The toll-like receptor 4 Asp299Gly variant: no influence on LPS responsiveness or susceptibility to pulmonary tuberculosis in The Gambia
Introduction
Mycobacterium tuberculosis infects 2 billion people globally, yet only 10% develop clinical disease.1 Even so, tuberculosis (TB) remains a major cause of morbidity and mortality worldwide. Prolonged treatment with multiple drugs is required and compliance is poor. This has contributed to the global rise in multi-drug-resistant TB.2 Furthermore, BCG vaccination does not protect against TB in countries where disease is most prevalent.3 The identification of factors that predispose to (or protect against) disease could aid the development of new therapies and vaccines.
The increased rate of TB in immunodeficient individuals, particularly those co-infected with the human immunodeficiency virus, highlights the importance of the host-immune response in the containment of disease. However, most people who develop TB are not immunosuppressed, and genetic variation in the host immune response is an important determinant of susceptibility to TB.4 Most of the genes identified to date are involved in innate immune responses, including solute carrier family 11 member 1, SLC11A1 (formerly natural resistance associated macrophage protein 1, NRAMP1), the vitamin D receptor gene and genes within the interleukin-12/interferon-γ (IL-12/IFN-γ) pathway.4., 5., 6., 7. The innate response is activated by the interaction of microbial components with receptor complexes expressed on the surface of host cells including macrophages and dendritic cells.8 This interaction induces macrophage antimicrobial functions, the production of inflammatory cytokines such as tumour necrosis factor (TNF), and primes specific immune responses by the production of IL-12. Several receptors are involved in the recognition of mycobacterial cell wall components. More recently, the importance of Toll-like receptors (TLRs) in cellular activation by M. tuberculosis has been described.9., 10. TLR2 interacts with M. tuberculosis cell wall components to induce cellular activation, killing of intracellular microbes and apoptosis.11 TLR4, initially identified as the mediator of lipopolysaccharide (LPS) inflammatory responses,12 can also interact with both heat labile soluble mycobacterial factor and whole viable M. tuberculosis to initiate innate responses.13., 14. M. tuberculosis-induced TNF and nitric oxide production can be blocked by the lipopolysaccharide (LPS) lipid A antagonist E5531.15 In a recent study, Tlr4-deficient mice developed chronic lung infection resembling human disease when exposed to aerosolized M. tuberculosis.16 This was associated with uncontrolled M. tuberculosis growth within the lung tissue, reduced macrophage recruitment to lung tissue, and reduced amounts of IL-12p40, TNF and monocyte chemoattractant protein-1 in lung homogenates.
Two mis-sense mutations have been identified in the extracellular domain of the human homologue, TLR4, (Asp229Gly and Thr399Ile) that are associated with hyporesponsiveness to LPS in alveolar macrophages and epithelial cells, and peripheral blood mononuclear cells.17., 18. We have investigated the role of the Asp229Gly polymorphism in susceptibility to TB in an outbred Gambian population sample: the Thr399Ile polymorphism was absent in a different Gambian population sample.19
Section snippets
Methods
This study had the approval of the MRC/Gambia Government Ethics Committee. The study cohort has been described elsewhere.20 Briefly, 320 men with pulmonary TB (mean age 36 years, range 19–58) were recruited from the TB clinic at Serrekunda Health Centre, The Gambia. All cases had microscopically proven, smear-positive TB in the context of clinical and radiological findings consistent with pulmonary TB, in the absence of other chronic illness, HIV infection, or treatment with corticosteroids.
Results
Allele and genotype frequencies for the TLR4 Asp299Gly polymorphism in the TB cases and matched control subjects are shown in Table 1. No differences were observed in either allele or genotype frequency between the TB cases and the controls, and no deviation from Hardy-Weinberg equilibrium was detected. Allele frequency differences were assessed in an additional population sample of 148 individuals, representing five Gambian ethnic groups (Table 2). The genotype frequencies in each sample were
Discussion
We have found no association between the Asp299Gly variant of TLR4 and pulmonary TB, suggesting that it has no major role in susceptibility to TB in this population. Furthermore, there is no association between carriage of the Asp299Gly G allele and LPS hyporesponsiveness using a whole blood assay in this Gambian population. Our negative findings have a number of possible interpretations. Firstly, the Asp299Gly polymorphism may influence susceptibility to TB, but if the effect were small (i.e.
