In situ locations of Mycobacterium leprae-specific antigens. Immunoelectronoptical studies.

Lipid or protein antigen sites in Mycobacterium leprae proper and in M. leprae -infected human or armadillo tissues were investigated by immunogold-electron microscopy. Simultaneous preservation of immunogenicity of antigens and conservation of ultrastructural details of M. leprae and host cells was aimed at by subjecting organisms and tissues, prior to immunolabelling, to differing fixation, embedding and ultramicrotomy techniques. The M. leprae-specificity of monoclonal antibodies (MoAbs) utilized in the study was tested first. Hereto, ultracryosections of M. leprae, M. tuberculosis and M. nonchromogenicum suspended in gelatin were employed. MoAb anti-phenolic glycolipid I (PGL I) and MoAb anti-36 kD were found to be specific for M. leprae. MoAb anti-65 kD also labelled the cytoplasm of M. tuberculosis. After incubation with MoAb anti-lipid MAIS, employed as control MoAb, no gold labelling of leprosy bacilli or host cells was seen. PGL-I immunogenicity was still present after "hard" fixation of M. leprae and host cells in glutaraldehyde-OsO4 and after Araldite embedding. This enabled the qualitative demonstration of PGL-I inside the cell wall and capsular area of M. leprae and in vacuoles of bacillated phagolysosomes of macrophages in Araldite-embedded human skin biopsies and armadillo liver parenchymal cells. Sites of 65 kD and, to a lesser extent, of 36 kD protein antigens in M. leprae were demonstrable only in ultracryosections of non-fixed organisms and not in Araldite sections. Results are discussed and recommendations for future investigations on M. leprae antigen sites are presented.