Relationship between amount of Epstein–Barr virus-determined nuclear antigen per cell and number of EBV–DNA copies per cell

Abstract

EPSTEIN–BARR virus-determined nuclear antigen (EBNA) can be detected in all EBV–DNA-carrying cells1,2. This includes Burkitt's lymphoma (BL) and nasopharyngeal carcinoma (NPC) tumour biopsy cells and EBV-carrying lymphoid lines1–5. Of the known EBV-associated antigens only EBNA is regularly associated with the presence of viral genetic material, no matter whether the cell line produces virus or not6,7. The composition and function of EBNA are largely unknown. Some recent reports suggest that EBNA is a protein that binds to DNA in vitro8,9 and is associated with chromosomes in vivo at least in part1. EBNA might be a virally determined or virally altered chromosomal protein of the non-histone type9. It is tempting to speculate that EBNA has a role in EBV-induced cell transformation (“immortalisation”10) and/or in the control of viral gene expression. There is a wide variation in the average number of EBV genome equivalents between different EBV–DNA-carrying cell lines. In virus non-producer cell lines this number is a better approximation of the true EBV genome number for individual cells than in virus producer lines, and is relatively stable over long periods of serial passage11. The EBNA content of EBV-containing cell lines also seems to vary between different cell lines, as judged visually in the fluorescence microscope. We have measured the amount of EBNA per cell, by quantitative immunofluorimetry in different cell lines, in parallel with determining the average number of EBV–DNA copies, and established a correlation between these two parameters.