In order to examine critically the closeness of association between Epstein-Barr virus (EBV) DNA and nasopharyngeal carcinoma (NPC) a correlated histopathological and nucleic acid hybridization study was performed on 51 undifferentiated NPC, 4 NPC with some signs of squamous differentiation, 7 nasophayngeal tumors of other histological types and 14 head and neck carcinomas located outside the nasopharynx. All 51 undifferentiated NPCs contained significant numbers of EBV-genome copies per cell. Two of the somewhat differentiated NPCs were also EBV-DNA-positive, whereas 2 were negative. Of the 7 other nasopharyngeal tumors, 1 was EBV-DNA-positive. Histological examination, however, showed that this was a typical Burkitt lymphoma. The other 6 tumors were all EBV-DNA-negative lymphoproliferative malignancies. All 14 had head and neck carcinomas located outside the nasopharynx were EBV-DNA-negative. The sera of undifferentiated NPC patients had elevated antibody titers against the EBV-determined antigens, the EA (D) componet in particular. These findings confirm that there is a regular association between EBV-DNA and undifferentiated NPC.

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Most human lymphoid cell lines contain multiple copies of circular, nonintegrated Epstein-Barr virus (EBV) DNA molecules as well as viral DNA sequences with properties of integrated DNA. The physical state of the EBV DNA in a human lymphoma line that only contains one virus genome equivalent per cell has now been studied by three different methods, neutral CsCl density gradient centrifugation, actinomycin D-CsCl gradient centrifugation, and Hirt fractionation. This cell line, AW-Ramos, has been obtained by EBV infection in vitro of the apparently EBV-negative Ramos lymphoma line. The results indicate that the EBV DNA in AW-Ramos is present exclusively in a linearly integrated form. Similar data were obtained with two other EBV-converted sublines of Ramos cells.

Burkitt's lymphoma (BL) has been widely investigated and has attracted attention because of the possible etiologic role of the Epstein-Barr virus (EBV). To further determine the role of EBV in the causation of this tumor, we measured EBV-specific nuclear antigen (EBNA) and EBV DNA using immunofluorescence and nucleic acid hybridization techniques, respectively. Of 34 BL biopsies, 27 tissues (79%) were EBNA-positive, whereas none of the 25 non-BL biopsy tissues were EBNA-positive. Of 15 BL tumors tested, 14 (93%) were EBV DNA-positive with a mean of 39 (range, 8-86) EBV genome equivalents per cell. Each of the 15 non-BL biopsy specimens subjected to nucleic acid hybridization had less than two virus genome equivalents per cell, although all had serologic evidence of past EBV infection. The findings further supported the possible etiologic role of EBV in African BL and negated the passenger hypothesis. The EBV genome could, therefore, be used as a separating marker between African BL and non-BL lymphomas.

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