Cellular Pathways Leading to Patterns of Lytic Epstein-Barr Virus Reactivation in Immortalized B Cell Lines

Lymphoblastoid cell lines (LCLs) are created by culturing lymphocytes from the peripheral blood and adding Epstein-Barr virus (EBV), a ubiquitous human herpesvirus which infects, activates, and transforms B cells. These cell lines are used for genotyping, as targets for cytotoxic cells, and as models for EBV immortalization of B cells, particularly post-transplant lymphoproliferative disease (PTLD) in which EBV-immortalized cells proliferate in the absence of a cytotoxic T-cell response. Studies have shown more diversity in LCLs than would be expected from cell lines that are often treated as interchangeable. It is not known how their diversity in factors like morphology, growth factor production, or cellular gene expression influences the EBV life cycle. In this study I investigated connections between LCLs' cellular and viral phenotypes, categorizing them as either low in EBV copy number or fluctuating within a high range. As measured by lytic EBV replication and viral gene expression, LCLs showed high or low lytic permissivity, with permissivity defined as the likelihood that a cell will switch from stable latent infection into the lytic EBV life cycle. Permissivity was not affected by blocking the late events of the lytic cycle. I used flow cytometry to characterize 19 aspects of LCL surface phenotype, but found little association with lytic permissivity. Microarrays and PCR were used to identify genes expressed at higher levels in non-permissive LCLs, including transcription factors that maintain B cell lineage. Unfolded protein response (UPR) genes and the UPR protein Grp94 were expressed at higher levels in permissive LCLs. A drug was used to investigate effects of the UPR on permissive and non-permissive LCLs that had been maintained for short or long periods of time. The UPR enhanced permissivity, causing more cells to enter the lytic cycle, but this did not lead to lytic replication. This study enhances our knowledge about EBV life cycles by giving us new information about host factors that contribute to the lytic switch. This data about LCL diversity has public health relevance to the diversity of PTLD cases, since identifying risk factors for PTLD is a significant part of care for EBV-positive transplant recipients