Possible involvement of epidermodysplasia verruciformis human papillomaviruses in the immunopathogenesis of psoriasis: a proposed hypothesis

We have shown previously in psoriasis a very high prevalence of epidermodysplasia verruciformis-associated human papillomavirus 5 (EVHPV5) DNA and antibodies to human papillomavirus 5 (HPV5) virus-like particle (VLP)L1, and we suggested that this benign hyperproliferative disorder could be a reservoir for EVHPVs. Here we provide new data confirming the expression of EVHPVs in psoriasis and present our hypothesis on their possible involvement in the immunopathogenesis of the disorder. The new important finding was detection by a radioimmunoprecipitation assay of a very high prevalence of antibodies to E6/E7 HPV5 oncoproteins, known to enhance keratinocyte proliferation. More recently, EV genes were identified, EVER1 and EVER2, whose mutations are responsible for epidermodysplasia verruciformis. Epidermodysplasia verruciformis-associated human papillomaviruses are harmless to the general population as a result of genetic restriction, which in psoriasis appears to be partly alleviated, and this may allow the viral gene expression. We hypothesize that induction of keratinocyte proliferation in psoriasis by various stimuli initiates the EVHPV life cycle with expression of early (E6/E7) and late (L1) viral proteins. The early proteins may, in turn, enhance the keratinocyte proliferation, and the late proteins could serve as a target for specific B- and T-cell-mediated responses. Immune responses against the viral antigens in the epidermis may result in chemoattraction of leukocytes and Munro abscess formation, as well as in production of proinflammatory cytokines, leading to self perpetuation of the psoriatic process. The novel immunomodulatory therapies could also inhibit immune responses against EVHPV proteins, leading to decreased cytokine production, keratinocyte proliferation and EVHPV expression. Thus the beneficial effect of these therapies is not discordant with the proposed hypothesis of possible involvement of EVHPVs in the immunopathogenesis of psoriasis.