Abstract

Background: Systemic sclerosis (SSc) is a complex autoimmune disease characterized by inflammation and fibrosis across different organ systems, including the gastrointestinal tract and the lungs. Studies have demonstrated that gut microbiota modulate pulmonary immune function [1], and alterations of intestinal microbiota communities can influence disease outcomes in distant organs, including the lungs, through gut transfer experiments of dysbiotic microbiota [2]. To our knowledge, no prior studies have investigated the gut-lung axis in SSc-associated interstitial lung disease (ILD) using an international, multicentre study. Objectives: We aimed to identify differentially abundant bacterial species in SSc patients with ILD compared to without ILD and to determine whether specific bacterial species are associated with ILD severity based on the quantitative radiological extent of ILD. Methods: SSc patients with and without ILD were recruited from 7 international SSc Centres (University of California, Los Angeles [UCLA], USA; Lund University [LU], Sweden; Duke-National University of Singapore; Johns Hopkins University, USA; Ghent University, Belgium; University of Adelaide, Australia; Pontificia Universidad Católica de Chile) and provided a stool sample. Shotgun metagenomics were performed using the Illumina NovaSeq 6000 with a target depth of 10 million 150x2 sequences per sample. Shotgun reads were inputted into MetaPhlAn4 for taxonomic identification of species for compositional analysis and subsequently underwent center log-ratio transformation. Samples were filtered to retain species with at least 10% non-zero counts. High-resolution computed tomography (HRCT) scans of the chest underwent quantitative image analysis to determine the radiological extent of ILD (QILD) in patients from UCLA and LU. General linear models were applied to identify differentially abundant species based on ILD presence and determine associations between QILD scores and species abundance, adjusting for body mass index, current proton pump inhibitor use, current probiotic use, current or prior immunomodulatory therapy, presence of small intestinal bacterial overgrowth and site. We considered p<0.05 at the threshold for reporting and provide 5% false discovery rate corrected p-values (q). We also computed effect size estimates, Cohen's D for mean differences and standardized Beta for association analyses. Results: Among the 261 SSc participants, 220 (84%) were female and 167 (64%) had HRCT-defined ILD. The mean age was 54.6 (SD 13) years; the mean body mass index (BMI) was 24.9 (SD 4.8); and the median disease duration was 6.8 (IQR 3.5, 12.9) years. Among 254 species analyzed, the abundance of 12 bacterial species was altered in patients with ILD compared to without ILD in all study participants, including Anaerotignum faecicola (Cohen's d= 0.37 [95% CI 0.07-0.68]; p=0.017; q=0.868) and Roseburia hominis (Cohen's d= 0.42 [95% CI 0.11-0.72]; p=0.007; q=0.868). Among 113 SSc-ILD participants who had an HRCT scan amenable to quantitative image analysis, 16 bacterial species were associated with severity of ILD based on the QILD scores, including Dysosmobacter welbionis (Standardized beta 0.33; p<0.0001; q=0.34 [Figure 1]) and Bifidobacterium adolescentis (Standardized beta -0.24; p=0.02; q=0.56 [Figure 1]). Conclusion: Patients with SSc-ILD recruited from several international centres have a unique microbiota signature compared with SSc patients without ILD. The finding that the abundance of certain bacterial species is associated with ILD and its severity supports the hypothesis that intestinal dysbiosis may contribute to ILD pathogenesis. Future studies are needed to identify additional mediators of the gut-lung axis in SSc-ILD, including bacterial metabolites. REFERENCES: [1] Sencio V, et al. Mucosal Immunol 2021;14:296–304. [2] Skalaski JH, et al. PLoS Pathog 2018;14:e1007260. Acknowledgements: Funding Sources: Anonymous donation (EV), NHLBI (EV), Boehringer Ingelheim (EV and KA) Disclosure of Interests: Kristofer Andréasson Johnson & Johnson Innovative Medicine, Swapna Joshi: None declared, Jen Labus: None declared, Arissa Young: None declared, Andrea Low: None declared, Vanessa Smith Boehringer Ingelheim, Zsuzsanna McMahan Boehringer Ingelheim, Susanna M. Proudman Boehringer Ingelheim, Janssen, Boehringer Ingelheim, Janssen, Antonia Valenzuela Vegara: None declared, Grace Kim: None declared, Jonathan Goldin: None declared, Ezinne Aja: None declared, Jonathan Jacobs: None declared, Elizabeth Volkmann Boehringer Ingelheim, GSK, Horizon, Prometheus, Boehringer Ingelheim.