Development of equine herpesvirus 1 persistently infected human lymphoblastoid cells expressing latency-associated transcripts

Equid herpesvirus 1 (EHV1) is one of the most important equine viral pathogens causing respiratory disease in young animals, late-term abortions, neonatal foal mortality and myeloencephalopathy. Following acute infection, recovered animals develop life-long latent infection, with periodic reactivation. Latency is detected by demonstration of latency-associated transcripts (LATs) in selected tissues by PCR-based assays. EHV1 produces productive lytic infection in available susceptible cell culture systems within 1 week of infection and no in vitro model for studying the mechanism of EHV1 persistence, latency and reactivation is available. The objective of the present study was to establish persistently infected cells and to see whether these cells express LATs. Epstein-Barr Virus (EBV)-transformed human lymphoblastoid cells (LCs) were infected with EHV1 and observed for 120 days. Infectious extracellular and intracellular EHV1 was detected in LCs with mean titres of 10^4.35±0.09/ml and 10^1.78±0.12/ml, respectively, at 8, 30 and 120 days post-infection. Virus in infected LCs was also demonstrated by immunofluorescence and nested PCR. LATs corresponding to ORF64 in EHV1-infected LCs were detected from day 16 to day 120 post-infection by nested PCR and quantitative PCR. This is the first report of expression of LAT in EHV1 persistently infected LCs. These persistently infected cells may serve as model for understanding EHV1-associated latency.