Characterization of Kaposi sarcoma-associated herpesvirus/human herpesvirus-8 infection of human vascular endothelial cells: early events.

Kaposi sarcoma–associated herpesvirus (KSHV)/human herpesvirus-8 (HHV-8) is causally associated with Kaposi sarcoma (KS). The absence of a cell culture system that effectively reproduces the composite mechanisms governing initiation and maintenance of HHV-8 infection (lytic and latent) in KS endothelial cells, however, has left important questions unanswered. Here, we report a culture system in which the earliest events that accompany HHV-8 infection could be surveyed in primary endothelial cells. Binding of HHV-8 to microvascular dermal endothelial cells (MVDECs) was directly compared with other primary target cells implicated in HHV-8–associated diseases. Virus attachment, fusion, internalization and transport within MVDECs was monitored by electron microscopy. Studies of genome configuration revealed that rapid circularization of the viral DNA occurred on entry, though by 72 hours after infection linear DNAs accumulated and early as well as late lytic RNAs (T1.1, K8.1) could be detected. The latency transcripts (LT1/LT2) were first detected on day 8, demonstrating that both lytic and latent infection were initiated. Although most lytic transcripts accrued until passage, open-reading frame–74 RNAs fluctuated with a fixed periodicity, suggesting that early replication after infection of MVDECs was synchronous.