Frequent presence of subtype A virus in Epstein-Barr virus-associated malignancies

Epstein-Barr virus (EBV) is associated with many human malignancies. It is implicated in a pathogenetic role in some of these tumours. Two subtypes, type A and B have been identified on the basis of DNA sequence divergence in the nuclear protein genes (EBNA) 2, 3, 4 and 6. They differ in their transforming efficiency and prevalence pattern in different geographical locations. We aimed to identify the virus subtype infection pattern in our EBV-associated diseases.

Paraffin-embedded tissue from 38 lymphomas (17 Hodgkin's, 14 Burkitt's, four T cell and 3 B cell non-Hodgkin's lymphomas) and 14 nasopharyngeal carcinomas (NPC) were studied, with 12 reactive lymph nodes and tonsils as normal control. EBER in situ hybridisation was performed to confirm EBV association in the tumour cells. A nested polymerase chain reaction (PCR) protocol was employed using two pairs of consensus primers which flanked a 105-bp deletion in the type A virus. U2 region encoding for EBNA-2 was chosen as the target of amplification, with cell lines B95.8 and AG876 serving as positive controls for types A and B virus, respectively.

All cases showed presence of type A virus, consistently detected with nested PCR protocol but not with single step PCR. There was no type B virus or mix infections detected.

Nested PCR technique has successfully increased the sensitivity of EBV subtype detection, and type A virus is the prevalent strain associated with human diseases in Malaysia.