Immunoglobulin G, A and M responses in serum and circulating immune complexes elicited by the 16-Kilodalton antigen of Mycobacterium tuberculosis.
Alamelu Raja; Uma Devi, K.R.; Ramalingam, B.; Patrick J. Brennan.
Clinical and Diagnostic Laboratory Immunology; 2002; 9; 308-312.
The 16-kDa cytosolic antigen of M. tuberculosis was purified to homogeneity by molecular sieving chromatography, and the diagnostic potential of the antigen was evaluated in various categories of patients by enzyme-linked immunosorbent assay (ELISA). The immunoglobulin G (IgG), IgA and IgM antibody levels to 16-kDa antigen were estimated in the two polar groups, namely, smear- and culture-positive pulmonary tuberculosis (S + C + ) patients and healthy subjects (HS). Sensitivities of 62, 52 and 11% with specificities of 100, 97 and 95% were obtained for the three isotypes, respectively. The total number of positives by a combination of the three isotypes was analysed in the polar groups, and the sensitivity improved to 83% with a specificity of 93%. Even when a combination of IgG and IgA alone was considered, the sensitivity was 82% with a specificity of 97%. Polyethylene glycol precipitation of the circulating immune complex (CIC) in sera was carried out. The CIC-bound antibodies to 16-kDa antigen were assessed by ELISA in the S + C + , S - C + , and S - C - categories of patients. Measuring the IgG-IgA-IgM combination positivities of the CIC-bound antibodies gave sensitivities of 97.5, 100 and 45.3%, respectively. The specificity of the assay with these combinations was maintained at 95.4%.
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