Abstract
Tuberculosis (TB) is the leading cause of death worldwide due to an infectious agent. Data have accumulated over decades suggesting that variability in human susceptibility to TB disease has a genetic component. Toll-like receptors (TLRs) play a critical role in initiating the innate immune response to many pathogens in mouse models, but little is known about their role in human infections. Human TLRs have been reported to recognize mycobacterial antigens and initiate an immune response. We tested the hypothesis that amino acid-altering polymorphisms in five TLRs were associated with susceptibility to TB disease using a population-based case-control study with 1,312 adult TB patients and controls. Full-coding region sequencing of the five TLR genes in all 1,312 subjects yielded a data set in excess of 16 Mb. Rare nonsynonymous polymorphisms in TLR6-TLR1-TLR10 were significantly overrepresented among African-American TB cases compared with ethnically-matched control subjects. Common nonsynonymous polymorphisms in TLR6-TLR1-TLR10 also were significantly associated with TB disease in certain ethnic groups. Among African Americans, homozygotes for the common-variant haplotype TLR1-248S, TLR1-602I, and TLR6-249S had a significantly increased TB disease risk. A transmission/disequilibrium test on an independent sample found that the TLR1-248S variant was preferentially transmitted to diseased children, thereby confirming disease association. These results are consistent with recent reports implicating TLR1 variants, including TLR1-602, in significantly altered innate immune responses. Also consistent with disease association, rare TLR6 variants were defective in their ability to mediate NF-κB signal transduction in transfected human cells. Taken together, the data suggest that variant TLRs contribute to human susceptibility to TB disease. Extensive full-exon resequencing was critical for revealing new information about the role of TLRs in human-pathogen interactions and the genetic basis of innate immune function.
Highlights
Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (MTB), is a leading public health problem in the United States and throughout the world [1]
There was a significant increase in the frequency of rare nonsynonymous polymorphisms (NSPs) in TB patients compared to the matched controls
In the case of TLR1, the transmission/ disequilibrium test (TDT) analysis revealed that the allele encoding the Toll-like receptors (TLRs)-248S variant was significantly overrepresented among diseased children (P = 0.021)
Summary
Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (MTB), is a leading public health problem in the United States and throughout the world [1]. The molecular mechanisms responsible for susceptibility to clinical disease caused by this pathogen are poorly understood. Many lines of evidence suggest that host genetics contributes to the susceptibility of humans to developing disease after exposure to MTB [2,3,4,5,6]. Studies have identified associations between polymorphisms in several candidate genes and clinical TB [4,5,6,7,8,9,10,11,12,13,14]. With few exceptions, the disease-associated alleles reported in these studies have only relatively modest effects, suggesting that additional susceptibility genes remain to be discovered
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