Macrophages in Tumor Microenvironments and the Progression of Tumors

• Main Authors: Ning-Bo Hao, Mu-Han Lü, Ya-Han Fan, Ya-Ling Cao, Zhi-Ren Zhang, Shi-Ming Yang
• Format: Article
• Language: English
• Published: Hindawi Limited 2012-01-01
• Series: Clinical and Developmental Immunology
• Online Access: http://dx.doi.org/10.1155/2012/948098
• ISSN: 1740-2522; 1740-2530

Macrophages are widely distributed innate immune cells that play indispensable roles in the innate and adaptive immune response to pathogens and in-tissue homeostasis. Macrophages can be activated by a variety of stimuli and polarized to functionally different phenotypes. Two distinct subsets of macrophages have been proposed, including classically activated (M1) and alternatively activated (M2) macrophages. M1 macrophages express a series of proinflammatory cytokines, chemokines, and effector molecules, such as IL-12, IL-23, TNF-α, iNOS and MHCI/II. In contrast, M2 macrophages express a wide array of anti-inflammatory molecules, such as IL-10, TGF-β, and arginase1. In most tumors, the infiltrated macrophages are considered to be of the M2 phenotype, which provides an immunosuppressive microenvironment for tumor growth. Furthermore, tumor-associated macrophages secrete many cytokines, chemokines, and proteases, which promote tumor angiogenesis, growth, metastasis, and immunosuppression. Recently, it was also found that tumor-associated macrophages interact with cancer stem cells. This interaction leads to tumorigenesis, metastasis, and drug resistance. So mediating macrophage to resist tumors is considered to be potential therapy.