Narrow‐band ultraviolet B therapy attenuates cutaneous T‐cell responses in hapten‐induced, experimental contact dermatitis in beagles

Background In human medicine, narrow‐band ultraviolet B (NB‐UVB) phototherapy has been used to treat various T‐cell‐mediated skin diseases. However, the effect of NB‐UVB on inflamed canine skin remains uncertain. Objectives To investigate the effect of NB‐UVB phototherapy on the skin of dogs with hapten‐induced contact dermatitis. Animals Seven healthy beagles without skin problems. Methods and materials Dogs were irradiated with varying doses of NB‐UVB to determine the minimal erythema dose (MED). After determining the MEDs of six dogs (excluding one of the seven whose skin did not show a visible reaction), we investigated the effect of NB‐UVB on their inflamed skin by topically applying 2,4‐dinitrochlorobenzene (DNCB), which causes type 1 helper T cell (Th1)‐ and cytotoxic T‐cell (Tc)1‐induced skin inflammation. We then irradiated the skin with NB‐UVB. We analysed the treated skin samples via histopathological and immunohistochemical methods, and TdT‐mediated dUTP nick‐end labelling (TUNEL) to demonstrate apoptotic cells. We also analysed the cytokine gene transcription via real‐time quantitative reverse transcription PCR. Results The NB‐UVB MEDs caused mild inflammatory changes yet no severe epidermal exfoliations in the irradiated skin. In DNCB‐treated skin irradiated by the NB‐UVB MEDs, TUNEL‐positive dermal apoptotic cells were increased significantly compared with those of DNCB‐treated, nonirradiated skin. INF‐γ and TNF‐α transcription levels in DNCB‐treated, irradiated skin were significantly lower than those in the DNCB‐treated, nonirradiated skin. Conclusion and clinical relevance Phototherapy using NB‐UVB MEDs attenuated cutaneous Th1 and Tc1 cytokine responses with minimal skin damage in a canine model of hapten‐induced contact dermatitis.