A STRATEGY FOR PRECISION OF GENOTYPING OF EPSTEIN-BARR-VIRUS BY POLYMERASE CHAIN-REACTION - APPLICATION FOR STUDYING HODGKINS LYMPHOMA

Previous studies on the genotyping of Epstein-Barr virus (EBV) have been based on the analysis of a single gene locus. The assignment of genotype of an isolate could easily be overlooked with this assay. Our strategy for precision of EBV genotyping has exploited the existence of two families of EBV strains (type A and B) that can be distinguished at three divergent gene loci (EBNA-2, EBNA-3C, and EBER). To precisely determine the genotype of EBV in Hodgkin's disease (HD), we designed primers and simultaneously analysed these three gene loci that distinguish type A and B viruses by the polymerase chain reaction (PCR) technique. The primers designed to amplify these three gene loci encompass either type-specific deletion sequences (EBNA-2 and EBNA-3C) or type-specific point mutations (EBER) that identify the virus strain based on the sizes of PCR-amplified products or the mobility shifts in single-strand conformation polymorphism (SSCP) analysis. The locations of point mutations were identified by direct sequencing of the PCR-amplified DNA. Fifteen EBV-infected cell lines were analysed and a good correlation between EBNA-2 and EBNA-3C typing results was found. In contrast, approximately 33% of the cell lines analysed maintained type A sequences in EBNA-2 and EBNA-3C genes while carrying type B sequences in the EBER region. Data obtained from analysis of cell lines served as a reference for studying HD samples. EBV DNA was detected in about 70% of HD. Among the EBV-positive samples, 56% were associated with type A virus, 13% with type B, and 31% with dual viral sequences. Thus, type A virus is predominant in HD. Based on the histology, the frequencies of EBV positivity were 83%, 71%, and 33% for mixed cellularity, nodular sclerosis and lymphocyte predominance, respectively. The detection of high frequency of both type A and B sequences in HD may provide a lead in investigating the role of dual viral infection in EBV pathogenesis.