ANTIGENIC AND STRUCTURAL SIMILARITIES BETWEEN MYCOBACTERIUM-TUBERCULOSIS 50-KILODALTON TO 55-KILODALTON AND MYCOBACTERIUM-BOVIS BCG 45-KILODALTON TO 47-KILODALTON ANTIGENS

The relationship between Mycobacterium tuberculosis 50- to 55-KDa prot ein and Mycobacterium bovis BCG 45-to 47-kDa antigen was examined by u sing immunological and biochemical criteria. Reciprocal cross-reactivi ty with a rabbit polyclonal antiserum against the M. bovis BCG protein and with a monoclonal antibody raised against the M. tuberculosis ant igen was observed. The epitope recognized by this antibody was apparen tly present only in proteins of M. tuberculosis and M. bovis BCG among the 11 mycobacterial species tested. The amino-terminal sequences and total amino acid contents of these proteins showed strong similaritie s. Both antigens are glycoproteins as assessed by binding of concanava lin A, labeling of carbohydrate moieties with biotin-hydrazide, and di gestion of carbohydrates,vith jack bean alpha-D-Dmannosidase, which pr oduced a reduction of the molecular weights of the proteins and totall y eliminated concanavalin A binding. Both M. tuberculosis and M. bovis BCG proteins are secreted, since they were found mainly in the cultur e medium. Analysis of M. tuberculosis 50- to 55-kDa antigen by two-dim ensional gel electrophoresis showed at least seven different component s, as previously described for the M. bovis BCG antigen. Solid-phase i mmunoassays showed that the purified M. tuberculosis 50- to 55-kDa pro tein was recognized by serum specimens from 70% of individuals with pu lmonary tuberculosis from a total of 77 Mexican patients examined.