Cells expressing the Epstein-Barr virus growth program are present in and restricted to the naive B-cell subset of healthy tonsils.

In this paper we demonstrate, for the first time, that Epstein-Barr virus (EBV)-infected cells expressing the lymphoblastoid growth program are present in healthy carriers of the virus. Previously we observed that latently infected naive B cells are present in tonsils only when viral replication is detected, suggesting that these may represent newly infected B cells. We have tested this idea by performing a reverse transcription-PCR analysis for the expression of latent genes (EBNA2 and the EBNA3s) that are characteristically expressed only by newly infected cells expressing the growth latency program. EBNA2 expression is regularly detected in purified naive (IgD(+)) tonsillar B cells (13 of 16 tonsils tested) but was never found in the IgD(-) population (0 of 16). More detailed analysis revealed that the mRNAs for the latent genes EBNA1 (3 of 3 tonsils tested), EBNA3a (3 of 5), EBNA3b (3 of 5), EBNA3c (3 of 5), LMP1 (6 of 6), and LMP2 (5 of 6) were also present in the IgD(+) population, but the EBNA1Q-K transcript, characteristic of nonlymphoblastoid forms of latency, was never detected (0 of 6). Finally, we demonstrate that the latently infected naive (IgD(+)) cells express CD80 (B7.1), a marker characteristically expressed on activated naive lymphoblasts but absent from resting naive B cells. The infected naive (IgD(+)) population in the tonsil therefore has the viral and cellular phenotype of a B-cell directly infected with EBV-an activated lymphoblast expressing the growth program.