. We further identified bacterial biomarkers that differentiate disease phenotypes, which could potentially aid in predicting the transition from PsO to PsA.

Severe Scalp Psoriasis Microbiome Has Increased Biodiversity and Relative Abundance of Pseudomonas Compared to Mild Scalp Psoriasis

Psoriasis is a chronic inflammatory skin disease associated with various factors. Recently, alterations in the gut and skin microbiomes have been shown to interact with host immunity, affect skin barrier function, as well as development and progression of psoriasis. We aimed to analyze the microbiota of the scalp of patients with psoriasis and determine the characteristics of the microbiome according to disease severity. We investigated the scalp microbiome of 39 patients with psoriasis scalp lesions and a total of 47 samples were analyzed. The patients were divided into mild, moderate, and severe groups according to the European recommendations for scalp psoriasis. For bacterial identification, we utilized the SILVA database targeting the V3 region of the 16 S rRNA gene. The mean Shannon index escalated along with disease severity, and the diversity of the scalp microbiome tended to increase with disease severity (R = 0.37, p < 0.01). The relative abundance of Pseudomonas was increased in severe scalp psoriasis (0.49 ± 0.22) compared to the mild group (0.07 ± 0.03, p = 0.029), and Diaphorobacter was enriched in the mild group (0.76 ± 0.16%) compared to the severe group (0.44 ± 0.22, p < 0.001). We identified that increased diversity of the scalp microbiome and the relative abundance of Pseudomonas are associated with the severity of scalp psoriasis.

Environmental Risks for Spondyloarthropathies

Spondyloarthropathies, also known as spondyloarthritis, encompasses a spectrum of diseases classified by it's axial and peripheral musculoskeletal manifestations. Extra-articular features are common in SpA making these systemic rheumatologic diseases involve the skin, eye, gut, and other organ systems.Research has identified risk factors for the development of spondyloarthritis, particularly regarding genetic susceptibility and the strong association with HLA-B27. Multiple studies have elucidated clinical risk factors associated with SpA disease activity and severity. In this review, we aim to explore the environmental risk factors for spondyloarthritis.

Role of the microbiome and its metabolites in ankylosing spondylitis

Ankylosing spondylitis (AS), a chronic condition that commonly influences the spine and sacroiliac joints, usually progresses to stiffness and progressive functional limitation. Its fundamental etiology and pathogenesis are likely multifactorial and remain elusive. As environmental factors, gut microbiota performs critical functions in the pathogenesis of AS through various mechanisms, including interacting with genes, enhancing intestinal permeability, activating the gut mucosa immune system, and affecting the intestinal microbiota metabolites. This review provides an overview of recent advances in investigating gut microbiota in AS pathogenesis and discusses potential methods for future therapeutic intervention.

Quantitative method for the determination of antibiotic-resistant gut bacterial strains for the early diagnosis of chronic arthritis

Based on the clinical and microbiological monitoring of two groups of children aged 3 to 17 years with acute (n=78) and chronic (n=46) course of reactive arthritis (ReA), a method for early diagnosis of chronic arthritis was developed by determining the number of antibiotic-resistant coprostrains in patients with ReA, characterized by the absence of the need to isolate a pure culture of the pathogen and its identification; inoculation of faeces at a dilution of 10-5 on solid 1.5% GRM-agar with an antibacterial agents used in the treatment of a particular patient, at a minimum inhibitory concentration in the resistance range, followed by incubation and counting of the colonies of microorganisms grown on the plate. A significant relationship between the number of antibiotic-resistant gut bacterial strains and the course of arthritis (acute, chronic) was revealed, and the borderline value of the number of antibiotic-resistant gut bacterial strains was determined - 5×103 CFU/g, which allows differentiating the acute course from the chronic one: in the acute course< 5×103 CFU/g, with chronic - ≥ 5×103 CFU/g. The method allows, at the stage of completion of anti-inflammatory therapy in the active phase of the disease, to identify a risk group for the development of a chronic course of arthritis among patients with ReA, which can contribute to timely therapeutic measures aimed at preventing recurrence of the disease and making the patient disabled.

COVID-19-associated arthritis: an emerging new entity?

The current COVID-19 pandemic raises several clinical challenges. Cases of COVID-19-associated arthritis have been reported, and inconsistently described as either COVID-19 viral arthritis or COVID-19 reactive arthritis. We aimed to review all the reported cases of 'COVID-19-associated arthritis', which we propose, is a better term to define the entire spectrum of new-onset arthritis believed to be associated with SARS-CoV-2 infection. We performed a systematic literature review using MEDLINE, EMBASE and the Cochrane Database of Systematic Reviews to search for articles published up to 13 December 2021. We included cohort studies, case series and case reports describing patients diagnosed with COVID-19 reactive or viral arthritis by a physician, irrespective of fulfilment of classification criteria. To identify relevant studies, medical subject headings and keywords related to 'COVID-19/SARS-CoV-2 infection' and 'reactive arthritis' were used. Our search retrieved 419 articles, of which 31 were included in the review. A total of 33 cases were reported in these 31 articles, the majority being adults (28/33=85%) with peripheral joint involvement (26/33=79%). Most of the patients responded well to treatment and the disease was self-limiting. These 33 case reports describe a possible causal relationship between exposure to SARS-CoV-2 and the onset of arthritis. However, since these cases were reported during a pandemic, other aetiologies cannot be fully excluded. The exact mechanism through which SARS-CoV-2 might trigger arthritis is not fully understood and robust epidemiological data to support a causal relationship are still lacking.

