Figure 1: Role of macrophage activation in parasitic infections. A type 1 cytokine-dependent proinflammatory response inducing classically activated macrophages (CaM 𝜙 s) leads to NO production and also to the synthesis of several products of NO reaction. CaM 𝜙 s are crucial for parasite control during protozoan infections but can also contribute to the development of immunopathological disease symptoms. Type 2 cytokines such as IL-4 and IL-13 antagonize CaM 𝜙 s inducing alternatively activated macrophages (AaM 𝜙 s) that upregulate arginase-1 expression. Arginase-1 can also be induced during the infection by apoptotic cells or even directly by parasites or parasite components. Arginase-1 limits CaM 𝜙 -dependent parasite clearance promoting parasite proliferation. Additionally, arginase-1 suppresses T cell response. Therefore, generation of alternative activation states of macrophages could limit collateral tissue damage because of excessive type 1 inflammation. However, they affect disease outcome by promoting parasite survival and proliferation.