Characterization of a 2,4-dinitrochlorobenzene-induced chronic dermatitis model in rats.

Although many mouse models of atopic dermatitis have been reported, few rat models have been studied. In this study, a rat chronic allergic dermatitis model was developed and evaluated as a pharmacological model of atopic dermatitis. Prominent ear thickening and scratching were induced after the application of 2,4-dinitrochlorobenzene to the right ear of Brown Norway rats 3 times per week for 3 weeks. Histopathologically, infiltration of T cells in the ear was observed on day 7, and eosinophils and mast cells were found in addition to T cells on day 21. The expression of interferon-gamma and interleukin-4 was increased on day 7 when compared with normal rats. However, interferon-gamma expression had disappeared by day 21. Tacrolimus ointment applied after ear tissue thickening fully developed, suppressed chronic dermatitis in a dose-dependent manner. This model has some symptomatic and histopathological similarities to atopic dermatitis and might be useful in pharmacological studies.