Figure 2.

A schematic illustrating the possible relationships among monocyte/macrophage subpopulations found in tumors. Tumor-infiltrating macrophages are known to derive from circulating CCR2+ inflammatory monocytes; however, it remains to be investigated whether inflammatory monocytes give raise to each of the distinct macrophage subpopulations found in tumors. The contribution of CCR2–resident monocytes to tumor macrophages is currently unknown. Dashed arrows indicate putative developmental relationships.