The 45 kilodalton molecule of Mycobacterium tuberculosis identified by immunoblotting and monoclonal antibodies as antigenic in patients with tuberculosis

The object of this study was to discover new M. tuberculosis antigens which are recognized by patients with tuberculosis, because effective serodiagnostic tests are likely to require combinations of different antigens. In our early experiments using immunoblotting, the findings suggested that human sera from smear-negative tuberculosis patients bound to an antigen in the 45 kDa region. Subsequently, estimates of molecular weight in the immunoblots confirmed that the murine monoclonal antibody (MAB) HGT-6 and sera from patients both recognized the same 45 kDa molecule. An antibody-antibody competition assay between MAB HGT-6 and sera from smear-positive tuberculosis patients yielded a positive result in 23 out of 43 sera from patients, but in only four out of 23 from controls. This is further evidence that the 45 kDa antigen is recognized by tuberculous patients. We analysed whether a combination of the 45 kDa antigen results and those of known antigens might better discriminate between minimal smear-negative disease and healthy controls than could test with single antigens. There is no clinically useful laboratory test for smear-negative tuberculosis. In immunoblotting, combining the results with the 65, 45, 38 and 10 kDa antigens gave the best discrimination. This suggests that future serodiagnostic tests for minimal disease, such as the antibody-antibody competition assay, should contain a MAB against the 45 kDa antigen and possibly also against the 10 kDa antigen.