Limited transmission of Kaposi's sarcoma-associated herpesvirus in cultured cells

Kaposi's sarcoma-associated herpesvirus (KSHV) (also called human herpesvirus 8) is a novel gammaherpesvirus strongly implicated in the pathogenesis of Kaposi's sarcoma. Although virions can be produced in high yield from latently infected B-cell lines treated with phorbol esters, little is known about the infectivity of such virus, and efficient serial propagation of KSHV has been problematic. Here we report on the infectivity of KSHV produced from phorbol-induced BCBL-1 cells, employing an assay based on the detection of a spliced late mRNA by a sensitive reverse transcriptase PCR (RT-PCR) method. The results of this study confirm previous observations that 293 cells are susceptible to viral infection; however, infection with BCBL-1-derived virus is inefficient and the pattern of viral gene expression in infected cells may not fully reproduce that of authentic lytic infection. In keeping with this finding, serial propagation of BCBL-1-derived virus could not be demonstrated on 293 cells. Eleven of 38 other cell lines tested also supported KSHV infection, as judged by this RT-PCR assay, including cells of B-cell, endothelial, epithelial, and fibroblastic origin; however, in all cases, infection proceeded at or below the levels observed in 293 cells.