Fig. 1.

Immune gateways (left). In addition to the resident microglia, there are three distinct macrophage populations within the CNS present at so-called ‘immune gateways’ that act as ports of entry for activated T cells into the CNS. Perivascular macrophages, derived from the embryonic yolk sac, are located around parenchymal vessels (top). The other two populations, derived from bone marrow, are located in the meningeal spaces (middle) and the choroid plexus (bottom) (adapted from ref. ¹⁵⁶). Immune evasion in glioblastoma (right): the immunosuppressive tumour microenvironment (TME) of glioblastoma is the result of complex interactions between tumour cells, microglia, tumour-associated macrophages (TAMs), components of the extracellular matrix and tumour infiltrating lymphocytes (TILs), which are predominantly regulatory in phenotype (T-regs). Hypoxia promotes angiogenesis of abnormal blood vessels, further driving tumour growth (adapted from ref. ¹⁰)