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Background and Objectives: Toll-like receptor 4 (TLR4) links human innate and adaptive immunity via bacterial endotoxin recognition, and has a considerable role in the pathogenesis of asthma.Although some genetic association studies on TLR4 and asthma have been performed, the effects of the genetic variants of TLR4 on asthma are still largely unknown.This study aimed to evaluate the effects of polymorphisms in TLR4 on asthma risk and asthma-related phenotypes in a Chinese Han population.Methods: We consecutively recruited 318 unrelated adult asthmatic patients and 352 healthy volunteers.Four tagging single nucleotide polymorphisms (SNPs) in TLR4 gene were detected using GenomeLab SNPstream or TaqMans Genotyping.We conducted case-control and case-only association studies between the selected tagging SNPs in TLR4 and asthma or asthma-related phenotypes.Results: We found no evidence to support a significant association between TLR4 SNPs and asthma susceptibility.However, our results revealed that TT homozygote of rs1927914 was associated with lower FEV1% and FEV1/FVC in asthmatic patients.An evidently positive association was found between the TT genotype of rs1927914, or the GG genotype ofrs10983755 and rs1927907, and asthma severity (P=0.008, 0.002, 0.004, respectively), which indicated that C allele of rs 1927914, and A allele of rs 10983755 and rs 1927907 had a protective effect on asthma severity.Associations between genetic variants in TLR4 and other asthma-related phenotypes, such as eosinophil counts, serum high-sensitivity C reactive protein and total serum immunoglobulin E levels, were not found.Conclusion: TLR4 polymorphisms do not contribute to asthma susceptibility, but may influence the severity of asthma.