Humoral immunity in leprosy: immunoglobulin G and M antibody responses to Mycobacterium leprae in relation to various disease patterns.

A solid-phase radioimmunoassay, applying whole Mycobacterium leprae as antigen and radiolabeled protein A from Staphylococcus aureus as antibody-detecting reagent, was used for the determination of specific immunoglobulin G (IgG) and IgM antibody responses in leprosy patients. High IgG anti-M. leprae antibody levels were found in lepromatous leprosy patients, whereas the antibody response in tuberculoid leprosy patients varied from negative, i.e., comparable with responses measured in normal individuals, to strongly positive. In tuberculoid leprosy patients, a significant increase in IgG anti-M. leprae antibody levels was observed in the more widespread forms of the disease, but positive antibody responses were especially predominant among patients with active lesions. Lepromatous leprosy patients generally demonstrated high levels of both IgG and IgM anti-M. leprae antibodies, but no relation was found between the antibody responses and bacillary load or other clinical parameters. A marked decrease in specific IgG and IgM antibody levels was observed in lepromatous leprosy patients during their first year of treatment. Differences in mechanisms regulating the humoral immune response in tuberculoid and lepromatous leprosy patients were indicated, and the application of antibody assessments in leprosy control programs is discussed.