Rv2204c, Rv0753c and Rv0009 antigens specific T cell responses in latent and active TB - a flow cytometry-based analysis.

High global prevalence of latent TB infection (LTBI) is a key challenge in distinguishing patients with active pulmonary TB (PTB) from those with LTBI. The functional profile of CD4+ and CD8+ T cell cytokines produced as a response to Mycobacterium tuberculosis antigens vary during the course of tuberculosis (TB) infection. We evaluated antigen-specific CD4+ and CD8+ T cell cytokine response after overnight in vitro stimulation of peripheral blood with mycobacterial antigens ESAT-6, CFP-10, Rv2204c, Rv0753c and Rv0009 by flow cytometry. A significantly higher frequency of antigen-specific CD4+ or CD8+ IFN-γ+ T cells were found in LTBI than in PTB. Among all the antigens used, Rv2204c-specific CD8+ IFN-γ+ displayed the positivity of 72% and 24% in LTBI and PTB respectively. In contrast to IFN-γ, the frequencies of CD4+ or CD8+ secreting TNF-α+ cells were significantly high in PTB compared to LTBI. CD8+TNF-α+ analysis showed 60% positivity in PTB and 13.6% positivity in LTBI against Rv0753c antigen stimulation. We also predicted Rv2204c specific CD8+ T cells secreting IL-10 or IL-4 showed maximum differentiation between LTBI and PTB. In conclusion, altered expression of Rv2204c-specific CD4+IFN-γ+ and CD8+IL-4+ T cells in LTBI and PTB might be a useful biomarker to differentially diagnose LTBI and active TB.