To investigate whether the B cells and macrophages depletion observed in mice following A/WSN/1933 virus infection was due to apoptosis, we cultured peritoneal cells harvested from untreated BALB/c mice in the presence of PBS, A/WSN/1933 virus, or UV-WSN virus and stained them with Annexin V that binds to phosphatidylserine, a marker of apoptosis. This evidence concerns the gene ANXA5 and viral infectious disease.