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P031. Probiotic bacteria enhance antigen sampling and processing by dendritic cells in pediatric IBD

C. Strisciuglio, E. Miele, F.P. Giugliano, S. Vitale, M. Andreozzi, A. Vitale, S. Cenni, A. Staiano, R. Troncone, C. Gianfrani, University Federico II, Department of Translational and Medical Science, Naples, Italy

Background

The role of commensal gut microbiota is essential to induce and preserve a balanced intestinal immune response. Several bacteria strains, such as Bifidobacterium species, have been reported to reduce inflammation and contribute to the maintenance of intestinal homeostasis. However, the interaction between these bacteria and the gut immune system remains largely unknown. Because of the central role played by dendritic cells (DCs) in regulating immune responses and inducing tolerance, we examined in vitro the effects of a probiotic mixture, composed from three different Bifidobacterium species (B. Longum, B. Breve, B. Infantis), on the phenotype and function of monocyte-derived DCs from children with inflammatory bowel disease (IBD).

Methods

DCs obtained from peripheral blood monocytes of pediatric patients with Crohn's disease (CD; N = 16), ulcerative colitis (UC; n = 17), and healthy controls (HC; n = 9) were incubated with fluorescein labeled bacteria (E.coli) particles or DQ-Ovalbumin (DQ-OVA) after a 24 hours pre-treatment with the probiotic mixture, in order to evaluate DC phenotype, antigen sampling and processing by flow cytometry. Moreover, after each incubation, supernatants from cells were collected to measure TNF-alfa, INF-gamma and IL-17 cytokine secretion by ELISAs.

Results

DCs generated from both CD and UC pediatric patients showed significant higher bacteria particles uptake after incubation with the probiotic mixture (p = 0.0009 and p = 0.009, respectively for CD and UC). Also DQ-OVA processing improved after the exposure to the probiotic mixture, showing a significant increase, but only in CD patients (p = 0.03). In contrast DCs from HC showed no significant changes in bacterial uptake and DQ-OVA processing upon incubation with the probiotic mixture. No effect was observed on DCs expression of the activation markers HLADR and CD86, or on TNF-alfa production induced by antigens. By contrast, INF-gamma and IL-17 resulted almost undetectable in cellular medium upon bacteria particle incubation independently of probiotic exposure.

Conclusion

In IBD patients an altered capacity to capture and process luminal bacteria antigens can lead to intestinal inflammation. Bifidobacteria significantly improve E.coli-derived particles uptake by DCs from both CD and UC patients. Interestingly, in DC from HC, in which autophagic mechanism is not altered, no prominent effect of probiotic mixture was observed. This improvement of antigen sampling and processing could partially solve the impairment of intestinal innate immunity reducing uncontrolled microorganism growth in the intestine of children with IBD.