Toll-like Receptor - Ligands

Ligands

Because of the specificity of Toll-like receptors (and other innate immune receptors) they cannot easily be changed in the course of evolution, these receptors recognize molecules that are constantly associated with threats (i.e., pathogen or cell stress) and are highly specific to these threats (i.e., cannot be mistaken for self molecules). Pathogen-associated molecules that meet this requirement are usually critical to the pathogen's function and cannot be eliminated or changed through mutation; they are said to be evolutionarily conserved. Well-conserved features in pathogens include bacterial cell-surface lipopolysaccharides (LPS), lipoproteins, lipopeptides, and lipoarabinomannan; proteins such as flagellin from bacterial flagella; double-stranded RNA of viruses; or the unmethylated CpG islands of bacterial and viral DNA; and certain other RNA and DNA. For most of the TLRs, ligand recognition specificity has now been established by gene targeting (also known as "gene knockout"): a technique by which individual genes may be selectively deleted in mice. See the table below for a summary of known TLR ligands.