Toll-like receptor 9 (TLR-9) promotor polymorphisms and gene expression are associated with persistent Staphylococcus aureus nasal carriage.

OBJECTIVES: Toll-like receptor (TLR) 9 could have importance in human Staphylococcus aureus immunity, but population-level evidence for this hypothesis is missing. METHODS: We phenotyped S. aureus nasal carriage of 603 volunteers using four consecutive swabs, genotyped TLR9 promotor variants in 106 persistent carriers and 219 noncarriers, measured TLR9-mRNA expression in whole blood after stimulation with viable S. aureus and studied mutual associations of carriage, transcriptional activity and single nucleotide polymorphisms while accounting for sex and hormone contraceptive use (HCU). RESULTS: The -1486 (rs187084) and -1237 (rs5743836) CT haplotype was more common in noncarriers (185/438, 42%) than in carriers (63/212, 30%), with the TT haplotype showing a reverse association (noncarriers, 180/438, 41%; carriers 117/212, 55%) (χ2 p 0.001). Mean TLR9 mRNA expression in whole blood was higher in noncarriers (ratiocarriers/noncarriers 0.63; 95% confidence interval, 0.43-0.92; p 0.017). A duplication of TLR9 transcriptional activity lowered the odds of persistent S. aureus carriage by 37% in the overall group (odds ratio = 0.63; 95% confidence interval, 0.42-0.94; p 0.022) and by 54% in women (odds ratio = 0.46; 95% confidence interval, 0.23-0.90; p 0.023). Promotor haplotype and HCU had a combined effect on TLR9 transcription (interaction model): women in the TT (risk) haplotype/HCU- stratum (baseline) had lower mRNA levels than women in the CT (protective) haplotype/HCU- (ratio 1.92; p 0.055), the CT haplotype/HCU+ (ratio 2.02; p 0.032) and the TT haplotype/HCU+ (ratio 2.59; p < 0.004) strata. No such associations were observed in men. CONCLUSIONS: We provide evidence that TLR9 affects human S. aureus immunity and present potential explanations for differences according to sex in S. aureus colonization and infection.

Structure-function relationships of Toll-like receptor domains through homology modelling and molecular dynamics.

TLRs (Toll-like receptors) are pattern-recognition receptors of the immune system and recognize pathogens based on distinct molecular signatures. Although different TLRs within the same species (orthologues) or individual TLRs across different species (homologues) are similar in protein sequence, they differ considerably with regard to their function, for example with regard to ligand discrimination or adaptor selection. Owing to the lack of structural information, explanations for these phenomena have been difficult to provide. We have combined homology modelling with energy minimization and Molecular Dynamics simulation in order to address these interesting biological phenomena from a structural angle. Thus three-dimensional models of human and mouse TLR3 and TLR4 domains were successfully generated. Apart from providing a structural framework in which mutagenesis studies (both site-directed and random) can be interpreted and designed, Molecular Dynamics also allowed us to study and simulate protein structure under solution-like conditions. We have applied this approach to the human TLR3 and TLR4 ECDs (ectodomains) providing insights into the dynamics of TLR ECDs. Other conclusions drawn from our structural models are also discussed. We hope that our structural modelling approach, which can be extended to other members of the TLR family or other signal transduction pathways, will serve as a valuable tool for the design of experiments to address questions of TLR biology further.

Evolutionary relationships, but functional differences, between the Drosophila and human Toll-like receptor families.

The Toll receptor was first found to function in the dorsoventral patterning pathway of Drosophila embryos. It is activated by a specific protein ligand, Spätzle, generated at ventral positions in the early embryo. Drosophila Toll (dToll) also functions in innate immune responses to Gram-positive bacteria and fungi, and Spätzle is required for this response. We have shown that Spätzle is necessary and sufficient for activation of the dToll pathway, and that it probably acts by cross-linking two molecules of Toll to form homodimers. In the present paper, we contrast this mode of regulation with that proposed for the vertebrate Toll-like receptor family, which mediate analogous responses to pathogen pattern antigens. In contrast with dToll, these receptors appear to be activated by direct exposure to pathogen patterns, such as peptidoglycan and lipopolysaccharide. We discuss the evolutionary basis of this functional divergence of the vertebrate and invertebrate Toll-like receptors.