[History of reactive arthritis. Historical milestones and future]

The introduction of the term reactive arthritis (ReA) for the joint inflammation observed after infection with Yersinia enterocolitica, in which "a causative pathogen cannot be isolated from the synovial fluid", and the association with the HLA-B27 were the historical milestones for a new classification and assignment to the spondylarthritides (SpA). The division into postinfectious and reactive arthritis proposed in 1976 was put into perspective in the 1990s because of investigations with the newly available molecular biological method of the polymerase chain reaction. Microbial products could be identified from joint samples of patients with ReA. Therefore, it was proposed to abandon the distinction between the two groups of diseases and to prefer the term ReA for both. This created a terminological and nosological issue. On the one hand, there are generally accepted classification and diagnostic criteria for the classical HLA-B27-associated ReA that are assigned to SpA. On the other hand, an increasing number of bacterial pathogens, viruses, amoebas, helminths as well as antiviral and antibacterial vaccinations are described as triggers of arthritis, which have been published under the term ReA. Since the beginning of the SARS-CoV‑2 pandemic, cases of acute post-COVID-19 arthritis have been described, which were also classified as ReA because of comparable clinical features.

Quo vadis reactive arthritis?

PURPOSE OF REVIEW

We provide an overview of recent articles which describe new thinking regarding HLA-B27-associated reactive arthritis (ReA), including those additional infection-related arthritides triggered by microbes that often are grouped under the term ReA.

RECENT FINDINGS

With the advent and continuation of the pandemic, an increasing number of cases and case series of post-COVID-19 arthritis have been reported and classified as ReA. Further, arthritis after COVID-19 vaccination is a new entity included within the spectrum of ReA. New causative microorganisms identified in case reports include Clostridium difficile, Mycoplasma pneumoniae, Giardia lamblia, Leptospira , and babesiosis. SARS-CoV-2 is emerging as a significant etiologic agent for apparent ReA.

SUMMARY

It is now clear that comprehensive clinical and laboratory investigations, synovial fluid analyses, and close follow-up of patients all are essential to differentiate ReA from diseases that may present with similar clinical attributes. Further, and importantly, additional research is required to define the wide diversity in causative agents, epidemiology, and rare case presentations of these arthritides. Finally, new classification and diagnostic criteria, and updated treatment recommendations, are essential to the advancement of our understanding of ReA.

Safety of Biologic-DMARDs in Rheumatic Musculoskeletal Disorders: A Population-Based Study over the First Two Waves of COVID-19 Outbreak

This study aims to explore disease patterns of coronavirus disease (COVID-19) in patients with rheumatic musculoskeletal disorders (RMD) treated with immunosuppressive drugs in comparison with the general population. The observational study considered a cohort of RMD patients treated with biologic drugs or small molecules from September 2019 to November 2020 in the province of Udine, Italy. Data include the assessment of both pandemic waves until the start of the vaccination, between February 2020 and April 2020 (first), and between September 2020 and November 2020 (second). COVID-19 prevalence in 1051 patients was 3.5% without significant differences compared to the general population, and the course of infection was generally benign with 2.6% mortality. A small percentage of COVID-19 positive subjects were treated with low doses of steroids (8%). The most used treatments were represented by anti-TNF agents (65%) and anti-IL17/23 agents (16%). More than two-thirds of patients reported fever, while gastro-intestinal symptoms were recorded in 27% of patients and this clinical involvement was associated with longer swab positivity. The prevalence of COVID-19 in RMD patients has been confirmed as low in both waves. The benign course of COVID-19 in our patients may be linked to the very low number of chronic corticosteroids used and the possible protective effect of anti-TNF agents, which were the main class of biologics herein employed. Gastro-intestinal symptoms might be a predictor of viral persistence in immunosuppressed patients. This finding could be useful to identify earlier COVID-19 carriers with uncommon symptoms, eventually eligible for antiviral drugs.

Role of Gut Microbiota in Pulmonary Arterial Hypertension

Gut microbiota and its metabolites play an important role in maintaining host homeostasis. Pulmonary arterial hypertension (PAH) is a malignant clinical syndrome with a frightening mortality. Pulmonary vascular remodeling is an important feature of PAH, and its pathogenesis is not well established. With the progress of studies on intestinal microbes in different disease, cumulative evidence indicates that gut microbiota plays a major role in PAH pathophysiology. In this review, we will systematically summarize translational and preclinical data on the correlation between gut dysbiosis and PAH and investigate the role of gut dysbiosis in the causation of PAH. Then, we point out the potential significance of gut dysbiosis in the diagnosis and treatment of PAH as well as several problems that remain to be resolved in the field of gut dysbiosis and PAH. All of this knowledge of gut microbiome might pave the way for the extension of novel pathophysiological mechanisms, diagnosis, and targeted therapies for PAH.

