Epstein-Barr virus entry and trafficking in epithelial cells and B cells

Epstein-Barr virus (EBV) is a human herpesvirus that is associated with both lymphoid and epithelial malignancies. EBV traffics between B lymphocytes and epithelial cells in the oropharynx. In vitro virus binds via gp350 to CR2 on B cells, entry occurs via endocytosis, fusion is triggered by a gp42/HLA class II interaction and infection is efficient. Virus binds to CR2 on some epithelial cells, but in its absence binds to integrins via gH/gL. Fusion is triggered by the gH/gL:integrin interaction, but integrins do not trigger endocytosis. Instead virus enters directly at the cell surface. Attachment and kinetics of fusion are similar in B cells and epithelial cells, but only virus bound via CR2 infects efficiently.;Initial studies analyzed the differing fate of virus in B cells and epithelial cells. Quantitative PCR indicated that virus internalized into B cells is stable whereas in an epithelial cell virus internalization was efficient but then few copies remained at 4h pi. Leupeptin increased the survival of virus DNA and a PI3K inhibitor increased infection, which is consistent with virus loss to autophagy. Microtubule disruption reduced nuclear transport in both B cells and epithelial cells. Actin inhibitors reduced the amount of virus that entered a B cell. In contrast they increased the amount that entered an epithelial cell, but significantly inhibited intracellular transport in both. Infection of epithelial cells was blocked with inhibitors of a signaling pathway important for actin remodeling and retrograde flow. Our current model is that lateral movement on the cell surface is important for infection.;CR2-negative AGS cells express three populations of virus binding sites. A gH-null virus binds specifically to the lowest avidity sites. Binding shows positive cooperativity and cannot be blocked by an antibody to BMRF2. It suggests that, in the absence of CR2, virus first attaches via low affinity carbohydrate interactions before interacting with integrins. Fusion is decreased when the affinity of the gH/gL:integrin interaction is increased. We hypothesize that attachment via sugars followed by a high affinity gH/gL:integrin interaction reduces the ability of a fusion pore to expand and that the presence of CR2 alleviates this constraint.