Immunohistochemical staining of macrophages in the skin lesions of leprosy: the role of antibody to mycobacteria in human serum and various polyclonal immune rabbit antisera.

Immunohistochemical staining of tuberculoid and lepromatous leprosy skin lesions was performed using various rabbit antisera. Macrophages in both stained with serum containing antibodies against lysozyme and alpha-1-antitrypsin, while macrophages in lepromatous leprosy also reacted with other antibodies. An immunoglobulin fraction of positive serum stained following pepsin digestion, indicating that reactivity was not Fc dependent. Positive serum contained antibody against Mycobacterium butyricum, which caused macrophage staining, since affinity-purified antibody did not stain and absorption with M. butyricum removed staining. Staining was also produced by serum of subjects with leprosy or a positive tuberculin test. By immunoblotting, the anti-mycobacterial antibody was directed against surface components of M. butyricum of molecular weights 20 000-70 000. Electron microscopy showed M. leprae in phagolysosomes of macrophages, while immunoelectron microscopy demonstrated labelling along bacterial cell membranes. Therefore, macrophages in lepromatous leprosy skin lesions stain because they contain M. leprae, which reacts with antibody to either M. leprae, M. tuberculosis or atypical mycobacteria in human serum and with antibody to M. butyricum in serum from rabbits immunized with various antigens and Freund's complete adjuvant. These results indicate that immunohistochemical studies on leprosy are misleading if performed using intact polyclonal immune sera rather than affinity purified or monoclonal antibodies.