T regulatory cells and related immunoregulatory factors in polymorphic light eruption following ultraviolet A1 challenge

BackgroundPolymorphic light eruption (PLE) is considered to be an autoimmune-mediated skin condition in which the normal ultraviolet (UV)-induced local immunosuppression appears to be absent, leading to recognition of photoinduced autoantigens and subsequent inflammation. ObjectivesTo investigate T regulatory cells (Tregs) and related immunoregulatory factors in PLE lesions and controls. MethodsSkin biopsies were performed in 13 patients with UVA1-challenged PLE, 12 female patients with chronic discoid lupus erythematosus (CDLE) and 11 healthy controls who had exposure to UVA1. Immunohistochemistry and four-colour immunofluorescence studies were performed. ResultsPatients with CDLE and UVA1-exposed controls showed significantly decreased epidermal immunoreactivity for CD1a compared with patients with PLE (P=00001). Four-colour immunofluorescence revealed a median percentage of CD4+CD25+FOXP3+ Tregs of 76% (range 37-136%) in PLE, a median of 117% (range 95-139%) in CDLE and a median of 34% (range 0-68%) in controls. Compared with UVA1-exposed controls, PLE and CDLE lesions showed significantly decreased transforming growth factor (TGF)-1 immunoreactivity in the epidermis (P=00003). In PLE lesions, we observed significantly decreased interleukin (IL)-10 expression compared with CDLE (P=0022). In the dermis, receptor activator of nuclear factor-B ligand (RANKL) expression was increased in UVA1-exposed controls compared with PLE and CDLE (P=0018). ConclusionsSimilar to CDLE lesions, UVA1-challenged PLE lesions display an altered immunoregulatory network, as indicated by decreased epidermal or dermal expression of TGF-1, IL-10 and RANKL, and a relatively low number of Tregs, particularly when compared with other inflammatory skin conditions reported in the literature.