Cloning and characterization of the murine toll-like receptor 5 (Tlr5) gene: sequence and mRNA expression studies in Salmonella-susceptible MOLF/Ei mice.

Toll-like receptors (TLRs) are a group of evolutionarily conserved pattern recognition receptors involved in the activation of the immune system in response to various pathogens. In this paper, we describe the cloning and characterization of the mouse homologue of human TLR5. Mouse Tlr5 encodes a 859-amino-acid protein that contains an N-terminal signal sequence, 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 mouse Tlr5 protein shows 81% homology to human TLR5 and approximately 40% similarity to other TLR family members. Northern blot analysis reveals that Tlr5 is expressed predominantly in liver and lung with low-level expression in most other tissues examined. We have mapped Tlr5 to distal chromosome 1 using the (C57BL/6J x Mus spretus) x C57BL/6J Jackson BSB panel as well as a (C57BL/6J x MOLF/Ei)F(2) panel with the following position: D1Mit112-8.0 cM-Tlr5-9.6 cM-D1Mit17. The presence of a quantitative trait locus for susceptibility to Salmonella typhimurium on distal chromosome 1 prompted the examination of Tlr5 in susceptible MOLF/Ei mice. Polymorphic sequence variants in Tlr5 allowed us to identify a unique 4-allele haplotype in MOLF/Ei. Furthermore, using both Northern blot analysis and reverse transcription-polymerase chain reaction, we have shown a reduced expression of Tlr5 during infection of MOLF/Ei mice with Salmonella. The assignment of Tlr5 to a chromosomal region known to harbor a Salmonella-susceptibility locus together with decreased expression of Tlr5 mRNA in liver of susceptible MOLF/Ei mice suggests the possibility that, as with other members of this family, Tlr5 may play a role in host response to bacterial gram-negative infections.