Studies on the antigenic specificity of Mycobacterium leprae. I. Isoelectric and chromatofocusing separation

Cell sonicates of Mycobacterium leprae and other mycobacteria were subjected to isoelectric focusing and chromatofocusing to evaluate their protein antigens and to determine if the patterns were significantly different. Isoelectric focusing showed that the proteins of all mycobacteria focused within the pH range of 3.5 to 5.5, except those of M. leprae which extended beyond 5.5 to 6.5. These studies have indicated for the first time that the protein antigens of mycobacteria are acidic in nature. Comparison between the proteins of untreated and autoclaved M. leprae showed distinct differences between the two preparations, in respect of loss of some antigens in the autoclaved M. leprae sonicate. This indicates that the bands that were not visible in the autoclaved M. leprae were those of heat-labile proteins. It is possible, however, that the absent bands could have been of a low order of intensity and hence were not discernible. On the other hand, the proteins could have coagulated due to the heat treatment, thus causing confirmational changes or ionic interactions with membrane components, due to their acidic nature. It is possible that the proteins in the autoclaved M. leprae are the ones that possess immunogenic properties since the protective ability of heat-killed M. leprae has already been established. Chromatofocusing studies have confirmed the isoelectric focusing data in respect of the number of antigens and their respective protein content, besides permitting the availability of the various fractions for further biological characterization.