Chicken TLR21 acts as a functional homologue to mammalian TLR9 in the recognition of CpG oligodeoxynucleotides

Brownlie, Robert; Zhu, Jianzhong; Allan, Brenda; Mutwiri, George; Babiuk, Lorne A.; Potter, Andrew; Griebel, Philip

doi:10.1016/j.molimm.2009.06.002

Cited by 230 publications

(150 citation statements)

References 41 publications

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“…One unique characteristic of chTLR21 is its broader CpG DNA ligand specificity compared with mammalian TLR9 as apparent from the response to both human-and murinespecific TLR9 ligand as well bacterial genomic DNA. Recent observations by Brownlie et al (37) further underpin the conclusion that chTLR21 responds to DNA.…”

Section: Discussionmentioning

confidence: 90%

Chicken TLR21 Is an Innate CpG DNA Receptor Distinct from Mammalian TLR9

Keestra

Zoete

Bouwman

et al. 2010

The Journal of Immunology

193

117

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TLRs comprise a family of evolutionary conserved sensory receptors that respond to distinct classes of ligands. For one major evolutionary branch of TLRs, the ligands are still largely unknown. Here we report the cloning and function of one member of this group, chicken TLR21 (chTLR21). This TLR is absent in the human species but has homologs in fish and frog and displays similarity with mouse TLR13. Expression of chTLR21 in HEK293 cells resulted in activation of NF-κB in response to unmethylated CpG DNA, typically recognized by mammalian TLR9. Silencing of chTLR21 (but not chTLR4) in chicken macrophages inhibited the response to CpG-DNA (but not to LPS), indicating similar functionality of the endogenous receptor. ChTLR21 responded to human- and murine-specific TLR9 ligands, as well as to bacterial genomic DNA isolated from Salmonella enterica serovar Enteritidis. Confocal microscopy located chTLR21 in the same intracellular compartments as human TLR9. Inhibition of the chTLR21 response by the endosomal maturation inhibitor chloroquine suggested that the receptor is functional in endolysosomes, as known for TLR9. The analogous localization and function of the phylogenetically only distantly related chTLR21 and mammalian TLR9 suggest that during evolution different classes of TLRs have emerged that recognize the same type of ligands.

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Section: Discussionmentioning

confidence: 90%

Chicken TLR21 Is an Innate CpG DNA Receptor Distinct from Mammalian TLR9

Keestra

Zoete

Bouwman

et al. 2010

The Journal of Immunology

193

117

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“…The interactions between chTLR21 and CpG-ODN have been characterized. CpG-ODNs containing GTCGTT motifs has been shown to have better activity to chTLR9 compared with CpGODNs with GACGTT motifs, whereas the GACGTT motifs containing CpG-ODN also activate chTLR21 (23,24). In this aspect, the ligand recognition specificity of TLR21 is somewhat conserved between chicken and zebrafish.…”

Section: Discussionmentioning

confidence: 99%

“…Of the 10 avian TLRs, TLR1La, TLR1Lb, TLR2a, TLR2b, TLR3, TLR4, TLR5, and TLR7 are orthologs to mammalian TLRs, whereas TLR15 and TLR21 are not found in mammals (22). It was recently demonstrated that chicken TLR21 (chTLR21) is a functional homolog to mammalian TLR9 in terms of response to CpG-ODN stimulation (23,24).…”

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confidence: 99%

Toll-like receptor 9 and 21 have different ligand recognition profiles and cooperatively mediate activity of CpG-oligodeoxynucleotides in zebrafish

Yeh

Liu

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

113

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CpG-oligodeoxynucleotides (CpG-ODNs) are potent immune stimuli currently under investigation as antimicrobial agents for different species. Toll-like receptor (TLR) 9 and TLR21 are the cellular receptors of CpG-ODN in mammals and chickens, respectively. The avian genomes lack TLR9, whereas mammalian genomes lack TLR21. Although fish contain both of these genes, the biological functions of fish TLR9 and TLR21 have not been investigated previously. In this study, we comparatively investigated zebrafish TLR9 (zebTLR9) and TLR21 (zebTLR21). The two TLRs have similar expression profiles in zebrafish. They are expressed during early development stages and are preferentially expressed in innate immune function-related organs in adult fish. Results from cell-based activation assays indicate that these two zebrafish TLRs are functional, responding to CpG-ODN but not to other TLR ligands. zebTLR9 broadly recognized CpG-ODN with different CpG motifs, but CpG-ODN with GACGTT or AACGTT had better activity to this TLR. In contrast, zebTLR21 responded preferentially to CpG-ODN with GTCGTT motifs. The distinctive ligand recognition profiles of these two TLRs were determined by their ectodomains. Activation of these two TLRs by CpG-ODN occurred inside the cells and was modulated by UNC93B1. The biological functions of these two TLRs were further investigated. The CpGODNs that activate both zebTLR9 and zebTLR21 were more potent than others that activate only zebTLR9 in the activation of cytokine productions and were more bactericidal in zebrafish. These results suggest that zebTLR9 and zebTLR21 cooperatively mediate the antimicrobial activities of CpG-ODN. Overall, this study provides a molecular basis for the activities of CpG-ODN in fish.pattern recognition receptor | innate immunity | adjuvant B acterial and viral CpG-deoxynucleotides containing DNA (CpG-DNA) represent a type of pathogen-associated molecular pattern (PAMP) that activates immune cells and triggers host responses to microbial infections (1-3). Synthetic phosphorothioate-modified CpG-oligodeoxynucleotides (CpG-ODNs) mimic the functions of CpG-DNA and have been investigated as immune modulators for their adjuvant and antimicrobial activities in different species (4-7). In general, a CpG-ODN contains one or more copies of CpG-deoxynucleotides containing hexamer motifs (CpG motifs). A CpG-ODN's immunostimulatory activities are dependent on its length, the number of CpG motifs, and the position, spacing, and surrounding bases of these CpG motifs.A CpG-ODN can have varying immunostimulatory activity in different species. This species-specific property is determined by the nucleotide context of the CpG motifs within the CpG-ODN. For example, CpG-ODNs containing a purine-purine-CGpyrimidine-pyrimidine motif, such as a GACGTT motif, are more potent in activating murine cells compared with those containing a GTCGTT motif. In contrast, the GTCGTT motif containing CpG-ODN generates stronger immune responses in humans and various domestic animals (8, 9).Toll-like receptors (...

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“…In mammals, TLR 9 recognizes bacterial DNA as well as unmethylated CpG DNA motifs and viral nucleic acids (Akira and Takeda 2004). The counterpart of TLR 9 in chicken is TLR 21 (Brownlie et al 2009, Keestra et al 2010. CpG ODNs are utilized for a variety of therapeutic purCorrespondence to: K. Chrząstek, e-mail: klaudia.chrzastek@up.wroc.pl, tel./fax: 0048 71 532 03 36 poses.…”

Section: Introductionmentioning

confidence: 99%