MAPK3 and infection: Staining with activation-specific phospho-antibodies has revealed that both PAK1 (phosphorylated in T-423) and ERK1/2 (phosphorylated at both T-202 and Y-204) activity is increased continuously during infection, whereas activity of c-Src (phosphorylated at Y-416) is transient: while being activated for 0.5–2 h it is subsequently inactivated [24].