Figure 1.

Macrophage Recruitment and Polarization. Monocytes from the bloodstream can be recruited to differentiate into macrophages under the influence of cytokines and growth factors such as CCL2, CCL18, CCL20, colony-stimulating factor -1 (CSF-1), and vascular endothelial growth factors (VEGFs). These recruited macrophages, along with resident macrophages, present in lung alveoli and peritoneum, epidermal Langerhans cells, Kupffer cells, and brain microglia, take part in the macrophage polarization process. Macrophages turn into either the proinflammatory M1 phenotype in the presence of LPS, TNF α, and IFN-ƴ or by, IL-4, IL-10 and IL-13 into the M2-polarized macrophages, which are generally known as TAMs. Tumors and macrophages present in the TME can release HIF, CSF-1, and interleukins CXCR4, CXCL12, and IL10, respectively, to stimulate the macrophage polarization process. Macrophages with M1 phenotype show antitumor characteristics while M2 type macrophages demonstrate protumor characteristics.