MLKL and infection: Interestingly, the levels of the phosphorylated forms of RIPK1, RIPK3, and MLKL, the major signaling molecules in the RIPK1-dependent necroptosis pathway, were observed as early as 4 hpi and continuously increased to 20 hpi in response to infection with both RVA strains (Fig. 1C and D and Fig. 2C and D).