Objectives Analysis of oral dysbiosis in individuals sharing genetic and environmental risk factors with rheumatoid arthritis (RA) patients may illuminate how microbiota contribute to disease susceptibility. We studied the oral microbiota in a prospective cohort of patients with RA, first-degree relatives (FDR) and healthy controls (HC), then genomically and functionally characterised streptococcal species from each group to understand their potential contribution to RA development.
Methods After DNA extraction from tongue swabs, targeted 16S rRNA gene sequencing and statistical analysis, we defined a microbial dysbiosis score based on an operational taxonomic unit signature of disease. After selective culture from swabs, we identified streptococci by sequencing. We examined the ability of streptococcal cell walls (SCW) from isolates to induce cytokines from splenocytes and arthritis in ZAP-70-mutant SKG mice.
Results RA and FDR were more likely to have periodontitis symptoms. An oral microbial dysbiosis score discriminated RA and HC subjects and predicted similarity of FDR to RA. Streptococcaceae were major contributors to the score. We identified 10 out of 15 streptococcal isolates as S. parasalivarius sp. nov., a distinct sister species to S. salivarius. Tumour necrosis factor and interleukin 6 production in vitro differed in response to individual S. parasalivarius isolates, suggesting strain specific effects on innate immunity. Cytokine secretion was associated with the presence of proteins potentially involved in S. parasalivarius SCW synthesis. Systemic administration of SCW from RA and HC-associated S. parasalivarius strains induced similar chronic arthritis.
Conclusions Dysbiosis-associated periodontal inflammation and barrier dysfunction may permit arthritogenic insoluble pro-inflammatory pathogen-associated molecules, like SCW, to reach synovial tissue.
- rheumatoid arthritis
- first-degree relatives
- cell walls
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RM, YW and KB are joint first authors.
PH, HB, K-ALC and RT are joint senior authors.
Handling editor Josef S Smolen
Correction notice This article has been corrected since it published Online First. Figures 1 and 2 have been updated.
Contributors Study concept and design: KB, PH, HB, KALC, RT. Acquisition and analysis and interpretation of data: All authors. Drafting of the manuscript: RM, KB, AB, RT. Critical revision of the manuscript for important intellectual content: All authors. Obtained funding: RT, PH, LMR.
Funding Supported by NHMRC grant 1071822 and 1159458, an Arthritis Australia project grant and by Mrs Joan Stagg, facilitated by Arthritis and Osteoporosis Tasmania. RT was supported by Arthritis Queensland and a NHMRC Senior Research Fellowship, LMR by a University of Queensland post-doctoral fellowship.
Competing interests None declared.
Patient and public involvement statement At what stage in the research process were patients/the public first involved in the research and how? Patients and the public were involved at the recruitment stage. How were the research question(s) and outcome measures developed and informed by their priorities, experience and preferences? No direct patient involvement. How were patients/the public involved in the design of this study? Not involved. How were they involved in the recruitment to and conduct of the study? Not involved. Were they asked to assess the burden of the intervention and time required to participate in the research? No. How were (or will) they be involved in your plans to disseminate the study results to participants and relevant wider patient communities (eg, by choosing what information/results to share, when and in what format)? Preliminary results were shared via a newsletter to the involved participants to inform them of study progress.
Patient consent for publication Not required.
Ethics approval Studies approved by Metro South Hospital and Health Service (HREC/94/QPAH/6), The University of Queensland (2012000275) and by Greenslopes Private Hospital (GREC 14/53) Human Research Ethics Committees.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available in a public, open access repository. All data relevant to the study are included in the article or uploaded as supplementary information. Assembled genomes and raw 16S rRNA gene amplicon sequencing data are available via NCBI BioProject PRJNA656387. Prokka annotated genomes available at https://github.com/katebowerman/Streptococcus. Other data are available on request to corresponding author.
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