Modulation of phenotypic and functional maturation of dendritic cells by intestinal bacteria and gliadin: relevance for celiac disease

DC maturation and functions are influenced by microbial and environmental stimuli, which could contribute to immune dysfunction. Here, we have investigated the role of enterobacteria (Escherichia coli CBL2 and Shigella CBD8) isolated from CD patients, bifidobacteria (Bifidobacterium longum CECT 7347 and Bifidobacterium bifidum CECT 7365), and gliadins on phenotypic and functional features of MDDCs and in coculture with Caco-2 cells. The ultimate goal of our study is to understand the roles played by specific components of the gut microbiota in CD. Enterobacteria induced marked alterations in MDDC morphology, inducing podosome dissolution and dendrites, and activated MDDC adhesion and spreading. Enterobacteria also induced inflammatory cytokine production (IFN-γ, TNF-α, and IL-12), partially resembling the gliadin-induced Th1-type cytokine profile. B. longum CECT 7347 and B. bifidum CECT 7365 induced minor MDDC morphological changes and activated adhesion and spreading and inflammatory cytokine production to a lesser extent compared with enterobacteria. B. longum CECT 7347 also induced lower CD86 and CD40 expression on MDDCs than the two enterobacteria. The aforementioned bifidobacterial strain also reduced gliadin-induced IFN-γ production and increased IL-10 secretion when both stimuli were combined. Similar trends were detected for MDDCs cocultured with Caco-2 cells. B. longum CECT 7347 reversed the gliadin-reduced ZO-1 expression in Caco-2 cells. Thus, our results suggest that specific components of the gut microbiota may influence phenotypic and functional maturation of DCs differently and their interactions with epithelial cells. This could ultimately define the role of DCs in CD progression.