Figure 3. Reactive microgliosis promotes brain tumor progression.
Microglial cells become hyper-activated through two mechanisms in brain tumor microenvironment. First, microglial cells become active, produce cytokines, growth factors and matrix-metalloproteases (MMPs) in response to initial tumor cell stimuli. Microglia-secreted factors then promote tumor growth and invasion. Second, tumor cells release growth, chemoattractant, and chemokine factors that recruit and induce another wave of microglial activation, resulting in a perpetuating cycle of microglia activation in the brain tumor. IL-6: Interleukin IL-6, IL-10: Interleukin 10, TGF-β: Transforming growth factor, PGE2: Prostaglandin E2, GM-CSF: granulocyte-macrophage colony stimulating factor, MCP-1: Monocyte chemoattractant protein-1, ATP: Adenosine triphosphate, miRNAs: microRNAs.