BackgroundThe adaptive immune response in rheumatoid arthritis (RA) is influenced by an interaction between host genetics and environment, particularly the host microbiome. Association of the gut microbiota with various diseases has been reported, though the specific components of the microbiota that affect the host response leading to disease remain unknown. However, there is limited information on the role of gut microbiota in RA. In this study we aimed to define a microbial and metabolite profile that could predict disease status. In addition, we aimed to generate a humanized model of arthritis to confirm the RA-associated microbe.MethodsTo identify an RA biomarker profile, the 16S ribosomal DNA of fecal samples from RA patients, first-degree relatives (to rule out environment/background as confounding factors), and random healthy non-RA controls were sequenced. Analysis of metabolites and their association with specific taxa was performed to investigate a potential mechanistic link. The role of an RA-associated microbe was confirmed using a human epithelial cell line and a humanized mouse model of arthritis.ResultsPatients with RA exhibited decreased gut microbial diversity compared with controls, which correlated with disease duration and autoantibody levels. A taxon-level analysis suggested an expansion of rare taxa, Actinobacteria, with a decrease in abundant taxa in patients with RA compared with controls. Prediction models based on the random forests algorithm suggested that three genera, Collinsella, Eggerthella, and Faecalibacterium, segregated with RA. The abundance of Collinsella correlated strongly with high levels of alpha-aminoadipic acid and asparagine as well as production of the proinflammatory cytokine IL-17A. A role for Collinsella in altering gut permeability and disease severity was confirmed in experimental arthritis.ConclusionsThese observations suggest dysbiosis in RA patients resulting from the abundance of certain rare bacterial lineages. A correlation between the intestinal microbiota and metabolic signatures could determine a predictive profile for disease causation and progression.Electronic supplementary materialThe online version of this article (doi:10.1186/s13073-016-0299-7) contains supplementary material, which is available to authorized users.

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Cigarette smoke (CS) causes considerable morbidity and mortality by inducing cancer, chronic lung and vascular diseases, and oral disease. Despite the well-recognized risks associated with smoking, the habit remains unacceptably prevalent. Several toxins present in CS have immunomodulatory effects. CS also contains trace amounts of microbial cell components, including bacterial lipopolysaccharide. These and other CS constituents induce chronic inflammation at mucosal surfaces and modify host responses to exogenous antigens. The effects of CS on immunity are far-reaching and complex; both pro-inflammatory and suppressive effects may be induced. The net effect of CS on immunity depends on many variables, including the dose and type of tobacco, the route and chronicity of exposure, and the presence of other factors at the time of immune cell stimulation, such as Toll receptor ligands or other inflammatory mediators. CS impairs innate defenses against pathogens, modulates antigen presentation, and promotes autoimmunity. CS also impairs immunity in the oral cavity and promotes gingival and periodontal disease and oral cancer. The recognition of specific mechanisms by which CS affects host immunity is an important step toward elucidating mechanisms of tobacco-induced disease and may identify novel therapeutic approaches for the management of diseases that afflict smokers.

SUMMARY The human gut is colonized by a large number of microorganisms (~1013 bacteria) that support various physiologic functions. A perturbation in healthy gut microbiome might leads to the development of inflammatory diseases including multiple sclerosis (MS). Therefore, gut commensals can provide promising therapeutic options for treating autoimmune diseases such as MS. We report identification of human gut–derived commensal bacteria, Prevotella histicola, which can suppress an autoimmune disease in HLA class-II transgenic model of experimental autoimmune encephalomyelitis (EAE); an animal model of MS. P. histicola suppresses disease through modulation of systemic immune responses. P. histicola challenge led to a decrease in pro-inflammatory Th1 and Th17 cells, and increase in the frequencies of CD4+FoxP3+ regulatory T cells, tolerogenic dendritic cells, and suppressive macrophage. Our study provides evidence that administration of gut commensals may regulate a systemic immune response and may, therefore, have a possible role in the treatment strategies for MS.

