Epstein-Barr virus (EBV) receptors were implanted into the membranes of receptor-negative cells, using Sendai virus envelopes as vehicles. The presence of the receptors in the target cell membrane was demonstrated by monitoring the fate of radioiodinated donor membranes. Receptors could be detected for at least 36 hr after implantation. [3HJThymi-dine-labeled EBV bound efficiently to receptor-implanted cells but not to control cells. Binding was inhibited by an excess of nonlabeled virus. Of the [3Hlthymidine-labeled EBV DNA, 50-75% was found inside the receptor-implanted, EBV-exposed cells 24 hr after the infection. The viral genome was functionally active in B lymphocyte-derived cell lines of human, murine, and baboon origin; in T lymphocyte-derived lines of human and murine origin; in mouse fibroblasts; and in freshly explanted mouse lymphocytes, as shown by the expression of EBV-determined nuclear, early, and viral capsid antigens.

The major goal of this investigation was to examine the cytotoxic properties of both HgCl2 and MeHgCl, in terms of their ability to alter human T-cell and monocyte viability. Following treatment with HgCl2 (0-20 micrograms/ml) or MeHgCl (0-2 micrograms/ml), there was minimal reduction in lymphocyte viability at 1-4 hr. However, after exposure to mercury for 24 hr, cell death was apparent. In comparison, monocytes exhibited significant loss of viability during the early exposure periods. MeHgCl was approximately 5-10 times more potent than HgCl2. Other indicators of cell death were also determined. Measurement of the energy charge ratio indicated profound changes in cellular energy conservation. Electron microscopic analysis of cells treated with mercury revealed early nuclear alterations characterized by hyperchromaticity, nuclear fragmentation and condensation of nucleoplasm. In concert with these nuclear changes, there was destruction of cytoplasmic organelles with loss of membrane integrity. Studies of phospholipid synthesis by mercury treated cells confirmed that there were alterations in membrane structure. Thus, there was a decrease in total phosphatide synthesis by treated cells. Moreover, monocyte phospholipid synthesis appeared to be more sensitive to the presence of mercury then lymphocytes. Finally, both forms of mercury caused a rapid and sustained elevation in the intracellular levels of Ca++. These morphological and biochemical changes are consistent with the notion that mercury initiates cytotoxic changes associated with programmed cell death.

Primary cultures of epithelial cells were grown from the tonsils and adenoids of patients with diseases not related to Epstein-Barr virus. The cells could not be infected by Epstein-Barr virus. Fluorescein-labeled Epstein-Barr virus and a cytofluorograph were then used to show that the epithelial cells do not have detectable receptors for the virus. However, implantation with Epstein-Barr virus receptors gave the cells the ability to bind the labeled virus. One to 5 percent of receptor-implanted cells exposed to the transforming B95-8 substrain of the virus expressed Epstein-Barr nuclear antigen. The early and viral capsid Epstein-Barr virus-determined antigens were not detected in the virus-infected cultures. The results show that normal human epithelial cells from the nasopharynx become susceptible to infection by Epstein-Barr virus when the membrane barrier resulting from the lack of viral receptors is overcome by receptor implantation.

SUMMARYEpstein-Barr virus (EBV) was labelled with aH-thymidine and purified about 1000-fold from the culture medium by ultracentrifugation on 5 to 30% dextran gradients. The presence of the virus was monitored by radioactivity and Epstein-Barr virus-determined nuclear antigen (EBNA) induction in sensitive indicator cells (Ramos). Peaks for both activities occurred in the 17 to 18 % dextran fractions. Unlabelled virus recovered in the peak fraction was labelled with 125I. Both thymidine and 12~I-labelled purified virus bound quantitatively to receptor-positive Burkitt lymphoma-derived cell lines but not to EBV-receptor-negative T-lymphocytederived cell lines. Thymidine-labelled virus that was allowed to bind to Raji cells was present in the interior of briefly trypsinized cells after 3 h incubation at 37 °C. The results provide a convenient method for detecting the EBV receptor by radioactively labelled virus.

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