Histamine suppresses regulatory T cells mediated by TGF‐β in murine chronic allergic contact dermatitis

Regulatory T cells (Tregs) suppress effector T cells and ameliorate contact hypersensitivity (CH); however, the role of Tregs in chronic allergic contact dermatitis (CACD) has not been assessed. Repeated elicitation of CH has been used to produce CACD models in mice. We previously showed that the presence of histamine facilitates the creation of eczematous lesions in this model using histidine decarboxylase (HDC) (?/?) mice. Therefore, the effects of histamine on Tregs in the CACD model were investigated in this study. CACD was developed by repeated epicutaneous application of 2, 4, 6‐trinitro‐1‐chlorobenzene (TNCB) on HDC (+/+) and HDC (?/?) murine skin to assess the effects of histamine in CACD. Histamine aggravated CACD in the murine model and suppressed the number of Tregs in the skin. Histamine also suppressed the level of TGF‐β1 in this model. Recombinant TGF‐β1 or anti‐TGF‐β1 antibody was injected into the dorsal dermis of HDC (+/+) mice daily just before TNCB challenge to determine the effects of histamine‐regulated TGF‐β on the Treg population in CACD. Recombinant TGF‐β1 injection promoted the infiltration of Tregs in the skin and the production of IL‐10; however, anti‐TGF‐β1 antibody injection suppressed the number of Tregs in the skin and the production of IL‐10. Histamine suppresses the number of Tregs in CACD, and this effect is mediated by TGF‐β.