Which macrophage phenotype is often associated with immune suppression in tumors?

• A. M1 macrophages
• B. M2-like tumor-associated macrophages
• C. Alveolar macrophages
• D. Microglia

Answer: (B)

The key idea is how macrophage polarization shapes the tumor environment. Macrophages can become either pro-inflammatory and anti-tumor (M1) or anti-inflammatory and pro-tumor (M2-like). In many tumors, signals from cancer and stromal cells—like IL-4, IL-10, TGF-β, and CSF-1—drive macrophages toward an M2-like, tumor-associated state. These cells express markers such as CD206 and CD163 and secrete IL-10 and TGF-β, which dampen cytotoxic T cell activity. They also promote angiogenesis with VEGF and remodel the extracellular matrix, creating an environment that favors tumor growth and hinders immune attack. Because of these activities, M2-like tumor-associated macrophages are closely linked with immune suppression in tumors. While M1 macrophages are inflammatory and anti-tumor, and alveolar macrophages or microglia are specialized resident macrophages, the M2-like TAMs are the ones most consistently associated with immune suppression in the tumor setting.