Background Repeated exposure to allergens induces chronic allergic lesions in the skin and a shift in the cutaneous cytokine milieu to T helper (Th)2. Aim To assess the relationships between Th17 and Th2 response during allergic contact dermatitis (ACD) in mice. Methods ACD was induced in C57BL/6 mice by single or repeated epicutaneous challenge of 2,4,6-trinitro-1-chlorobenzene. Relationships between Th17 and Th2 response were analyzed by immunohistochemical observations and activity of cytokines on days 8 (first challenge), 18 (11th challenge), 28 (21st challenge) and 38 (31st challenge). Results On day 8, tissue levels of interleukin (IL)-17 and IL-22 were high, whereas tissue levels of IL-4 and serum IgE concentration were low. Following acute contact dermatitis, mice developed chronic eczematous lesions on day 18, and gradually improved on days 28 and 38. Tissue IL-4 and serum IgE levels corresponded to the development and improvement of chronic eczematous lesions. Numbers of Th17 cells and tissue levels of IL-17 and IL-22 rapidly decreased as IL-4 and IgE levels increased on day 18. As levels of IL-4 and IgE decreased, the number of Th17 cells and tissue levels of IL-17 and IL-22 increased again on days 28 and 38. On day 18, tissue levels of Th17 response-inducing cytokines (IL-6, IL-23 and transforming growth factor-β) were high, and IL-23-expressing cells appeared in abundance, when Th2 response was extremely high. IL-17 injection decreased tissue IL-4 and serum IgE levels. Conclusions Th17 correlates closely with Th2 in murine chronic ACD induced by repeated epicutaneous challenge.
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