Specificity in the innate response: pathogen recognition by Toll-like receptor combinations

A key aspect of innate immunity is the recognition of pathogen-derived factors by macrophages. Toll-like receptors (TLRs) play a key role in this process, with TLR-4 recognizing lipopolysaccharide (LPS) from Gram-negative bacteria, and TLR-2 recognizing products such as peptidoglycan and lipopeptide from Gram-positive bacteria and zymosan from yeast. Eight other TLRs have been found, with TLR-9 recently being shown to recognize bacterially-derived CpG DNA. The function of the other TLRs is not known.