Tuberculosis and genes of the IL12/IL23/IFNγ pathway: Exploring functional significance of novel mutations in the IL12p40 promoter

Includes bibliographical references.The aim of this work was to screen the IL12p40 gene promoter for association with TB disease. Initially a subcohort of children (TB cases and healthy controls) from a TB-endemic area was screened for DNA changes by the WAVE method. Thereafter, the entire paediatric cohort and a cohort of healthy adult controls were screened by Amplification Refractory Mutation System PCR. Functional testing was done by reporter assay and immunological phenotype was investigated by measurement of cytokines levels and cytokine receptor expression. WAVE screening identified two heterozygous SNPs, -1523 A/G and -1564 C/T. Statistical analysis showed that -1523 A/G may be protective against TB disease (p=0.02). This possibility was supported by the location of -1523 A/G occurring within a GTATA sequence reported to bind nuclear proteins. Specific ARMS-PCR assays were then designed for screening of additional paediatric subjects and healthy adult controls for these SNPs. Analysis of the larger group, showed that -1564 C/T may contribute to susceptibility to TB disease (p=0.03) Exploring functional relevance, normal and mutant promoter fragments were PCR amplified, using uniquely adapted primers that included restriction sites corresponding to those in the multiple cloning site of an expression vector, facilitating cloning. A truncated promoter and one with essential regions deleted, were created as negative controls. These five promoter fragments were cloned into the expression vector and functional differences tested by reporter. No significant functional differences between variant and normal promoter fragments were observed. A predictive immune phenotype was investigated by measurement of IFNγ, TNFα and IL12p70 cytokine levels and IL12βR1 receptor expression. While distinct patterns of cytokine responses were seen, these did not predict genotype. These results show that the IL12p40 gene promoter is highly conserved and sequence variants may be just one of many factors contributing to TB susceptibility

X-linked Hyper IgM (HIGM1) in an African kindred: the first report from South Africa

BACKGROUND:The objective of this study was to describe the clinical and molecular features of the first South African family with X-linked hyper-IgM syndrome (HIGM1). METHODS: Diagnoses were based on immunoglobulin results and the absence of CD40 ligand (CD40L) expression on activated T-cells. Complete molecular characterisation involved CD40L cDNA sequencing, and genomic DNA analysis by polymerase chain reaction amplification, restriction enzyme digestion and sequencing. A PCR-based diagnostic assay was established for carrier detection and prenatal diagnosis in this family. RESULTS: There were originally six children, three males and three females. The eldest boy died after being diagnosed with hypogammaglobulinaemia, before HIGM1 was considered. This disorder was diagnosed in the second eldest boy at the age of 5 years, after failing to detect CD40L expression on his activated T-cells. A deficiency of CD40L was also confirmed in the youngest male at the age of 5 years. Both younger brothers have since died of infections relating to HIGM1. Molecular investigation showed that exon 3 was deleted from the CD40L mRNA of the affected males. Genomic DNA analysis identified a 1.5 kilobase deletion, spanning exon 3 and including extended flanking intronic sequence. Carrier status in the mother was confirmed by RT-PCR of her CD40L mRNA. Genetic analysis of the three female children was deferred because they were below the legal consenting age of 18 years. A PCR-based assay for genomic DNA was established for easy identification of female carriers and affected males in the future. CONCLUSIONS: This study confirmed the diagnosis of HIGM1 in the first South African family to be investigated and identified a novel mutation in the CD40L gene

Urine lipoarabinomannan testing for diagnosis of pulmonary tuberculosis in children: a prospective study

Background Urine tests for mycobacterial lipoarabinomannan might be useful for point-of-care diagnosis of tuberculosis in adults with advanced HIV infection, but have not been assessed in children. We assessed the accuracy of urine lipoarabinomannan testing for the diagnosis of pulmonary tuberculosis in HIV-positive and HIV-negative children. Methods We prospectively recruited children (aged ≤15 years) who presented with suspected tuberculosis at a primary health-care clinic and paediatric referral hospital in South Africa, between March 1, 2009, and April 30, 2012. We assessed the diagnostic accuracy of urine lipoarabinomannan testing with lateral fl ow assay and ELISA, with mycobacterial culture of two induced sputum samples as the reference standard. Positive cultures were identifi ed by acid-fast staining and tested to confi rm Mycobacterium tuberculosis and establish susceptibility to rifampicin and isoniazid. Findings 535 children (median age 42·5 months, IQR 19·1–66·3) had urine and two induced specimens available for testing. 89 (17%) had culture-confi rmed tuberculosis and 106 (20%) had HIV. The lateral fl ow lipoarabinomannan test showed poor accuracy against the reference standard, with sensitivity of 48·3% (95% CI 37·6–59·2), specifi city of 60·8% (56·1–65·3), and an area under the receiver operating characteristic curve of 0·53 (0·46–0·60) for children without HIV and 0·64 (0·51–0·76) for children with HIV. ELISA had poor sensitivity in children without HIV (sensitivity 3·0%, 95% CI 0·4–10·5) and children with HIV (0%, 0·0–14·3); overall specifi city was 95·7% (93·4–97·4). Interpretation Urine lipoarabinomannan tests have insuffi cient sensitivity and specifi city to diagnose HIV-positive and HIV-negative children with tuberculosis and should not be used in this patient population

