ABSTRACT
BACKGROUND: Serological techniques like enzyme linked immunosorbent assay (ELISA) and immunoblotting are useful for detection of mycobacterial antigens of diagnostic importance in tuberculosis. AIM: To isolate and identify circulating tuberculous antigens reactive with sputum positive and sputum negative pulmonary tuberculosis (PTB) sera. METHODS: Circulating tuberculous antigen was isolated by ammonium sulphate fractionation from the sera of sputum positive and sputum negative (clinically and radiologically diagnosed) PTB cases. The circulating antigen fractions and individual patients' serum samples were resolved by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting was performed using anti M.tb sonicate IgG as a probe to detect antigens. RESULTS: Anti M.tb sonicate IgG was found to be reactive with mycobacterial proteins 170 kDa, 140 kDa, 85 kDa, 55 kDa, 43 kDa, 20 kDa and 16 kDa in the antigen fraction isolated from sputum positive tuberculosis sera by immunoblotting. However only 85 kDa, 55kDa, 43 kDa and 20 kDa antigenic proteins were found to be recognized by anti sonicate IgG in the antigen isolated from sputum negative sera. These observations were further confirmed by analysis of individual S+ and S- PTB serum by immunoblotting. CONCLUSION: Seroreactive studies of circulating tuberculous antigens showed the presence of 170 kDa, 140 kDa, 85 kDa, 55 kDa, 43 kDa, 20 kDa and 16 kDa protein antigens in sputum positive sera, while 85 kDa, 55 kDa, 43 kDa and 20 kDa antigens were found to be present in sputum negative PTB which need further evaluation for their use in serological diagnosis of tuberculosis.