The effect of PUVA on Langerhans cells in rat oral epithelium photosensitized with systemic methoxsalen or topical trioxsalen

Background/purpose: Ultraviolet‐A radiation (UVA) of the oral mucosa after photosensitization with either systemic methoxsalen (8‐MOP) or topical trioxsalen (TMP), i.e. mouth‐PUVA, has been reported to be successful in the treatment of oral lichenoid lesions. In the case of PUVA treatment of skin disorders, local immune suppressive effects have been demonstrated, and the antigen presenting epithelial Langerhans cells (LCs) have been shown to be especially sensitive to ultraviolet treatments. Our aim was to compare the photobiological effects of PUVA in oral mucous membrane (OMM) using topical TMP or systemic 8‐MOP photosensitization. Methods: Rat OMM photosensitized with topical TMP or systemic 8‐MOP was treated with PUVA using UVA doses of 1–8 J/cm2. The LCs were demonstrated in epithelial sheets of the treated OMM with ATPase staining. Results: Both treatments caused a similar, dose‐dependent depletion of ATPase‐positive LCs, with a maximal depletion of 80% or 73% with 8 J/cm2 at 2 days after irradiation as photosensitized with TMP or 8‐MOP, respectively. This contrasts with earlier published findings in human skin, where topical TMP is an order of magnitude greater a sensitizer than 8‐MOP, and PUVA‐induced depletion of LCs occurs maximally 5 days after irradiation. Conclusion: The depletion of LCs of rat OMM after PUVA treatment is greater using topical TMP compared to systemic 8‐MOP, but the difference is significantly smaller than reported earlier in human skin.