Background: Epstein-Barr virus (EBV) is maintained as an episome in most infected cells. The presence of fused terminal restriction enzyme fragments distinguishes the circular DNA form from the linear virion form.
Methods: EBV genomic structure was analyzed in 8 lymphoid cell lines and 21 human lymphoma specimens by the Southern blot technique.
Results: Evidence of viral integration into host chromosomal DNA was identified in four cell lines. In the Namalwa and BL30-B95.8 cell lines, integration occurred through the terminal repeat (TR) sequences. In the BL41-P3HR1 and BL41-B95.8 cell lines, there was loss of left-end viral genomic sequences, including ori-P sequences required for episome maintenance, implying that integration was required for viral genome persistence. Integration was not detected in four other cell lines (Raji, Daudi, B95.8, and BL30-P3HR1). In 21 EBV-containing human lymphomas, including 18 immunodeficiency-related lymphomas, fused TR sequences were identified without evidence of viral genomic integration.
Conclusions: These findings suggest that, although viral integration is common in Burkitt lymphoma cell lines infected in vitro, integration is not common in human lymphomas that develop in vivo in normal or immunodeficient people.