The expression of the Epstein-Barr virus nuclear antigen (EBNA-1) in oral hairy leukoplakia

Oral hairy leukoplakia (OHL) is characterised by the presence of a replicative Epstein-Barr virus (EBV) in the superficial layers of the epithelium. There is some doubt, however, whether this reflects activation of a latent infection of the basal epithelial cells. EBV latency is associated with the expression of the viral gene product EBNA-1 and the aim of this study was to investigate EBNA-1 expression in OHL. METHODS: 22 biopsies of clinically suspicious OHL and three cases of normal mucosa were available as fresh frozen or paraffin embedded material-1 was detected immunocytochemically using a rat monoclonal antibody (IH4-I) following microwave irradiation. Lytic EBV infection was confirmed by the identification of the BZLF-1 protein. RESULTS: 16 of the 22 cases displayed focal replicative EBV meeting the criteria for OHL, and in 13 of these, EBNA- 1 expression was restricted to the nuclei of epithelial cells in the upper layers of the epithelium. EBNA-1 expression was absent from the basal cells in all cases and in the nine BZLF-1 negative mucosal biopsies. CONCLUSION: These findings suggest that lytic EBV infection in OHL is not the result of activation of a latent infection of basal cells and suggests a role for EBNA- 1, not only in latent EBV infection, but also in virus replication.