Toll-like receptors; their physiological role and signal transduction system

Int Immunopharmacol. 2001 Apr;1(4):625-35. doi: 10.1016/s1567-5769(01)00010-8.


Drosophila Toll protein is a transmembrane receptor whose function is to recognize the invasion of microorganisms as well as to establish dorso-ventral polarity. Recently, mammalian homologues of Toll, designated as Toll-like receptors (TLRs) have been discovered. So far, six members (TLR1-6) have been reported and two of these, TLR2 and TLR4, have been shown to be essential for the recognition of distinct bacterial cell wall components. TLR2 discriminates peptidoglycan (PGN), lipoprotein, lipoarabinomannan (LAM) and zymosan, whereas TLR4 recognizes lipopolysaccharide (LPS), lipoteichoic acid (LTA) and Taxol. Bacterial components elicit the activation of an intracellular signaling cascade via TLR in a similar way to that occurs upon ligand binding to IL-1 receptor (IL-1R). This signaling pathway leads to the activation of a transcription factor NF-kappaB and c-Jun N-terminal kinase (JNK), which initiate the transcription of proinflammatory cytokine genes. Particularly, analysis of knockout mice revealed a pivotal role for MyD88 in the signaling of the TLR/IL-1R family. Taken together, TLRs and the downstream signaling pathway play a key role in innate immune recognition and in subsequent activation of adaptive immunity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Animals
  • Antigens, Differentiation / physiology
  • Drosophila Proteins*
  • Humans
  • I-kappa B Kinase
  • Lipopolysaccharides / pharmacology
  • Membrane Glycoproteins / physiology*
  • Myeloid Differentiation Factor 88
  • NF-kappa B / physiology
  • Protein Serine-Threonine Kinases / physiology
  • Receptors, Cell Surface / physiology*
  • Receptors, Immunologic*
  • Receptors, Interleukin-1 / physiology
  • Signal Transduction*
  • Toll-Like Receptor 1
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • Toll-Like Receptors


  • Adaptor Proteins, Signal Transducing
  • Antigens, Differentiation
  • Drosophila Proteins
  • Lipopolysaccharides
  • MYD88 protein, human
  • Membrane Glycoproteins
  • Myeloid Differentiation Factor 88
  • NF-kappa B
  • Receptors, Cell Surface
  • Receptors, Immunologic
  • Receptors, Interleukin-1
  • TLR2 protein, human
  • TLR4 protein, human
  • Toll-Like Receptor 1
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • Toll-Like Receptors
  • Protein Serine-Threonine Kinases
  • CHUK protein, human
  • I-kappa B Kinase
  • IKBKB protein, human
  • IKBKE protein, human