Diagnostic Potential of Ag85C in Comparison to Various Secretory Antigens for Childhood Tuberculosis

Abstract

Childhood tuberculosis is difficult to diagnose. A rapid, simple and relatively inexpensive diagnostic test will be crucial to future control efforts. Therefore, efficacy and diagnostic potential of different secretory antigens of Mycobacterium tuberculosis (CFP‐10, Ag85complex, Ag85 A, B, C) and their combinations along with ESAT‐6 in the detection of antibody profiles of childhood tuberculosis cases were evaluated using ELISA technique and reactivity was compared with the gold standards (smear, culture and IS6110 targeted PCR). In the present study, 88 fresh, untreated childhood tuberculosis (TB) cases, 17 children undergoing anti‐tubercular therapy, 17 children having disease other than TB and 25 healthy children were included. ROC curve analysis was used to calculate the sensitivity and specificity of each antigen for antibody detection. Ag85C was found to be showing highest sensitivity of 89.77% and specificity of 92% among all the antigens used (P < 0.0001). Positivity with antigen was 95% in smear and culture negative patients. Antibody reactivity was noted in 92.62% of patients who were positive for IS6110 by PCR. Cocktail of all the antigens showed 67.1% sensitivity and 80% of specificity. Sensitivity of 29.55%, 57.95%, 64.77% and specificity of 80%, 72%, 64% was observed using CFP‐10, Ag85complex and Ag85B. Low reactivity of 31.82% in patients and least specificity of 24% was noted with Ag85A. Our finding demonstrates the potential of Ag85C in the detection of antibody in childhood TB cases and this antigen showed good concordance with PCR positivity.

Antibody Responses to Mycobacterial Antigens in Children with Tuberculosis: Challenges and Potential Diagnostic Value

“…Of these antigens, only ESAT-6 and CFP10 are M. tuberculosis complex specific, while the other antigens can be found in several other mycobacteria. As in adult TB, Ab responses to ESAT-6 and CFP10 were lower than those against several other antigens in pediatric TB (31,57,71). Sensitivities and specificities for the reported studies varied widely (Table 2), influenced by the factors discussed in detail.…”

“…Sensitivities and specificities for the reported studies varied widely (Table 2), influenced by the factors discussed in detail. Of note, most investigators evaluating in-house Ab detection assays used the same groups of cases and controls to determine cutoff values and estimate sensitivity and specificity values (30,31,47,74). In addition, many studies lacked a description of their assays, making data interpretation not possible (3,6,20,21,48).…”

“…Furthermore, the use of crude mycobacterial antigen mixtures in Ab detection assays by many investigators introduced considerable data variability. In addition, several investigators used the same groups of cases and controls to determine cutoff values and estimate sensitivity and specificity values (30,31,47,74). This approach, although valid in pilot studies, limits the reproducibility of data and is likely to have contributed to the wide variability of reported Ab responses.…”

“…Ab responses to further mycobacterial antigens evaluated via an in-house ELISA included (i) antigen 5 (Ag5)/the 38-kDa protein (2), (ii) the 30-kDa antigen, a culture filtrate protein, more commonly known as antigen 85B (47,74), (iii) fractions 4 and 5 of polar lipids belonging to the lipo-oligosaccharide family (LOS) (58), (iv) 2,3-diacyl trehalose, formerly also referred to as 2,3-diacyl-trehalose-2=-sulfate (SLIV) antigen (DAT) (58), (v) the glycolipid antigen triglycosyl phenol phthiocerol dimycocerosate (PGLTb1) (58), (vi) the 16-kDa heat shock protein (30,47), (vii) the 60-kDa heat shock protein (HSP60) (3), (viii) the excretorysecretory antigen (ES-31) (6), (ix) the early secretory antigen 6 (ESAT-6) (21, 31), (x) the antigen 85 complex consisting of the proteins Ag85A, 85B, and 85C (Ag85 complex) (20,31), and (xi) culture filtrate protein 10 (CFP10) (31). Of these antigens, only ESAT-6 and CFP10 are M. tuberculosis complex specific, while the other antigens can be found in several other mycobacteria.…”

Immunologic evaluation and validation of methods using synthetic peptides derived from Mycobacterium tuberculosis for the diagnosis of tuberculosis infection

“…A successful serodiagnostic test for TB hinges on the capacity of the assay to detect the pauci and multibacillary forms of TB, paediatric TB cases and TB-infected patients coinfected with human immunodeficiency virus (HIV) (Mabey et al 2004, Tiwari et al 2007). Many reports have proposed utilising several combinations of antigens or specific antibodies for a serological assay for the diagnosis of TB (Araujo et al 2004, Kumar et al 2008, He et al 2011.…”