Purification of a major Mycobacterium bovis antigen for the diagnosis of bovine tuberculosis.

A Mycobacterium bovis antigen has been purified from culture filtrate by chromatofocusing. This antigen is a major component of culture filtrate and cell extracts and shows a considerable degree of micro-heterogeneity in electric charge and molecular weight. Studies with monoclonal and polyclonal antibodies raised against the purified antigen show that some of its antigenic determinants also occur in higher molecular weight species in culture filtrate and particularly in whole cell preparations. Immunoblotting and ELISA studies, using sera from M.bovis-infected animals, showed that this antigen is one of the most immunoreactive components of M. bovis, recognized by the majority of animals with detectable antibody response to M. bovis. The specificity of the purified antigen is far superior to that of the crude culture filtrate, with very few false positive results. The purified antigen also elicits strong in vivo and in vitro cell-mediated responses. The amino acid compositions of two variants of this antigen have been determined and found to be similar to that of MPB-70.