Diet Components, Immune Function and IgE-Mediated Food Allergy

Food allergies are rising globally, posing a multifactorial public health challenge driven by complex interactions among diet, immune development, and environmental exposures. This review highlights emerging insights into the cellular and molecular mechanisms by which specific dietary components, particularly vitamin A, fibre, indole compounds, and proteins, modulate microbiota-immune crosstalk to promote intestinal homeostasis. These nutrients act through both microbiota-dependent and independent pathways, primarily in the small intestine, enhancing epithelial barrier integrity and supporting tolerogenic immune responses. Two key signalling axes, mediated by retinoic acid (RA) and aryl hydrocarbon receptor (AhR) ligands, converge to regulate RORγt-expressing immune cells, including group 3 innate lymphoid cells, TCRγδ⁺CD8αα⁺ intraepithelial lymphocytes (IELs), and Th17 cells, which are essential for secondary lymphoid organ development and barrier reinforcement. RA and AhR also guide the homing and specialization of diverse regulatory T cell subsets and CD4⁺ IELs, which collectively sustain peripheral tolerance to dietary antigens. Recent findings implicate RORγt⁺ antigen-presenting cells in the induction of peripheral Tregs during early life, particularly at weaning, underscoring a critical window for tolerance establishment. Microbial metabolites and commensal-derived signals further shape these immune pathways, reflecting the intricate interplay between host, diet, and microbiota in the regulation of oral tolerance.