MAPK4 and infection: There was no change in viability of MAPK4-KO HCT-8 cells in the absence of C. parvum (Fig. 1C), whereas infected MAPK4-KO HCT-8 cells showed a 2.3-fold higher rate of cell death compared with infected WT HCT-8 cells at 24 h post-infection (Fig. 3A).