MAPK3 and infection: In addition, Colao et al. showed that HSV-1 infection in HEp-2 cells increased cytoplasmic phospho-ERK1/2 at 0.25–0.5 hpi to 2- to 1.4-fold compared to those of mock infection, whereas cytoplasmic phospho-ERK1/2 decreased to 10% after 24 hpi compared49.