Levels of Epstein-Barr virus DNA in lymphoblastoid cell lines are correlated with frequencies of spontaneous lytic growth but not with levels of expression of EBNA-1, EBNA-2, or latent membrane protein

The process of Epstein-Barr virus (EBV)-induced transformation of human B lymphocytes results in a cell line that is a mixture of latently and lytically infected cells, with the lytic cells composing roughly 5% to less than 0.0001% of the overall population. A set of nine normal lymphoblastoid cell lines that span a 100- to 200-fold range in average EBV DNA content were studied, and the frequency with which these cells entered a lytic phase of viral growth correlated with their EBV DNA copy number (as a population average). However, neither factor correlated with the levels of expression of transcript for the viral genes EBNA-1, EBNA-2, and latent membrane protein, nor did they correlate with the levels of EBNA-2 protein and latent membrane protein. The rate at which a cell line enters into lytic growth spontaneously is therefore not dependent on the overall steady-state levels of expression of these latent-phase genes.