Analysis of Viral Gene Expression and Genome Persistence in CD23-Positive and -Negative Subpopulations of Epstein-Barr-Virus-lnfected BL2 Cells

Abstract

Epstein-Barr virus (EBV) infection of the EBV-negative Burkitt lymphoma (BL) cell line BL2 has been studied in vitro, to assess the efficiency of stable infection and the state of the viral genome in these cells. Expression of the EBV nuclear antigen complex (EBNA 1-6) was detected by 24 h post-infection, but expression of the latent membrane protein (LMP) and of the B cell activation antigen CD23 were delayed until 8 days post-infection, and were then only detectable in a subpopulation of EBNA-positive cells. Separation of cells into CD23-positive and -negative fractions 8 days after infection showed that the CD23-positive cells expressed EBNA 1-6 and LMP and contained viral episomes, whereas the CD23-negative cells were EBNA 1-6 positive, LMP negative and had very low levels of episomal viral genome. Cloning of the CD23-positive and -negative populations showed that EBV infection in the majority of clones was lost, with only 29 out of the 164 investigated still EBNA positive after 6 months of culture. Stable infection correlated with expression of EBNA 1-6, LMP, CD23 and the presence of viral episomes. One clone stably expressed EBNA 1-6 and LMP in the absence of detectable linear or episomal viral genome; this clone was assumed to have a viral genome integrated into the cellular chromosomes. Thus integration of the viral genome following in vitro infection of BL2 cells is a rare event.