<P> To enter B cells, viral glycoprotein gp350 binds to cellular receptor CD21 (also known as CR2). Then, viral glycoprotein gp42 interacts with cellular MHC class II molecules . This triggers fusion of the viral envelope with the cell membrane, allowing EBV to enter the B cell . Human CD35, also known as complement receptor 1 (CR1), is an additional attachment factor for gp350 / 220, and can provide a route for entry of EBV into CD21 - negative cells, including immature B - cells . EBV infection downregulates expression of CD35 . </P> <P> To enter epithelial cells, viral protein BMRF - 2 interacts with cellular β1 integrins . Then, viral protein gH / gL interacts with cellular αvβ6 / αvβ8 integrins . This triggers fusion of the viral envelope with the epithelial cell membrane, allowing EBV to enter the epithelial cell . Unlike B cell entry, epithelial cell entry is actually impeded by viral glycoprotein gp42 . </P> <P> Once EBV enters the cell, the viral capsid dissolves and the viral genome is transported to the cell nucleus . </P> <P> The lytic cycle, or productive infection, results in the production of infectious virions . EBV can undergo lytic replication in both B cells and epithelial cells . In B cells, lytic replication normally only takes place after reactivation from latency . In epithelial cells, lytic replication often directly follows viral entry . </P>

Where does the epstein barr virus come from