Epstein-Barr virus in B-cell non-Hodgkin's lymphomas: Unexpected infection patterns and different infection incidence in low- and high-grade types

Two hundred and eight cases of B‐cell non‐Hodgkin's lymphoma (B‐NHL) occurring in Europeans without any signs of HIV infection were investigated for their association with an Epstein‐Barr virus (EBV) infection. The polymerase chain reaction (PCR) was applied for EBV‐DNA detection, in situ hybridization (ISH) for the cellular localization of EBV‐encoded small nuclear RNAs (EBER) and immediate‐early RNAs (BHLF), and immunohistology (IH) for the detection of EBV‐encoded latent membrane protein (LMP) and EBV nuclear antigen 2 (EBNA2) expression. PCR and EBER‐ISH produced congruent results in those cases with amplifiable DNA. EBV was present overall in 26 per cent (54/208) of the B‐NHL cases. Through EBER‐ISH, the virus could be localized merely in rare non‐neoplastic bystander lymphocytes in 27 and additionally in tumour cells of 27 cases. Unexpectedly, the proportion of EBV‐infected tumour cells present in the different cases varied between 1 and 100 per cent. All but three of the cases with infected tumour cells were of high‐grade malignancy. Correlation with the morphological and immunological tumour phenotype revealed that all cases with more than 80 per cent EBER‐positive tumour cells were either B‐anaplastic large cell lymphomas (B‐ALCL), sporadic Burkitt's lymphomas, or B‐NHLs with partial or full plasmacellular differentiation. LMP was consistently absent from Burkitt's lymphomas and constantly expressed in B‐ALCLs with EBER‐positive tumour cells, while in all other instances it varied greatly and was rarer than EBER expression. The above findings suggest that in cases where EBV is present in 80–100 per cent of tumour cells, EBV infection takes place before malignant transformation and thus may have contributed to the malignant phenotype, whereas in the other cases with only a smaller number of infected tumour and single bystander cells, EBV infection may have occurred following malignant transformation. In these cases, infection would appear to be of little or no significance in tumourigenesis.