A polymorphism in human MR1 is associated with mRNA expression and susceptibility to tuberculosis.

The MR1 antigen-presenting system is conserved among mammals and enables T cells to recognize small molecules produced by bacterial pathogens, including Mycobacterium tuberculosis (M.tb). However, it is not known whether MR1-mediated antigen presentation is important for protective immunity against mycobacterial disease. We hypothesized that genetic control of MR1 expression correlates with clinical outcomes of tuberculosis infection. We performed an MR1 candidate gene association study and identified an intronic single-nucleotide polymorphism (rs1052632) that was significantly associated with susceptibility to tuberculosis in a discovery and validation cohort of Vietnamese adults with tuberculosis. Stratification by site of disease revealed that rs1052632 genotype GG was strongly associated with the development of meningeal tuberculosis (odds ratio=2.99; 95% confidence interval (CI) 1.64-5.43; P=0.00006). Among patients with meningeal disease, absence of the G allele was associated with an increased risk of death (hazard ratio=3.86; 95% CI 1.49-9.98; P=0.005). Variant annotation tools using public databases indicate that rs1052632 is strongly associated with MR1 gene expression in lymphoblastoid cells (P=0.004) and is located within a transcriptional enhancer in epithelial keratinocytes. These data support a role for MR1 in the pathogenesis of human tuberculosis by revealing that rs1052632 is associated with MR1 gene expression and susceptibility to tuberculosis in Vietnam.

MARCO variants are associated with phagocytosis, pulmonary tuberculosis susceptibility and Beijing lineage.

Macrophage receptor with collagenous structure (MARCO) has an important role in the phagocytosis of Mycobacterium tuberculosis (M. tuberculosis). We hypothesized that MARCO polymorphisms are associated with phagocytosis, tuberculosis (TB) disease susceptibility and presentation, and infecting lineage. We used a human cellular model to examine how MARCO genotype mediates the immune response; a case-control study to investigate tuberculosis host genetic susceptibility; and a host-pathogen genetic analysis to study host-pathogen interactions. Two MARCO heterozygous (AG) genotypes (single-nucleotide polymorphisms rs2278589 and rs6751745) were associated with impaired phagocytosis of M. tuberculosis trehalose 6,6'-dimycolate-cord factor and ß-glucan-coated beads in macrophages. The heterozygous genotypes of rs2278589 and rs6751745 were also associated with increased risk of pulmonary TB (PTB; rs2278589, P=0.001, odds ratio (OR)=1.6; rs6751745, P=0.009, OR=1.4), and with severe chest X-ray abnormalities (P=0.007, OR=1.6). These two genotypes were also associated with the Beijing lineage (rs2278589, P=0.001, OR=1.7; rs6751745, P=0.01, OR=1.5). Together, these results suggest that MARCO polymorphisms may regulate phagocytosis of M. tuberculosis and susceptibility and severity of PTB. They also suggest MARCO genotype and Beijing strains may interact to increase the risk of PTB.

TLR9 gene region polymorphisms and susceptibility to tuberculosis in Vietnam.

Humans exposed to Mycobacterium tuberculosis (Mtb) show variation in susceptibility to infection and differences in tuberculosis (TB) disease outcome. Toll-like receptor 9 (TLR9) is a pattern recognition receptor that mediates recognition of Mtb and modulates Mtb-specific T-cell responses. Using a case-population design, we evaluated whether single nucleotide polymorphisms (SNPs) in the TLR9 gene region are associated with susceptibility to pulmonary or meningeal TB as well as neurologic presentation and mortality in the meningeal TB group. In a discovery cohort (n = 352 cases, 382 controls), three SNPs were associated with TB (all forms, p < 0.05) while three additional SNPs neared significance (0.05 < p < 0.1). When these six SNPs were evaluated in a validation cohort (n = 339 cases, 367 controls), one was significant (rs352142) while another neared significance (rs352143). When the cohorts were combined, rs352142 was most strongly associated with meningeal tuberculosis (dominant model; p = 0.0002, OR 2.36, CI 1.43-3.87) while rs352143 was associated with pulmonary tuberculosis (recessive model; p = 0.006, OR 5.3, CI 1.26-31.13). None of the SNPs were associated with mortality. This is the first demonstration of an association between a TLR9 gene region SNP and tuberculous meningitis. In addition, this extends previous findings that support associations of TLR9 SNPs with pulmonary tuberculosis.

