M2 polarization of tumor-associated macrophages is dependent on integrin β3 via peroxisome proliferator-activated receptor-γ up-regulation in breast cancer

Macrophages are particularly abundant and play an important role throughout the tumor progression process, namely, tumor-associated macrophages (TAM) in the tumor microenvironment. TAM can be polarized to disparate functional phenotypes, the M1 and M2 macrophages. M1-like type macrophages are defined as pro-inflammatory cells involved in killing cancer cells, while M2-like type cells can specially promote tumor growth and metastasis, tissue remodeling and immunosuppression. In this study, we first found that integrin β3 was highly expressed on the surface of TAM, both in vivo and in vitro, that displayed the M2-like characteristics. Under intervention of CYC or triptolide, the integrin β3 inhibitors, the M2 polarization of TAM could be inhibited. Moreover, in the cell model of M2 polarization, either blockade or knockout/knockdown of integrin β3 could also suppress macrophage M2 polarization, which suggested that the M2 polarization was dependent on integrin β3. Using knockdown of peroxisome proliferator-activated receptor-γ (PPARγ), an M2 regulator, we found that expression and activation of PPARγ participated in M2 polarization that was mediated by integrin β3. Finally, to verify the activity of integrin β3 inhibitors on TAM in vivo, 4T1 tumor-bearing mice were treated with CYC or triptolide; in response, the M1/M2 ratio of TAM was up-regulated, while the infiltration of total lymphocytes into tumor tissue was not altered. In general, our study found a connection between integrin β3 and macrophage polarization, which provides a strategy for facilitating M2 to M1 repolarization and reconstructing the tumor immune microenvironment.     

Dynamic Changes of Microglia/Macrophage M1 and M2 Polarization in Theiler's Murine Encephalomyelitis

Microglia and macrophages play a central role for demyelination in Theiler's murine encephalomyelitis (TME) virus infection, a commonly used infectious model for chronic‐progressive multiple sclerosis. In order to determine the dynamic changes of microglia/macrophage polarization in TME, the spinal cord of Swiss Jim Lambert (SJL) mice was investigated by gene expression profiling and immunofluorescence. Virus persistence and demyelinating leukomyelitis were confirmed by immunohistochemistry and histology. Electron microscopy revealed continuous myelin loss together with abortive myelin repair during the late chronic infection phase indicative of incomplete remyelination. A total of 59 genes out of 151 M1‐ and M2‐related genes were differentially expressed in TME virus‐infected mice over the study period. The onset of virus‐induced demyelination was associated with a dominating M1 polarization, while mounting M2 polarization of macrophages/microglia together with sustained prominent M1‐related gene expression was present during the chronic‐progressive phase. Molecular results were confirmed by immunofluorescence, showing an increased spinal cord accumulation of CD16/32⁺ M1‐, arginase‐1⁺ M2‐ and Ym1⁺ M2‐type cells associated with progressive demyelination. The present study provides a comprehensive database of M1‐/M2‐related gene expression involved in the initiation and progression of demyelination supporting the hypothesis that perpetuating interaction between virus and macrophages/microglia induces a vicious circle with persistent inflammation and impaired myelin repair in TME.     

Partners in crime: VEGF and IL-4 conscript tumour-promoting macrophages

Tumour-associated macrophages (TAMs) foster tumour progression by several mechanisms, including the promotion of angiogenesis, tissue remodelling, and immunosuppression. Such pro-tumoural activities are thought to be executed by TAM subtypes that harbour features of alternatively activated (or M2-polarized) macrophages. However, the molecular signals in tumours that induce recruitment and differentiation of M2-like macrophages are not fully defined. In this issue of The Journal of Pathology, Linde et al investigate the role of the tumour-derived cytokines, VEGF and IL-4, in the recruitment and polarization of macrophages in a mouse model of skin cancer. The authors report that while VEGF-A recruits monocytes from the peripheral circulation, IL-4 induces their differentiation into tumour-promoting, M2-like macrophages. IL-4 signalling blockade was sufficient to reprogram TAMs away from the M2-like phenotype and inhibited tumour angiogenesis and growth. This study attests to the potential of reprogramming TAMs to abate their pro-angiogenic and pro-tumoural functions in tumours.     

Role of tumor‐associated macrophages in human malignancies: friend or foe?

