Human genetic susceptibility to tuberculosis: time for a bottom-up approach?

IL-6 and IL-18 cytokine gene variants of pulmonary tuberculosis patients with co-morbid diabetes mellitus and their household contacts in Hyderabad

PURPOSE

Association of cytokine genes reflects their susceptibility towards infection and disease in household contacts (HHC) of pulmonary tuberculosis (PTB) patients. Hyperglycemia, a common factor in diabetics might influence their risk towards mycobacterium tuberculosis infection and disease development. This study determines the association of IL-6 and IL-18 cytokine gene variants of TB patients with diabetes mellitus (TBDM) and their HHC in Hyderabad.

METHODS

Single nucleotide polymorphisms of IL-6 (-174 G>C and -572 G>C) and IL-18 (-137 G>C and -607 C>A) cytokine genes were genotyped by Amplification Refractory Mutation System and Restriction Fragment Length polymerase chain reaction in total of 705 subjects comprising of TBDM, their HHC, PTB, DM and Healthy controls (HC).

RESULTS

At IL-6 -174G>C variant, GG genotype, G allele in TBDM and TBDM HHC, at -572G>C variant, C allele in TBDM and GG haplotype in TBDM HHC were showing positive association, however DM have not shown any association at IL-6 polymorphic sites. With respect to the IL-18 gene polymorphisms, at -137 G>C variant, GG genotype was positively associated in PTB while at -607 C>A variant positive association was shown with AC genotype in TBDM, their HHC and DM; GACC diplotype in TBDM and GCGC in PTB.

CONCLUSION

Our findings suggest that susceptible combination of IL-6 and IL-18 cytokine genes associated with disease in the HHCs highlight their risk of inclination towards the disease.

A rare variant at 11p13 is associated with tuberculosis susceptibility in the Han Chinese population

Genome-wide association studies (GWASs) have yet to be conducted for tuberculosis (TB) susceptibility in China. Two previously identified single nucleotide polymorphisms (SNPs) from tuberculosis GWASs, rs2057178 and rs4331426, were evaluated for TB predisposition. The associations between SNPs and gene expression levels were analyzed using the genomic data and corresponding whole-genome expression of the Han Chinese in Beijing, China. Genotyping was successfully completed for 763 pulmonary TB patients and 763 healthy controls. The T allele of the rare variant rs2057178 was significantly associated with TB predisposition (χ² = 14.07, P = 0.0002). Meanwhile, the CT genotype of rs2057178 was associated with a decreased risk of TB (adjusted OR = 0.52, 95% CI, 0.34–0.78). The CT genotype of rs2057178 was also associated with decreased expression levels of infection-related gene, suppressor of cytokine signaling 2 (SOCS2), and increased expression levels of v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB). No gene expression levels were found to be associated with the genotype of rs4331426. We found that the rare variant rs2057178 was significantly associated with TB in the Han Chinese population. Moreover, the expression levels of MAFB and SOCS2 correlated with rs2057178 and might be potential candidates for assessing TB susceptibility.

Genetic polymorphisms of CCL1 rs2072069 G/A and TLR2 rs3804099 T/C in pulmonary or meningeal tuberculosis patients

CCL1, one of the members of the CC chemokine family, is an inflammatory mediator that stimulates the migration of human monocytes. CCL1 expression is induced by Mycobacterium tuberculosis and TLR ligands in macrophage. TLR2 plays critical role in host immune response against M. tuberculosis infection by regulating the macrophage activation and cytokine secretion. M. tuberculosis causes different clinical forms of tuberculosis (TB) disease. Single-nucleotide polymorphisms (SNPs) in the CCL1 gene and TLR2 gene may be associated with the development of different clinical forms of TB, depending on the different immune mechanisms. This study was to evaluate the possible association between CCL1 rs2072069 G/A or/and TLR2 rs3804099 T/C (T597C) polymorphisms and pulmonary tuberculosis (PTB) or/and tuberculous meningitis (TBM) in a sample of the Chinese adult population. A case-control study was designed to compare the allele frequency and genotype distribution between control (n=386) and TB (n=341) who had either PTB (n=230) or TBM (n=111). The genotype typing was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. TLR2 variant genotype 597CC was associated with susceptibility to PTB rather than to TBM. In the male PTB subgroup, 597CC genotype was identified in a higher rate, compared with male control subgroup. This study demonstrates that T597C polymorphism of TLR2 is a risk factor for susceptibility to PTB rather than to TBM in a sample of Chinese adult population. Patient gender may affect the outcome of M. tuberculosis infection. TLR2 gene may influence the development of PTB and TBM by different immune mechanisms.

