Structure of mycobacteria: recent developments in defining cell wall carbohydrates and proteins

Work from this laboratory on the immunogens of Mycobacterium species has focused on those based on carbohydrates (with a view to the development of specific tools for the serodiagnosis of mycobacterioses) and on the cell-wall proteins, as a source of protective immunity and as a means of observing specific delayed-type hypersensitivity. Most mycobacteria are endowed with specific, highly antigenic glycolipids that are powerful for the serodiagnosis of individual mycobacterial infections: e.g., the phenolic glycolipids of Mycobacterium leprae and Mycobacterium bovis, the glycopeptidolipids of the Mycobacterium avium complex, and the acylated trehalose-containing lipooligosaccharides of species such as Mycobacterium kansasii, Mycobacterium szulgai, and Mycobacterium malmoense. A search for analogous structures in Mycobacterium tuberculosis has revealed an antigenic diglycosyl diacylglycerol and the immunogenic phosphomannoinositides. Others have reported on the presence of a novel phenolic glycolipid in the Canetti strain of M. tuberculosis. The dominant carbohydrate-containing antigen of M. tuberculosis (responsible for the high-titer anti-arabinofuranosyl activity in tuberculous sera) is lipoarabinomannan, which has been purified in the native state from M. tuberculosis and shown to contain both phosphatidylinositol and phosphoinositol side-branches. The cell wall of M. tuberculosis--more precisely, the peptidoglycan skeleton--is a source of a few distinct, highly immunogenic protein antigens. The recognition, isolation, and characterization of these antigens will also be described.