Abstract: Latent TB infection (LTBI) is one of the major contributing factors for the high incidence of TB in India that in turn significantly contributes to the pool of active TB. Hence, identification and treatment of LTBI is of utmost importance. Currently, no specific diagnostic test is available for LTBI. Earlier, in our immunoproteomic analysis, we identified Rv2204c and Rv0753c protein-containing fractions induced significantly higher interferon-gamma (IFN- c ) response in LTBI than in active TB. In this study, we evaluated cytokine and chemokine response against M. tuberculosis antigens for improving LTBI identification. Two M. tb proteins Rv2204c and Rv0753c were cloned, over expressed in E. coli and purified by affinity chromatography. Antigen-specific immune response was evaluated in 39 pulmonary TB patients (PTB) and 35 healthy house-hold contacts (HHC). After whole blood culture for 6 days, the secretion of cytokines and chemokines were quantified in culture supernatants using Enzyme Linked Immune Sorbent Assay (ELISA). Antigen specific cytokines such as interferon gamma (IFN- c ), interleukin-6 (IL-6), IL-8, IL-12p40 and chemokines like monocyte chemotactic proteins MCP-1, MCP-2 were significantly higher in HHC than PTB. In contrast to other cytokines, tumor necrosis factor-alpha (TNF)- a response was significantly increased in PTB compared with HHC. Both Rv2204c and Rv0753c antigen specific IFN- c response showed 86% positivity in HHC; whereas in PTB, these antigens showed 18% and 21% positivity respectively. Rv2204c antigen-specific IFN- c /TNF- a response displayed maximum positivity of 91% in HHC and minimum positivity of 10% (4/39) in PTB. Rv2204c and Rv0753c specific IFN- c and IFN- c /TNF- a responses showed the most promising accuracy in identifying LTBI. Keywords: Latent tuberculosis; Biomarker; Cytokines; IGRA

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