A polymorphism in human CD1A is associated with susceptibility to tuberculosis.

CD1 proteins are antigen-presenting molecules that evolved to present lipids rather than peptides to T cells. However, unlike major histocompatibility complex genes, CD1 genes show low rates of polymorphism and have not been clearly associated with human disease. We report that an intronic polymorphism in CD1A (rs411089) is associated with susceptibility to tuberculosis in two cohorts of Vietnamese adults (combined cohort odds ratio 1.78; 95% confidence interval: 1.24-2.57; P=0.001). These data strengthen the hypothesis that CD1A-mediated lipid antigen presentation is important for controlling tuberculosis in humans.

Epiregulin (EREG) variation is associated with susceptibility to tuberculosis.

Although host genetics influences susceptibility to Mycobacterium tuberculosis, the human genes regulating pathogenesis remain largely unknown. We used M. tuberculosis-stimulated macrophage gene expression profiling in conjunction with a case-control genetic association study to discover epiregulin (EREG), as a novel candidate tuberculosis (TB) susceptibility gene. Using a genome-wide association study dataset, we found that among the 21 genes with greater than 50-fold induction, EREG had the most polymorphisms associated with TB. We genotyped haplotype-tagging polymorphisms in discovery (N = 337 cases, N = 380 controls) and validation (N = 332 cases) datasets and an EREG polymorphism (rs7675690) was associated with susceptibility to TB (genotypic comparison; corrected P = 0.00007). rs7675690 was also associated more strongly with infections caused by the Beijing lineage of M. tuberculosis when compared with non-Beijing strains (controls vs Beijing, OR 7.81, P = 8.7 × 10(-5); non-Beijing, OR 3.13, P = 0.074). Furthermore, EREG expression was induced in monocytes and peripheral blood mononuclear cells stimulated with M. tuberculosis as well as TLR4 and TLR2/1/6 ligands. In murine macrophages, EREG expression induced by M. tuberculosis was MYD88- and TLR2-dependent. Together, these data provide the first evidence for an important role for EREG as a susceptibility gene for human TB.

A polymorphism in human TLR2 is associated with increased susceptibility to tuberculous meningitis.

Tuberculous meningitis (TBM) results from the haematogenous dissemination of Mycobacterium tuberculosis from the lung to the brain. Dissemination is believed to occur early during infection, before the development of adaptive immunity. Toll-like receptor 2 (TLR2) mediates recognition of M. tuberculosis and initiates the innate immune response to infection. We hypothesized that polymorphisms in the TLR2 gene influence bacterial dissemination and the development of TBM. A case-control study was designed to test the hypothesis. Cases of bacteriologically confirmed pulmonary tuberculosis (TB) (n=183) and TBM (n=175), and cord blood controls (n=389) were enrolled in Vietnam. TLR2 genotype 597CC was associated with susceptibility to TB (odds ratio (OR)=2.22, 95% confidence interval (CI): 1.23-3.99). The association was found with meningeal rather than pulmonary TB (TBM vs control, OR=3.26, 95% CI: 1.72-6.18), and was strongest when miliary TB was found on chest radiography (controls vs TBM with miliary TB, OR=5.28, 95% CI: 2.20-12.65). Furthermore, the association increased with the severity of neurologic symptoms (grade I TBM, OR=1.93, 95% CI: 0.54-6.92; grade II, OR=3.32, 95% CI: 0.84-13.2; and grade III, OR=5.70, 95% CI: 1.81-18.0). These results demonstrate a strong association of TLR2 SNP T597C with the development of TBM and miliary TB and indicate that TLR2 influences the dissemination of M. tuberculosis.