Polymorphic Variation in TIRAP Is Not Associated with Susceptibility to Childhood TB but May Determine Susceptibility to TBM in Some Ethnic Groups

Host recognition of mycobacterial surface molecules occurs through toll like receptors (TLR) 2 and 6. The adaptor protein TIRAP mediates down stream signalling of TLR2 and 4, and polymorphisms in the TIRAP gene (TIRAP) have been associated with susceptibility and resistance to tuberculosis (TB) in adults. In order to investigate the role of polymorphic variation in TIRAP in childhood TB in South Africa, which has one of the highest TB incidence rates in the world, we screened the entire open reading frame of TIRAP for sequence variation in two cohorts of childhood TB from different ethnic groups (Xhosa and mixed ancestry). We identified 13 SNPs, including seven previously unreported, in the two cohorts, and found significant differences in frequency of the variants between the two ethnic groups. No differences in frequency between individual SNPs or combinations were found between TB cases and controls in either cohort. However the 558C→T SNP previously associated with TB meningitis (TBM) in a Vietnamese population was found to be associated with TBM in the mixed ancestry group. Polymorphisms in TIRAP do not appear to be involved in childhood TB susceptibility in South Africa, but may play a role in determining occurrence of TBM

Childhood tuberculosis is associated with decreased abundance of T cell gene transcripts and impaired T cell function

The WHO estimates around a million children contract tuberculosis (TB) annually with over 80 000 deaths from dissemination of infection outside of the lungs. The insidious onset and association with skin test anergy suggests failure of the immune system to both recognise and respond to infection. To understand the immune mechanisms, we studied genome-wide whole blood RNA expression in children with TB meningitis (TBM). Findings were validated in a second cohort of children with TBM and pulmonary TB (PTB), and functional T-cell responses studied in a third cohort of children with TBM, other extrapulmonary TB (EPTB) and PTB. The predominant RNA transcriptional response in children with TBM was decreased abundance of multiple genes, with 140/204 (68%) of all differentially regulated genes showing reduced abundance compared to healthy controls. Findings were validated in a second cohort with concordance of the direction of differential expression in both TBM (r2 = 0.78 p = 2x10-16) and PTB patients (r2 = 0.71 p = 2x10-16) when compared to a second group of healthy controls. Although the direction of expression of these significant genes was similar in the PTB patients, the magnitude of differential transcript abundance was less in PTB than in TBM. The majority of genes were involved in activation of leucocytes (p = 2.67E-11) and T-cell receptor signalling (p = 6.56E-07). Less abundant gene expression in immune cells was associated with a functional defect in T-cell proliferation that recovered after full TB treatment (p<0.0003). Multiple genes involved in T-cell activation show decreased abundance in children with acute TB, who also have impaired functional T-cell responses. Our data suggest that childhood TB is associated with an acquired immune defect, potentially resulting in failure to contain the pathogen. Elucidation of the mechanism causing the immune paresis may identify new treatment and prevention strategies

Genotype at position 558 of <i>TIRAP</i> and disease phenotype in the mixed ancestry cohort.

<p>Numbers of patients with mixed ancestry who had extrapulmonary TB compared to those that had pulmonary TB (top panel) and patients that had TBM compared with those that had other forms of TB (middle panel) for each genotype at position 558 of <i>TIRAP</i>. The lower panel shows the number of TBM patients compared with the healthy controls.</p

Frequency of SNP combinations in Xhosa and mixed ancestry groups.

*<p>Combination not present.</p

Combinations of SNPs in <i>TIRAP</i> found in individual patients or controls.

<p>Graph shows the frequency of 53 SNP combinations found in the A) Mixed ancestry and B) Xhosa groups. The blue bars are the cases and the orange bars are the controls. No combination of SNP was statistically significant between cases and controls when analysed by Fishers exact test.</p

Frequency of <i>TIRAP</i> variants in cases and controls for Xhosa and Mixed ancestry groups.

<p>The p-values for differences between cases and controls in each ethnic group were calculated by Fishers exact test or the Freeman Halton extension of the Fishers exact test when all three genotypes were present. No significant differences in the frequency of any SNP or genotype was observed between cases and controls. Differences in numbers of samples are due to sequence failures.</p