Toll-like receptor heterodimer variants protect from childhood asthma

Early exposure to microbes reduces the risk for asthma. Toll-like receptors (TLRs) represent a major group of receptors for the specific recognition of pathogen-associated molecular patterns of microbes capable of activating innate and adaptive immunity.

Because TLRs can influence key events in the induction and perpetuation of asthma and atopy, we sought to determine whether genetic alterations in TLR genes affect asthma risk.

We systematically evaluated putatively functional genetic variants in all 10 human TLR genes for their association with different asthma phenotypes in a case-control study (n = 1872) by using matrix-assisted laser desorption/ionization time-of-flight genotyping. For polymorphisms showing association with atopic asthma, effects on gene and protein expression were studied by means of RT-PCR and flow cytometry ex vivo. T-cell cytokine production was evaluated by means of ELISA after stimulation of the respective TLRs with specific ligands.

Protective effects on atopic asthma were identified for single nucleotide polymorphisms in TLR1 (odds ratio [OR], 0.54; 95% CI, 0.37-0.81; P = .002), TLR6 (OR, 0.54; 95% CI, 0.37-0.79; P = .003), and TLR10 (OR, 0.58; 95% CI, 0.39-0.86; P = .006), all capable of forming heterodimers with TLR2. Effects remained significant after correction for multiple comparisons. PBMCs of minor allele carriers showed increased levels of the respective TLR mRNA and proteins, augmented inflammatory responses, increased T(H)1 cytokine expression, and reduced T(H)2-associated IL-4 production after specific stimulation.

These results suggest that functional relevant TLR1 and TLR6 variants are directly involved in asthma development.