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Toll-like receptor 9
Symbols TLR9; CD289
External IDs OMIM605474 MGI1932389 HomoloGene68126 GeneCards: TLR9 Gene
Species Human Mouse
Entrez 54106 81897
Ensembl ENSG00000173366 ENSMUSG00000045322
UniProt Q9NR96 Q4L0K3
RefSeq (mRNA) NM_017442 NM_031178
RefSeq (protein) NP_059138 NP_112455
Location (UCSC) Chr 3:
52.26 - 52.27 Mb
Chr 9:
106.08 - 106.08 Mb
PubMed search [1] [2]

Toll-like receptor 9 is a protein that in humans is encoded by the TLR9 gene.[1] TLR9 has also been designated as CD289 (cluster of differentiation 289).



TLR9 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 named for the high degree of conservation in structure and function seen between mammalian TLRs and the Drosophila transmembrane protein Toll. TLRs are transmembrane proteins, expressed on the cell surface and the endocytic compartment and recognize pathogen-associated molecular patterns (PAMPs) that are expressed on infectious agents and initiate signalling to induce production of cytokines necessary for the innate immunity and subsequent adaptive immunity. The various TLRs exhibit different patterns of expression. This gene is preferentially expressed in immune cell rich tissues, such as spleen, lymph node, bone marrow and peripheral blood leukocytes. Studies in mice and human indicate that this receptor mediates cellular response to unmethylated CpG dinucleotides in bacterial DNA to mount an innate immune response.[2]

TLR9 recognizes unmethylated CpG sequences in DNA molecules. CpG sites are relatively rare (~1%) on vertebrate genomes in comparison to bacterial genomes or viral DNA. TLR9 is expressed by numerous cells of the immune system such as dendritic cells, B lymphocytes and natural killer (NK) cells. TLR9 is expressed intracellularly, within the endosomal compartments and functions to alert the immune system of viral and bacterial infections by binding to DNA rich in CpG motifs. TLR9 signals leads to activation of the cells initiating pro-inflammatory reactions that result in the production of cytokines such as type-I inteferon and IL-12. There are new immunomodulatory treatments undergoing testing which involve the administration of artificial DNA oligonucleotides containing the CpG motif. CpG DNA has applications in treating allergies such as asthma, immunostimulation against cancer, immunostimulation against pathogens, and as adjuvants in vaccines.


TLR9 has been shown to interact with RNF216.[3]


  1. ^ Du X, Poltorak A, Wei Y, Beutler B (Dec 2000). "Three novel mammalian toll-like receptors: gene structure, expression, and evolution". Eur Cytokine Netw 11 (3): 362–71. PMID 11022119. 
  2. ^ "Entrez Gene: TLR9 toll-like receptor 9". 
  3. ^ Chuang, Tsung-Hsien; Ulevitch Richard J (May. 2004). "Triad3A, an E3 ubiquitin-protein ligase regulating Toll-like receptors". Nat. Immunol. (United States) 5 (5): 495–502. doi:10.1038/ni1066. ISSN 1529-2908. PMID 15107846. 

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



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