Which Toll-like receptor (TLR) binds to lipopolysaccharide (LPS) found on gram-negative bacteria?

The correct answer is TLR 4, which is specifically responsible for recognizing lipopolysaccharide (LPS) molecules that are present on the outer membrane of gram-negative bacteria. This interaction is crucial for initiating the immune response against gram-negative pathogens.

TLR 4 is part of the innate immune system and plays a vital role in detecting bacterial infections. When LPS binds to TLR 4, it triggers a cascade of signaling events that result in the activation of immune cells, leading to an inflammatory response and the production of cytokines. This helps the body effectively respond to and eliminate the bacteria.

The other TLR options have different roles in the immune system. For instance, TLR 2 typically recognizes peptidoglycan and other components from both gram-positive bacteria and some gram-negative bacteria, but not specifically LPS. TLR 5 is known for detecting bacterial flagellin, while TLR 6 is involved in the sensing of diacylated lipopeptides. These distinct specificities highlight the importance of TLR 4 in the context of gram-negative bacterial infections.