Patterned entry and egress by Epstein-Barr virus in polarized CR2-positive epithelial cells.

In polarized epithelium direction of viral entry and release correlates with proclivity of a virus to establish local versus systemic infection. The Epstein-Barr virus (EBV), whose principal tissue reservoir is B lymphocytes, also has disease manifestations in epithelium, suggesting intertissue spread potentially influenced by epithelial cell polarity. We stably transfected the B lymphocyte EBV receptor (CR2/CD21) into Madin-Darby canine kidney (MDCK) epithelial cells used extensively to study effects of cell polarity on infection by both DNA and RNA viruses. CR2/CD21 was detected on both apical and basolateral surfaces of polarized MDCK cells, with predominant expression basolaterally. However, infectivity was up to four-fold greater apically, suggesting that endogenous cell surface molecules, sorted asymmetrically onto polarized plasma membranes, may be involved in EBV entry into MDCK cells. EBV gp350/220, a replicative cycle glycoprotein added to the virus envelope on egress through the cell membrane, was immunolocalized by confocal microscopy to basolateral cell surfaces only. Apical entry of EBV with subsequent basolateral release of newly replicated virus favors systemic infection by viral dissemination to underlying lymphocytic aggregations. Under conditions of long-term culture, latent EBV was not stably maintained in these cells, suggesting that the epithelial phase of acute EBV infection may be transient.

Eradication of latent Epstein-Barr virus by hydroxyurea alters the growth-transformed cell phenotype.

The hallmark of infection by human herpesviruses, life-long persistence in the host, is unaffected by current antiviral therapies effective against replication of virus. In vitro studies indicated that low concentrations of the ribonucleotide reductase inhibitor, hydroxyurea, completely eliminated Epstein-Barr virus (EBV) episomes from latently infected Burkitt's lymphoma (BL) cell subsets, providing the first example of chemotherapeutic eradication of a latent herpesvirus from any cell population. Unlike parental EBV-positive BL cells, virus-free cell progeny from one treated cell line no longer exhibited the malignant phenotype in tumorigenicity assays. Hydroxyurea-treated primary B lymphocytes immortalized by EBV ceased to proliferate as episomes were lost. The altered growth phenotype of both BL cells and immortalized primary B cells suggests that latent EBV is an appropriate and accessible therapeutic target for treatment of some EBV-induced lymphoproliferations.