Fig. 1

The origin and function of TAMs. As the main source of macrophages, bone marrow-derived monocytes are derived from hematopoietic stem cells (HSCs) that undergo differentiation into granulocyte-macrophage progenitors (GMPs) and subsequently into monocyte-dendritic cell progenitors (MDPs). Monocytes in the blood can be recruited and differentiated into TAM by chemokines (e.g., CCL2, CCL5 and CCL7) or growth factors (e.g., VEGF and PDGF). In addition, yolk sac progenitor cells are another important source of TAMs. Under the stimulation of cytokines (such as IL-6 and IL-8, etc.) and chemokines (such as CCL2 and CXCL8, etc.), TAMs play an important role in tumor invasion, immune regulation, angiogenesis and metastasis. HSCs hematopoietic stem cells, GMPs granulocyte-macrophage progenitors, MDPs monocyte-dendritic cell progenitors, BMDMs bone marrow-derived macrophages, TRMs tissue-resident macrophages, TAMs tumor-associated macrophages