DUSP4 and infection: Our previous studies with L. mexicana had demonstrated the increased susceptibility of non-stimulated MKP-2−/− macrophages to infection to be related to elevated Arginase-1 levels compared with MKP-2+/+ macrophages and similarly enhanced levels of Arginase-1 were found in MKP-2−/− macrophages following infection with L. major promastigotes (Figure 2E).