Thoracic duct lymphocytes in experimental lepromatous leprosy in mice.

Progress in leprosy research was very restricted until recently, for it was, and still is, impossible to grow the causative organism M ycohacterium leprae in vitro. The work of Shepard (Ii) , however, opened up new possibilities, for he demonstrated that M. leprae can be grown in the footpads of mice. Rces and Weddell (2,3) and colleagues have further contributed to experimental leprosy in mice for they have shown that in mice, as in men, the disease depends upon the immunologic capacity of the individual. Mice act as experimental models for the production of different forms of leprosy, which correspond to those in patients in Ridley and Jopling's classification scale (.). In particular, they have shown that the lesions in mice, indistinguishable from those of lepromatous leprosy in man, can be evoked by reducing their immunologic capacity by thymectomy and 900r total-body irradiation prior to infection. They have further shown that it is possible to produce an immunologic upgrading or a reversal reaction in heavily infected mice if a total syngeneic lymphoid tissue replacement, originating from the spleen and other sources of lymphoid tissue, is given to the animal after infection with M. leprae. However, this lymphoid replacement tissue contained, in addition to mac-rophages and other cells, a mixed population of at least two types of lymphocyte, viz., thymic-dependent and bone marrowderived cells. It was thus possible that the reactions observed were due not solely to long lasting thymic-dependent lymphocytes but to the spectrum of cel1s which