The skin as an immune organ: Tolerance versus effector responses and applications to food allergy and hypersensitivity reactions.

Skin is replete with immunocompetent cells that modulate signaling pathways to maintain a salubrious immunogenic/tolerogenic balance. This fertile immune environment plays a significant role in the development of allergic responses and sensitivities, but the mechanisms underlying these pathways have been underappreciated and underused with respect to developing therapeutics. Among the complex repertoire of cells that promote tolerogenic pathways in the periphery, 2 key classes include dendritic cells and regulatory T (Treg) cells. Immature dendritic cells are the first line of defense, patrolling the periphery, sampling antigens, and secreting cytokines that suppress immune cells and promote the survival of Treg cells. Skin-homing Treg cells also play a critical role in mitigating the reactivity of immune cells, secreting high levels of cytokines that promote tolerance. Therapeutic approaches that capitalize on our knowledge of the rich cellular and molecular environment are emerging and show great promise. We will discuss the advantages and challenges of 5 such strategies and how these therapies might mitigate the atopic march by facilitating tolerance. We conclude that skin is a multifaceted structure that provides a fertile ground for therapeutic discovery. Accordingly, ongoing work in this domain will no doubt continue to deliver exciting progress for improved health outcomes.