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P082. Divergent effects of gut bacteria altered in dysbiosis of inflammatory bowel disease on monocytes and macrophage polarisation

T. Kruis1, A. Batra1, G. Loh2, M. Blaut2, B. Siegmund1, 1Charité Universitätsmedizin Berlin, Abteilung für Gastroenterologie, Infektiologie und Rheumatologie, Berlin, Germany, 2Deutsches Institut für Ernährungsforschung Potsdam-Rehbrücke, Abteilung für Gastrointestinale Mikrobiologie, Potsdam, Germany

Background

In inflammatory bowel disease (IBD) a dysbiosis of the gut microbiota is well-established. Since intestinal macrophages (Mφ) reside in close proximity to luminal bacteria alterations in microbiota composition might affect Mφ phenotype and related functions. To assess the consequence of such a dysbiosis the effect of bacterial species known to be altered in IBD on viability, polarisation, and function of human monocytes (Mo) and monocyte derived M1- or M2-Mφ was evaluated in vitro.

Methods

Human CD14+ Mo were isolated and stimulated for 20 h with supernatants (s/n) or inactivated cells of Faecali-bacterium prausnitzii (Fp), Akker-mansia mucini-phila (Am), Rumino-coccus gnavus (Rg), Bacteroides fragilis (Bf), Bifido-bacterium adolescentis (Ba), and Escherichia coli (Ec). Cytokine production (IL-6, IL-1β, IL-10, TNF-α) and apoptosis induction were assessed by flow cytometry. For M1- or M2-polarisation, Mo were cultured for 6 d in the presence of GM-CSF or M-CSF and s/n of Fp, Ba, or Ec. Following polarisation cells were stimulated with LPS for 20 h and production of IL-6, IL-8, IL-10, TNF-α and surface marker expression (CD14, CD163, CD80 and CD206) were assessed by flow cytometry.

Results

Except for s/n of Bf no cytotoxic effects were observed. S/n of Fp, Am, Rg, and Ba even enhanced cell survival. While s/n of gram-negative Am, Bf, and Ec induced secretion of IL-6, IL-1β, IL-10, and TNF-α comparable to LPS, s/n of gram-positive Fp, Rg, and Ba did not or only to a lesser extent. Polarisation of Mo to either M1- or M2-Mφ in the presence of s/n of Fp or Ba favoured cell survival compared to Ec. CD14 and CD163 expression was significantly increased on M1-Mφ cultured in presence of Fp s/n; LPS and s/n of Ba or Ec induced non-significant increases. No significant alterations of surface markers were observed for M2-Mφ. In both M1- and M2-Mφ, LPS-induced release of IL-6, IL-8, IL-10, or TNF-α was significantly suppressed if cells were polarised in presence of Fp and Ec s/n.

Conclusion

The bacterial supernatants evaluated have divergent effects on Mo with gram-negative strains favouring pro-inflammatory responses. Polarisation of Mo to M1-Mφ is modulated by Fp s/n resulting in increased expression of M2 surface markers like CD14 and CD163. S/n of Fp, Ba, and Ec differ in their potential to induce LPS tolerance in both M1- and M2-Mφ. Thus, targeting intestinal microbiota by increasing strains that promote anti-inflammatory capacities of Mφ might be a therapeutic option in IBD.