To further investigate the ROS overload through which GCRV-II infection may induce apoptosis in IgM+ B and CD4+ T lymphocytes, PBLs with or without virus exposure were stained with anti-IgM or anti-CD4 mAbs and then counterstained with Annexin V. As our data showed, the frequency of apoptotic B and T lymphocytes was significantly increased in the GCRV-II-infected PBLs (Figure 4E), suggesting that ROS overproduction upon viral infection may be a potential inducer to provoke apoptosis in bystander B and T lymphocytes. This evidence concerns the gene CD40LG and viral infectious disease.