Epstein-Barr virus exploits host endocytic machinery for cell-to-cell viral transmission rather than a virological synapse.

Epstein-Barr virus (EBV) establishes a lifelong latent infection in B lymphocytes and often is found in epithelial cells. Several lines of evidence indicate that viral transmission mediated by cell-to-cell contact is the dominant mode of infection by EBV for epithelial cells. However, its detailed molecular mechanism has not been fully elucidated. We investigated the role of host membrane trafficking machinery in this process. We have found that adhesion molecules critical for this process are expressed in EBV-positive and -negative Burkitt's lymphoma (BL) cells and multiple epithelial cell lines. Treatment with blocking antibodies against β1 and β2 integrin families and their ligands suppressed EBV transmission in a dose-dependent manner. We also confirmed that adhesion molecules are upregulated in co-cultured BL cells. Immunofluorescence staining revealed that the intracellular adhesion molecule 1 (ICAM-1) distributed to the cell surface and partially co-localized with recycling endosomes in co-cultured BL cells. Moreover, cell-to-cell EBV transmission was inhibited upon blocking endocytic recycling by expression of a dominant-negative form of a small GTPase Rab11 or by knockdown of Rab11, supporting the notion that the endocytic pathway-dependent trafficking of ICAM-1 to the cell surface of BL cells contributes to viral transmission by stabilizing cell-to-cell contact between the donor cells and recipient cells. Finally, we demonstrated that co-cultivation upregulated clathrin-mediated endocytosis in the recipient cells, allowing EBV to be internalized. Taken together, our findings demonstrate that EBV exploits host endocytic machinery in both donor and recipient cells, a process which is facilitated by cell-to-cell contact, thereby promoting successful viral transmission.