CASP8 and viral infectious disease: Because either polyI:C or viral infection can induce necroptosis when Casp8 activity is inhibited, there are two possible mechanisms to explain the BM failure phenotype observed in Mx1Cre+Casp8fx/fx mice: either Casp8−/− HSPCs undergo intrinsic necroptosis, or they are sensitive to polyI:C or viral infection-induced necroptosis.