Fold changes in relative mRNA expression of three immune response genes viz. IL1–β, iNOS and TLR15 were determined in bursa, spleen and thymus tissues of Rhode Island Red chicken. Total RNA was ...isolated from 12 birds, aged around 6–8 weeks. Relative quantification of mRNA expression was assessed by qRT-PCR. Fold expressions were determined using average threshold cycle (Ct) values employing 2(–∆∆Ct) method. There was wide variation in basal expression levels of immune response genes among different tissues. Basal mRNA expression of IL1–β, iNOS and TLR15 genes was several folds higher in bursa than in spleen and thymus. This investigation has generated important findings related to immune response genes expression which could pave way to further investigation in host-pathogen genetics and finally to develop breeding strategies for improvement of diseases resistance so as to have better protection and production in chicken.
Toll-like receptors (TLRs) activate innate immunity in response to pathogen-associated molecular patterns (PAMPs). The ectodomain of a TLR directly senses a PAMP and the intracellular TIR domain ...dimerizes to initiate a signaling cascade. The TIR domains of TLR6 and TLR10, which belong to the TLR1 subfamily, have been structurally characterized in a dimer, whereas those of other subfamilies, including TLR15, have not been explored at the structural or molecular level. TLR15 is a TLR unique to birds and reptiles that responds to virulence-associated fungal and bacterial proteases. To reveal how the TLR15 TIR domain (TLR15
) triggers signaling, the crystal structure of TLR15
was determined in a dimeric form and a mutational study was performed. TLR15
forms a one-domain structure in which a five-stranded β-sheet is decorated by α-helices, as shown for TLR1 subfamily members. TLR15
exhibits substantial structural differences from other TLRs at the BB and DD loops and αC2 helix that are involved in dimerization. As a result, TLR15
is likely to form a dimeric structure that is unique in its intersubunit orientation and the contribution of each dimerizing region. Further comparative analysis of TIR structures and sequences provides insights into the recruitment of a signaling adaptor protein by TLR15
.
Toll-like receptors (TLRs) form an ancient family of innate immune receptors that detect microbial structures and activate the host immune response. Most subfamilies of TLRs (including TLR3, TLR5, ...and TLR7) are highly conserved among vertebrate species. In contrast, TLR15, a member of the TLR1 subfamily, appears to be unique to birds and reptiles. We investigated the functional evolution of TLR15. Phylogenetic and synteny analyses revealed putative TLR15 orthologs in bird species, several reptilian species and also in a shark species, pointing to an unprecedented date of origin of TLR15 as well as large scale reciprocal loss of this TLR in most other vertebrates. Cloning and functional analysis of TLR15 of the green anole lizard (
), salt water crocodile (
), American alligator (
), and chicken (
) showed for all species TLR15 specific protease-induced activation of NF-κB, despite highly variable TLR15 protein expression levels. The variable TLR15 expression was consistent in both human and reptilian cells and could be attributed to species-specific differences in TLR15 codon usage. The species-specific codon bias was not or barely noted for more evolutionarily conserved TLRs (e.g., TLR3). Overall, our results indicate that TLR15 originates before the divergence of chondrichthyes fish and tetrapods and that TLR15 of both avian and reptilian species has a conserved function as protease activated receptor. The species-specific codon usage and large scale loss of TLR15 in most vertebrates suggest evolutionary regression of this ancient TLR.
Toll-like receptors (TLRs) constitute a multi-gene family, which plays a pivotal role in sensing invading pathogens by virtue of conserved microbial patterns. TLR repertoire of chicken and zebra ...finch has been well studied. However TLR family of other avian species is yet to be characterized. In the present study, we identified TLR repertoire of turkey, characterized avian specific receptor
TLR15
in turkey and profiled the TLRs expressions in a range of tissues of turkey poults. All ten TLR genes orthologous to chicken TLR repertoire were found in turkey. Turkey TLR genes showed 81–93 % similarity at amino acid level to their chicken counter parts. Phylogenetic analysis confirmed the orthologous relationship of turkey TLRs with chicken and zebra finch TLRs. Open reading frame of turkey
TLR15
was 2,607 bp long encoding 868 amino acids similar to that of broiler chicken and showed 92.4, 91.1 and 69.5 % identity at amino acid levels with chicken, Japanese quail and zebra finch TLR15 sequences respectively. Overall TLR expression was highest for
TLR4
and lowest for
TLR21. TLR1A
,
2A
,
2B
and
21
were significantly higher in liver than other tissues investigated (
P
< 0.01).
TLR3
expression was significantly higher in bone marrow (BM) and spleen in comparison to other tissues studied (
P
< 0.01). Furthermore, no significant differences in the expression levels of
TLR1B
,
4
,
5
,
7
and
15
genes were detected among the tissues studied. Our findings contribute to the characterization of innate immune system of birds and show the innate preparedness of young turkey poults to a range of pathogens.
Aim: To assess the basal constitutive expression levels of ch-TLR3, ch-TLR 4, ch-TLR 15 and ch-TLR 21 in the peripheral blood mononuclear cells (PBMCs) in Aseel and Kadaknath chicks (Indian native ...poultry breeds) and to evaluate the differences in their general innate immune competence. Materials and Methods: PBMCs were isolated from 21 day old Aseel and Kadaknath chicks (n = 4) and were subjected to RNA isolation and cDNA synthesis. The basal expression of ch-TLR 3, 4, 15 and 21 was studied using real time PCR with SYBR green chemistry using 18 S-rRNA as the housekeeping gene. Results: PBMCs isolated from Kadaknath chicks exhibited a significantly higher (p < 0.05) constitutive expression of ch-TLR 3, ch-TLR 15 and ch-TLR 21 genes when compared to Aseel chicks. In comparison to Aseel, Kadaknath chicks recorded 14.774, 7.182 and 3.507 fold higher expressions of ch-TLR 3, ch-TLR 15 and ch-TLR 21 genes, respectively. In contrast, the constitutive expression of ch-TLR 4 was found to be higher (by 1.733 fold) in Aseel chicks. Conclusion: Our results indicate that Kadaknath chicks are equipped with a better innate immune competence in comparison to Aseel chicks. Keywords: Aseel, ch-TLR3, ch-TLR4, ch-TLR15, ch-TLR21, Kadaknath, Innate immune competence
PDF
