Supernatant of Bifidobacterium breve induces dendritic cell maturation, activation, and survival through a Toll-like receptor 2 pathway

International audienceBackground: Commensal gut bacteria are essential for the development and maintenance of the gut's immune system. Some bacteria strains, such as Lactobacillus and Bifidobacterium species, have been reported to provide protection from allergic and inflammatory bowel diseases. However, the interactions between these commensal bacteria and the immune system are largely unknown. Objective: We studied the effects of a supernatant from the culture of B breve C50 (BbC50) on the maturation, activation, and survival of human dendritic cells (DCs). Methods: DCs were differentiated from human monocytes with IL-4 and GM-CSF for 5 days and cultured with BbC50 supernatant (BbC50 SN) or LPS for 2 days. Results: BbC50 SN induced DC maturation, with increase in CD83, CD86, and HLA-DR expression. We also showed, for the first time, that BbC50 SN prolonged DC survival, with high IL-10 and low IL-12 production compared with that seen in LPS-DCs. Moreover, BbC50 SN inhibited the effects of LPS on DCs, both in terms of IL-12 production and in terms of survival. The prolonged DC survival was independent of IL-10 production and nuclear factor kB pathway but was associated with an upregulation of Bcl-x L and Phospho-Bad. Finally, BbC50 SN induced activation of Toll-like receptor 2 (TLR2)–transfected cells in contrast to TLR4-, TLR7-, and TLR9-transfected cells. Conclusion: The supernatant of B breve C50 can induce DC maturation and prolonged DC survival through TLR2, with high IL-10 production. These properties might correspond to a regulatory DC profile, which could limit the excessive T H 1 response and control the excessive T H 2 polarization observed in atopic newborns. (J Allergy Clin Immunol 2006;117:696-702.) Live commensal microflora is essential for the development of the gut's immune system. 1 Some bacteria, such as Lactobacillus and Bifidobacterium species, described as ''living microorganisms exerting health benefit,'' 2 define the concept of probiotics. These bacteria have been reported to prevent and treat rotavirus infections and postantibiotic diarrhea, 3,4 allergic diseases, 5-7 and recurrence of inflammatory bowel disease. 8,9 These studies suggest that the intestinal immune system could be a privileged target of probiotics. Nevertheless, despite several studies reporting modifications of immunologic parameters induced by probiotic bacteria, the interactions between the cells of the intestinal immune system and bacteria remain largely unknown. 10 However, it has been shown that killed probiotic bacteria can affect the maturation and cytokine secretion profile of dendritic cells (DCs), 11,12 which represent potent antigen-presenting cells. DCs also have properties to induce negative regulation , with generation of regulatory T cells. 13 DCs can be activated by bacterial components through the interaction between pathogen-derived immunostimulatory molecules from bacteria and membrane receptors called pattern-recognition receptors, including the Toll-like receptor (TLR) family. 14 The different TLRs recognize a broad spectrum of highly conserved microbial structures, such as proteins, lipids, glycoproteins, and nucleic acid motifs, contained in the wall, cytoplasm, and nucleus of bacteria. TLR engagement could therefore have different types of effects on DC activation according to the bacteria strain. 15 Because of these properties, DCs represent a potential target of probi-otic bacteria. Menard et al 16 recently reported that active bacterial products from Bifidobacterium breve C50 (BbC50) could cross an intestinal monolayer of epithelial cells. We therefore studied the effects of a supernatant of BbC50 (BbC50 SN) on human monocyte-derived DCs in vitro to define the interactions with the immune system. In our model BbC50 SN was able to mature and fully activate DCs, inducing a particular cytokine synthesis profile and prolonged DC survival through a TLR2 pathway. Abbreviations used 7-AAD: 7-Amino actinomycin D BbC50: Bifidobacterium breve C50 BbC50 SN : Supernatant of Bifidobacterium breve C50 BbC50 SN-DC: DC treated with BbC50 SN DC: Dendritic cell NF: Nuclear factor PE: Phycoerythrin TLR: Toll-like recepto