Early events in transformation of human cord leukobytes by Epstain-Barr virus: induction of DNA synthesis, mitosis and the virus-associated nuclear antigen synthesis

The present investigations were undertaken to establish the early events in EBV-induced transformation of human cord lymphocytes with particular reference to the induction of DNA synthesis, mitosis and viral synthesis. When cord leukocytes were exposed to a 3 h pulse of²H-TdR at 3 h intervals following EBV infection and examined by autoradiography, blastoid cells with labelled nuclei appeared 12-24 h after virus exposure, reaching a maximum of 7.5% in 15 h. When the infected leukocytes were reincubated after each pulse for an additional 20-40 h with colchicine added 10 h prior to termination of incubation, 18% of the positive cells were in mitosis. The cells were examined by immunofluorescence for the synthesis of EBV-associated antigens. Early antigen (EA)—and viral capsid antigen (VCA)—were not detected, but EBV-associated nuclear antigen (EBNA) synthesis became evident as early as 2 days after infection. The frequency of EBNA-positive cells, mostly blastoid cells, increased with continued incubation, and at 10 days the majority of the cells were positive. These findings strongly suggest that the human cord leukocytes are non-permissive for replication of EBV, and that the virus can induce in them early DNA synthesis followed by high-frequency mitosis and cell proliferation, in close association of the viral genome with the host-cell genome as shown by the synthesis of EBV-specific “footprint”.