Monochromatic excimer light (308 nm): an immunohistochemical study of cutaneous T cells and apoptosis-related molecules in psoriasis

BACKGROUND: Various types of UVB radiation source (290-320 nm) are used in treating psoriasis and their therapeutic mechanism has been attributed to immunosuppressive properties. Recently, a new UVB source generated by a 308-nm excimer laser has been introduced for the treatment of psoriasis. OBJECTIVE: In this study we investigated the immunohistochemical evaluation of T cells and the expression of various apoptosis-related molecules in the psoriatic hyperproliferative skin before and after treatment with 308-nm monochromatic excimer light (MEL). METHODS: Ten patients (three women and seven men), ranging in age from 29 to 79 years, affected by plaque-type psoriasis vulgaris, were treated with MEL. Biopsies from psoriatic lesions of MEL-treated sites were taken before, 24 h and/or 48 h after the first irradiation and analysed by the immunophosphatase alkaline technique (APAAP). RESULTS: MEL treatment was found to cause a significant decrease in the rate of proliferation of keratinocytes and a relevant depletion of T cells in all psoriatic lesions, 48 h after the first irradiation: 308 nm light eliminated T cells from the psoriatic epidermis and also from the dermis, highlighting the ability of this UVB source to penetrate the skin compared with normal UVB and establish direct cytotoxic action on T cells infiltrating skin lesions. Rapid clearing of psoriatic lesions involves potential molecular targets of UVB in T cells including p53, which is upregulated after direct irradiation with 308-nm UVB. Moreover, Bcl-2 expression in healing psoriasis epidermis after MEL treatment is significantly decreased compared with untreated skin and the TUNEL (TdT-mediated dUTP-biotin nick end labelling) technique revealed the presence of relevant apoptotic keratinocytes in the irradiated epidermis. CONCLUSIONS: These results indicate that psoriatic skin after monochromatic excimer light therapy is associated with significant T-cell depletion and alterations of apoptosis-related molecules accompanied by a decreased proliferation index and clinical remission.