Association between cytokine gene polymorphisms and tuberculosis in a Chinese population in Shanghai: a case-control study

BACKGROUND

Polymorphisms in cytokine genes are known to influence cytokine levels, which may influence susceptibility to tuberculosis (TB) infection and disease. Differences in cytokine expression probably determine whether TB progresses, resolves, or becomes latent. In particular, the balance between the Th1 and Th2 cytokine responses influences the expression of disease in individuals with pulmonary TB (PTB). We performed a case-control study of 120 patients diagnosed with PTB, 240 with latent TB infection (LTBI), and 480 healthy controls (HC), to explore the association between polymorphisms in cytokine genes and a predisposition to Mycobacterium tuberculosis infection and TB disease.

RESULTS

A single-gene analysis showed a dominant association between the AA genotype or A allele at nucleotide -874 of the interferon γ (IFN-γ) gene and LTBI. The A allele at nucleotide -1082 of the interleukin 10 (IL-10) gene was significantly more common in PTB patients than in LTBI subjects. Moreover, the polymorphisms at IFN-γ -874 and IL10 - 1082 were associated with protein levels of IFN-γ and IL-10, respectively, in the PTB group. The genotype frequencies of other polymorphisms did not differ between the PTB patients, LTBI and HC subjects. Furthermore, combinations of polymorphisms with IFN-γ -874 were associated with LTBI, whereas combinations with IL10 - 1082 were more likely associated with PTB.

CONCLUSIONS

There are positive associations between the IFN-γ -874 polymorphism and TB and between the IL10 - 1082 polymorphism and LTBI. Our data provide genetic evidence of the multiple disease hypothesis that many cytokine genes are involved in TB susceptibility.

Early clearance of Mycobacterium tuberculosis: a new frontier in prevention

Early clearance (EC) is the successful eradication of inhaled Mycobacterium tuberculosis before an adaptive immune response develops. Evidence for EC comes from case contact studies that consistently show that a proportion of heavily exposed individuals do not develop M. tuberculosis infection. Further support for the existence of this phenotype comes from genetic loci associated with tuberculin reactivity. In this review we discuss aspects of the innate response that may underpin EC and hypotheses that can be tested through field laboratory link studies in M. tuberculosis case contacts. Specifically, we consider mechanisms whereby alveolar macrophages recognize and kill intracellular M. tuberculosis, and how other cell types, such as neutrophils, natural killer T cells, mucosa-associated invariant T cells and cd T cells may assist. How EC may be impaired by HIV infection or vitamin D deficiency is also explored. As EC is a form of protective immunity, further study may advance the development of vaccines and immunotherapies to prevent M. tuberculosis infection.

Mannose-binding lectin promoter polymorphisms and gene variants in pulmonary tuberculosis patients from cantabria (northern Spain)

Mannose-binding lectin is a central molecule of the innate immune system. Mannose-binding lectin 2 promoter polymorphisms and structural variants have been associated with susceptibility to tuberculosis. However, contradictory results among different populations have been reported, resulting in no convincing evidence of association between mannose-binding lectin 2 and susceptibility to tuberculosis. For this reason, we conducted a study in a well genetically conserved Spanish population in order to shed light on this controversial association. We analysed the six promoter and structural mannose-binding lectin 2 gene variants in 107 patients with pulmonary tuberculosis and 441 healthy controls. Only D variant and HYPD haplotype were significantly more frequents in controls which would indicate that this allele could confer protection against pulmonary tuberculosis, but this difference disappeared after statistical correction. Neither the rest of alleles nor the haplotypes were significantly associated with the disease. These results would indicate that mannose-binding lectin promoter polymorphisms and gene variants would not be associated with an increased risk to pulmonary tuberculosis. Despite the slight trend of the D allele and HYPD haplotype in conferring protection against pulmonary tuberculosis, susceptibility to this disease would probably be due to other genetic factors, at least in our population.