Psoriatic arthritis from a mechanistic perspective

Psoriatic arthritis (PsA) is part of a group of closely related clinical phenotypes ('psoriatic disease') that is defined by shared molecular pathogenesis resulting in excessive, prolonged inflammation in the various tissues affected, such as the skin, the entheses or the joints. Psoriatic disease comprises a set of specific drivers that promote an aberrant immune response and the consequent development of chronic disease that necessitates therapeutic intervention. These drivers include genetic, biomechanical, metabolic and microbial factors that facilitate a robust and continuous mobilization, trafficking and homing of immune cells into the target tissues. The role of genetic variants involved in the immune response, the contribution of mechanical factors triggering an exaggerated inflammatory response (mechanoinflammation), the impact of adipose tissue and altered lipid metabolism and the influence of intestinal dysbiosis in the disease process are discussed. Furthermore, the role of key cytokines, such as IL-23, IL-17 and TNF, in orchestrating the various phases of the inflammatory disease process and as therapeutic targets in PsA is reviewed. Finally, the nature and the mechanisms of inflammatory tissue responses inherent to PsA are summarized.

The association between intestinal microbiome and autoimmune uveitis

INTRODUCTION AND OBJECTIVES

The microbiome is strongly implicated in a wide spectrum of immune-mediated diseases, whereas gut commensal microbiota plays a pivotal role in immune and intestinal homeostasis.

MATERIALS AND METHODS

A thorough literature search was performed in PubMed database. An additional search was made in Google Scholar to complete the collected items.

RESULTS

Due to complex interactions with the host genetics and other factors, intestinal dysbiosis has been linked to various immune-mediated disorders. In particular, the role of intestinal microbiota in the pathogenesis of uveitis has been demonstrated by several studies, indicating that changes in the microbiome can trigger autoimmune ocular inflammatory processes or affect their severity.

CONCLUSIONS

This review summarizes how alterations in the intestinal microbiota can conduce to immune-mediated ocular pathologies and how microbiome can be targeted in order to form novel therapeutic approaches to treat these severe and potentially blinding conditions.

The microbiomes of the eyelid and buccal area of patients with uveitic glaucoma

Background

The microbiome could trigger inflammation leading to epigenetic changes and is involved in the pathophysiology of eye diseases; however, its effect on uveitic glaucoma (UG) has not been fully investigated. This study analysed the differences in eyelid and buccal microbiomes in patients with UG using next-generation sequencing.

Methods

The eyelid and buccal specimens of 34 UG and 25 control patients were collected. The taxonomic composition of the microbiome was obtained via 16S ribosomal DNA sequencing. Diversity and differential gene expression analyses (DEG) determined taxon differences between the microbiomes of UG and control groups.

Results

In both the eyelid and buccal microbiomes, alpha-diversity was lower in UG patients than controls, while beta-diversity in patients with UG was higher than in controls. DEG analysis of the eyelid microbiome revealed various taxa differences, including enrichment of Paenibacillus and Dermacoccus (p-value, 1.31e⁻⁶ and 1.55e⁻⁷, respectively) and depletion of Morganella and Lactococcus (p-value, 6.26e⁻¹² and 2.55e⁻⁶, respectively) in patients with UG. In the buccal microbiome, taxa such as Lactococcus was significantly depleted (p-value, 1.31e⁻¹⁷), whereas Faecalibacterium was enriched in patients with UG (p-value, 6.12e⁻⁸).

Conclusions

The eyelid and buccal microbiomes in patients with UG differ from controls, which raises concerns surrounding environmental influences on the pathogenesis of UG. The reduced Lactococcus in the eyelid and buccal area suggest that microbiota dysbiosis is associated with UG.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-022-02395-x.

Altered Gut Microbiota as an Auxiliary Diagnostic Indicator for Patients With Fracture-Related Infection

Preoperative diagnosis of fracture-related infection (FRI) is difficult for patients without obvious signs of infection. However, specific profiles of gut microbiota may be used as a potential diagnostic tool for FRI as suggested by a previous study. The fecal microbiome was compared between 20 FRI patients (FRI group), 18 fracture healed patients (FH group), and 12 healthy controls (HC group) included after collection of fecal samples and evaluation. The α and β diversity indices were used to characterize the fecal microbiome. Dysbiosis indexes were constructed based on the characteristic high-dimensional biomarkers identified in the fecal microbiota from the three groups by linear discriminant analysis and generalized linear model analysis to quantify the dysbiosis of fecal microbiota. The effectiveness of α and β diversity indices and dysbiosis indexes was assessed in distinguishing the fecal microbiome among the three groups. The influences of serum inflammatory factors on gut microbiota were also addressed. The α diversity indices were significantly different between the three groups, the highest in HC group and the lowest in FRI group (P < 0.05). The β diversity indices showed significant phylogenetic dissimilarity of gut microbiome composition among the three groups (P < 0.001). The dysbiosis indexes were significantly higher in FRI group than in FH and HC groups (P < 0.001). The area under Receiver operating characteristic curve showed the characteristics of gut microbiota and the gut microbiota was found as effective in distinguishing the three groups. The dysbiosis in the FRI patients was associated with systemic inflammatory factors. In addition, significant differences in the gut microbiota were not observed between the FRI patients versus without sinus tract or pus before operation. Since FRI patients, with or without sinus tract or pus, have a characteristic profile of gut microbiota, their gut microbiota may be used as an auxiliary diagnostic tool for suspected FRI.

