EVIDENCE FOR LYTIC INFECTION BY EPSTEIN-BARR-VIRUS IN MUCOSAL LYMPHOCYTES INSTEAD OF NASOPHARYNGEAL EPITHELIAL-CELLS IN NORMAL INDIVIDUALS

Normal nasopharyngeal tissues from 23 individuals who died of causes u nrelated to the upper respiratory system and had no evidence of Epstei n-Barr virus (EBV)-related diseases were studied using in situ hybridi sation (ISH) and immunohistochemistry for the detection of EBV RNA and expression of EBV proteins, respectively. ISH using S-35-labelled rib oprobe for EBV EBER RNA showed occasional to a few EBER+ lymphocytes i n the stroma of nasopharyngeal mucosa in 14/16 cases with available pa raffin-embedded tissues. In addition, very rare intraepithelial EBERlymphocytes were also detected in 3/16 cases. However, in none of thes e cases was EBER detected in the epithelial cells. Similar results wer e obtained using a nonradioactive ISH method for EBER (Dako). In 3/23 cases, immunostaining using monoclonal antibodies for EBV proteins on cryostat sections showed occasional cells in the stroma expressing EBV nuclear antigen 2 (EBNA2), latent membrane protein-1 (LMP), and switc h protein encoded by BZLF1 gene (ZEBRA) in two cases and only Very rar e LMP+ and ZEBRA+ cells in one other case. Double immunostaining combi ning alkaline phosphatase anti-alkaline phosphatase (APAAP) for CD mar kers and indirect immunofluorescence for LMP showed that the LMP+ cell s were either CD19+ or less frequently CD3+, but none were CD68+. Thes e results show that both B and T lymphocytes harbouring EBV can be fou nd in the normal nasopharyngeal tissues. Interestingly, EBV proteins a ssociated with lytic viral replication-diffuse early antigen (EA-D), v iral capsid antigen (VCA), or membrane antigen (MA)-were also detected in rare cells in the stroma in one case, and in another case only one MA+ cell was detected. These results provide evidence for a lytic typ e of infection by EBV in the normal nasopharynx involving a very small proportion of stromal lymphocytes and support the view that nasophary ngeal lymphocytes can act as a reservoir for EBV in normal individuals . (C) 1995 Wiley-Liss, Inc.