TLR4 and brain ischemia: Damage-associated molecular patterns (DAMPs) and pathogen-associated molecular pattern ligands (PAMPs) generated by cerebral ischemia and hypoxia cross the blood-brain barrier (BBB) into the CNS and activate the Toll-like receptor 4 (TLR4) on the surface of neurons, microglia, and astrocyte cell membranes (Shi et al., 2019).