Tumor‐associated macrophages (TAMs) play a pivotal role in tumor growth in human malignancies. Published studies have analyzed the relationship between TAM infiltration and the prognosis of patients for many human tumors. Most studies reported a positive correlation between TAM density and a poor prognosis. Studies focusing on macrophage phenotypes emphasized the protumor role of M2 anti‐inflammatory macrophages in many types of human tumors. However, TAMs influence tumor progression in various ways that depend on differences in tumor sites, histology, and microenvironments. In this review, we summarize the function of TAMs in various human malignancies by reviewing the data provided in studies of TAMs in human malignancies.     

Convergent pathways of macrophage polarization: The role of B cells

The construction of an inflammatory microenvironment provides the fuel for cancer development and progression. Hence, solid tumors promote infiltration of leukocyte populations, among which tumor‐associated macrophages (TAM) represent a paradigm for cancer‐promoting inflammation. TAM orchestrate various aspects of cancer, including diversion and skewing of adaptive responses, cell growth, angiogenesis, matrix deposition and remodelling, the construction of a metastatic niche and actual metastasis, response to hormones and chemotherapeutic agents. Several lines of evidence indicate that TAM show a remarkable degree of plasticity and functional heterogeneity, suggesting that during tumor progression macrophages undergo a phenotypic “switch”, eventually exhibiting the alternatively activated, “M2”, phenotype that is associated with immunosuppression, promotion of tumor angiogenesis and metastasis. Although recent studies have attempted to address the role of microenvironmental signals on TAM “reprogramming”, the interplay between innate and adaptive immunity is emerging as a crucial step of this event. In this issue of the European Journal of Immunology, a study demonstrates that B1 lymphocytes expressing IL‐10 play a key role in promoting a pro‐tumoral M2‐biased phenotype of macrophages. This article defines a new in vivo pathway of macrophage polarization and suggests that targeting B cells is a possible therapeutic intervention to reinstate anti‐cancer functions by TAM.     

Neem leaf glycoprotein regulates function of tumor associated M2 macrophages in hypoxic tumor core: Critical role of IL-10/STAT3 signaling

Heterogeneous tumor microenvironment (TME), broadly divided into tumor core and peripheral sub-microenvironments, differentially polarize normal macrophages into a different form known as tumor associated M2 macrophages (M2TAMs) to promote tumor growth. In view of the extensive immune-editing role of NLGP, here, we have observed that NLGP is effective to convert M2TAMs (CD11b⁺F4/80^high) to M1 (CD11b⁺F4/80^low) more prominently in tumor core, along with downregulation of other M2 associated markers, like, ManR, Ym1, Fizz1. High IL-10:IL-12 ratio at tumor core was downregulated in NLGP treated melanoma bearing mice. Decrease in IL-10 by NLGP is again associated with the decrease in hypoxia, as indicated by prominent downregulation of HIF1α and VEGF, particularly at tumor core. Macrophages exposed to hypoxic tumor core lysates in vitro exhibited high IL-10, HIF1α and VEGF expression that was significantly downregulated by NLGP. Further evidences suggest M2TAM to M1 conversion by NLGP is associated with STAT3-regulated IL-10 dependent pathway without affecting the IL-4 dependent one. Such TAM modulatory functions of NLGP might help in the restriction of melanoma growth by increasing the proportion of M1 TAMs in tumor core that helps in prevention of tumor relapse and dissemination of the tumor mass.     

肿瘤相关巨噬细胞与食管癌关系的研究进展

中国是食管癌(esophageal carcinoma,EC)发病率及死亡率最高的国家之一.在EC的进展中,肿瘤相关巨噬细胞(tumor-associated macrophages,TAMs)在肿瘤微环境(tumor microenvironment,TME)的作用下分化为M1和M2巨噬细胞,M1巨噬细胞主要发挥抗肿瘤作用,M2巨噬细胞分泌大量的细胞因子、趋化因子、金属蛋白酶等免疫调节因子影响巨噬细胞分化和免疫抑制的过程,促进上皮-间质转化(epithelial-mesenchymal transition,EMT),同时还能通过促进肿瘤血管及淋巴管生成等途径影响EC进展的各个方面.因为传统治疗方案的局限性,我们亟需为EC的治疗开发新的方案,因此研究TAMs在EC发病起始及进展中的作用具有重要意义.     