Objective The gut microbiome regulates host immune homeostasis. Rheumatoid arthritis (RA) is associated with intestinal dysbiosis. In this study we used a human gut-derived commensal to modulate immune response and treat arthritis in a humanized mouse model. Methods We have isolated a commensal bacterium, Prevotella histicola, native to the human gut that has systemic immune effects when administered enterally. Arthritis-susceptible HLA-DQ8 mice were immunized with type II collagen and treated with P. histicola; disease incidence, onset and severity were monitored. Changes in the gut epithelial proteins and immune response as well as systemic cellular and humoral immune responses were studied in treated mice. Results DQ8 mice when treated with P. histicola in prophylactic or therapeutic protocols exhibited significantly decreased incidence and severity of arthritis as compared to controls. The microbial mucosal modulation of arthritis was dependent on the regulation by CD103+ dendritic cells and myeloid suppressors, CD11b+Gr-1, and by generation of T regulatory cells, CD4+CD25+FoxP3+, in the gut, resulting in suppression of antigen-specific Th17 response and increased transcription of IL-10. Treatment with P. histicola led to reduced intestinal permeability by increasing expression of enzymes that produce antimicrobial peptides as well as tight junction proteins, Zo-1 and Occludin. However, the innate immune response via TLR4 and TLR9 were not affected in treated mice. Discussion Our results demonstrate that enteral exposure to P. histicola suppresses arthritis via mucosal regulation. P. histicola is a unique commensal that can be explored as a novel therapy for RA and may have low/no side effects.

BackgroundHLA-DRB1*0401 is associated with susceptibility, while HLA-DRB1*0402 is associated with resistance to developing rheumatoid arthritis (RA) and collagen-induced arthritis in humans and transgenic mice respectively. The influence of gut-joint axis has been suggested in RA, though not yet proven.Methodology/Principal FindingsWe have used HLA transgenic mice carrying arthritis susceptible and -resistant HLA-DR genes to explore if genetic factors and their interaction with gut flora gut can be used to predict susceptibility to develop arthritis. Pyrosequencing of the 16S rRNA gene from the fecal microbiomes of DRB1*0401 and DRB1*0402 transgenic mice revealed that the guts of *0401 mice is dominated by a Clostridium-like bacterium, whereas the guts of *0402 mice are enriched for members of the Porphyromonadaceae family and Bifidobacteria. DRB1*0402 mice harbor a dynamic sex and age-influenced gut microbiome while DRB1*0401 mice did not show age and sex differences in gut microbiome even though they had altered gut permeability. Cytokine transcripts, measured by rtPCR, in jejuna showed differential TH17 regulatory network gene transcripts in *0401 and *0402 mice.Conclusions/SignificanceWe have demonstrated for the first time that HLA genes in association with the gut microbiome may determine the immune environment and that the gut microbiome might be a potential biomarker as well as contributor for susceptibility to arthritis. Identification of pathogenic commensal bacteria would provide new understanding of disease pathogenesis, thereby leading to novel approaches for therapy.

Objective. To generate a mouse model that can mimic human rheumatoid arthritis (RA). A major difference between RA in humans and collagen-induced arthritis (CIA) in mice is the lack of sex bias and autoantibodies in the animal model. We used DRB1*0401-transgenic mice to understand the role of DR4 in susceptibility and sex bias in RA.Methods. A transgenic mouse was generated that lacked all endogenous mouse class II genes (AE o ) and expressed the RA susceptibility allele HLA-DRB1*0401. These transgenic mice were tested for incidence, severity, and sex distribution of CIA.Results. DRB1*0401.AE o mice developed CIA predominantly in females and produced rheumatoid factors, similar to the features of human RA. Another feature similar to human RA is the expression of class II molecules on antigen-presenting cells as well as T cells. Activated and sorted CD4؉ T cells can present DR4-restricted type II collagen (CII)-derived peptide in vitro, but cannot process the antigen. This suggests a role for these cells in epitope presentation locally in joints, which affects disease severity. After challenge with CII, female mice had higher cellularity and increased T cell proliferation and produced higher levels of proinflammatory cytokines than did the male mice.Conclusion. DR4.AE o mice expressed HLA similar to humans and displayed increased arthritis susceptibility in females, thus mimicking RA in humans. This model may be valuable for studying sex differences observed in humans and for understanding why autoimmunity is increased in women. These mice may also be useful for developing future therapeutic strategies.

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