Serodiagnosis of tuberculosis: specific detection of free and complex-dissociated antibodies anti-mycobacterium tuberculosis recombinant antigens

Abstract

The diagnostic test characteristics of detecting free and complex-dissociated IgG to three recombinant antigens of Mycobacterium tuberculosis (38-kDa, Ag16 and Ag85B), singly and in combination, were evaluated in sera from 161 tuberculous patients [smear-positive pulmonary TB (50), smear-negative pulmonary TB (pTBsm-) (60) and extrapulmonary TB (51)) and 214 control patients (mycobacteriosis (14), mycoses(14), leprosy(4), other underlying diseases (82) and healthy people (100)]. The individual antigens ranged from 25% to 42% in sensitivity and from 93% to 96% in specificity, while considering free IgG response. Addition of complex-dissociated antibodies against each individual antigen improved the sensitivity up to 55%. The number and levels of specific antibodies varied greatly from individual to individual. Combination of individual results for free and complex-dissociated IgG to 38-kDa, Ag16 and Ag85B offered 76% sensitivity and 83% specificity. When the three antigens were placed in the same well, the sensitivity was lower than that expected on the basis of single antigen (63%) but with a good specificity (95%), even in the group of mycobacteriosis or mycoses. The highest contribution of complex-dissociated IgG results to free IgG results was seen for the diagnosis of pTBsm-patients. In conclusion, although neither single recombinant antigen was reactive with most sera from TB patients even after the measurement of both free and complex-dissociated antibodies, the use of multi-antigen cocktails improved the diagnostic utility of the ELISA assay, allowing the identification of almost 70% of pTBsm-, with a high level of specificity; the use of additional, well selected antigens should lead to the detection of almost all patients with TB.

Efficacy of ELISA test in diagnosis of Mycobacterium tuberculosis infection

“…Other technique that uses two antigens isolated from the H37Ra strain had a sensitivity of 66% in patients with meningeal TB who had negative cultures (Krishnan and Mathai, 1991). A third technique is a serodiagnosis test that uses 38-kDa, Ag16 and Ag85B as antigenic complex to detect IgG antibodies and had a sensitivity of 76% (Imaz et al, 2008). In 2000, a comparative list of 7 diagnostic tests was published and all of them showed different sensitivities (Pottumarthy et al, 2005).…”

Rapid immunodiagnostic assays for Mycobacterium Tuberculosis infection

“…Thus, even with 75% specificity, getting 97.6% sensitivity with ESAT-6 in ELISA format has improved the diagnostic potential of this antigen for TB diagnosis. Imaz et al [18] suggested the use of multi-antigen cocktail to improve the diagnostic utility of the ELISA. The design of antigen combinations would achieve the high diagnostic accuracy of the assay.…”

“…Because of their ease of performance and cost effectiveness, serodiagnostic tests constitute a promise for early detection of TB. In fact, no serological test is commonly used in the diagnosis of TB [18].…”

The overview and perspectives of biosensors and Mycobacterium tuberculosis: A systematic review

“…For decades, serological techniques based on the detection of antibodies against M. tb antigens have been available although no international guidelines have recommended their use (Steingart, Ramsay, Dowdy, & Pai, 2012). For instance, enzyme‐linked immunosorbent assay (ELISA) is a commercial method applied to detect the immunoglobulin G against the antigen 85 complex (Ag85 complex) in serum samples (Imaz, Schmelling, Kaempfer, Spallek, & Singh, 2008). PCR‐based techniques are diagnostic molecular tests, which include real‐time PCR, strand‐displacement amplification methods, line probe assay, and loop‐mediated isothermal amplification; these techniques have high accuracy, as well as limitations such as high cost.…”