TLR4

TLR4, or Toll-like receptor 4, is a protein that plays a critical role in the innate immune system. It is a type of pattern recognition receptor (PRR) that identifies pathogen-associated molecular patterns (PAMPs), which are molecules derived from microbes such as bacteria, viruses, and fungi. TLR4 is primarily expressed on the surface of immune cells such as macrophages, dendritic cells, and monocytes.

The primary function of TLR4 is to detect lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria. Upon recognition of LPS, TLR4 initiates a signaling cascade that activates inflammatory responses. This process involves the recruitment of adaptor proteins like MyD88 and TRIF, leading to the activation of transcription factors such as NF-κB and IRF3. These factors promote the expression of pro-inflammatory cytokines, chemokines, and type I interferons, which help orchestrate an immune response against invading pathogens.

TLR4 signaling is tightly regulated to prevent excessive inflammation, which can contribute to inflammatory and autoimmune disorders. Dysregulation or overactivation of TLR4 has been linked to conditions like sepsis, atherosclerosis, and autoimmune diseases.

Research on TLR4 extends into therapeutic applications, including vaccine development and treatments aimed at modulating immune responses in infectious and inflammatory diseases. Its central role in immune surveillance makes TLR4 a significant target for understanding host-pathogen interactions and developing immunomodulatory therapies.

In summary, TLR4 is a vital component of the innate immune system, responsible for detecting microbial lipopolysaccharides and initiating defensive inflammatory responses.