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TLR 9 is a toll-like receptor.
It recognizes unmethylated CpG sites on DNA molecules. CpG sites are extremely rare (~1%) on vertebrate genomes but prevalent on bacterial and 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.
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Transmembrane receptors: immune receptors |
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| Cytokine receptor |
Type I: Interleukins ( 2, 3, 4, 5, 6, 7, 9, 11, 12, 13, 15, 21, 23, 27), CSF receptors ( EPO, GM-CSF, G-CSF), GH, prolactin, Oncostatin M, Leukemia inhibitory factor - common subunits ( Common gamma chain, common beta chain, CSF2RB)
Type II: Interleukins (10, 20, 22, 28) - interferon (-α/β, -γ)
immunoglobulin superfamily: CSF1, C-kit, IL-1, IL-18
Tumor necrosis factor: CD27, CD30, CD40, CD120, Lymphotoxin β
Chemokines: IL-8 (α, β), CCR1,CXCR4
Other: IL-17, TGF-beta ( 1, 2)
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| Pattern recognition/Toll-like |
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| Fc receptor |
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| Lymphocyte homing receptor |
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| other |
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