Immunology in the clinic review series; focus on cancer: tumour-associated macrophages: undisputed stars of the inflammatory tumour microenvironment

Mononuclear phagocytes are cells of the innate immunity that defend the host against harmful pathogens and heal tissues after injury. Contrary to expectations, in malignancies, tumour-associated macrophages (TAM) promote disease progression by supporting cancer cell survival, proliferation and invasion. TAM and related myeloid cells [Tie2(+) monocytes and myeloid-derived suppressor cells (MDSC)] also promote tumour angiogenesis and suppress adaptive immune responses. These divergent biological activities are mediated by macrophages/myeloid cells with distinct functional polarization, which are ultimately dictated by microenvironmental cues. Clinical and experimental evidence has shown that cancer tissues with high infiltration of TAM are associated with poor patient prognosis and resistance to therapies. Targeting of macrophages in tumours is considered a promising therapeutic strategy: depletion of TAM or their 're-education' as anti-tumour effectors is under clinical investigation and will hopefully contribute to the success of conventional anti-cancer treatments.     

Tumor associated macrophages provide the survival resistance of tumor cells to hypoxic microenvironmental condition through IL-6 receptor-mediated signals

Hypoxia and infiltration of tumor-associated macrophages (TAM) are intrinsic features of the tumor microenvironment. Tumor cells that remain viable in hypoxic conditions often possess an increased survival potential and tend to grow aggressively. TAM also respond to a variety of signals in the hypoxic tumor microenvironment and express a more M2-like phenotype. In this study, the established mouse tumor tissues showed a dense infiltration of CD206⁺ macrophages at the junctions between the normoxic and hypoxic regions and an increased IL-6 receptor (IL-6R) expression of tumor cells in the areas of CD206⁺ TAM accumulation, which indicates a role of M2 phenotype TAM in survival adaptation of tumor cells preparing for an impending hypoxic injury before changes in oxygen availability. Cocultured mouse FM3A or human MCF-7 tumor cells with tumor infiltrating macrophages isolated from mouse tumor tissues and M2-polarized macrophages generated from human THP-1 cells, respectively, showed significantly decreased rate of cell death in cultures exposed to hypoxia. The acquisition of survival resistance was attributed to increased IL-6 production by M2 TAM and increased expression of IL-6R in tumor cells in the coculture system. MCF-7 cells cocultured with M2 TAM showed activated JAK1/STAT3 and Raf/MEK/JNK pathways contributing to tyrosine and serine phophorylation of STAT3, respectively. However, only tyrosine phosphorylated STAT3 was detected in the nucleus, which induced upregulation of Bcl-2 and downregulation of Bax and Bak. Finally, knockdown of IL-6R by small interfering RNA significantly counteracted coculture-induced signals and completely abolished the survival resistance to hypoxic injury. Thus, we present evidence for the role of M2 phenotype TAM in IL-6 receptor-mediated signals, particularly tyrosine phosphorylation of STAT3, responsible for the prosurvival adaptation of tumor cells to hypoxia.     

肿瘤微环境中的基质细胞在转移形成中的角色

传统观念认为癌症的进展仅仅是由癌细胞基因和表型变化的多个过程所致.但最近20年的研究显示肿瘤微环境(tumor microenvironment,TME)对于肿瘤行为的影响是同等重要的.TME的组成包括局部的基质细胞,如定植的成纤维细胞(cancer-associated fibroblasts,CAF)和巨噬细胞,远处招募的细胞如内皮细胞、免疫细胞包括髓系和淋巴系细胞、骨髓来源的前体细胞和循环中的血小板.TME能够分泌影响并调控肿瘤表型的分子,如能揭示成瘤细胞与微环境之间的关系,必定能够为肿瘤的发生发展及治疗等一系列难题提供全新的视角.     

Nodal promotes the generation of M2‐like macrophages and downregulates the expression of IL‐12

Nodal, a member of the TGF‐β superfamily, is an embryonic morphogen that is upregulated in different types of tumors. Nodal increases the tumorigenesis by inducing angiogenesis and promoting metastasis. Importantly, Nodal inhibition suppresses the growth and invasion of tumor. Since tumor‐associated macrophages (TAMs) are the major infiltrating leukocytes in most cancers, we investigated whether Nodal is involved in the differentiation of TAMs. Our results revealed that Nodal inhibition in tumor microenvironment upregulated the production of IL‐12 in macrophages and reversed TAMs to classically activated macrophage phenotype. In contrast, treatment with recombinant Nodal (rNodal) decreased the expression of IL‐12 in murine macrophages. Furthermore, rNodal promoted macrophage polarization to an alternatively activated macrophage‐like/TAM phenotype and modulated its function. These results suggest that Nodal may play an important role in macrophage polarization and downregulation of IL‐12. The rescued antitumor function of TAMs via the inhibition of Nodal expression could be a new therapeutic strategy for cancer treatment.     

