T lymphocytes in food allergy: Overview of an intricate network of circulating and organ-resident cells

Although food hypersensitivity might be divided in IgE- and non-IgE mediated food allergy, there is a large body of evidence implicating T lymphocytes overall in the pathogenesis of food allergy. Priming of naive T cells will occur mainly in Peyer's patches (PP), where surface receptors (l-selectin, CCR7 and CXCR4) will help to initiate diapedesis of the cells to the submucosa. Various antigen-presenting cells (e.g. dendritic cells, M cells) will present food antigen-derived epitopes and initiate either non-responsiveness, or a food-mediated immune response. Food-specific memory T cells express various surface receptors such as the alpha4beta7-integrin, or the cutaneous lymphocyte antigen. It is speculated, that they might also express specific chemokine receptors (CCR4, CCR7 or CCR9). Organ-specific homing will be facilitated through the corresponding receptors (i.e. MAdCAM-1 in the gut, VCAM-1 or fibronectin in other mucosal organs, or E-selectin in the skin). Locally secreted chemokines might help to attract T cells through their corresponding chemokine receptors. Finally, potential T-cell directed therapeutic interventions (peptide-derived immunotherapy, DNA vaccination, or strategies preventing T cells from trafficking to target organs) are discussed.