Toll like receptors

Toll like receptors (TLRs) are a class of proteins that play a key role in the innate immune system.  TLRs are the oldest class of pattern recognition receptors (PRRs) with the most extensive spectrum of pathogen recognition, with many TLRs identified across a wide range of invertebrate and vertebrate species.  TLRs are single transmembrane cell surface receptors, expressed on sentinel cells such as macrophages and dendritic cells, that recognize molecules derived from microbes.  TLRs are classified into two subfamilies based on their localization - cell surface and intracellular TLRs.   Types of molecules recognised by TLRs include lipids, lipoproteins, proteins, lipopolysaccharides, peptidoglycans, lipotechoic acids, zymosan, mannan and bacterial flagellin.  Although pathogen associated molecular pattern (PAMP) recognition by TLRs is crucial for host defense responses to infection, aberrant activation of TLR signaling is implicated in the development of several diseases such as autoimmune, chronic inflammatory and allergic diseases as well as cancer and thrombosis.

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