Taking advantage of the abundant expression of the small Epstein-Barr virus (EBV)-encoded RNAs (EBERs) in latently infected cells, we have analyzed 72 normal and hyperplastic lymph nodes and three tonsils of acute infectious mononucleosis (IM) for the presence and distribution of EBV⁺ cells using EBER-specific in situ hybridization, in some cases combined with immunohistologic demonstration of cell type-character-istic antigens. In IM, large numbers of EBV⁺ lymphoid B blasts were detectable in extrafollicular areas, whereas germinal centers were generally free of EBV⁺ cells. In reactive lymph nodes, the frequency of EBV⁺ cells varied with the degree of lymphoid hyperplasia and underlying immune status. The lowest numbers of EBV⁺ cells were detected in nonactivated lymph nodes and highest in human immunodeficiency virus-associated lymphadenopathy. If present in these lymph nodes, EBV⁺ cells were almost exclusively localized to extrafollicular areas, as also observed in IM. However, in contrast to IM, these cells were mainly small lymphocytes. Furthermore, in some instances, occasional scattered EBV⁺ cells were seen within germinal centers, and in two cases diffuse expansions of EBV+ cells occurred within a single germinal center each, indicating that under certain circumstances EBV+ B lymphocytes may participate in physiologic germinal center reactions. These findings reflect the interference of EBV with physiologic lymphoid differentiation pathways and provide a link to EBV-associated malignant lymphomas with a postulated origin from germinal center cells.

© 1992 by The American Society of Hematology