The Epstein-Barr virus （EBV）， also called Human herpes virus 4 （HHV-4）， is a virus of the herpes family （which includes Herpes simplex virus and Cytomegalovirus. On infecting the B-lymphocyte， the linear virus genome circularizes and the virus subsequently persists within the cell as an episome. The virus can execute several distinct programs of gene expression which can be broadly categorized as being lytic cycle or latent cycle. The lytic cycle or productive infection results in staged expression of a host of viral proteins with the ultimate objective of producing infectious virions. Formally， this phase of infection does not inevitably lead to lysis of the host cell as EBV virions are produced by budding from the infected cell. The latent cycle （lysogenic） programs are those that do not result in production of virions. A very limited， distinct set of viral proteins are produced during latent cycle infection. These include Epstein-Barr nuclear antigen （EBNA）-1， EBNA-2， EBNA-3A， EBNA-3B， EBNA-3C， EBNA-leader protein （EBNA-LP） and latent membrane proteins （LMP）-1， LMP-2A and LMP-2B and the Epstein-Barr encoded RNAs （EBERs）.
