Spontaneous reduction in Epstein-Barr virus (EBV) DNA copy number in EBV-infected epithelial cell lines

We found that spontaneous and 12-0-tetradecanoylphorbol-13-acetate-induced Epstein-Barr virus (EBV) reactivation occurred in short-term (ST)-cultured EBV-infected epithelial cell lines GT38 and GT39 after their establishment; however, it diminished in the long-term (LT)-cultured cells passaged for m ore than 2 years from ST-cultured cells. We hypothesized that the EBV react ivation may be related to the EBV DNA copy number in the cells. A higher le vel of EBV DNA content was detected in ST-cultured cells than in LT-culture d cells by Southern hybridization using an EBV DNA XhoI probe. Fluorescence in situ hybridization using EBV DNA BamHI W fragments showed that ST-cultu red cells contained a higher EBV DNA copy number than that of LT-cultured c ells. EBV DNA-negative cells were detected in small proportions in IT-cultu red cells, but were undetected in ST-cultured cells. These results demonstr ate that EBV genomes are not maintained stably in the cell lines, and some of them are lost in continuous passages of the cells. We discuss the mechan isms of reduction of EBV reactivation and EBV DNA in the cell lines. (C) 20 01 Editions scientifiques et medicales Elsevier SAS.