Gut microbiota changes in patients with spondyloarthritis: A systematic review

OBJECTIVE

Gut microbiota has been proposed as a pivotal role in the progression of Spondyloarthritis (SpA), however diverse results remain to be synthesized. We performed a systematic review to collect evidence on the characteristic of the gut microbiota in patients with SpA, as compared to controls.

METHODS

We systematically searched MEDLINE, EMBASE, Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials databases, through June 1, 2021 for studies that compared gut microbiota of cases with SpA versus healthy controls.

RESULTS

Of 3756 records identified, 28 studies from 23 articles were included in the analysis. Results of β-diversity showed SpA patients hold a significantly different microbial composition compared with controls. Several taxa-level differences of gut microbiota between SpA (and its subtypes) cases and controls were identified. Fourteen studies including only patients with ankylosing spondylitis (AS) reported increased amounts of Actinobacteria, Dialister, Streptococcus, and Clostridium bolteae, and decreased amounts of Bacteroidales and Parasutterella in AS cases versus controls in ≥ 3 studies. Dialister invisus was increased in axial-SpA cases versus controls in 3 studies. Bacteroides fragilis was increased in enthesitis-related arthritis (ERA) cases versus controls in 2 studies. For all SpA studies, Proteobacteria, Enterobacteriaceae, and Bacteroidaceae were increased, whereas Bacteroidetes, Bacteroidales, and Akkermansia were decreased in cases versus controls in ≥ 3 studies. Over 40% of the studies showed comparable data of both sex and age between cases and controls.

CONCLUSION

The microbial characteristics of SpA summarized in the systematic review laid the groundwork for evidence-based microbial treatment. The microbial variance among subtypes of SpA remains to be explored. Further studies are needed to elucidate how the altered microbiota participate in the pathogenesis of SpA.

Reactive arthritis: a clinical review

Reactive arthritis (ReA) is a form of inflammatory arthritis triggered by a remote antecedent infection, usually in the genitourinary or gastrointestinal tract. It is part of the spondyloarthropathy (SpA) spectrum, an umbrella term for a group of distinct conditions with shared clinical features. Typically, it presents with an asymmetric oligoarthritis of the lower limb joints, and patients may also have sacroiliitis, enthesitis and dactylitis. Other features often seen include anterior uveitis, urethritis and skin manifestations such as pustular lesions on the plantar areas. Although ReA was characterised initially as a sterile arthritis, the detection of metabolically active Chlamydia species in the joint fluid of some affected patients has generated further questions on the pathophysiology of this condition. There are no formal diagnostic criteria, and the diagnosis is mainly clinical. HLA-B27 can support the diagnosis in the correct clinical context, and serves as a prognostic indicator. The majority of patients have a self-limiting course, but some develop chronic SpA and require immunomodulatory therapy.

Post-COVID-19 Arthritis and Sacroiliitis: Natural History with Longitudinal Magnetic Resonance Imaging Study in Two Cases and Review of the Literature

Severe acute respiratory coronavirus-2 syndrome (SARS-CoV-2) is a well-known pandemic infectious disease caused by an RNA virus belonging to the coronaviridae family. The most important involvement during the acute phase of infection concerns the respiratory tract and may be fatal. However, COVID-19 may become a systemic disease with a wide spectrum of manifestations. Herein, we report the natural history of sacroiliac inflammatory involvement in two females who developed COVID-19 infection with mild flu-like symptoms. After the infection they reported inflammatory back pain, with magnetic resonance imaging (MRI) studies showing typical aspects of sacroiliitis. Symptoms improved with NSAIDs therapy over the following months while MRI remained positive. A literature review was performed on this emerging topic. To our knowledge, this is the first MRI longitudinal study of post-COVID-19 sacroiliitis with almost one year of follow-up. Predisposing factors for the development of articular involvement are unclear but a long-lasting persistence of the virus, demonstrated by nasopharyngeal swab, may enhance the probability of altering the immune system in a favourable background.

A Review of the Role of the Intestinal Microbiota in Age-Related Macular Degeneration

Blindness from age-related macular degeneration (AMD) is an escalating problem, yet AMD pathogenesis is incompletely understood and treatments are limited. The intestinal microbiota is highly influential in ocular and extraocular diseases with inflammatory components, such as AMD. This article reviews data supporting the role of the intestinal microbiota in AMD pathogenesis. Multiple groups have found an intestinal dysbiosis in advanced AMD. There is growing evidence that environmental factors associated with AMD progression potentially work through the intestinal microbiota. A high-fat diet in apo-E-/- mice exacerbated wet and dry AMD features, presumably through changes in the intestinal microbiome, though other independent mechanisms related to lipid metabolism are also likely at play. AREDS supplementation reversed some adverse intestinal microbial changes in AMD patients. Part of the mechanism of intestinal microbial effects on retinal disease progression is via microbiota-induced microglial activation. The microbiota are at the intersection of genetics and AMD. Higher genetic risk was associated with lower intestinal bacterial diversity in AMD. Microbiota-induced metabolite production and gene expression occur in pathways important in AMD pathogenesis. These studies suggest a crucial link between the intestinal microbiota and AMD pathogenesis, thus providing a novel potential therapeutic target. Thus, the need for large longitudinal studies in patients and germ-free or gnotobiotic animal models has never been more pressing.

