Protein G-based enzyme-linked immunosorbent assay for anti-MPB70 antibodies in bovine tuberculosis

MPB70 is a highly species specific protein which is secreted from Mycobacterium bovis during culture. To investigate whether antibodies against MPB70 can be used as an indicator of infection with M. bovis, an enzyme-linked immunosorbent assay was developed, based on the use of biotinylated protein G, to provide a common indicator for antibody formation in different species. During experimental infection with M. bovis in cattle, a characteristic pattern of anti-MPB70 antibody production was observed with an initial flat plateau followed by a marked rise 18 to 20 weeks after infection. Skin testing with bovine tuberculin purified protein derivative (PPD), which was shown to contain antibody-reactive MPB70, was a potent stimulator of antibody production in infected animals. In experimentally infected cattle, we observed an inverse relationship between antibody activity and delayed-type hypersensitivity skin test reactions. In natural M. bovis infections, skin testing with PPD was also a potent stimulator of anti-MPB70 formation. Comparison between the enzyme-linked immunosorbent assay for antibodies to MPB70 and that for antibodies to the widely cross-reacting M. bovis BCG antigen 85B in animals with M. bovis, Mycobacterium avium, Mycobacterium paratuberculosis, and Corynebacterium pseudotuberculosis infections showed that formation of antibody to MPB70 was highly specific for infection with M. bovis. The use of an MPB70-containing PPD preparation for skin testing followed by this anti-MPB70 assay is a highly specific indicator of M. bovis infection. Adjustment of the test conditions is expected to provide an increased sensitivity of the procedure for the diagnosis of natural M. bovis infections.