In order to determine whether the reduced expression of BAFFR on Syk-deficient B cells was the cause of their failure to survive in response to BAFF, we used a retroviral vector expressing BAFFR and a truncated form of human CD2 (as a marker of infection) to increase receptor amounts on both control and conditional Syk-deficient B cells. This evidence concerns the gene TNFRSF13C and infection.