Drivers of Inflammation in Psoriatic Arthritis: the Old and the New

PURPOSE OF REVIEW

The recognition that IL-17 is produced by many lymphoid-like cells other than CD4+ T helper (Th17) cells raises the potential for new pathogenic pathways in IBD/psoriasis/SpA. We review recent knowledge concerning the role of unconventional and conventional lymphocytes expressing IL-17 in human PsA and axSpA.

RECENT FINDINGS

Innate-like lymphoid cells, namely gamma delta (γδ) T-cells, invariant natural killer T (iNKT) cells and mucosal-associated invariant T (MAIT) cells, together with innate lymphoid cells (ILCs) are found at sites of disease in PsA/SpA. These cells are often skewed to Type-17 profiles and may significantly contribute to IL-17 production. Non-IL-23 dependent IL-17 production pathways, utilising cytokines such as IL-7 and IL-9, also characterise these cells. Both conventional CD4 and CD8 lymphocytes show pathogenic phenotypes at sites of disease. A variety of innate-like lymphoid cells and conventional lymphocytes contribute towards IL-17-mediated pathology in PsA/SpA. The responses of these cells to non-conventional immune and non-immune stimuli may explain characteristic clinical features of these diseases and potential therapeutic mechanisms of therapies such as Jak inhibitors.

Characteristics of the intestinal microbiome in ankylosing spondylitis

The importance of intestinal microbiota in the development of various systemic diseases has been highlighted over time. Ankylosing spondylitis (AS) is a systemic disease with a complex pathogenesis involving a particular genetic marker and distinctive environmental triggers such as a specific gut dysbiosis. We conducted a prospective case-control study which included 60 subjects from Iasi Rehabilitation Hospital: 28 AS cases and 32 healthy controls. Intestinal microbiota analysis was performed by real-time polymerase chain reaction (qPCR) in stool samples. We performed the quantitative analysis of gut microbiome, focusing both on anti-inflammatory (Bifidobacterium, Lactobacillus, Faecalibacterium prausnitzii) and pro-inflammatory (Bacteroides, Escherichia coli) species. Overall, intestinal bacterial diversity in the AS group was decreased compared to that noted in the control. A significantly decreased level of Clostridium leptum was observed, associated with an increased level of Escherichia coli. We showed correlations between laboratory tests (liver and kidney functional tests, inflammatory syndrome), the presence of HLA-B27, smoker status, the forms of AS with peripheral arthritis vs. pure axial forms and bacterial structures. No significant correlations were shown for disease activity scores, radiological stage of sacroiliitis or for body mass index. Our findings support that the intestinal microbiome in AS patients has a special signature characterized by an inflammatory status. Numerous environmental, genetical, clinical and paraclinical factors can lead to changes in gut bacterial diversity in these cases.

Treatment of reactive arthritis with biological agents: a review

The pathogenesis of reactive arthritis (ReA) has not been fully elucidated. In recent years, many researchers have confirmed that multiple cytokines are involved in the occurrence and development of ReA. Although ReA is self-limiting, it is still incurable for some patients who have no or a weak response to traditional drugs, such as non-steroidal anti-inflammatory agents, glucocorticoids and immunosuppressive agents. This is called refractory reactive arthritis. Currently, there is insufficient evidences for the treatment of refractory ReA with biological agents, though biological agents against cytokines have been developed over the past few years. This review summarizes the current development of clinical treatments of ReA with biological agents, which provides future investigations on refractory ReA with more evidence and references.

Methotrexate impacts conserved pathways in diverse human gut bacteria leading to decreased host immune activation

Immunomodulatory drugs can inhibit bacterial growth, yet their mechanism of action, spectrum, and clinical relevance remain unknown. Methotrexate (MTX), a first-line rheumatoid arthritis (RA) treatment, inhibits mammalian dihydrofolate reductase (DHFR), but whether it directly impacts gut bacteria is unclear. We show that MTX broadly alters the human gut microbiota. Drug sensitivity varied across strains, but the mechanism of action against DHFR appears conserved between mammalian and bacterial cells. RA patient microbiotas were sensitive to MTX, and changes in gut bacterial taxa and gene family abundance were distinct between responders and non-responders. Transplantation of post-treatment samples into germ-free mice given an inflammatory trigger led to reduced immune activation relative to pre-treatment controls, enabling identification of MTX-modulated bacterial taxa associated with intestinal and splenic immune cells. Thus, conservation in cellular pathways across domains of life can result in broad off-target drug effects on the human gut microbiota with consequences for immune function.

