Epstein-Barr virus infection of monocytoid B-cell proliferates - An early feature of primary viral infection?

Monocytoid cells are a subset of B lymphocytes with characteristic morphology and immunophenotype, which proliferate in a broad variety of reactive lymph node conditions. Up to now, no direct infection of these cells by a pathogenic organism has been identified. We found in a series of lymph node specimens from 13 patients having in common a prominent monocytoid B (MCB)-cell reaction in the absence of epithelioid cells or necrosis evidence that Epstein-Barr virus (EBV) can infect MCB cells. Clinical and serologic findings indicative for an acute EBV infection were reported only in 2 cases. By in situ hybridization and immunohistology, a number of MCB cells in all cases was found to contain EBV-encoded small nuclear RNAs and to express the EBV-encoded nuclear antigen (EBNA)-2 and, in lesser extent, the latent membrane protein-1. EBV-transcripts and proteins were also detectable in a number of extrafollicular B blasts and germinal center B cells in 10 of 13 cases. Our findings imply that an EBV infection of MCB cells associated with predominant EBNA-2 expression represents an early sign of primary infection and that it should be included in the differential diagnosis of activated lymph nodes with prominent MCB-cell reaction in the absence of epithelioid cells.