TLR4 and Alzheimer disease: Lactobacillus plantarum MA2 can improve the cognitive impairment and anxiety-like behavior of AD rats induced by D-Galactose/AlCl3, reduce neuronal degeneration and A β accumulation in the brain, regulate gut microbiota imbalance, alleviate intestinal mucosal injury through TLR4/MYD88/NLRP3 signal pathway, and inhibit microglial activation and neuroinflammation.