title: Immunoglobulin G, A, and M responses in serum and circulating immune complexes elicited by the 16-kilodalton antigen of Mycobacterium tuberculosis.
abstract: 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 analyzed 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%.
authors.affiliation: Department of Immunology, Tuberculosis Research Centre (ICMR), Chetput, Chennai-600 031, India. alameluraja@yahoo.com
authors.forename: Alamelu
authors.initials: A
authors.lastname: Raja
authors.forename: K R
authors.initials: KR
authors.lastname: Uma Devi
authors.forename: B
authors.initials: B
authors.lastname: Ramalingam
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Brennan
mesh_terms: D000907:Antibodies, Bacterial / Q000097:blood; D000918:Antibody Specificity; D000936:Antigen-Antibody Complex / Q000276:immunology*; D000942:Antigens, Bacterial / Q000276:immunology*; D003600:Cytosol / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood; D007074:Immunoglobulin G / Q000097:blood; D007075:Immunoglobulin M / Q000097:blood; D009169:Mycobacterium tuberculosis / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D000936:Antigen-Antibody Complex; D000942:Antigens, Bacterial; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M