We therefore hypothesized that compartmentalization of different myeloid cell populations may be driven by the degree of hypoxia in the surrounding tissue, assessed here through the up-regulation of GLUT1 and pERK (phospho-Erk1/2, Thr202/Tyr204), markers which have been previously shown to increase in response to tissue hypoxia in GBM (34–37). Here, MAPK3 is linked to glioblastoma.