Allelic variation in TLR4 is linked to susceptibility to Salmonella enterica serovar Typhimurium infection in chickens - PubMed (original) (raw)

Allelic variation in TLR4 is linked to susceptibility to Salmonella enterica serovar Typhimurium infection in chickens

Gary Leveque et al. Infect Immun. 2003 Mar.

Abstract

Toll-like receptor 4 (TLR4) is part of a group of evolutionarily conserved pattern recognition receptors involved in the activation of the immune system in response to various pathogens and in the innate defense against infection. We describe here the cloning and characterization of the avian orthologue of mammalian TLR4. Chicken TLR4 encodes a 843-amino-acid protein that contains a leucine-rich repeat extracellular domain, a short transmembrane domain typical of type I transmembrane proteins, and a Toll-interleukin-1R signaling domain characteristic of all TLR proteins. The chicken TLR4 protein shows 46% identity (64% similarity) to human TLR4 and 41% similarity to other TLR family members. Northern blot analysis reveals that TLR4 is expressed at approximately the same level in all tissues tested, including brain, thymus, kidney, intestine, muscle, liver, lung, bursa of Fabricius, heart, and spleen. The probe detected only one transcript of ca. 4.4 kb in length for all tissues except muscle where the size of TLR4 mRNA was ca. 9.6 kb. We have mapped TLR4 to microchromosome E41W17 in a region harboring the gene for tenascin C and known to be well conserved between the chicken and mammalian genomes. This region of the chicken genome was shown previously to harbor a Salmonella susceptibility locus. By using linkage analysis, TLR4 was shown to be linked to resistance to infection with Salmonella enterica serovar Typhimurium in chickens (likelihood ratio test of 10.2, P = 0.00138), suggesting a role of TLR4 in the host response of chickens to Salmonella infection.

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Figures

FIG. 1.

FIG. 1.

Predicted protein alignments of chicken TLR4 (chTLR4; GenBank accession no. AY064697), human TLR4 (hTLR4; GenBank accession no. U93091), murine Tlr4 (mTlr4; GenBank accession no. AF110133), chicken TLR2 type 1 (chTLR2type1; GenBank accession no. AB050005), and chicken TLR2 type 2 (chTLR2type2; GenBank accession no. AB046533). Amino acid identity between all five species is indicated in black; the identity or similiarity between three or more species is highlighted in gray. Gaps are represented by a dash. The predicted transmembrane domain (TD) of TLR4 is underlined. The locations of degenerate primers are marked “degF” and “degR.”

FIG. 2.

FIG. 2.

(A) Northern blot analysis of TLR4 expression in various chicken tissues. The blot contains 10 μg of total RNA per tissue and was hybridized with a 2.1-kb chicken TLR4 cDNA subfragment. (B) The Northern blot was probed with a partial chicken β-actin cDNA probe for normalization.

FIG. 3.

FIG. 3.

Graphic representation of the chicken TLR4 coding region and localization of sequence variations detected between W1-resistant and C-susceptible chickens. Roman numerals represent exons. The LRR and TIR homology domain are shown. The hatched area represents the transmembrane domain. Conservative substitutions at the predicted protein level are flagged in white, and nonconservative substitutions are flagged in black.

FIG. 4.

FIG. 4.

Chromosomal mapping of chicken TLR4 to microchromosome E41W17 with respect to the microsatellite markers ADL0293, MCW0330, and TNC. cM, centimorgans.

FIG. 5.

FIG. 5.

Effects of TLR4 and NRAMP1 genotypes on survival of chickens to infection with serovar Typhimurium. (A) Survival curves for (W1 × C)F1 × C progeny harboring CC or CW1 genotype at TLR4. (B) Survival curves for backcross progeny grouped according to their genotypes at NRAMP1 and TLR4 jointly.

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