TLR4MD2reseptoreihin

TLR4MD2reseptoreihin refers to the complex of Toll-like receptor 4 (TLR4) with the co-receptor myeloid differentiation protein 2 (MD‑2). This heterodimer is expressed predominantly on immune cells such as macrophages, dendritic cells, and certain non‑immune cell types, and is a key sensor of bacterial lipopolysaccharide (LPS) and other danger signals.

The receptor complex is embedded in the plasma membrane. MD‑2 is a soluble protein that nonspecifically associates with the extracellular domain of TLR4 via a hydrophobic groove that accommodates the lipid A portion of LPS. Binding of LPS to MD‑2 induces conformational changes that bring the TLR4 intracellular Toll/Interleukin‑1 receptor (TIR) domains into proximity. This dimerization triggers recruitment of adaptor proteins such as MyD88 and TRIF and activates downstream signaling cascades, including nuclear factor‑κB (NF‑κB) and MAP kinase pathways. The result is the transcription of pro‑inflammatory cytokines, chemokines, and type I interferons.

Genetic polymorphisms in TLR4 or MD‑2 can alter LPS sensitivity, influencing susceptibility to sepsis, bacterial meningitis, and other inflammatory diseases. In contrast, certain pathogens have evolved LPS variants that evade the TLR4‑MD‑2 axis, underscoring the complex interplay between host defense and microbial adaptation.

Beyond LPS, the TLR4‑MD‑2 complex also recognizes endogenous danger‑associated molecular patterns such as heat‑shock proteins and oxidized lipids, linking microbial recognition to tissue injury responses. Therapeutic modulation of this receptor complex, through antagonists or agonists, is being explored for conditions ranging from septic shock to cancer immunotherapy.

The term TLR4MD2reseptoreihin thus denotes the receptor system wherein TLR4 and MD‑2 cooperate to initiate innate immune signaling in response to lipid‑based pathogen products and endogenous danger signals.