OP0271 Gastrointestinal damage and microbial translocation are involved in the development of immune system activation in inflammatory bowel disease-associated spondyloarthritis
Authors: D. Benfaremo, M.M. Luchetti, F. Ciccia, C. Avellini, T. Spadoni, S. Svegliati, M. Ciferri, A. Gabrielli
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> The altered composition of the gastrointestinal (GI) microbiota, known as dysbiosis, can induce and modulate the systemic inflammation, through microbial translocation and T-cell activation, in several immuno-mediated diseases, such as inflammatory bowel disease (IBD), HIV infection, and ankylosing spondylitis. <h3>Objectives</h3> In a cohort of 85 patients with inflammatory bowel disease-associated spondyloarthritis (SpA/IBD), we assessed gut bacterial infiltration and intestinal damage. In systemic circulation, GI epithelial damage, microbial translocation and immune system activation were assessed with intestinal-fatty acid binding protein (I-FABP), lipopolysaccharide (LPS), soluble CD14 (sCD14), respectively. Moreover, the <i>in vitro</i> activity of the latter two was evaluated on osteoblast cells. <h3>Methods</h3> I-FABP, LPS, sCD14, sclerostin (SOST) and anti-SOST antibodies (anti-SOST-IgG) were assayed with ELISAs. LPS and sCD14 were used <i>in vitro</i> to stimulate the MG63 human osteoblast-like cell line. Occludin, claudin-1, claudin-4, and the presence of bacteria were assessed, respectively, by real-time-PCR analysis and immunohystochemical staining of the ileum. <h3>Results</h3> Bacteria were detectable in the ileal epithelium of IBD patients, but only in SpA/IBD they were associated with epithelial damage and downregulation of occludin, claudin-1 and claudin-4 (figure 1A-B). The serum levels of I-FABP, LPS and sCD14 resulted significantly higher in axial (187.9, 14.03, and 26.97, respectively) and peripheral SpA/IBD (130.3, 11.55, and 18, respectively) than in IBD patients (IFABP 43.65, p&lt;0.0001 for both patients' groups; LPS 9.625, p&lt;0.0001 vs Ax-SpA/IBD and=0.007 vs Per-SpA/IBD; sCD14 12.34, p&lt;0.0001 for both patients' groups) (figure 1C). In the SpA/IBD cohort, SOST was weakly correlated with I-FABP (r=-0.2683), LPS (r=-0.3063) and sCD14 (r=-0.3075), and anti-SOST-IgG with LPS (r=- 0.3959) and sCD14 (r=-0.3414). Moreover, sCD14 showed significant correlation with I-FABP (r=0.3316) and LPS (r=0.5649). <i>In vitro</i>, LPS, but not sCD14, significantly induced SOST expression through the upregulation of both Wnt3a and Wnt5a and the downregulation of the b-catenin proteins (figure 1D). On the opposite, the combination of LPS and sCD14 downregulated SOST expression through the upregulation of ERK1/2 and b-catenin protein (figure 1D). <h3>Conclusions</h3> The role of gut inflammation and microbial translocation in the onset of arthritis in IBD patients are still under investigation. We have demonstrated that in SpA/IBD there is a significant bacterial infiltration of the ileal tract, associated with the downregulation of tight-junctions' proteins (occludin, claudin-1 and claudin-4) and epithelial damage, that cause microbial translocation and higher plasma levels of I-FABP, LPS, and sCD14. LPS and sCD14, thus, could trigger a complex systemic inflammatory response acting on several biochemical pathways, linking the immune system (anti-SOST-IgG) and the bone (SOST). <h3>Disclosure of Interest</h3> None declared