Tumor-associated macrophages and cancer development

Abstract

Accumulation of macrophages in solid tumor tissue has been recognized clinically by histopathological examination. However, the function and molecular characteristics of these macrophages got elucidated only recently. These macrophages, called tumor-associated macrophages (TAMs), can enhance tumor invasion, migration, and angiogenesis, and human TAMs have been characterized by the expression of CD163 and CD68 on plasma membrane. Similar to alternatively activated macrophages (M2 macrophages), TAMs are known to express arginase-1, chitinase 3-like proteins 3 and 4, and RELMα and also express VGEF. In addition, TAMs can suppress T cell proliferation or induce regulatory T cells by a way relevant to the expression of IL-10, TGFβ, and prostaglandins. These immunosuppressive features of TAMs connect them to the macrophages called myeloid-derived suppressor cells (MDSCs). Therefore, an important aim for TAMs research is to repolarize TAMs from tumor promotive macrophages to tumor suppressive macrophages, meaning to establish new strategies efficient for reeducating TAMs to be cytotoxic in tumors.