Recognition of pathogenic microorganisms by Toll-like receptors.

Toll-like receptors (TLRs) have been identified as a major class of pattern-recognition receptors. Recognition of pathogen-associated molecular patterns (PAMPs) by TLRs, either alone or in heterodimerization with other TLR or non-TLR receptors, induces signals responsible for the activation of innate immune response. Recent studies have demonstrated a crucial involvement of TLRs in the recognition of all the major classes of microbial pathogens. By studying fungal infection in knock-out mice deficient in either TLRs or TLR-associated adaptor molecules, it appeared that specific TLRs play differential roles in the activation of the various arms of the innate immune response. Recent data also suggest that TLRs offer escape mechanisms to certain pathogenic microorganisms, especially through TLR2-driven induction of antiinflammatory cytokines. These new data have substantially increased our knowledge of the recognition of microbial pathogens, and this remains one of the most active areas of research in the field of infectious diseases.