CD4 and Allergy: The regulation of oral tolerance versus allergy is mediated in part by antigen-presenting cells, including dendritic cells, monocytes and macrophages, which present food antigens to CD4+ T cells and depending on tissue-specific signals either drive expansion of T-helper type 2 cells and promote IgE-specific B-cell responses (allergy), or expansion of regulatory T cells (tolerance) (Olivera et al., 2021).