Regulatory T Cells and Histamine in Allergic Contact Dermatitis

Abstract

Regulatory T cells (Tregs) are crucial in preventing excessive immune responses and autoimmunity. Tregs elicit a direct or indirect response on target cells (such as lymphocytes, dendritic cells, monocytes, and mast cells). In allergic contact dermatitis and its animal model contact hypersensitivity, Tregs suppress sensitization and elicitation of delayed-type hypersensitivity responses to allergens. Chronic allergic contact dermatitis (CACD) induced by repeated exposure of the skin to the same allergen bears clinical, histological and immunological similarities with those of atopic dermatitis. Allergic responses of CACD are ameliorated as a result of infiltration of Tregs and elevation of IL-10 and transforming growth factor-beta1 (TGF-β1) levels. In CACD, histamine suppresses Tregs infiltration and IL-10 production by decreasing the TGF-β1 levels through histamine H1 and H4 receptors. As a result, histamine amplifies eczema and maintains allergic reactions in CACD.