Differential combination of cytokine and interferon- γ +874 T/A polymorphisms determines disease severity in pulmonary tuberculosis.

BACKGROUND: Mycobacterium tuberculosis infects nearly 1/3 of the world population and this reservoir forms the largest pool from which new cases arise. Among the cytokines, IFN-γ is a key determinant in protection against tuberculosis. Single nucleotide polymorphisms (SNPs) in IFN-γ gene (+874 T/A) which determine TT high ((hi)), AA low ((lo)) and TA intermediate ((int)) responder phenotypes have shown variable associations with tuberculosis disease outcome in different ethnic populations. The objective of the current study was to analyze IFN-γ gene combinations with other IFN-γ regulating cytokine genes (IL-10, TNF -α, IL-6) to see the effect of gene- combinations on disease severity outcome in pulmonary tuberculosis. METHODS AND FINDINGS: Study groups comprised of pulmonary TB patients stratified according to lung tissue involvement into mild (Pmd = 74) or advance (Pad = 23) lung disease and compared with healthy controls (TBNA = 166). Genotype analysis was carried out using amplification refractory mutation system-PCR (ARMS-PCR). IFN-γ gene (+874 T/A) functional SNP combinations in TNFα (-308 G/A), IL-10 (-1082 A/G) and IL-6 (-174 G/C) were analyzed. Single gene analysis (Pearson χ²) showed a dominant association of IFN-γ TT (hi) genotype (p = 0.001) and T allele (p = 0.001) with mild disease. IFN-γ(lo) -IL-10(lo) genotype combination was associated with advanced disease (p = 0.002). IFN-γ(hi) -IL-6(hi) combination was associated with mild disease (p = 0.0005) while IFN-γ(lo) -IL-6(int) was associated with protection against both forms of pulmonary disease (p = 0.002). CONCLUSION: Our results show that a limited number of IFN-γ gene combinations with other cytokine functional SNPs determine the outcome of disease severity in tuberculosis.

CCL2/MCP-I genotype-phenotype relationship in latent tuberculosis infection.

Among the known biomarkers, chemokines, secreted by activated macrophages and T cells, attract groups of immune cells to the site of infection and may determine the clinical outcome. Association studies of CCL-2/MCP-1 -2518 A/G functional SNP linked to high and low phenotypes with tuberculosis disease susceptibility have shown conflicting results in tuberculosis. Some of these differences could be due the variability of latent infection and recent exposure in the control groups. We have therefore carried out a detailed analysis of CCL-2 genotype SNP -2518 (A/G transition) with plasma CCL-2 levels and related these levels to tuberculin skin test positivity in asymptomatic community controls with no known exposure to tuberculosis and in recently exposed household contacts of pulmonary tuberculosis patients. TST positivity was linked to higher concentrations of plasma CCL2 (Mann Whitney U test; p = 0.004) and was more marked when the G allele was present in TST+ asymptomatic controls (A/G; p = 0.01). Recent exposure also had a significant effect on CCL-2 levels and was linked to the G allele (p = 0.007). Therefore association studies for susceptibility or protection from disease should take into consideration the PPD status as well as recent exposure of the controls group used for comparison. Our results also suggest a role for CCL-2 in maintaining the integrity of granuloma in asymptomatic individuals with latent infection in high TB burden settings. Therefore additional studies into the role of CCL-2 in disease reactivation and progression are warranted.

Endogenously activated interleukin-4 differentiates disease progressors and non-progressors in tuberculosis susceptible families: a 2-year biomarkers follow-up study.

OBJECTIVE: Dynamic cytokine profiles from endogenously activated T cells in transit from lymph node to the infected sites via the blood compartment after recent exposure to Mycobacterium tuberculosis may differentiate disease progressors from non-disease progressors in a BCG-vaccinated population. METHODS: Household contacts (N = 107) from families with (six families) or without (14 families) secondary cases were assessed for Types 1 and 2 cytokines serially in plasma of whole blood cultures without exogenous stimulation. "ARMS" PCR was carried out for detection of single nucleotide polymorphism T/A in IFN-γ +874. RESULTS: In the absence of IFN-γ expansion, raised IL-4 at 6 months was associated with disease progression in TB-susceptible families. Resistant families on the other hand showed overrepresentation of IFN-γ +874 A allele and expansion of IFN-γ secreting cells at 6 months followed by contraction at 12 months. CONCLUSION: Six months may be an important checkpoint for biomarker assessment in high-risk individuals post-exposure.

Cytokine gene polymorphisms across tuberculosis clinical spectrum in Pakistani patients.

BACKGROUND: Pakistan ranks 7(th) globally in terms of tuberculosis (TB) disease burden (incidence 181/100000 pop./yr; prevalence of 329/pop./yr). Reports from different populations show variable associations of TB susceptibility and severity with cytokine gene polymorphisms. Tuberculosis clinical severity is multi-factorial and cytokines play a pivotal role in the modulation of disease severity. We have recently reported that the ratio of two key cytokines (IFNgamma and IL10) show significant correlation with the severity spectrum of tuberculosis. The objective of the current study was to analyze the frequency of cytokine gene polymorphisms linked to high and low responder phenotypes (IFNgamma +874 T(hi)-->A(lo) and IL10 -1082 G(lo)-->A(hi)) in tuberculosis patients. METHODS AND FINDINGS: STUDY GROUPS WERE STRATIFIED ACCORDING TO DISEASE SITE AS WELL AS DISEASE SEVERITY: Pulmonary N = 111 (Minimal, PMN = 19; Moderate, PMD = 63; Advance, PAD = 29); Extra-pulmonary N = 67 (Disseminated DTB = 20, Localized LTB = 47) and compared with healthy controls (TBNA = 188). Genotype analyses were carried out using amplification refractory mutation system-PCR (ARMS-PCR) and stimulated whole blood (WB) culture assay was used for assessing cytokine profiles. Our results suggest that the IFNgamma +874 TT genotype and T allele was overrepresented in PMN (p = 0.01) and PMD (p = 0.02). IFNgamma +874 TT in combination with IL10 GG(lo) genotypes showed the highest association (chi(2) = 6.66, OR = 6.06, 95% CI = 1.31-28.07, p = 0.01). IFNgamma AA(lo) on the other hand in combination with IL10 GG(lo) increased the risk of PAD (OR = 5.26; p = 0.005) and DTB (OR = 3.59; p = 0.045). CONCLUSION: These findings are consistent with the role of IL10 in reducing collateral tissue damage and the protective role of IFNgamma in limiting disease in the lung.