MONOCYTES IN KAPOSIS-SARCOMA LESIONS ARE PRODUCTIVELY INFECTED BY HUMAN-HERPESVIRUS-8

PCR analysis and serological studies demonstrated a close association between Kaposi's sarcoma (KS)associated herpesvirus, or human herpesvi rus 8 (HHV-8), and the development of Kaposi's sarcoma (KS). The major ity of the KS cells were shown to be latently infected by the virus, I n this study we investigated which type of cell is productively infect ed in KS lesions. In situ hybridization was performed with strand-spec ific RNA probes complementary to the sequences coding for the minor ca psid protein (VP23) of HHV-8. The VP23 gene is specifically expressed during the lytic or replicative period of the virus life cycle, and th erefore it is a useful marker to detect productively infected cells. B y in situ hybridization of KS lesions, a strong hybridization signal w as detected only in a small subset of the KS cells of the lesions. Sim ultaneous application of immunohistochemical staining and in situ hybr idization identified the virus-replicating cells to be of monocytic or igin. Productively infected monocytes may be an important reservoir fo r transmission of the virus and for the increase and maintenance of th e high load of HHV-8 generally observed in nodular KS lesions during l ate stages of infection.