Roles of Epstein-Barr virus glycoproteins gp350 and gp25 in the infection of human epithelial cells

Epstein-Barr virus (EBV) is associated with various epithelial malignancies such as nasopharyngeal carcinoma and gastric carcinoma, and causes oral hairy leukoplakia, a productive EBV infection of the differentiated epithelium of the tongue. However, it is not clear by what mechanism EBV infects epithelial cells. We generated a recombinant EBV that expresses enhanced green fluorescent protein in order to monitor EBV entrance into epithelial cells quickly and quantitatively. Using this monitoring system, we examined the roles of gp350 and gp25 in EBV infection of epithelial cells by utilizing soluble forms of the gp350 and gp25 proteins. EBV infection of three of four examined epithelial cell lines, 293, NU-GC-3 and Lovo, was almost completely blocked by pretreatment of cells with a soluble form of gp350 (designated gp350lg), and this blockage was dependent on the CD21-binding region of gp350. On the other hand, infection of the other epithelial cell line, AGS, was not inhibited at all by pretreatment with gp350lg. Moreover, we found that a soluble form of gp25 (designated gp25lg) preferentially bound to epithelial cells rather than B cells, and pretreatment of cells with gp25lg substantially blocked EBV infection of some epithelial cells. These results indicate the existence of two distinct pathways in EBV infection of epithelial cells, a gp350-dependent pathway and a gp350-independent pathway, and that gp25 can play a role in the infection of some epithelial cells.