Epstein-Barr virus preferentially induces proliferation of primed B cells

EBV can induce human B cells to proliferate, differentiate, and undergo transformation into continuously growing lymphoblastoid cell lines. The EBV responsiveness appears to be confined to a very limited subpopulation of B cells, the nature of which is still unclear. In these studies, we sorted tonsillar B cells on the basis of their expression of the early surface activation Ag, Bac-1, and compared their proliferative responses to EBV. Bac-1+ cells responded to EBV with a relatively high level of DNA synthesis, whereas the Bac-1- cells did not. Both large and small Bac-1+ cells were responsive to EBV and the responsiveness was unrelated to the level of Bac-1 immunofluorescence intensity. Bac-1+ cells were relatively enriched for surface IgM and IgD expression. When the Bac-1- population was enriched for IgM+ cells, the proliferative response was still significantly lower than that of the Bac-1+ population. B cells acquire the ability to bind IgM relatively late after activation, and this feature did not distinguish the EBV-responsive B cells. The results suggest B cells become responsive to EBV after an early activation signal.