Predictive Metagenomic Analysis of Autoimmune Disease Identifies Robust Autoimmunity and Disease Specific Microbial Signatures

Within the last decade, numerous studies have demonstrated changes in the gut microbiome associated with specific autoimmune diseases. Due to differences in study design, data quality control, analysis and statistical methods, many results of these studies are inconsistent and incomparable. To better understand the relationship between the intestinal microbiome and autoimmunity, we have completed a comprehensive re-analysis of 42 studies focusing on the gut microbiome in 12 autoimmune diseases to identify a microbial signature predictive of multiple sclerosis (MS), inflammatory bowel disease (IBD), rheumatoid arthritis (RA) and general autoimmune disease using both 16S rRNA sequencing data and shotgun metagenomics data. To do this, we used four machine learning algorithms, random forest, eXtreme Gradient Boosting (XGBoost), ridge regression, and support vector machine with radial kernel and recursive feature elimination to rank disease predictive taxa comparing disease vs. healthy participants and pairwise comparisons of each disease. Comparing the performance of these models, we found the two tree-based methods, XGBoost and random forest, most capable of handling sparse multidimensional data, to consistently produce the best results. Through this modeling, we identified a number of taxa consistently identified as dysregulated in a general autoimmune disease model including Odoribacter, Lachnospiraceae Clostridium, and Mogibacteriaceae implicating all as potential factors connecting the gut microbiome to autoimmune response. Further, we computed pairwise comparison models to identify disease specific taxa signatures highlighting a role for Peptostreptococcaceae and Ruminococcaceae Gemmiger in IBD and Akkermansia, Butyricicoccus, and Mogibacteriaceae in MS. We then connected a subset of these taxa with potential metabolic alterations based on metagenomic/metabolomic correlation analysis, identifying 215 metabolites associated with autoimmunity-predictive taxa.

Microbiome or Infections: Amyloid-Containing Biofilms as a Trigger for Complex Human Diseases

The human microbiota is the community of microorganisms that live upon or within their human host. The microbiota consists of various microorganisms including bacteria, fungi, viruses, and archaea; the gut microbiota is comprised mostly of bacteria. Many bacterial species within the gut microbiome grow as biofilms, which are multicellular communities embedded in an extracellular matrix. Studies have shown that the relative abundances of bacterial species, and therefore biofilms and bacterial byproducts, change during progression of a variety of human diseases including gastrointestinal, autoimmune, neurodegenerative, and cancer. Studies have shown the location and proximity of the biofilms within the gastrointestinal tract might impact disease outcome. Gram-negative enteric bacteria secrete the amyloid curli, which makes up as much as 85% of the extracellular matrix of enteric biofilms. Curli mediates cell-cell attachment and attachment to various surfaces including extracellular matrix components such as fibronectin and laminin. Structurally, curli is strikingly similar to pathological and immunomodulatory human amyloids such as amyloid-β, which has been implicated in Alzheimer's disease, α-synuclein, which is involved in Parkinson's disease, and serum amyloid A, which is secreted during the acute phase of inflammation. The immune system recognizes both bacterial amyloid curli and human amyloids utilizing the same receptors, so curli also induces inflammation. Moreover, recent work indicates that curli can participate in the self-assembly process of pathological human amyloids. Curli is found within biofilms of commensal enteric bacteria as well as invasive pathogens; therefore, evidence suggests that curli contributes to complex human diseases. In this review, we summarize the recent findings on how bacterial biofilms containing curli participate in the pathological and immunological processes in gastrointestinal diseases, systemic autoimmune diseases, and neurodegenerative diseases.

Microbial-derived antigens and metabolites in spondyloarthritis

Spondyloarthritis (SpA) is a group of chronic, immune-mediated, inflammatory diseases affecting the bone, synovium, and enthesis. Microbiome, the community of microorganisms that has co-evolved with human hosts, plays a pivotal role in human health and disease. This invisible "essential organ" supplies the host with a myriad of chemicals and molecules. In turn, microbial metabolites can serve as messengers for microbes to communicate with each other and in the cross-talk with host cells. Gut dysbiosis in SpA is associated with altered microbial metabolites, and an accumulated body of research has contributed to the understanding that changes in intestinal microbiota can modulate disease pathogenesis. We review the novel findings from human and animal studies to provide an overview of the contribution of individual microbial metabolites and antigens to SpA.

Putative Pathobionts in HLA-B27-Associated Spondyloarthropathy

Spondyloarthritis (SpA) is a group of immune mediated inflammatory diseases with a strong association to the major histocompatibility (MHC) class I molecule, HLA-B27. Although the association between HLA-B27 and AS has been known for almost 50 years, the mechanisms underlying disease pathogenesis are elusive. Over the years, three hypotheses have been proposed to explain HLA-B27 and disease association: 1) HLA B27 presents arthritogenic peptides and thus creates a pathological immune response; 2) HLA-B27 misfolding causes endoplasmic reticulum (ER) stress which activates the unfolded protein response (UPR); 3) HLA-B27 dimerizes on the cell surface and acts as a target for natural killer (NK) cells. None of these hypotheses explains SpA pathogenesis completely. Evidence supports the hypothesis that HLA-B27-related diseases have a microbial pathogenesis. In animal models of various SpAs, a germ-free environment abrogates disease development and colonizing these animals with gut commensal microbes can restore disease manifestations. The depth of microbial influence on SpA development has been realized due to our ability to characterize microbial communities in the gut using next-generation sequencing approaches. In this review, we will discuss various putative pathobionts in the pathogenesis of HLA-B27-associated diseases. We pursue whether a single pathobiont or a disruption of microbial community and function is associated with HLA-B27-related diseases. Furthermore, rather than a specific pathobiont, metabolic functions of various disease-associated microbes might be key. While the use of germ-free models of SpA have facilitated understanding the role of microbes in disease development, future studies with animal models that mimic diverse microbial communities instead of mono-colonization are indispensable. We discuss the causal mechanisms underlying disease pathogenesis including the role of these pathobionts on mucin degradation, mucosal adherence, and gut epithelial barrier disruption and inflammation. Finally, we review the various uses of microbes as therapeutic modalities including pre/probiotics, diet, microbial metabolites and fecal microbiota transplant. Unravelling these complex host-microbe interactions will lead to the development of new targets/therapies for alleviation of SpA and other HLA-B27 associated diseases.

