The relationship between allergen-induced tissue eosinophilia and markers of repair and remodeling in human atopic skin

Several in vitro studies suggest that eosinophils may play a role in fibrosis, remodeling, and repair processes associated with IgE-mediated hypersensitivity. However, the relationship in vivo, between allergen-induced tissue eosinophilia and markers of repair has yet to be established in human atopic subjects. Using the allergen-induced cutaneous late-phase reaction as a model of allergic inflammation, we have tested the hypothesis that eosinophil-derived TGF-β1 and IL-13 are temporarily associated with myofibroblast formation and deposition of tenascin and procollagen 1. Biopsies were taken from atopic volunteers at 1, 3, 6, 24, 48, and 72 h after intradermal allergen challenge and were examined by immunohistochemistry. Following the peak of the late-phase reaction (6 h) there were persisting TGF-β1 eosinophils, α-smooth muscle actin⁺ myofibroblasts, tenascin immunoreactivity, and procollagen-I⁺ cells 24-48 h postchallenge. Direct evidence of generation of repair markers was obtained by coculture of eosinophils and fibroblasts. This resulted in α-smooth muscle actin immunoreactivity that was inhibitable by neutralizing Abs to TGF-β as well as production of tenascin transcripts and protein product. TGF-β1 and IL-13 also induced tenascin expression. We conclude that TGF-β1 and IL-13, provided partially by eosinophils, contribute to repair and remodeling events in allergic inflammation in human atopic skin.