Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterized by pruritus, barrier dysfunction, and complex immune dysregulation. Phototherapy with narrow-band ultraviolet B (NB-UVB) or 308 nm excimer devices is clinically effective for AD, but the underlying mechanisms remain incompletely understood. In this study, we investigated the therapeutic effects of a 308-nm excimer lamp using a murine model of AD induced by topical application of the vitamin D3 analog MC903. C57BL/6 mice were treated with MC903 for 13 consecutive days, with or without irradiation by a 308-nm excimer lamp at 100 mJ/cm2 every other day. Clinical severity was assessed daily, and histological, immunohistochemical, and molecular analyses were performed on lesional skin. Excimer irradiation significantly alleviated MC903-induced dermatitis from days 4 to 12, with reduced clinical severity scores, epidermal thickness, and acanthosis compared with non-irradiated controls. Immunohistochemical analysis revealed a significant decrease in intraepidermal PGP9.5-positive nerve fibers in irradiated mice, suggesting that excimer therapy attenuates pruritus through neuroimmune modulation. Furthermore, excimer irradiation increased dermal infiltration of Foxp3-positive regulatory T cells and decreased plasma IgE levels, although no significant upregulation of IL-10 mRNA was detected. Importantly, quantitative PCR demonstrated that excimer irradiation reduced thymic stromal lymphopoietin (TSLP) expression in lesional skin, while levels of other Th2-related cytokines such as IL-4 and IL-13 remained unchanged. These findings indicate that 308-nm excimer lamp therapy ameliorates AD-like dermatitis through dual mechanisms: suppression of intraepidermal nerve fibers and downregulation of epithelial-derived TSLP, together with enhanced regulatory T-cell infiltration. This study provides new mechanistic insights into the immunological and neurocutaneous effects of excimer phototherapy, supporting its clinical use in AD and potentially other inflammatory skin diseases.
Bastos et al. (Sat,) studied this question.