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 immune response by recognizing specific molecules from pathogens, such as bacteria and viruses. When TLR4 detects these molecules, it activates signaling pathways that lead to the production of inflammatory cytokines, helping the body fight off infections. TLR4 is part of a larger family of proteins known as Toll-like receptors, which are essential for detecting various pathogens. This receptor is particularly important for recognizing lipopolysaccharides (LPS), components of the outer membrane of gram-negative bacteria. By triggering immune responses, TLR4 helps maintain the body's defense against infections.