MRC1 and central nervous system cancer: To further investigate tumor-associated cells in this hypoxic glioma microenvironment and to clarify the cellular sources of IL6, we collected 5 freshly removed, surgical WHO grade IV glioma tissue samples for fast-frozen sectioning, and staining revealed most of the tumor-associated cells in the microenvironment, including T cells (CD3), macrophages (CD68, CD11B), microglia (CD68), M1 tumor-associated macrophages (CD11B, CD16), M2 tumor-associated macrophages (CD206), tumor-associated dendritic cells (CD11C), monocytes and some NK cells (CD16) (Fig. S2A).