Analysis of the transformation of human lymphocytes by Epstein-Barr virus. I. Sequential occurrence from the virus-determined nuclear antigen synthesis, to blastogenesis, to DNA synthesis.
A B-cell population of human cord blood lymphocytes was exposed to the B95-8 strain of Epstein-Barr virus (EBV), and simultaneous observations of immunofluorescence, cellular morphology and autoradiography were carried out in each individual cell. It was evident that EBV-determined nuclear antigen (EBNA) synthesis occurred prior to blastogenic response and DNA synthesis. EBNA-positive cells could be observed as early as 12 h after infection and reached a maximum of 17% at 24 h, followed by a plateau for a subsequent 12 h. The positive cells were seen exclusively as morphologically normal lymphocytes until 18 h; at 24 h, blastogenesis became evident, without cell division. DNA synthesis was detected at 36 h in EBNA-positive blast cells, after which these cells increased rapidly. EBNA synthesis was similarly evident in the presence of cytosine arabinoside, but was significantly inhibited by a short-term exposure to cycloheximide immediately after infection. These findings suggest that the early events in EBV-induced transformation of human lymphocytes occur sequentially from EBNA synthesis, to blastogenesis, to DNA synthesis and that the crucial step of such transformation is probably involved in protein synthesis occurring in the very early stage of EBV infection.