Demonstration of a shared epitope among mycobacterial antigens using a monoclonal antibody.

An IgM monoclonal antibody designated TB-C-1 which is broadly reactive with mycobacteria has been studied to characterize the antigens with which it reacts. Enzyme linked immunosorbent assay (ELISA) demonstrated reactivity not only with culture filtrates of several mycobacterial species but with several purified antigens of Mycobacterium tuberculosis, including protein antigens 5 and 6 and polysaccharides arabinogalactan and arabinomannan. Immunoblotting demonstrated reactivity with four distinct components of M. tuberculosis. Reactions with components of similar mol. wt were demonstrated for several other mycobacterial species, although fewer components bound with TB-C-1 in these other mycobacteria than in M. tuberculosis. Immunoabsorbents were prepared from TB-C-1 and used to isolate antigens with which the antibody reacted. Multiple antigens were identified in the eluates from M. tuberculosis, including protein antigens 6 and 7, arabinomannan, and arabinogalactan. Fewer components were recovered from other species of mycobacteria. Affinity of binding of immunoabsorbents was similar for all antigens bound. These results indicate that a common epitope is widely shared among antigens of M. tuberculosis and other mycobacteria and they suggest that species specificity of mycobacterial antigens may rest with individual epitopes rather than intact antigenic molecules.