Biological and biochemical observations on isolates of EB virus from the malignant epithelial cells of two nasopharyngeal carcinomas

Foetal, adult seronegative, and cotton‐top marmoset lymphocytes have been transformed into cell lines by EB virus from the malignant epithelial cells of two nasopharyngeal carcinomas. The nature of the cell lines was checked by karyotyping and by light and electron microscopy, and the presence of the EB virus genome was demonstrated by immunofluorescence tests. Immunofluorescence also showed the incidence of EB virus‐producing cells in each line and this was checked by electron microscopy and the use of a lymphocyte transformation assay. Two foetal‐derived lines did not produce virus spontaneously, could not be activated with various inducers, and were found by DNA reassociation kinetics to carry only small numbers of genome copies per cell. An adult‐derived line produced virus, could be activated to produce more, and provided enough infectivity to transform marmoset cells. The resulting marmoset line made profuse transforming virus; it thus provides the first abundant source of NPC‐derived infectious EB virus for comparative studies. The results are discussed in relation to the interactions with comparable target cells of EB virus from normal individuals and from patients with other diseases.