Toll-Like Receptor 4 (TLR4) is a protein found on the surface of certain immune cells. It plays a crucial role in the body's defense system by recognizing harmful substances, such as bacteria and viruses. When TLR4 detects these pathogens, it activates the immune response, helping the body to fight off infections. TLR4 specifically recognizes a component of the cell wall of Gram-negative bacteria called lipopolysaccharide (LPS). This interaction triggers a signaling cascade that leads to the production of inflammatory cytokines, which are essential for coordinating the immune response. Understanding TLR4 is important for developing treatments for various infections and inflammatory diseases.