TLR4 and autism: The central pathway by which LPS leads to an inflammatory environment in the brain causing neurodegeneration in patients with autism is as follows: gut endotoxins may enter the blood due to a leaky gut and subsequently enter the brain tissue by crossing the blood-brain barrier and cause brain inflammation via activation of the TLR4–MyD88–NF-κB transcriptional pathway in macrophages to induce pro-inflammatory cytokines, such as tumor necrosis factor α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), interleukin-1 (IL-1), IL-6, and IL-1β [28, 45, 46].