CXCL8 and glioblastoma: Amongst the soluble factors secreted by microglial cells, IL-1 is known to activate GBM cells, partially due to the activation of TGFβ pathway, and also to alter their secretome, resulting in the up-regulation of interleukin-8 (IL-8) and C–C motif chemokine ligand 2 (CCL2), and the down-regulation of collagen type IV α 2 chain (COL4A2) [197].