Background: Psoriasis is a common inflammatory skin disease characterized by uncontrolled proliferation of keratinocytes and recruitment of T lymphocytes into the skin. The possible role of human endogenous retroviruses (HERVs) in the induction of psoriasis has been suggested, based upon the previous observations of retrovirus-like particles in psoriasis from skin lesional plaques, urine and stimulated lymphocytes.
Objectives: To investigate the expression of HERV-E transmembrane envelope glycoprotein (HERV-E env) in normal, psoriatic and atopic human skin, and to examine the influence of ultraviolet (UV) B irradiation on HERV-E env expression in normal human epidermal keratinocytes.
Methods: The analysis was performed on both skin biopsies and organotypic skin cultures using immunofluorescence and Western immunoblotting. UVB irradiation (312 nm) of cultured normal human keratinocytes was performed using a dose of 30 mJ cm(-2).
Results: Positive staining was observed in most of the psoriatic and atopic skin samples, whereas only 15% of the normal skin samples were faintly positive. In addition, the pattern of expression of HERV-E env differed markedly in psoriasis vs. atopy. By Western blotting analysis, two main proteins of 54 and 57 kDa were detected in extracts of normal skin, normal keratinocyte cultures and reconstructed epidermis from psoriatic and normal punch biopsies. An increased level of expression of these proteins was noted in extracts from psoriatic vs. normal reconstructed epidermis. The overexpression of the 57-kDa protein in normal human cultured keratinocytes was dramatically reduced by UVB irradiation.
Conclusions: These data suggest for the first time that HERV-E env is expressed in normal and pathological human skin. Further studies are now required to elucidate the role of such viral proteins in the pathogenesis of psoriasis.