Infection of human B lymphocytes with high multiplicities of Epstein-Barr virus: Kinetics of EBNA expression, cellular DNA synthesis, and mitosis

Abstract

We studied the time course of early events during the transformation of human B lymphocytes by Epstein-Barr virus (EBV). EBV nuclear antigen (EBNA) was first detectable 6–8 hr after infection in 1–10% of the cells. Even though cells were exposed to virus under conditions which would maximize the chances of synchronous infection, the proportion of EBNA (+) cells increased until 32–36 hr when a maximum level was reached. DNA synthesis in infected cultures increased above control levels between 20 and 36 hr after exposure to virus and thereafter increased progressively. The first cell divisions observed in EBNA (+) cells occurred between 36 and 48 hr after infection and the mitotic index of EBNA (+) cells increased with time reaching 25% of the EBNA (+) cells by 96 hr. However, the total cell number and the percentage of EBNA (+) cells remained unchanged after 36 hr, suggesting that the rate of cell death in EBNA (+) cells was equivalent to the rate of proliferation. Adenine arabinoside (Ara A) and cytosine arabinoside (Ara C), at concentrations which inhibit VCA expression in EBV producer cell lines, did not affect EBNA expression during the first 24 hr after infection. These data together with the very early appearance of EBNA after inoculation show that EBNA synthesis is independent of viral or cellular DNA synthesis and support the hypothesis that synthesis of EBNA is one of the crucial earliest events in lymphocyte transformation by EBV.