A new endogenous retroviral sequence is expressed in skin of patients with psoriasis

Background The origin of psoriasis, a chronic inflammatory skin disease involving keratinocyte proliferation, immune disturbances and complex inheritance, remains unknown. Human endogenous retroviruses (HERVs) are part of the normal human genome and their participation in the pathogenesis of various human diseases with complex genetic traits has been proposed. A possible role of HERVs in the induction of psoriasis was suggested many years ago. However, to date no study has searched for HERV expression in psoriasis. Objectives To determine firstly, which HERV families are expressed in the psoriatic lesion and secondly, whether specific variants can be detected. Methods HERV expression was analysed at the mRNA level after degenerated reverse transcription-polymerase chain reaction (RT-PCR) of retroviral pol sequences followed by sequencing. Screening for a specific variant was performed by RT-PCR on lesional and nonlesional psoriatic skin and compared with normal and atopic dermatitis skin. Results We report the expression of three HERV families in psoriatic lesions, namely HERV-W, K and E. We then partially characterized a new endogenous retroviral variant, which was related to the ERV-9/HERV-W family. This sequence contains at least two open reading frames that could encode for a gag protein and a retroviral protease. The expression of this sequence was detected in 29 of 43 lesional psoriasis skin samples and rarely in normal (two of 21) or atopic dermatitis (three of 14) skin samples. Conclusions In psoriatic lesions, HERV sequences of the W, K and E families are expressed and a new variant of the ERV-9/HERV-W family has been characterized. The possible role of HERV-related sequences in the pathogenesis of psoriasis is under investigation.