Detection of Epstein-Barr virus-infected mucosal lymphocytes in nasal polyps

Primary nasal lymphomas of T or NK cell origin are known to be associated with Epstein-Barr virus (EBV). However, it is not known whether EBV is normally present in nasal mucosa as distinct to nasopharyngeal tissue. This study investigates the prevalence of EBV infection in 13 cases of nasal polyps. EBV DNA was detected in 2 of 13 (15%) by Southern blot hybridization and in 9 of 13 (69%) by polymerase chain reaction. In situ hybridization for EBV-encoded small nuclear RNAs (EBER) was positive in 11 of 13 (85%) cases; the virus was present in stromal lymphocytes only and not in the epithelial cells. Immunohistochemistry for EBV proteins in 7 cases revealed EBV nuclear antigen (EBNA)-2, latent membrane protein (LMP)-1, and ZEBRA (the switch protein encoded by gene BZLF1) expression in rare isolated stromal lymphocytes in 3 cases. Double immunostaining in 1 case showed that the LMP-1+ cells were B or T cells. Immunohistochemistry for EBV lytic proteins showed very rare viral capsid antigen (VCA)+ and membrane antigen (MA)+ cells in 1 case and very rare diffuse early antigen (EA-D)+ and VCA+ cells in 1 other case. The expression of ZEBRA, EA-D, VCA, and MA suggested a disruption of latency in very rare stromal lymphocytes leading to a productive cycle. Although the incidence of EBV positivity in nasal polyps in our population is high (85%), very low numbers of EBV+ cells are found in each case. Nevertheless, they indicate that nasal mucosa could be one of the sites of EBV persistence through a low level of infection of the resident lymphocytes and thereby provide a possible setting for the emergence of virally associated tumors in this site.