Macrophage Polarization in Inflammatory Diseases

Liu, Yan-Cun; Zou, Xian-Biao; Chai, Yan-Fen; Yao, Yong-Ming

Although the previous hypotheses proposed an M1 role played by TAM in incipient and regressing tumors and necrotic areas of progressing tumors [68, 69] , some recent studies supported an M2-like role according to its biological characters [70] . TAM is initially poor in producing NO and reactive oxygen intermediates which are the hallmarks of M1 phenotype macrophages. Then, in response to M1 signals including LPS and TNF-α, TAM shows a defective NF-κB activation together with low levels of IL-12, IL-1β, TNF-α as well as IL-6. Finally, markers of M2 such as Arg1, Ym1, FIZZ1, and MRC1 are all expressed on TAM. Nevertheless, a wide accepted view is that different infiltrating leukocytes, mediators, and signals in tumor microenvironments interact with TAM, forming a series of distinct phenotypes of TAM, in which M1/M2 designations represent two extreme ends of a scale [64] .