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Clinical and Developmental Immunology
Volume 2012 (2012), Article ID 948098, 11 pages
Review Article

Macrophages in Tumor Microenvironments and the Progression of Tumors

1Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China
2Institute of Immunology, Third Military Medical University, Chongqing 400038, China
3Biomedical Analysis Center, Third Military Medical University, Chongqing 40038, China
4Chongqing Key Laboratory for Diseases Proteomics, Southwest Hospital, Third Military Medical University, Chongqing 400038, China

Received 26 February 2012; Revised 28 April 2012; Accepted 9 May 2012

Academic Editor: Senthamil R. Selvan

Copyright © 2012 Ning-Bo Hao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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.