Elimination of Mycobacterium leprae subsequent to local in vivo activation of macrophages in lepromatous leprosy by other mycobacteria.

This investigation studied the possibility of activating lepromatous macrophages by a local `in vivo' test. Lepromatous macrophages have an evident incapacity for clearing M. leprae. This is demonstrated by injecting lepromatous patients with an antigen containing M. leprae from human tissue at a concentration of 640 × 106 bacteria per ml. This produces a nodule which, at a 30-day biopsy, shows a macrophagic granuloma with numerous bacteria inside the macrophages, proving that these cells are unable to remove M. leprae. This incapacity is specific for M. leprae, and all other mycobacteria produce a different reaction. Local `in vivo' stimulation of the lepromatous macrophage was obtained by injecting M. leprae in the same concentration as above but mixed with other mycobacteria (M. lepraemurium or BCG). The mixed antigens produced a tuberculoid granuloma with abundant lymphoid cells. Fite–Faraco stains showed almost no acid-fast bacteria. Therefore, our mixture of antigens had activated the macrophages locally and made them competent for clearing M. leprae.