Fig. 1.

Macrophages origin and heterogeneity. Macrophages are the end cells of the mononuclear lineage. Erythromyeloid progenitors from yolk sac and fetal liver and HSCs from bone marrow develop into the progenitor of macrophages. Macrophages can be induced two distinct polarization phenotypes according to the spectrum of their responses by different microenvironmental stimuli. M1 macrophages exert cytotoxic function by releasing IL-1α, IL-1β, IL-12, IL-18, iNOS, and TNF-α which are induced by LPS, IFN-γ and GM-CSF. M2 macrophages exert anti-inflammatory activities by express low IL-12, high IL-10, arginase 1 and PD-L1 which are induced by IL-4, IL-10, IL-13, M-CSF and helminth. Arg-1, arginine-1; HSCs, hematopoietic stem cells; iNOS, inducible nitric oxide synthase; IFN-γ, interferon-γ; LPS, lipopolysachharide; GM-CSF, granulocyte–macrophage colony-stimulating factor; M-CSF, macrophage colony-stimulating factor; TNF-α, tumor necrosis factor α