Role of the CD21 antigen in lymphocyte transformation by Epstein-Barr virus

The human CD21 membrane antigen has been shown to bind Epstein-Barr Virus (EBV) and some binding and functional data imply a role for this interaction in the B cell tropism of EBV. In this report the technique of limit dilution analysis was used to provide evidence that B cell transformation by EBV only occurred when CD21 antigen was present and that all cells expressing CD21 were transformation-competent. The rate of transformation varied, being increased if B cells were activated by an additional B cell mitogen, and being dependent on, although not strictly proportional to, the intensity of CD21 expression. The possibility that EBV might enter by other means was examined by selectively deleting CD21 antigen from the cell surface. This was accompanied by a profound decrease in the transformation frequency. It is concluded that CD21 antigen is necessary for EBV transformation and that CD21 expression is the major limiting factor in these events.