Immunoregulatory Defects in Leprosy

It was over one hundred years ago that the causative organism of human leprosy, Mycobacterium leprae was recognized by the Norwegian investigator, Armauer Hansen. Since that time our knowledge of this disease has advanced but little. M. leprae is an obligate intracellular parasite growing in the cells of the mononuclear phagocyte system with a special affinity for those tissue macrophages found in association with the skin, nerves, and lymphoreticular system. The organism has a very long generation time, estimated to be 10 to 15 days, which stands in comparison to M. tuberculosis that divides approximately every 20 hours, and coliform bacteria which divide every 20 to 30 minutes. To date the cultivation of M. leprae in vitro has proved elusive, thus hampering studies of the basic biology of the organism as well as the development of a potential vaccine against leprosy. For twenty years the principal method of studying the growth kinetics of the organism, the pharmacology of anti-leprous drugs, and the local pathology and immunity to the bacillus has been the mouse footpad model (1). However, in 1971, it was discovered that armadillos were susceptible to M. leprae and will support its multiplication in enormous numbers in vivo (2).