Combinational recognition of bacterial lipoproteins and peptidoglycan by chicken Toll-like receptor 2 subfamily

Abstract

2 SummaryHuman TLR2 subfamily recognizes bacterial lipoproteins (BLP) and peptidoglycan (PGN). According to the genome information, chicken has structural orthologs of TLRs 1 and 2, in addition to TLRs3, 4, 5 and 7. Chicken has two additional TLRs, TLR15 and TLR21, which orthologs human lacks. The chicken (ch)TLR1 and 2 genes are individually duplicated to encode for two different proteins, chTLRs, chTLR1-1, 1-2, 2-1 and 2-2, of the TLR2 subfamily. Here we investigated the functional profile of these TLR2 subfamily proteins of chicken. By NF-κB reporter assay using HEK293 cells, we found that chTLR2-1 and chTLR1-2 cooperatively signal the presence of PGN. A combination of chTLR2-1 and chTLR1-2 also most efficiently recognized diacylated BLP, Malp-2, while the combination of chTLR2-1 and chTLR1-1 failed to recognize Malp-2. All combinations, however, recognized triacylated BLP, Pam3. Consistent with these results, human TLR2-stimulating mycobacteria preparations, BCG-cell wall and cell lysate of Mycobacterium avium, induced activation of NF-κB in cells expressing chTLR2-1 and 1-2 and to lesser extents, cells with chTLR2-2 and either of chTLR1. Strikingly, expression of either of these alone did not activate the reporter for NF-κB. These chTLRs are likely to have the combination functional feature as in the human TLR2 subfamily. Confocal and immunoprecipitation analyses of human cell transfectants showed that they cluster on the cell surface by a physical molecular association, causing all of them to merge and coprecipitate. These results suggest that chTLR2 subfamily members discriminate between their ligands by combinational events.

Activation of Human and Chicken Toll-Like Receptors by Campylobacter spp

“…Identification and characterization of the chicken TLRs revealed major species-specific characteristics. For instance, the chicken TLR2 complex does not seem to distinguish between different lipoproteins in contrast to its human counterpart (22,28), whereas chickens lack TLR9 but express the unique DNA-sensing TLR21 (9; A. M. Keestra et al, unpublished data (8). In the present study, we for the first time directly compared the potential of Campylobacter to activate individual human and chicken TLRs.…”

The Differential Evolutionary Dynamics of Avian Cytokine and TLR Gene Classes

“…All nine TLRs resequenced in this study have been associated with chicken bacterial and viral diseases through differential expression assays (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). Among the nine cytokines resequenced in this study, at least GM-CSF, IL-4, IL-8, IL-12a, and IL-13 have been linked with disease resistance or susceptibility (29)(30)(31)(32)(33)(34).…”

TLR15 Is Unique to Avian and Reptilian Lineages and Recognizes a Yeast-Derived Agonist

“…Many cTLRs have been characterized including TLR3, TLR4, TLR5, and TLR7, which are orthologous to their mammalian counterparts and share agonist specificity (16)(17)(18)(19)(20)(21). Unlike mammals, chickens possess two TLR1 genes (TLR1.1 and 1.2) and two TLR2 genes (TLR2.1 and TLR2.2) that can form homodimers or heterodimers and respond to peptidoglycan, diacylated lipopeptides, and triacylated lipopeptides (22)(23)(24). In mammalian species, these agonists are recognized by various heterodimers composed of TLR1 or TLR6 with the single TLR2.…”