Abstract
TB immunodiagnostics based on antibody and antigen detection for early detection and monitoring tubercular infections at low cost and flexible to adapt to field laboratories are a boon to developing countries. In this context we have explored in-house developed penicillinase based ELISA assays for the detection of antigen, antibody as well as immune-complexed antigen using various excretory secretory antigenic proteins and specific antibodies. Excretory secretory protein antigens such as ES-31, ES-41, ES-43, ES-6, ES-20, ES-100 and EST-6 were studied extensively and found to be useful in various pulmonary and extra pulmonary cases of tuberculosis infection. ES-31 has shown its diagnostic potential in chronic PTB cases, ES-43 in relapse cases and ES-41 in bone and joint TB. Elevated level of ES-20 antigen was observed in patients with weak immune response in TB lymphadenitis. Detection of ES-100 antigen and antibody by penicilinase ELISA was observed to be useful in detection of TB meningitis. ES-6 antigen was shown to be useful in detection of latent infection. These proteins with antigenic properties are utilized for production of specific antibodies against them and observed to be useful in immune diagnostics for detection of specific circulating and immune complexed antigens. Further user friendly peroxidase immunoassay has been standardised and is being routinely used for suspected TB cases attending 1000 bedded Kasturba Hospital attached to medical institute on physician’s request.
Highlights
Despite of declaration of tuberculosis (TB) as global emergency by World Health Organization in 1993, the problem continues to exist with 9.6 million new patients and 1.5 million deaths in the year 2014, including 0.4 million deaths among human immunodeficiency virus (HIV) positive individuals [1]
Excretory secretory (ES) proteins isolated from 10 day culture fluid of M. tuberculosis H37Ra bacilli grown in Soutan's media supplemented with thyroxin at concentration of 4 μg/ml [18] by precipitation with 50% ammonium sulphate and the soluble proteins were labelled as ESAS antigens [4,19]
Analysis of immune response in pulmonary and extra pulmonary TB cases is important in early diagnosis, prevention of spread of disease and its recurrence
Summary
Despite of declaration of tuberculosis (TB) as global emergency by World Health Organization in 1993, the problem continues to exist with 9.6 million new patients and 1.5 million deaths in the year 2014, including 0.4 million deaths among human immunodeficiency virus (HIV) positive individuals [1]. New technologies like the Xpert MTB/RIF assay, which enables simultaneous detection of Mycobacterium tuberculosis (MTB) bacilli and rifampicin (RIF) resistance, was endorsed by world Health Organization This assay was recommended for use as the initial diagnostic test for suspected drug-resistant or HIV-associated pulmonary tuberculosis. The isolation and characterization of antigens released by M. tuberculosis in short term cultures have been an active area of research in our laboratory for more than 20 years These antigenic proteins have their own significance as they are secreted by intact viable mycobacteria and are available for immune recognition in early stage of infection [9], can be targeted in early diagnosis and response to treatment. The transformation in TB diagnosis was brought about with the introduction of Genexpert test, which diagnoses TB by detecting the presence of TB bacteria, as well as testing for resistance to the drug Rifampicin [17]
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