Glioblastoma multiforme is characterized by high accumulation of microglia/macrophages. The function of these tumor-infiltrating myeloid cells is not sufficiently elucidated. Therefore, a better understanding of the precise immune cell composition and function in brain tumors is required. In rodent glioma models, two different myeloid cell populations exist, determined by the expression level of CD45, namely CD11b+CD45low and CD11b+CD45high. Previous analyses of cytokine and marker expression profiles were almost exclusively performed on the entire myeloid cell fraction. Consequently, described pro- and anti-tumoral characteristics were not assigned to the evident subpopulations. In the present study, we used a syngeneic glioblastoma mouse model and subsequent flow cytometric analyses to demonstrate the distinct properties of CD11b+CD45high and the CD11b+CD45low cells. First, the majority of CD11b+CD45high cells expressed high level of GR1 and around 6% of IL10 representing in part features of myeloid-derived suppressor cells, while the CD11b+CD45low fraction displayed no upregulation of these molecules. Second, we detected that specifically the CD11b+CD45high population showed antigen-presenting, co-stimulatory, and inflammatory features. Here, we identified up to 80% of MHCII and approximately 50% of CD86 and TNFα-expressing cells. Investigation of MHCI and CD80 revealed a moderate upregulation. By contrast, in the CD11b+CD45low cell fraction, merely MHCII and TNFα were marginally overexpressed. In summary, these data emphasize the specific phenotype of CD11b+CD45high cells in glioma with suppressive as well as pro-inflammatory characteristics whereas the CD11b+CD45low cells were almost unaffected. Hence, primarily, the subpopulation consisting of CD45high-expressing cells is activated by the tumor and should be considered as therapeutic target.
This is a preview of subscription content, log in to check access.
The authors thank Prof. Dr. Michael Synowitz (Charité, Berlin; UKSH, Kiel) for assistance with this study. Additionally, we thank Matthäus Felsenstein, Daphne Felsenstein-Moore, and Alexander D. Bungert for critical reading of the manuscript.
Compliance with ethical standards
Animal experiments were conducted according to the German Law for Animal Protection and the National Institute of Health Guidelines for Care and Use of Laboratory Animals. The protocol for the animal studies was approved by the Landesamt für Gesundheit und Soziales, Berlin (Permit Number: LaGeSo No. G0152/09).
This work was supported by the German Research Foundation (DFG) SPP1190 and SFB TRR43.
Conflict of interest
The authors declare that they have no conflict of interest.
Muller A, Brandenburg S, Turkowski K, Muller S, Vajkoczy P. Resident microglia, and not peripheral macrophages, are the main source of brain tumor mononuclear cells. Int J Cancer. 2015;137(2):278–88. doi:10.1002/ijc.29379.CrossRefPubMedGoogle Scholar
Roggendorf W, Strupp S, Paulus W. Distribution and characterization of microglia/macrophages in human brain tumors. Acta Neuropathol. 1996;92(3):288–93.CrossRefPubMedGoogle Scholar
Badie B, Schartner JM. Flow cytometric characterization of tumor-associated macrophages in experimental gliomas. Neurosurgery. 2000;46(4):957–61.PubMedGoogle Scholar
Brandenburg S, Muller A, Turkowski K, Radev YT, Rot S, Schmidt C, et al. Resident microglia rather than peripheral macrophages promote vascularization in brain tumors and are source of alternative pro-angiogenic factors. Acta Neuropathol. 2016;131(3):365–78. doi:10.1007/s00401-015-1529-6.CrossRefPubMedGoogle Scholar
Ellert-Miklaszewska A, Dabrowski M, Lipko M, Sliwa M, Maleszewska M, Kaminska B. Molecular definition of the pro-tumorigenic phenotype of glioma-activated microglia. Glia. 2013;61(7):1178–90. doi:10.1002/glia.22510.CrossRefPubMedGoogle Scholar
Komohara Y, Horlad H, Ohnishi K, Fujiwara Y, Bai B, Nakagawa T, et al. Importance of direct macrophage-tumor cell interaction on progression of human glioma. Cancer Sci. 2012;103(12):2165–72. doi:10.1111/cas.12015.CrossRefPubMedGoogle Scholar
Umemura N, Saio M, Suwa T, Kitoh Y, Bai J, Nonaka K, et al. Tumor-infiltrating myeloid-derived suppressor cells are pleiotropic-inflamed monocytes/macrophages that bear M1- and M2-type characteristics. J Leukoc Biol. 2008;83(5):1136–44. doi:10.1189/jlb.0907611.CrossRefPubMedGoogle Scholar
Yang L, DeBusk LM, Fukuda K, Fingleton B, Green-Jarvis B, Shyr Y, et al. Expansion of myeloid immune suppressor Gr+CD11b+ cells in tumor-bearing host directly promotes tumor angiogenesis. Cancer Cell. 2004;6(4):409–21. doi:10.1016/j.ccr.2004.08.031.CrossRefPubMedGoogle Scholar
Sliwa M, Markovic D, Gabrusiewicz K, Synowitz M, Glass R, Zawadzka M, et al. The invasion promoting effect of microglia on glioblastoma cells is inhibited by cyclosporin A. Brain. 2007;130(Pt 2):476–89. doi:10.1093/brain/awl263.CrossRefPubMedGoogle Scholar
Imai Y, Ibata I, Ito D, Ohsawa K, Kohsaka S. A novel gene iba1 in the major histocompatibility complex class III region encoding an EF hand protein expressed in a monocytic lineage. Biochem Biophys Res Commun. 1996;224(3):855–62. doi:10.1006/bbrc.1996.1112.CrossRefPubMedGoogle Scholar
Mantovani A, Sozzani S, Locati M, Allavena P, Sica A. Macrophage polarization: tumor-associated macrophages as a paradigm for polarized M2 mononuclear phagocytes. Trends Immunol. 2002;23(11):549–55.CrossRefPubMedGoogle Scholar
Chae M, Peterson TE, Balgeman A, Chen S, Zhang L, Renner DN, et al. Increasing glioma-associated monocytes leads to increased intratumoral and systemic myeloid-derived suppressor cells in a murine model. Neuro-Oncology. 2015;17(7):978–91. doi:10.1093/neuonc/nou343.CrossRefPubMedGoogle Scholar
Thaci B, Ahmed AU, Ulasov IV, Wainwright DA, Nigam P, Auffinger B, et al. Depletion of myeloid-derived suppressor cells during interleukin-12 immunogene therapy does not confer a survival advantage in experimental malignant glioma. Cancer Gene Ther. 2014;21(1):38–44. doi:10.1038/cgt.2013.81.CrossRefPubMedPubMedCentralGoogle Scholar