Diagnosis of adult tuberculous meningitis by use of clinical and laboratory features.

BACKGROUND: The diagnosis of tuberculous meningitis is difficult. Discrimination of cases from those of bacterial meningitis by clinical features alone is often impossible, and current laboratory methods remain inadequate or inaccessible in developing countries. We aimed to create a simple diagnostic aid for tuberculous meningitis in adults on the basis of clinical and basic laboratory features. METHODS: We compared the clinical and laboratory features on admission of 251 adults at an infectious disease hospital in Vietnam who satisfied diagnostic criteria for tuberculous (n=143) or bacterial (n=108) meningitis. Features independently predictive of tuberculous meningitis were modelled by multivariate logistic regression to create a diagnostic rule, and by a classification-tree method. The performance of both diagnostic aids was assessed by resubstitution and prospective test data methods. FINDINGS: Five features were predictive of a diagnosis of tuberculous meningitis: age, length of history, white-blood-cell count, total cerebrospinal fluid white-cell count, and cerebrospinal fluid neutrophil proportion. A diagnostic rule developed from these features was 97% sensitive and 91% specific by resubstitution, and 86% sensitive and 79% specific when applied prospectively to a further 42 adults with tuberculous meningitis, and 33 with bacterial meningitis. The corresponding values for the classification tree were 99% and 93% by resubstitution, and 88% and 70% with prospective test data. INTERPRETATION: This study suggests that simple clinical and laboratory data can help in the diagnosis of adults with tuberculous meningitis. Although the usefulness of the diagnostic rule will vary depending on the prevalence of tuberculosis and HIV-1 infection, we suggest it be applied to adults with meningitis and a low cerebrospinal fluid glucose, particularly in settings with limited microbiological resources.

Isoniazid resistance, mycobacterial genotype and outcome in Vietnamese adults with tuberculous meningitis.

SETTING: Centre for Tropical Diseases, a 500-bed hospital for infectious diseases in Ho Chi Minh City, Vietnam. OBJECTIVE: The factors that determine outcome in adults with tuberculous meningitis are poorly understood. The objective of the study was to investigate the relationship between admission clinical features, HIV infection, drug resistance, mycobacterial genotype and outcome in adults with tuberculous meningitis. DESIGN: Clinical and laboratory data were recorded prospectively for 56 Vietnamese adults with tuberculous meningitis confirmed by culture of cerebrospinal fluid. Variables associated with in-hospital mortality, IV infection, drug resistance and microbial genotype were assessed by univariate and multivariate analysis. RESULTS: Admission coma score independently predicted death in hospital (OR 0.73, 95%CI 0.61-0.87, P = 0.001). HIV-infected adults with tuberculous meningitis were more likely to be infected with Mycobacterium tuberculosis resistant to isoniazid (P = 0.011) and streptomycin (P = 0.002). Isoniazid resistance, streptomycin resistance, HIV infection and microbial genotype were not associated with increased in-hospital mortality. CONCLUSION: Treatment of tuberculous meningitis before the onset of coma saves lives. Resistance to isoniazid and/or streptomycin does not appear to affect outcome.

Malaria in injection drug abusers in Vietnam.

A prospective case-control study was conducted in a referral hospital in Ho Chi Minh City, Vietnam, to compare the clinical and laboratory features and outcome of severe falciparum malaria in injection drug abusers (IDAs) with those of patients who had acquired malaria by mosquito bite. From 1991 to 1996, 70 IDAs were admitted to the hospital, of whom at least 32 had acquired malaria by needle sharing. Although IDAs were more likely than control patients with severe malaria to be malnourished and to have coincident hepatitis B, hepatitis C, and human immunodeficiency virus infections, the overall rates of mortality, complications, and recovery were similar in the 2 groups. The route of malaria acquisition did not affect the outcome of severe malaria. The management of severe malaria in IDAs is similar to that for other patients.