Reactive Arthritis: Update

Purpose of Review

The aim of this paper is to provide an overview about reactive arthritis, with an update regarding pathophysiology and therapeutic approach of the disease, outlining the clinical features and diagnostic approach, based on recent literature review.

Recent Findings

Reactive arthritis is considered to be part of the spectrum of the spondyloarthritis. Its epidemiology is changing worldwide due to several reasons, among them are as follows: different diagnosis approach and clinical presentations, different grades of infection, microbiome changes, etc. The understanding of pathophysiological models is challenging, but recent studies contribute to elucidate the major factors involved in the development of the disease. The management of ReA depends on the triggering agent and the phase of disease, whether it is acute or chronic.

Summary

The association between the microbiome changes and spondyloarthropathies (ReA) is becoming increasingly evident. The results regarding the biologic treatment on refectory ReA are promising.

Elucidating potential molecular signatures through host-microbe interactions for reactive arthritis and inflammatory bowel disease using combinatorial approach

Reactive Arthritis (ReA), a rare seronegative inflammatory arthritis, lacks exquisite classification under rheumatic autoimmunity. ReA is solely established using differential clinical diagnosis of the patient cohorts, where pathogenic triggers linked to enteric and urogenital microorganisms e.g. Salmonella, Shigella, Yersinia, Campylobacter, Chlamydia have been reported. Inflammatory Bowel Disease (IBD), an idiopathic enteric disorder co-evolved and attuned to present gut microbiome dysbiosis, can be correlated to the genesis of enteropathic arthropathies like ReA. Gut microbes symbolically modulate immune system homeostasis and are elementary for varied disease patterns in autoimmune disorders. The gut-microbiota axis structured on the core host-microbe interactions execute an imperative role in discerning the etiopathogenesis of ReA and IBD. This study predicts the molecular signatures for ReA with co-evolved IBD through the enveloped host-microbe interactions and microbe-microbe 'interspecies communication', using synonymous gene expression data for selective microbes. We have utilized a combinatorial approach that have concomitant in-silico work-pipeline and experimental validation to corroborate the findings. In-silico analysis involving text mining, metabolic network reconstruction, simulation, filtering, host-microbe interaction, docking and molecular mimicry studies results in robust drug target/s and biomarker/s for co-evolved IBD and ReA. Cross validation of the target/s or biomarker/s was done by targeted gene expression analysis following a non-probabilistic convenience sampling. Studies were performed to substantiate the host-microbe disease network consisting of protein-marker-symptom/disease-pathway-drug associations resulting in possible identification of vital drug targets, biomarkers, pathways and inhibitors for IBD and ReA.Our study identified Na(+)/H(+) anti-porter (NHAA) and Kynureninase (KYNU) to be robust early and essential host-microbe interacting targets for IBD co-evolved ReA. Other vital host-microbe interacting genes, proteins, pathways and drugs include Adenosine Deaminase (ADA), Superoxide Dismutase 2 (SOD2), Catalase (CAT), Angiotensin I Converting Enzyme (ACE), carbon metabolism (folate biosynthesis) and methotrexate. These can serve as potential prognostic/theranostic biomarkers and signatures that can be extrapolated to stratify ReA and related autoimmunity patient cohorts for further pilot studies.

[Characteristics of intestinal flora in patients with primary Sjögren syndrome]

OBJECTIVE

To investigate changes in intestinal flora in patients with primary Sj?gren syndrome (pSS) and explore the relationship between pSS disease activity and intestinal flora structure.

METHODS

Fecal samples were collected from 18 female pSS patients, including 9 patients with active disease (group A) and 9 with disease inactivity or low activity (group B), with 10 healthy subjects as the control group. The total bacterial DNA was extracted from the fecal samples for PCR amplification, and Illumina Hiseq 2500 high-throughput sequencing was performed for the v3-v4 region of 16Sr DNA gene to obtain the biological information of the intestinal flora. The intergroup OTU analysis, structural diversity analysis, significant difference analysis and LEFSE analysis were performed with information mining of the literature think tanks.

