Identification and characterization of Kaposi's sarcoma-associated herpesvirus K8.1 virion glycoprotein

Kaposi's sarcoma-associated herpesvirus (KSHV) has been consistently identi fied in Kaposi's sarcomas (KS), body cavity-based lymphomas (BCBL), and som e forms of Castleman's disease. Previous serological tests with KS patient sera have detected lytic-cycle polypeptides from KSHV-infected BCBL cells. We have found that these polypeptides are predominantly encoded by the K8.1 open reading frame, which is present in the same genomic position as virio n envelope glycoproteins of other gammaherpesviruses. The cDNA of K8.1 from BCBL-1 cells was found to encode a glycosylated protein with an apparent m olecular mass of 37 kDa. K8.1 was found to be expressed during lytic KSHV r eplication in BCBL-1 cells and was localized on the surface of cells and vi rions. The results of immunofluorescence and immunoelectron microscopy sugg est that KSHV acquires K8.1 protein on its virion surface during the proces s of bidding at the plasma cell membrane. When KSHV K8.1 derived from mamma lian cells was used as an antigen in immunoblot tests, antibodies to K8.1 w ere detected in 18 of 20 KS patients and in 0 of 10 KS-negative control sub jects. These results demonstrate that the K8.1 gene encodes a KSHV virion-a ssociated glycoprotein and suggest that antibodies to K8.1 may prove useful as contributory serological markers for infection by KSHV.