Infection of lymphoblastoid cell lines by Kaposi's sarcoma-associated herpesvirus: critical role of cell-associated virus.

Kaposi's sarcoma-associated herpesvirus (KSHV) displays strong lymphotropism in vivo, but paradoxically, established B cell lines have largely been refractory to infection by soluble KSHV virions. Here we show that this block can be overcome by exposure to cell-associated virus. Doxycycline-inducible recombinant KSHV.219 (rKSHV.219)-harboring SLK (iSLK.219) cells were employed as KSHV donors. Cocultivation of lymphoid cell lines with reactivated iSLK.219 cells resulted in readily demonstrable viral entry into each cell line; similar observations were made in primary tonsillar B cell cultures. Moreover, infected lymphoid cells were able to outgrow upon puromycin selection, indicating development of persistent infection. Infected BJAB cells display signatures of latent infection, including classical latency-associated transcripts, a punctate pattern of LANA expression, and episomal maintenance of the KSHV genome. However, when lytically activated by various chemical stimuli, infected BJAB cells were able to produce only low levels of infectious virions. These data demonstrate that (i) cell-associated viruses can bypass viral entry blocks in most lymphoid cell lines, (ii) the determinants of cell-associated virus entry differ from those of soluble virion infection, and (iii) immortalized lymphoblastoid lines have partial postentry blocks to efficient lytic reactivation.