Alteration in Epstein-Barr virus-human lymphoid cell interactions caused by the presence of type-C viral genome

We have recently established a cell line, designated FVNC, by infection of non-EBV-productive human lymphoid NC-37 cells with the type-C virus FLV. The FVNC cell line has been maintained free of detectable EBV- and FLV-related immunofluorescent antigens for three years but both viral genomes exist in the cells in a repressed form. The FVNC cells were morphologically similar to the uninfected NC-37 cells but a D-group chromosome change was consistently seen. The colony-forming capacity of FVNC cells in semi-solid agar medium was about 1/10 of that of NC-37, although the former grew rather faster than the latter in fluid culture. FVNC cells were three times more sensitive to EBV superinfection than NC-37, as shown by immunofluorescence. In addition, an obvious induction of FLV antigenic markers occurred in FVNC cells on exposure to EBV. Nucleic acid hybridization experiments showed a striking decrease in the number of EBV genomes in FVNC cells. The number of genomes was too small to be measured, but EBNA was clearly present in all FVNC cells as well as in NC-37 cells. The implications of these findings were discussed from the point of view of a possible co-carcinogenesis in man by EBV and the type-C virus.