RESULTS

The dilution curves generated based on the OTUshannon index for analysis of sample complexity showed that the measured data were relatively complete and could reflect the diversity of the microorganisms in the subjects. Analysis of the Alpha diversity index showed that the Shannon index differed significantly between group A and group B, and the Simpson index differed significantly between group A and group B and between group A and the control group (P &lt; 0.05). Sequence analysis the 3 groups all consisted mainly of 4 phylum (Firmicutes, Bacteroidetes, Actinobacteria, showed that the intestinal flora in and proteobacteria) and 4 genera (finegoldia, Prevotella, Streptococcus, and Corynebacterium_1), all showing no significant differences among the 3 groups (P &gt; 0.05) with the exception of Streptococcus genus, which differed significantly among the 3 groups (P &lt; 0.05). The 16S v3-v4 region in the genus Alloscardovia, Bacteroides, Barnesiella, Butyricicoccus, Facklamia, Faecalibacterium, Lachnospiraceae_FCS020_group, Lachnospiraceae_ND3007_group, Lachnospiraceae_UCG-001, Lachnospirace, Lachnospirace, Ruminococcaceae_UCG-002, Streptococcus and Coprococcus_1 differed significantly among the 3 groups (P &lt; 0.05). The high-dimensional biometrics and genomic characteristics of the intestinal microorganisms differed significantly among the 3 groups (P &lt; 0.05). According to the size of LDA SCORE (effect size), the core flora in group A included the genera Barnesiellaccae, Aerococcaceae, Family-XIII, Bacteroidaceae, Lachnospiraceae_UCG-001, Barnesiella, Facklamia, Alloscardovia, Faecalibacterium and Bacteroides, as compared with the genera Streptococcaceae, Streptococcus, Coprococcus_1, Ruminococcaceae_ucg-002, Lachnospiraceae_FCS020_group, Lachnospiraceae_ucg-004, Lachnospiraceae_ND3007_group, Lachnospiraceae_ucg-008 and Butyricicoccus in the control group.

CONCLUSIONS

Patients with pSS have significant changes in the diversity of intestinal flora, especially in some specific bacteria in Streptococcu genus and in 16S v3-v4 region of the bacteria. The differences in the core bacteria in the intestinal flora of pSS patients suggest the role of flora structure changes in the pathogenesis of pSS.

Revisiting the gut-joint axis: links between gut inflammation and spondyloarthritis

Gut inflammation is strongly associated with spondyloarthritis (SpA), as exemplified by the high prevalence of inflammatory bowel disease (IBD) and the even higher occurrence of subclinical gut inflammation in patients with SpA. The gut-joint axis of inflammation in SpA is further reinforced by similarities in immunopathogenesis at both anatomical sites and by the clinical success of therapies blocking TNF and IL-23 in IBD and in some forms of SpA. Many genetic risk factors are shared between SpA and IBD, and changes in the composition of gut microbiota are seen in both diseases. Current dogma is that inflammation in SpA initiates in the gut and leads to joint inflammation; however, although conceptually attractive, some research does not support this causal relationship. For example, therapies targeting IL-17A are efficacious in the joint but not the gut, and interfering with gut trafficking by targeting molecules such as α4β7 in IBD can lead to onset or flares of SpA. Several important knowledge gaps remain that must be addressed in future studies. Determining the true nature of the gut-joint axis has real-world implications for the treatment of patients with co-incident IBD and SpA and for the repurposing of therapeutics from one disease to the other.

Identification of Cartilage Microbial DNA Signatures and Associations With Knee and Hip Osteoarthritis

OBJECTIVE

Alterations of the gut microbiota have been implicated in many forms of arthritis, but an examination of cartilage microbial patterns has not been performed. This study was undertaken to characterize the microbial DNA profile of articular cartilage and determine changes associated with osteoarthritis (OA).

METHODS

We performed 16S ribosomal RNA gene deep sequencing on eroded and intact cartilage samples from knee OA patients (n = 21 eroded and 21 intact samples) and hip OA patients (n = 34 eroded and 33 intact samples) and cadaver controls (n = 10 knee samples and 10 hip samples). Microbial DNA diversity was assessed, groups were compared, and metagenomic profiles were reconstructed. Confirmation was performed in an independent cohort by clade-specific quantitative polymerase chain reaction. Findings in human cartilage were compared to those in cartilage from OA-susceptible C57BL/6 (B6) mice and OA-resistant MRL/MpJ (MRL) mice. Germ-free B6 mouse cartilage was analyzed as a methodologic control.

RESULTS

Alpha diversity was reduced in human OA versus control samples (P < 0.0001), and in hip versus knee samples (P < 0.0001). Numerous clades were different in human OA versus control samples, and similar findings were noted in comparisons of murine B6 versus MRL mice. Hip samples were microbiologically distinct from knee samples. OA microbial DNA demonstrated increased gram-negative constituents (P = 0.02). Functional analysis demonstrated increases in lipopolysaccharide production (P = 9.9 × 10-3 ), phosphatidylinositol signaling (P = 4.2 × 10-4 ), and nitrogen metabolism (P = 8 × 10-3 ) and decreases in sphingolipid metabolism (P = 7.7 × 10-4 ) associated with OA.

CONCLUSION

Our study reveals a microbial DNA signature in human and mouse cartilage. Alterations in this signature, including increases in gram-negative constituents, occur during the development and progression of human OA. Furthermore, our findings indicate that strain-specific signatures exist within mouse cartilage that mirror human patterns. Further study of the establishment and potential pathogenic role of these DNA signatures is needed.