Altered microbial community structure and metabolism in cow’s milk allergic mice treated with oral immunotherapy and fructo-oligosaccharides. mouse gut metagenome

Background: Previously, we showed improved oral immunotherapy (OIT) efficacy by co-administration with fructo-oligosaccharides (FOS, prebiotics) in cow’s milk allergic mice shown by a reduction in clinically related symptoms and mast cell degranulation. Prebiotic fibers are fermented by gut bacteria, affecting both the microbial composition and availability of metabolites including short-chain fatty acids (SCFA). The contribution of the microbiome and SCFA in modulation of the allergic response induced by OIT+FOS is however unknown. Aim: To explore potential changes in the microbiota composition and availability of SCFA induced by OIT+FOS and to study epigenetic changes in bone marrow-derived mast cell (BMMC) progenitors. Materials and methods: Female C3H/HeOuJ mice were sensitized to the cow’s milk protein whey and received OIT (10 mg whey, 5x/week for 3 weeks) either or not in combination with a FOS supplemented diet. After three weeks, faecal samples were collected to analyze gut microbiota composition using 16S rRNA sequencing. SCFA concentrations were determined in cecum content. BMMC from treated mice were cultured and expression of the FcεRI and c-Kit receptor was analyzed with flow cytometry. BMMC functionality was assessed using an IgE-mediated degranulation assay. Results: No differences in α-diversity were observed between the groups. FOS supplementation in sensitized mice changed the overall microbial community structure in faecal samples compared to sensitized mice fed the control diet (p=0.03). In contrast, a high level of resemblance in bacterial community structure was observed between the non-sensitized control mice and the OIT+FOS treated mice. OIT mice showed an increased relative abundance of the dysbiosis-associated phylaum Proteobacteria compared to the OIT+FOS mice. FOS supplementation increased the relative abundance of genus Allobaculum (Firmicutes), putative butyrate producing bacteriaknown to produce butyric acid. OIT+FOS reduced the abundances of the genera’s unclassified Rikenellaceae (Bacteroidetes, putative proinflammatory bacteria) and unclassified Clostridiales (Firmicutes) compared to sensitized controls, and increased the abundance of Lactobacillus (Firmicutes, putative beneficial bacteria) compared to FOS. OIT+FOS mice had increased butyric acid and propionic acid concentrations. BMMC cultured from FOS-exposed mice showed reduced FcεRI and c-Kit expression after 6 weeks and degranulation levels were decreased accordingly. Conclusion: OIT+FOS induced a microbial profile closely linked to non-allergic mice and this was accompanied by increased concentrations of butyric acid and propionic acid in cecum content. FOS supplementation increased the butyric acid-producing Allobaculum (phylum Firmicutes) and affected in vitro development of BMMC, suggesting epigenetic changes in mast cell progenitors via bacterial metabolites. Future research should confirm whether there is a causal relationship between microbial modulation and the reduction in allergic symptoms induced by OIT+FOS.