Acknowledgements
We thank Professors Keith McAdam and Jenefer Blackwell for their support. This study was supported by the MRC (UK). MJ Newport holds a Wellcome Trust Advanced Clinical Fellowship. A Awomoyi received financial support from the Sir Halley Stewart Trust. GS thanks Mathurin Diatta for help with data collection.
References (26)
- et al.
Association between tuberculosis and a polymorphic NFkappaB binding site in the interferon gamma gene
Lancet
(2003) The mouse as a useful model for tuberculosis
Tuberculosis
(2003)- et al.
Consensus statement. Global burden of tuberculosisestimated incidence, prevalence, and mortality by country. WHO global surveillance and monitoring project
J Am Med Assoc
(1999) - et al.
Tuberculosis drug resistancea global threat
Clin Infect Dis
(2003) Bacille Calmette–Guerin vaccinesa rough guide
Clin Infect Dis
(1994)- et al.
Genetic dissection of immunity to mycobacteriathe human model
Ann Rev Immunol
(2002) - et al.
Interferon-gamma and interleukin-10 gene polymorphisms in pulmonary tuberculosis
Am J Respir Crit Care Med
(2003) - et al.
Influence of interleukin-12 receptor β1 polymorphisms on tuberculosis
Hum Genet
(2003) - et al.
Innate immune recognitionmechanisms and pathways
Immunol Rev
(2000) - et al.
Host defense mechanisms triggered by microbial lipoproteins through toll-like receptors
Science
(1999)
Cell activation and apoptosis by bacterial lipoproteins through toll-like receptor-2
Science
Toll-like receptor-2 mediates mycobacteria-induced proinflammatory signalling in macrophages
Proc Natl Acad Aci USA
Defective LPS signalling in C3H/HeJ and C57BL/10ScCr micemutations in the TLR4 gene
Science
Cited by (78)
Significance of CCL2 (−2518A/G), CCR2 (190G/A) and TLR4 polymorphisms (896 A/G and 1196C/T) in tuberculosis risk in Indian population
2018, Meta GeneCitation Excerpt :Numerous studies, conducted in separate ethnic groups, have shown association of 896 A/G (also known as D299G) or 1196C/T (also referred to as T399I) single nucleotide polymorphisms of the TLR4 gene (located at the chromosome 9 in humans) with enhanced susceptibility to tuberculosis (Pulido et al., 2010; Ferwerda et al., 2007; Najmi et al., 2010). In contrast, there have been reports that deny any relationship between TB and the 896 A/G or 1196C/T SNPs (Selvaraj et al., 2010; Newport et al., 2004). However, synergistic effect of polymorphisms of the TLR genes (TLR4 ‘1196C/T’ and TLR9 ‘−1486T/C’) have been reported.
The NRAMP1, VDR, TNF-α, ICAM1, TLR2 and TLR4 gene polymorphisms in Iranian patients with pulmonary tuberculosis: A case-control study
2016, Infection, Genetics and EvolutionSepsis: A roadmap for future research
2015, The Lancet Infectious DiseasesDiscovery of high frequencies of the Gly-Ile haplotype of TLR4 in Indian populations requires reformulation of the evolutionary model of its maintenance
2013, Infection, Genetics and EvolutionCitation Excerpt :Two non-synonymous SNPs rs4986790 (A/G, Asp > Gly) and rs4986791 (C/T, Thr > Ile) at amino acid positions 299 and 399, respectively, are found in the ligand-binding Leucine rich-repeat (LRR) domain of the TLR4 protein (Arbour et al., 2000). Population genetic studies have indicated a geographical structuring of these two TLR4 polymorphisms which showed that at the Asp299Gly and Thr399Ile loci, the Gly–Thr haplotype is mostly prevalent in Africa, the Gly–Ile in Europeans and that these polymorphisms are absent in Asia and the Americas (Arbour et al., 2000; Ferwerda et al., 2007, 2008; Mockenhaupt et al., 2006; Newport et al., 2004; Smirnova et al., 2001; Schroder and Schumann, 2005). These observations were used to formulate a plausible evolutionary model for maintenance of these polymorphisms in TLR4 (Ferwerda et al., 2007, 2008; Plantinga et al., 2012).
- 1
Co-corresponding author. Laboratory of Human Genetics, MRC The Gambia, PO Box 273, Banjul, The Gambia. Tel.: +220-4-494069; fax: +220-4-495919/496513.