TLR 2: Wikis

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Toll-like receptor 2

PDB rendering based on 1fyw.
Available structures
1fyw, 1fyx, 1o77
Identifiers
Symbols TLR2; CD282; TIL4
External IDs OMIM603028 MGI1346060 HomoloGene20695 GeneCards: TLR2 Gene
RNA expression pattern
PBB GE TLR2 204924 at tn.png
More reference expression data
Orthologs
Species Human Mouse
Entrez 7097 24088
Ensembl ENSG00000137462 ENSMUSG00000027995
UniProt O60603 Q811T5
RefSeq (mRNA) NM_003264 NM_011905
RefSeq (protein) NP_003255 NP_036035
Location (UCSC) Chr 4:
154.84 - 154.85 Mb
Chr 3:
83.92 - 83.93 Mb
PubMed search [1] [2]

Toll-like receptor 2 also known as TLR-2 is a protein which in humans is encoded by the TLR2 gene.[1] TLR2 has also been designated as CD282 (cluster of differentiation 282). TLR-2 plays a role in the immune system. TLR-2 is a membrane protein, a receptor, which is expressed on the surface of certain cells and recognizes foreign substances and passes on appropriate signals to the cells of the immune system.

Contents

Function

The protein encoded by this gene is a member of the Toll-like receptor (TLR) family which plays a fundamental role in pathogen recognition and activation of innate immunity. TLRs are highly conserved from Drosophila to humans and share structural and functional similarities. They recognize pathogen-associated molecular patterns (PAMPs) that are expressed on infectious agents, and mediate the production of cytokines necessary for the development of effective immunity. The various TLRs exhibit different patterns of expression. This gene is expressed most abundantly in peripheral blood leukocytes, and mediates host response to Gram-positive bacteria and yeast via stimulation of NF-κB.[2]

Background

The immune system recognizes foreign pathogens and eliminates them. This occurs in several phases. In the early inflammation phase, the pathogens are recognized by antibodies that are already present (innate or acquired through prior infection; see also cross-reactivity). Immune-system components (e.g. complement) that are bound to the antibodies and kept around in reserve then disable them, and they are phagocytized by scavenger cells (e.g. macrophages). Dendritic cells are likewise capable of phagocytizing but do not do it for the purpose of direct pathogen elimination. Rather, they infiltrate the spleen and lymph nodes, and each presents components of an antigen there, as the result of which specific antibodies are formed that recognize precisely that antigen.

These newly formed antibodies would arrive too late in an acute infection, however, so what we think of as "immunology" constitutes only the second half of the process. Because this phase would always start too late to play an essential role in the defense process, a faster-acting principle is applied ahead of it, one that occurs only in forms of life that are phylogenetically more highly developed.

What are called pattern-recognition receptors come into play here. This refers to receptors that recognize the gross, primarily structural features of molecules not innate to the host organism. These include, for example, lipids with a totally different basic chemical structure. Such receptors are bound directly to cells of the immune system and cause immediate activation of their respective nonspecific immune cells.

A prime example of such a foreign ligand is bacterial endotoxin, whose effects have been known for generations. When it enters the bloodstream it causes systematic activation of the early-phase response, with all the side effects of septic shock. This is known in the laboratory as the Shwartzman phenomenon. The intended effect is to mobilize the organism for combat, so to speak, and eliminate most of the pathogens.

Mechanism

As a membrane surface receptor, TLR-2 recognizes many bacterial, fungal, viral, and certain endogenous substances. In general, this results in the uptake (internalization, phagocytosis) of bound molecules by endosomes/phagosomes and in cellular activation; thus such elements of innate immunity as macrophages, PMNs and dendritic cells assume functions of nonspecific immune defense, B1a and MZ B cells form the first antibodies, and specific antibody formation gets started in the process. Cytokines participating in this include tumor necrosis factor-alpha (TNF-α) and various interleukins (IL-1α, IL-1β, IL-6, IL-8, IL-12). Before the TLRs were known, several of the substances mentioned were classified as modulins. Due to the cytokine pattern, which corresponds more closely to Th1, an immune deviation is seen in this direction in most experimental models, away from Th2 characteristics. Conjugates are being developed as vaccines or are already being used without a priori knowledge.

A peculiarity first recognized in 2006 is the expression of TLR-2 on Tregs (a type of T cell), which experience both TCR-controlled proliferation and functional inactivation. This leads to disinhibition of the early inflammation phase and of specific antibody formation. Following a reduction in pathogen count, many pathogen-specific Tregs are present that, now without a TLR-2 signal, become active and inhibit the specific and inflammatory immune reactions (see also TNF-β, IL-10). Older literature that ascribes a direct immunity-stimulating effect via TLR-2 to a given molecule must be interpreted in light of the fact that the TLR-2 knockouts employed typically have very few Tregs.

Functionally relevant polymorphisms are reported that cause functional impairment and thus generally reduced survival rates, particularly in infections/sepsis with Gram-positive bacteria.

