A microbial imbalance with over-proliferation of certain bacterial lineages is seen in patients with rheumatoid arthritis (RA), suggesting that decreased gut microbial diversity may result in over-expression of proinflmmatory cytokines that contribute to RA disease pathogenesis, according to a study published in Genome Medicine.
It has been recognized that the gut microbiome plays a role in maintaining mucosal immunity. In addition, it has been shown that microbes and their byproducts may play a role in the adaptive immune response.
To evaluate if there is an expansion of specific gut microbes in patients with RA, Jun Chen, PhD, of the Mayo Clinic, Minnesota, and colleagues, analyzed fecal samples of patients with RA (n=40) in addition to age- and sex-matched control samples from patients with no history of autoimmune disease (n=32). A subset of control subjects (n=15) were first-degree relatives (FDRs) of the participants with RA.
Study participants met American College of Rheumatology 2010 classification criteria for RA, were receiving treatment for RA, and had not taken antibiotics, probiotics, or pharmacotherapy for inflammatory bowel disease. Patients with comorbid autoimmune diseases like diabetes or multiple sclerosis were also excluded.
Microbial DNA was extracted from fecal samples taken from study participants, and polymerase chain reactions were run to sequence the 16S ribosomal DNA. Metabolites were analyzed by mass spectrometry from plasma samples obtained from patients with RA and FDRs.
Mice from a transgenic mouse model of collagen-induced arthritis (HLA-DQ8.AEo) maintained on a standard diet were treated with Collinsella aerofaciens (109 bacteria/100 μl) or bacteria-free media every other day for 4 weeks. Mean arthritic scores, graded on a scale of 0-3 for each paw, were recorded.
The human intestinal epithelial cell line CACP-2 was used to evaluate the expression of tight junction proteins and induction of interleukin (IL)-17 in the presence of Collinsella. Splenic CD4 T-cells from type II collagen (CII)-primed DQ8 mice were then used to evaluate the T-cell response to Collinsella-primed dendritic cells by measuring labeled-thymidine incorporation.
Researchers found that C. aerofaciens infected transgenic HLA-DQ8 arthritis-induced mice developed arthritis at an increased incidence and severity compared with non-infected mice. An antigen-specific recall response was shown in the cultured CII splenic cells in response to dendritic cells precultured with C. aerofaciens . A significant decrease was also found in tight junction protein ZO-1 expression in CACP-2 human intestinal epithelial cells treated with Collinsella, which was not found with exposure to Escherichia coli.
Gastrointestinal microbial diversity was found to be reduced in patients with RA as compared with controls. This reduction in diversity was correlated with increasing disease duration and autoantibody levels. Notably, there was an accompanying expansion in normally rare Actinobacteria.
Random forest algorithm analyses were used to developed prediction models that suggested that 3 specific genera (Collinsella, Eggerthella, and Faecalibacterium) segregated with RA.
Taken together, this data suggests that the distinct microbial community in patients with RA is driven by differences in microbiotic taxa.
“Collinsella [microbes may contribute] to hyper-permeability of the gut by reducing the expression of the tight junction protein ZO-1 directly, as well as by producing specific metabolites. In support of this, the abundance of Collinsella correlated strongly with high levels of beta-alanine, alpha-aminoadipic acid, and asparagines,” the authors stated.
Summary and Clinical Applicability
Gut dysbiosis in patients with RA may result from the overabundance of specific bacterial lineages. The reduced gut microbial diversity is correlated with RA disease duration and autoantibody levels.
“Our data suggest specific microbial clades may be viable targets for therapeutic manipulation by diet, probiotics, prebiotics, and/or beneficial gut commensals,” the authors concluded.
“Determining the functions of the microbial clades that expand or contractin RA will assist in developing effective means to target them.”
Limitations and Disclosures
The therapeutic implications of treatment such as probiotics to address the microbiome findings are still inconclusive.
The work was supported by Mark E. and Mary A. Davis to the Mayo Clinic, Mayo Clinic Center of Individualized Medicine and the U.S. National Institutes of Health
Chen J, Wright K, Davis JM, et al. An expansion of rare lineage intestinal microbes characterizes rheumatoid arthritis. Genome Med. 2016;8(1):43