Detection of Mycobacterium tuberculosis Antigens in Urinary Proteins of Tuberculosis Patients

A sensitive sandwich enzyme-linked immunosorbent assay (ELISA) that can detect up to 0.5 ng of culture filtrate proteins (CFPs) of Mycobacterium tuberculosis strain H37Ra is described. This detection system features several special characteristics: (i) the use of CFPs from the H37Ra strain of Mycobacterium tuberculosis to generate capture and detection antibodies in rabbits and mice, respectively; (ii) affinity purification of CFP-reactive antibodies and selection of the antibody preparations for best performance in the sandwich ELISA system; and (iii) the use of urine-derived protein preparations for antigen detection. The sandwich ELISA could detect up to 0.5 ng of CFPs of the H37Ra strain of Mycobacterium tuberculosis. The assay did not detect antigens of Escherichia coli, Candida albicans or Saccharomyces cerivisiae but efficiently detected CFP preparations from nine different clinical isolates of Mycobacterium tuberculosis. Significant variations, however, were noted in the relative efficacy of the assay to detect CFPs from different clinical isolates of Mycobacterium tuberculosis. The procedure was utilized for detecting tubercular antigens in urine samples from 29 patients with confirmed (sputum-positive) tuberculosis and from 25 healthy controls. Significant levels of antigen could be detected in 22 of the 29 samples tested.