Tumour‐associated macrophage‐mediated survival of myeloma cells through STAT3 activation

Overcoming drug resistance is one of the greatest challenges in the treatment of multiple myeloma (MM). The interaction of myeloma cells with the bone marrow (BM) microenvironment is a major factor contributing to drug resistance. Tumour‐associated macrophages (TAMs) with different polarization states constitute an important component of this microenvironment. Previous studies have revealed a role of TAMs in MM cell survival and drug resistance; however, the impact of macrophage polarization (anti‐tumoural ‘M1’ versus pro‐tumoural ‘M2’‐like phenotype) in this process has not yet been described. Here, the presence of TAMs was confirmed in BM sections from MM patients, both at diagnosis and relapse, with two M2 markers, CD163 and CD206. By following different TAM subpopulations during disease progression in the syngeneic murine 5T33MM model, we demonstrated a decrease in the number of inflammatory monocytes and an increase in the number of M2‐oriented TAMs in BM. Co‐culture experiments demonstrated that macrophages provide a survival benefit to myeloma cells that is maintained after treatment with several classes of anti‐myeloma agent (melphalan and bortezomib); the greatest effect was observed with M2‐polarized macrophages. The pro‐survival effect was associated with activation of the STAT3 pathway in 5T33MM cells, less cleavage of caspase‐3, and thus less apoptosis. AZD1480, an ATP‐competitive JAK2 inhibitor, abrogated the observed TAM‐mediated MM cell survival, and partially inhibited resistance to bortezomib. Despite having only a small quantitative impact on myeloid cells in vivo, AZD1480 treatment alone and in combination with bortezomib significantly reduced tumour load. In conclusion, M2 TAMs are present in the MM microenvironment, and contribute to MM cell survival and protection from drug‐induced apoptosis. As a result of TAM‐induced activation of the STAT3 pathway, 5T33MM cells are sensitized to AZD1480 treatment. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Tumour-associated macrophages in diffuse large B-cell lymphoma: a study of the Osaka Lymphoma Study Group

Wada N, Zaki M A A, Hori Y, Hashimoto K, Tsukaguchi M, Tatsumi Y, Ishikawa J, Tominaga N, Sakoda H, Take H, Tsudo M, Kuwayama M, Morii E & Aozasa K
(2012) Histopathology  60, 313–319
Tumour‐associated macrophages in diffuse large B‐cell lymphoma: a study of the Osaka Lymphoma Study Group Aims: To evaluate the role of tumour‐associated macrophages (TAMs) of the M1 and M2 types in the behaviour of diffuse large B‐cell lymphoma (DLBCL). Methods and results: Double immunohistochemical staining of HLA‐DR/CD68 (M1) or CD163/CD68 (M2) was performed in 101 cases of DLBCL. CD68+ cells represent the total number of TAMs. The average number of double‐positive cells was counted, and the cut‐off value was set at the mean number of counts, i.e. 30.7 and 27.0 for M1 TAMs and M2 TAMs, respectively. That for total TAMs was set at the 90th percentile number of total counts, i.e. 132.3. Cases were categorized into three pairs: high (34 cases) and low (67 cases) M1 TAM groups, high (39 cases) and low (62 cases) M2 TAM groups, and high (10 cases) and low (91 cases) total TAM groups. The difference in overall survival rates was statistically significant between the high and low M2 TAM groups (P < 0.01) and between the high and low total TAM groups (P < 0.05). Multivariate analysis revealed that the presence of a bulky mass and a higher number of M2 TAMs were significant factors for poor prognosis (P < 0.05). Conclusions: Estimation of specific type of macrophages, of the M1 and M2 types, is superior to the estimation of TAMs as a whole (CD68+ cells) for prediction of the prognosis of DLBCL patients.     

TGF-β signalling in tumour associated macrophages

Tumour associated macrophages (TAM) represent an important component of tumour stroma. They develop under the influence of tumour microenvironment where transforming growth factor (TGF)β is frequently present. Activities of TAM regulated by TGFβ stimulate proliferation of tumour cells and lead to tumour immune escape. Despite high importance of TGFβ-induction of TAM activities till now our understanding of the mechanism of this induction is limited. We have previously developed a model of type 2 macrophages (M2) resembling certain properties of TAM. We established that in M2 TGFβRII is regulated on the level of subcellular sorting by glucocorticoids. Further studies revealed that in M2 with high levels of TGFβRII on the surface TGFβ activates not only its canonical Smad2/3-mediated signaling, but also Smad1/5-mediated signaling, what is rather typical for bone morphogenetic protein (BMP) stimulation. Complexity of macrophage populations, however, allows assumption that TGFβ signalling may function in different ways depending on the functional state of the cell. To understand the peculiarities of TGFβ signalling in human TAMs experimental systems using primary cells have to be developed and used together with the modern mathematical modelling approaches.     

