Studies on the Patterns of Interferon-Gamma and Interleukin-10 Production as a Potential Immuno-biomarker for the Outcome of Mycobacterium tuberculosis Infection

Host immune response against Mycobacterium tuberculosis (MTb) is mediated by cellular immunity in which cytokines and MTb-specific T cells play an important role. The detection of MTb and discrimination between different states of MTb infection is possible by immunodiagnostic testing. However, deficiencies in current tuberculosis (TB) immunodiagnostics pipeline demand new approaches to control TB. There is need to identify biomarkers that improve the clinical performance of current immunodiagnostic methods in TB disease and treatment monitoring. Because the dynamic changes and balance in key pro- and anti- inflammatory cytokines production could control or predict clinical outcome of MTb infection, this study set out to determine the patterns of MTb-specific antigen-stimulated Interferon-gamma (IFN- ) and Interleukin-10 (IL-10) production in different clinical forms of MTb infection and to evaluate their concomitant changes during anti-TB treatment (ATT). Overall, 84 BCG-vaccinated HIV-negative adults, consisting of 25 Healthy Community Controls (HCC), 27 Latent Tuberculosis Infection (LTBI) cases, and a cohort of 32 Acute Pulmonary Tuberculosis (APTB) patients were investigated for IFN- and IL-10 responses at enrollment (base-line) and during ATT at 2-month (ATT1) and 6-month (ATT2). At enrollment, groups didn’t differ significantly in age, gender, or CD4+ T counts but differed in the other socio-demographics and hematological parameters, p<0.05. Base-line Sandwich ELISA – measured IFN- levels were significantly higher in HCC (223.50±58.11 pg/ml) compared with LTBI (128.82±41.81pg/ml) and APTB (47.82±22.05 pg/ml), p<0.0001 in each case. During treatment, IFN- levels increased significantly at ATT1 (125.37±16.09 pg/ml) and ATT2 (203.35±23.24 pg/ml), p<0.0001. Conversely, base-line IL-10 levels increased significantly in APTB (17.53±6.30 pg/ml), compared with LTBI (10.71±2.39 pg/ml) and HCC (7.49±2.02 pg/ml), P<0.0001, but declined significantly at ATT1 (10.54±2.25 pg/ml) and ATT2 (5.25±1.45 pg/ml), P=<0.0001. The cytokines response combination ratio showed: ‘High’ HCC, ‘Intermediate’ LTBI, or ‘Low’ APTB ratio that increased during successful ATT; the two identified MDR-TB patients recorded fluctuating but constantly low ratio during ATT. Although there was inter-individual variation in the observed cytokine responses, the results demonstrate the immuno-competence of MTb-exposed adults, and that IFN- and IL-10 cytokines cross-regulate, and strongly suggest a shift towards IFN- -mediated pro-inflammatory host immune phenotype during effective control of MTb infection. The IFN- /IL-10 response ratio is a novel potential immunological biomarker to assess if MTb infection is going to resolve, result in latency, progress to TB; or become drug-resistant.