Signal transduction is depicted under Toll-like receptor.

Expression

TLR-2 is expressed on microglia, Schwann cells, monocytes, macrophages, dendritic cells, polymorphonuclear leukocytes (PMNs or PMLs), B cells (B1a, MZ B, B2), and T cells, including Tregs (CD4+CD25+ regulatory T cells). In some cases it occurs in a heterodimer (combination molecule), e.g. paired with TLR-1 or TLR-6. TLR-2 is also found in the epithelia of air passages, pulmonary alveoli, renal tubules, and the Bowman's capsules in renal corpuscles. In the skin it is found on keratinocytes and sebaceous glands; spc1 is induced here, allowing a bactericidal sebum to be formed.

Agonists

Agonist Organism
Lipoteichoic acid Gram-positive bacteria
atypical LPS Leptospirosis and Porphyromonas gingivalis
MALP-2 and MALP-404 (lipoproteins) Mycoplasma
- Chlamydophila pneumoniae
OspA Borrelia burgdorferi (Lyme disease)
Porin Neisseria meningitidis Haemophilus influenzae
Antigen mixtures Propionibacterium acnes
LcrV Yersinia
Lipomannan Mycobacterium: Mycobacterium tuberculosis
GPI anchor Trypanosoma cruzi
Lysophosphatidylserine Schistosoma mansoni
Lipophosphoglycan (LPG) Leishmania major
Glycophosphatidylinositol (GPI) Plasmodium falciparum
Zymosan (a beta-glucan) Saccharomyces cerevisiae
- Malassezia (commensal yeast)
Antigen mixtures Aspergillus fumigatus, Candida albicans
hsp60, as peptide transporter and adjuvant for antigen presentation -
- Herpes simplex virus
- Varicella zoster virus
- Cytomegalovirus (CMV)
Hemagglutinin Measles

Interactions

TLR 2 has been shown to interact with TLR 1[3] and TOLLIP.[4]

References

  1. ^ Rock FL, Hardiman G, Timans JC, Kastelein RA, Bazan JF (January 1998). "A family of human receptors structurally related to Drosophila Toll". Proc. Natl. Acad. Sci. U.S.A. 95 (2): 588–93. doi:10.1073/pnas.95.2.588. PMID 9435236. PMC 18464. http://www.pnas.org/content/95/2/588. 
  2. ^ "Entrez Gene: TLR2". http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=7097. 
  3. ^ Takeuchi, Osamu; Sato Shintaro, Horiuchi Takao, Hoshino Katsuaki, Takeda Kiyoshi, Dong Zhongyun, Modlin Robert L, Akira Shizuo (Jul. 2002). "Cutting edge: role of Toll-like receptor 1 in mediating immune response to microbial lipoproteins". J. Immunol. (United States) 169 (1): 10–4. ISSN 0022-1767. PMID 12077222. 
  4. ^ Zhang, Guolong; Ghosh Sankar (Mar. 2002). "Negative regulation of toll-like receptor-mediated signaling by Tollip". J. Biol. Chem. (United States) 277 (9): 7059–65. doi:10.1074/jbc.M109537200. ISSN 0021-9258. PMID 11751856. 

Further reading

  • Aderem A, Ulevitch RJ (2000). "Toll-like receptors in the induction of the innate immune response.". Nature 406 (6797): 782–7. doi:10.1038/35021228. PMID 10963608. 
  • Muzio M, Polentarutti N, Bosisio D, et al. (2001). "Toll-like receptor family and signalling pathway.". Biochem. Soc. Trans. 28 (5): 563–6. PMID 11044375. 
  • Hallman M, Rämet M, Ezekowitz RA (2002). "Toll-like receptors as sensors of pathogens.". Pediatr. Res. 50 (3): 315–21. doi:10.1203/00006450-200109000-00004. PMID 11518816. 
  • Dziarski R, Gupta D (2001). "Role of MD-2 in TLR2- and TLR4-mediated recognition of Gram-negative and Gram-positive bacteria and activation of chemokine genes.". J. Endotoxin Res. 6 (5): 401–5. PMID 11521063. 
  • Lien E, Ingalls RR (2002). "Toll-like receptors.". Crit. Care Med. 30 (1 Suppl): S1–11. doi:10.1097/00003246-200201001-00001. PMID 11782555. 
  • Xu D, Komai-Koma M, Liew FY (2005). "Expression and function of Toll-like receptor on T cells.". Cell. Immunol. 233 (2): 85–9. doi:10.1016/j.cellimm.2005.04.019. PMID 15950961. 
  • Lorenz E (2007). "TLR2 and TLR4 expression during bacterial infections.". Curr. Pharm. Des. 12 (32): 4185–93. doi:10.2174/138161206778743547. PMID 17100621. 


This article incorporates text from the United States National Library of Medicine, which is in the public domain.

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