Differential macrophage programming in the tumor microenvironment

Of the multiple unique stromal cell types common to solid tumors, tumor-associated macrophages (TAMs) are significant for fostering tumor progression. The protumor properties of TAMs derive from regulation of angiogenic programming, production of soluble mediators that support proliferation, survival and invasion of malignant cells, and direct and indirect suppression of cytotoxic T cell activity. These varied activities are dependent on the polarization state of TAMs that is regulated in part by local concentrations of cytokines and chemokines, as well as varied interactions of TAMs with normal and degraded components of the extracellular matrix. Targeting molecular pathways regulating TAM polarization holds great promise for anticancer therapy.     

STAT of the union: Dynamics of distinct tumor‐associated macrophage subsets governed by STAT1

The tumor stroma has long been ignored as therapeutic target, but it has become clear that several stromal cell types play a nonredundant role during tumor progression. In particular, macrophages possess the capacity to stimulate tumor growth and metastasis via multiple mechanisms. In this issue of the European Journal of Immunology, a study by Tymoszuk et al. Eur. J. Immunol. 2014. 44: 2247–2262 demonstrates that both monocyte recruitment and local macrophage proliferation determines the tumor‐associated macrophage (TAM) pool size in HER2/Neu‐driven mammary carcinomas. These tumors contain two main TAM subsets—MHC class II (MHC‐II)^loF4/80^hi and MHC‐II^hiF4/80^lo—similar to what was observed in other tumor models. Interestingly, only the MHC‐II^loF4/80^hi subset is largely absent in a STAT1‐deficient background. STAT1 induces the expression of CSF‐1, which in turn drives TAM proliferation and possibly also the M2 gene signature of MHC‐II^loF4/80^hi TAM. Conversely, STAT1 deficiency upregulates M2 gene expression in MHC‐II^hiF4/80^lo TAM, demonstrating that both TAM subsets are differentially regulated, probably as a consequence of their distinct intratumoral localization. In this Commentary, we place these findings in the context of current knowledge and propose new avenues for future research.     

Detection of M2 macrophages and colony-stimulating factor 1 expression in serous and mucinous ovarian epithelial tumors

Tumor-associated macrophages (TAM) are known to possess the immunosuppressive M2 macrophage phenotype. They contribute to tumor growth, invasion, and metastasis by producing various mediators. Macrophages, especially M2 polarized macrophages, preferentially express CD163 and CD204, but few studies have investigated macrophage phenotypes in human ovarian tumors. The purpose of the present study was therefore to present results on macrophage differentiation in human ovarian serous and mucinous epithelial tumors. The method focused on immunostaining of paraffin-embedded tumor samples. Almost all macrophages infiltrating tumor tissues expressed CD163 and CD204, indicating the phenotypic shift toward M2 macrophage. The numbers of CD68-positive macrophages as well as of CD163- and CD204-positive macrophages in borderline and malignant tumors were significantly higher than in benign tumors. They correlated well with histological gradient of malignancy. Macrophage colony-stimulating factor (also known as colony-stimulating factor; CSF-1), which is one of the cytokines considered to induce TAM to polarize toward an M2 phenotype, was then evaluated. CSF-1 expression in malignant tumor cells was significantly higher than that in benign tumor cells and correlated with histological malignancy. These results suggest that CSF-1 derived from tumor tissues induces macrophages to shift toward the M2 phenotype, which is considered to promote tumor growth.     

The role of tumor-associated macrophages in primary hepatocellular carcinoma and its related targeting therapy

Liver macrophages consist of ontogenically distinct populations termed Kupffer cells and monocyte-derived macrophages. Tumor-associated macrophages (TAMs) inhepatocellularcarcinoma (HCC) play a prominent role in tumormicroenvironment by presenting M1(induced by IFN γ along with LPS) and M2(induced by IL-4 and IL13) polarization. Although TAMs are involved in tumor immune surveillance during the course of HCC, they contribute to tumour progression at different levels by inhibiting the anti-tumor immune response, promoting the generation of blood vessels and lymphatic vessels, and supporting the proliferation and survival of tumor cells. In this paper, the multiple functions of TAMs in HCC were reviewed to provide assistance for future researches about therapeutic approaches.