A dual effect of tilorone on multiplication of Mycobacterium leprae in mice

Tilorone, a synthetic inducer of interferon found earlier to inhibit multiplication of Mycobacterium leprae in the foot pad of the mouse while it enhanced infections of mice by M. lepraemurium and M. marinum, has been shown to exert a dual effect on M. leprae infection of the mouse. When administered continuously, incorporated into the mouse diet in a concentration of 0.015 g per 100 g diet, the drug was usually immunosuppressive, permitting enhanced multiplication of the organisms. When administered in a 3-fold larger concentration beginning during the lag phase or early during logarithmic multiplication, tilorone was antimicrobial; however, when administered in the larger concentration beginning after logarithmic multiplication had been well established, the drug was immunosuppressive. The antimicrobial action of tilorone against M. leprae appears to be a direct action that is weak and slow in onset. The mechanism of the immunosuppressive action remains to be elucidated.