Toll-like receptor 4 and Myeloid differentiation primary response gene 88 signaling pathway (TLR4/MyD88 pathway)

The Toll-like receptor 4 and Myeloid differentiation primary response gene 88 signaling pathway is a critical component of innate immunity. Toll-like receptor 4 (TLR4) is a transmembrane pattern recognition receptor that detects pathogen-associated molecular patterns such as bacterial lipopolysaccharide (LPS). Upon activation by its ligands, TLR recruits adaptor proteins including Myeloid differentiation primary response gene 88 (MyD88), which mediates signal transduction from activated receptors to downstream components through TIR domain interactions.[1] The canonical function involves two main pathways triggered by ligand binding: 1. The MyD88-dependent pathway: Activated at the plasma membrane by ligand-bound TLRs except for some endosomal receptors like TLR3. This leads to recruitment of adaptors such as TIRAP/Mal and ultimately results in activation of transcription factors NF-kB and AP1 via IRAK/TRAF6/TAK1 cascades. These transcription factors induce expression of pro-inflammatory cytokines including TNF-alpha and IL6.[2] 2. The TRIF-dependent pathway: Activated after internalization into endosomes; leads primarily to type I interferon production. Balanced activation between these pathways is crucial for appropriate immune responses against pathogens while avoiding excessive inflammation that could result in tissue damage or systemic complications like sepsis.[3] This signaling axis plays essential roles in host defense against infection but also contributes significantly to inflammatory diseases when dysregulated.

Other names

TLR4-MyD88 axisMyD88-dependent TLR4 signaling pathway[2][3]