TLR4 and aneurysm: Heme, oxygenated hemoglobin, methemoglobin, peroxidase-2, matricellular proteins, heat shock protein, fibrinogen and so on produced by erythrocyte degradation after aneurysm rupture can lead to the activation of early inflammatory signaling pathways (such as TLR4) in aSAH when large amounts of blood enter the subarachnoid space (28, 30).