Experimental transmission of murine leprosy to the guinea-pig by means of induced macrophage exudate and suppression of the natural defense mechanism.

The problem of transmission of human leprosy to laboratory animals remains unsolved, and presents a serious barrier to the study of the disease. Very many attempts have been made without success to produce the infection in animals, usually without but sometimes with attempts to suppress their defence forces. In approaching this problem it seemed to be logical to undertake to lower the native resistance of the animal to be used. The experiments were unavoidably conducted on a rather empirical basis, since the factors which govern resistance and susceptibiltiy are still unknown. Until more basic research is done to obtain fundamental information concerning the pathogenesis of the disease, and concerning factors which influence the hostparasite relationship and determine the outcome of the infection, the probability of success in the experimental transmission of human leprosy is rather small. Studying the behavior of macrophages from susceptible and resistant animals toward the murine leprosy bacillus (24,25), some observations were made which suggested the possibility of transmission of rat leprosy to the resistant guinea-pig. The theoretical basis, the experimental set-up, and the negative and the positive results obtained will be reported here, since the experiment may serve as a model for similar studies with the human leprosy bacillus. The problem can be formulated as follows: Would it be possible to transfer experimentally into a resistant host a chronic infectious disease caused by an obligate intracellular parasite, characterized by an intense tendency to invade specific host cells and by extreme susceptibility to extracellular inhibitors? The following factors must be taken into consideration.