Variable lepromin response to Mycobacterium leprae in resistant armadillos

Eight armadillos resistant to the infection of Mycobacterium leprae were lepromin tested. The tissue response was tuberculoid in 5, borderline in 2, and lepromatous in 1, thus showing a wide variation. It is seen that although cell-mediated immunity as evidenced by a tuberculoid granulomatous response to killed M. leprae is associated with resistance to the disease, there may be other yet unknown factors which protect armadillos from the infection. Lepromin responses were recognized histologically even at a low dose of 10(3) organisms, and the response increased with the dose up to 10(7) organisms. The tissue reaction to live organisms was the same as that to killed ones, and autoclaving of M. leprae produced no change in the tissue response to the antigens of M. leprae.