Concordance between IFNγ gene +874 A/T polymorphism and interferon-γ expression in a TB-endemic indigenous setting

Abstract

Introduction: Interferon-γ (IFN-γ) plays a crucial role in resistance to mycobacterial diseases; accordingly, variants of the gene encoding this cytokine may be associated with elevated risk of contracting pulmonary tuberculosis (TB). Methods: Blood samples were collected from 135 Warao indigenous individuals with newly diagnosed sputum culture-positive TB. Of these, 24 were diagnosed with active tuberculosis (ATB). The study comprised 111 participants, who were grouped as follows: 1) 14 tuberculin skin test (TST)-positive Warao indigenous individuals and 4 that were QuantiFERON-TB®Gold In-Tube (QFT-IT) test-positive, collectively comprising the latent TB infection group (LTBI), n = 18), and 2) healthy controls who were QFT-IT-and TST-negative, comprising the control group (CTRL, n = 93). Detection of the IFN γ gene (IFNG) +874A/T polymorphism was performed via PCR and quantification of IFNG expression via qPCR. Results: Relative to indigenous and white Americans, ATB and CTRL groups had a higher frequency of the IFNG SNP (+874A): 23 (95.8%) and 108 (97.3%), respectively. Indigenous Warao individuals homozygous for the IFNG (+874) A allele exhibited 3.59-fold increased risk of developing TB (95% confidence interval, 2.60-4.96, p =0.0001). A decreased frequency of the AT genotype was observed in individuals with pulmonary TB (4.16%) and controls (0.90%). The frequency of the TT genotype was decreased among controls (1.80%); none of the patients with TB were found to have this genotype. The differences in IFNG expression between the groups, under unstimulated and stimulated conditions, were not statistically significant. Conclusions: Preliminary results demonstrate concordance between IFNG +874 A/A genotype and low expression of IFNG.