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P091. Controlling the balance of immunity in colitis: Investigating the roles of intestinal microbiota and dendritic cell migration

S. Borg-Bartolo1, J. McLaughlin2, C. Ballestrem3, S. Cruickshank1, 1University of Manchester, Manchester Immunology Group, Faculty of Life Sciences, Manchester, United Kingdom, 2Salford Royal NHS Foundation Trust, School of Translational Medicine, Manchester, United Kingdom, 3University of Manchester, Wellcome Trust Centre for Cell Matrix Research, Manchester, United Kingdom

Background

The pathogenesis of Inflammatory Bowel Disease (IBD) is unclear which hinders effective targeted drug development. IBD and murine models of colitis are associated with the abnormal accumulation of activated dendritic cells (DCs) in the colonic epithelium. DCs play a critical role in promoting inflammatory responses and blockade of their activation prevents colitis development in mouse models. We now propose to address the mechanisms underlying the aberrant accumulation of DCs in the gut by focusing on microbial danger stimuli that drive activation and migration of DCs.

Methods

We analysed the expression of migration-associated activation markers on colonic DCs from normal and colitic mice using flow cytometry. Bone marrow derived DCs (BMDCs) from Wild Type (WT) or Beta-2 Integrin−/− (ITGB2−/−) mice were cultured in vitro and simulated with bacterial lipopolysaccharide (LPS), live Escherichia coli (EC), live Bacteroides fragilis (BF) or control (Phosphate buffered saline - PBS). BMDC migration-associated activation markers under these various conditions were assessed by flow cytometry and BMDC migratory behaviour was quantified using time-lapse microscopy and Imaris® software analysis.

Results

During colitis there was a marked increase in a population of CD103 (α ε [alpha epsilon] integrin) DCs. We were able to mirror these populations in vitro. DCs moved via random motion and their velocity after stimulation with LPS, BF or EC was significantly decreased (p < 0.001 for all). In comparison, BMDC track straightness was significantly decreased only after stimulation with EC whilst BMDC track displacement length was significantly decreased only after LPS (p < 0.05) or EC stimulation (p < 0.001). Unstimulated ITGB2−/− BMDC velocity, track straightness and track displacement length were significantly increased in comparison to that of unstimulated WT BMDC (p < 0.001 for all).

Conclusion

We have shown that dendritic cell integrin-defined phenotype is markedly altered in in vivo colitis and can be replicated in vitro using BMDCs. We have also shown that stimulation of BMDCs with bacterial components and whole bacteria causes stimulus-specific alterations in BMDC migratory phenotype. Additionally, unstimulated ITGB2−/− BMDCs have a significantly dysregulated migratory phenotype compared to WT BMDCs. In the future, understanding the complex relationship between gut microbiota, extracellular matrix, DC activation and DC migration may enable us to develop specific therapies that reduce colitis by controlling DC migration in IBD.