Demonstration of antibodies reacting with different determinants on Mycobacterium leprae antigen 7

A purified preparation of M. leprae antigen 7 was used to investigate the specificity of anti-M. Leprae 7 antibodies in leprosy sera in a radioimmunoassay. A solution containing arabinogalactan (AG) and arabinomannan (AM) inhibited the antibodies in some sera to a great extent, whereas the antibody activity was virtually unchanged in other sera under the same conditions. These findings indicate that the antibodies are directed against different determinants on M. leprae antigen 7. Antibodies against determinants other than AG and AM occurred particularly in lepromatous leprosy sera. In 12 out of 14 sera, AG and AM had similar inhibiting capacity. In one serum, AG had markedly higher inhibiting capacity than AM; in the last serum, the reverse was the case, demonstrating variation in anti-polysaccharide specificity in individual sera.