Development of Cellular Immunity in Cutaneous Leishmaniasis Due to Leishmania tropica

A laboratory worker was inadvertently inoculated with infectious material while passaging amastigotes of Leishmania tropica. The subsequent development of a cutaneous lesion was correlated with results of sequential in vitro bioassays of cell-mediated immunity. Induction of lymphocyte proliferation and interleukin 2 production by soluble L. tropica antigens appeared within five weeks of infection and reached maximal levels coincident with ulceration of the skin lesion. Thereafter interleukin 2 production rapidly decreased, whereas the lymphocyte proliferative response declined more slowly. Biopsy of the lesion after 12 weeks, at a time when antigen-induced lymphocyte proliferation was still significantly elevated but interleukin 2 activity had returned to near baseline values, demonstrated no organisms either histologically or by culture. Healing was complete after 20 weeks. These studies provide data on the kinetics of the development of cell-mediated immunity in human cutaneous leishmaniasis and suggest the usefulness of in vitro bioassays of specific immune reactivity to parasites for evaluating effective cell-mediated immunity.