LAUSR

Background The intestinal microbiota is believed to have a central role in SpA pathogenesis. However, the mechanism through which enteric microbes contribute to peripheral inflammation remains enigmatic. Objectives The primary objective of this study was to determine whether microbial translocation can be observed to extra-intestinal tissues in the HLA-B27/β2m transgenic rat – a foremost translational model of spondyloarthropathy. Moreover, since an arthritis phenotype only presents in less than half of HLA-B27/β2m transgenic animals, we could examine whether microbiota composition between transgenic animals with and without arthritic disease. Methods Intestinal tissue (cecal contents), mesenteric lymph nodes (MLN), spleen, serum, liver, lung, ankle joint and eye were collected from age matched (20–24wk old) HLA-B27/β2m trangenic rats with or without arthritis and WT controls (n=20–45 per group). DNA was extracted and the 16 s rRNA V4 region amplified according to the standard Earth Microbiome Project protocol. Extraction blanks were run with each tissue to control for environmental contamination. Sequencing data (generated by Illumina MiSeq) was first processed using the SourceTracker algorithm to identify and remove contaminant sequences. Remaining reads were run through the DADA2 pipeline implemented in QIIME2. Results Our study of microbial translocation revealed a number of striking observations. Firstly 16 s rRNA was detected at all tissue sites examined. Second, rather than observing a limited number of species, a highly polymicrobial and intestinal DNA signature was observed in all tissue sites examined. This observation was independent of genotype or disease state. The number of total reads in each tissue was highest in cecum as anticipated (approx. 1 00 000 reads) with the yield from other tissues roughly an order of magnitude lower. The most abundant species in joint tissue included Prevotella spp. Prevotella shahii and Prevotella stercorea, Roseburia faecis and Muribaculum intestinale. The microbe Blautia obeum, a close relative of [Ruminococcus] gnavus within the same genus was also found in joint tissue. This of interest since this microbe has recently been associated with disease activity in SpA patients. Interestingly an arthritis phenotype was strongly associated with a loss of intestinal bacterium Eubacterium Oxidoreducens. This is a flavone metabolising bacterium and supports previous metabolomic studies in which we have shown flavone compounds are greatly over-represented in the HLA-B27/ß2m transgenic rats vs WT controls. Conclusions We propose translocation of microbes/microbial products from the gut to extra-intestinal tissues may be a contributory mechanism to SpA pathogenesis, although alone is not sufficient to elicit inflammatory disease. Specific changes in microbial community DNA profile in the gut or elsewhere may serve as useful biomarkers of disease state in either patient populations or disease models. This approach may yield useful candidates for further study such as Eubacterium oxidoreducens. Future studies will verify our findings using PCR-independent methods. Acknowledgements JMA and JTR are supported by the Spondylitis Association of America and the Rheumatology Research Foundation. JTR also receives support from the William and Mary Bauman Foundation, the Stan and Madelle Rosenfeld Family Trust and Research to Prevent Blindness. Disclosure of Interest None declared