TLR4 and brain ischemia: Brain ischemia upregulates the microglial expression of MerTK (8) and Gal-3 (39), and this 7may be mediated, in part, by TLR4, because TLR4 is highly expressed in microglia during ischemia (e.g., 40) and has multiple potential ligands, including HMGB1, that are upregulated by ischemia (41).