Serological and immunohistochemical detection of human herpesvirus 8 in Kaposi's sarcoma after immunosuppressive therapy for bullous pemphigoid

Kaposi's sarcoma (KS) developed in an 87-year-old human immunodeficiency virus-negative woman from Hokkaido island 4 months after oral administration of prednisolone for the treatment of bullous pemphigoid (BP), and rapidly disseminated to almost the entire body within 2 months. The open reading frame (ORF) 59 and ORF73 proteins encoded by human herpesvirus 8 (HHV-8) were detected immunohistochemically in the nuclei of the tumour cells of KS. The protein coded by ORF73, latent protein, was detected in most of the nuclei of the tumour cells, but only a few tumour nuclei were positive for the ORF59 protein, a lytic protein expressed during active infection. The antibodies against both lytic and latent proteins of HHV-8 were detected retrospectively in the serum 4 months before the appearance of KS and before prednisolone therapy had been started. Immunosuppression associated with the treatment for BP possibly activated latent HHV-8 infection and induced the development of KS.