Immunodiagnosis of tuberculosis: An update

Abstract

Tuberculosis is still a major health problem in most developing countdes and its incidence is rising in many developed countries. This resurgence has been attributed to the HIV epidemic and TB has been declared as a global health emergency by WHO in 1993. The diagnosis of tuberculosis mainly depends upon initial clinical suspicion and radiographic findings with subsequent bacteriological confirmation by sputum smear examination and culture. Lack of sensitivity in smear examination, non specificity of radiological findings, extended turn around time of Mycobactedum tuberculosis culture and difficulties in diagnosing paucibacillary, childhood and extrapulmonary tuberculosis has necessitated to explore the utility of immunodiagnosis of tuberculosis as a convenient and cost effective test to supplement clinical information for definite diagnosis. Many commercial tests are available in the market for diagnosis of TB. Most of these tests are based on the detection of IgG, IgA and IgM antibodies to specific mycobacterial antigen or mixture of antigens. Indigenous immunoassay systems have explored excretory-secretory ES-31 mycobactedal antigen for immunodiagnosis of'lB. Many a time there is lack of consistent elevation in all the three Ig classes in active infection thus making it more important to determine the ideal antibody isotype assay for reliable diagnosis of tuberculosis and to save the costs of the patient for unnecessary investigations.

Elisa kit evaluation for IGG and IGM antibodies to A-60 tubercular protein antigen

“…Immunoglobulin G holds the great promise in diagnosis of active tuberculosis both in children and in adults. [10] Sensitivity and specificity for IgG antibody to A-60 was found to be in the range of 75-100% in various other Indian reports.…”

“…Reduction in IgG level could be due to the waning of the antigen following effective therapy and increased IgG level correlated with the continued immune response subsequent to the initial IgG level. Sero-diagnosis of tuberculosis using various antigens-based ELISA tests has been reviewed by Bhatia et al [10] The review…”

“…However, the IgM antibody appears to be less sensitive as evident in the present study and also has been reported by others. [6], [10], [12] Bhatia et al [10] reported IgG sensitivity of 94% and IgM sensitivity of only 33% in extra-PTB, whereas Maheshwari et al [6] observed IgG sensitivity of 75% and IgM sensitivity of 37.5% in tuberculoma cases. A limitation of the present study has been noninclusion of extra-PTB cases.…”

Diagnostic role of the antibody response to the 38kDa, 16kDa proteins and lipoarabinomannan of mycobacterium tuberculosis

“…Newer techniques such as polymerase chain reaction, DNA Probes, restriction fragment length polymorphism (RFLP) and BACTEC culture system for diagnosis of tuberculosis are sensitive and help in rapid diagnosis, but do not find their way into routine diagnosis as they are not cost effective and practical in developing countries (2). Various serodiagnostic tests based on different M.tb antigens have been developed for the diagnosis of TB and a few have been evaluated in our population (3,4,5,6,7,8). The present study aims to investigate the diagnostic utility of the antibody responses to the 38kDa, 16kDa proteins and Lipoarabinomannan (LAM) of M.tb using ELISA and western blot.…”

“…A western blot assay which evaluates the antibody response to multiple antigens of M.tb could be a better diagnostic test. Recently, ELISA based on ES-31 antigen and a new capture ELISA assay based on the whole pathogen were found to be highly sensitive and specific for the diagnosis of TB (3,4,30). Hence, multicentric evaluation of these methods and development of newer methods based on multiple antigens could throw light on whether there are any antigens to which there is a common antibody response in different populations around the world.…”