Butyrate and fructo-oligosaccharides support oral immunotherapy by suppressing basophil and mast cell activation and induce possible epigenetic changes in mast cell progenitors

Background: In previous work, we showed that a fructo-oligosac-charide (FOS) supplemented diet enhanced oral immunotherapy (OIT) efficacy in a mouse model for cow's milk allergy, which led to reduced mast cell activation upon allergen challenge. Fermentation of FOS by intestinal bacteria leads to production of short-chain fatty acids (SCFA, e.g. butyrate). Increased levels of butyrate were found in the caecum of OIT+FOS mice. The exact contribution of FOS and/or butyrate in dampening the allergic response is however unknown. Objective: Investigating the effect of combining OIT with butyrate or FOS supplementation on the development and IgE-mediated activation of mast cells and basophils. Method: C3H/HeOuJ mice were sensitized to the cow's milk protein whey and subjected to OIT with or without FOS or butyrate supplementation. Bone marrow was collected during and after OIT and cultured with IL-3 and SCF into bone marrow-derived mast cells (BMMC). c-Kit and FcϵRI expression on BMMC was analyzed using flow cytometry and IgE-mediated degranulation was determined by measuring β-hexosaminidase. After OIT, whole blood samples were used to perform a Basophil Activation Test (BAT) and intradermal (i.d.) and intragastric (i.g.) challenges were conducted to measure the acute allergic skin response (delta ear swelling) and mucosal mast cell degranulation (mMCP-1 in serum). After challenge, caecum content was collected to measure SCFA levels. Results: BMMC developed from bone marrow of FOS exposed mice showed reduced expression of c-Kit and FcϵRI and IgE-mediated activation was also reduced. Allergen-induced basophil activation was reduced in OIT+butyrate blood samples compared to OIT samples. These findings were in accordance with the observed reduction in the acute allergic skin response and the reduction in mast cell degranulation in OIT+FOS and OIT+butyrate mice compared to sensitized controls. A significant increase in butyrate in the caecum content was observed in OIT+FOS mice compared to sensi-tized controls and OIT mice. Conclusion: FOS and butyrate either or not combined with OIT have profound inhibitory effects on allergic effector cells like mast cells and basophils. These inhibitory effects may partly be explained by the induction of epigenetic changes, because in vitro development of mast cells from bone marrow progenitors is affected. Further research is needed to investigate if this approach may improve treatment strategies for food allergies in the future.