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What is Which of the following statements regardingGamma-Release-Assays for diagnosis of Tuberculosis is true - and explain in detail?
Ans. is 'b' i.e., Second Generation Quantiferon-TB (Gold) assay used ESAT-6 and CPF-10 These are also called Interferon-Gamma release assays because these detect release of IFN-y from persons who have been exposed to Mycobacterium-tuberculosis complex. It is an ELISA based test. Blood of the patient is exposed with a specific M. tuberculosis antigen and the production of IFN-y is measured by ELISA. Based on antigen used, these assays are divided into three types :- i) First generation or QuantiFERON TB (QFT) :- It responds to 1 tubercular protein, PPD (purified protein derivative). ii) Second generation or QuantiFERON TB Gold (QFT-G) :- This responds to 2 tubercular proteins : (1) ESAT-6 (earyl secretory antigen target-6), and (2) CFP-10 (culture filtrate protein-10). ESAT-6 and CFP-10 are secreted by all M. tuberculosis and pathogenic M. bovis strains. Therefore, test cannot distinguish between M. tuberculosis and M. bovis strains. Most non-tubercular mycobacteria do not secrete ESAT-6 and CFP-10. However, some nontubercular mycobacteria such as M. Kansasii, M. szulgai and M. maximum may secrete ESAT-6 and CFP-10 and hence test positive. iii) Third generation or QuantiFERON TB Gold In-Tube (QFT-GIT) :- This responds to 3 tubercular proteins : (1) ESAT-6, (2) CFP-10, and (3) TB 7.7.