Epstein-Barr virus replicative gene transcription during de novo infection of human thymocytes: simultaneous early expression of BZLF-1 and its repressor RAZ.

Epstein-Barr virus (EBV) is known to infect B cells and epithelial cells. We and others have shown that EBV can also infect a subset of thymocytes. Infection of thymocytes was accompanied by the appearance of linear EBV genome within 8 hr of infection. Circularization of the EBV genome was not detected. This is in contrast to the infection in B cells where the genome can circularize within 24 hr of infection. The appearance of the BamHI ZLF-1 gene product, ZEBRA, by RT-PCR, was observed within 8 hr of infection. The appearance of a novel fusion transcript (RAZ), which comprised regions of the BZLF-1 locus and the adjacent BRLF-1 locus, was detected by RT-PCR. ZEBRA protein was also identified in infected thymocytes by immunoprecipitation. In addition, we demonstrated that the EBNA-1 gene in infected thymocytes was transcribed from the Fp promoter, rather than from the Cp/Wp promoter which is used in latently infected B cells. Transcripts encoding gp350/220, the major coat protein of EBV, were identified, but we did not find any evidence of transcription from the LMP-2A or EBER-1 loci in infected thymocytes. These observations suggest that de novo EBV infection of thymocytes differs from infection of B cells. The main difference is that with thymocytes, no evidence could be found that the virus ever circularizes. Rather, EBV remains in a linear configuration from which replicative genes are transcribed.