Resistance to cutaneous leishmaniasis: acquired ability of the host to kill parasites at the site of infection.

The purpose of these studies was to follow the development of acquired resistance in experimental cutaneous leishmaniasis by measuring changes, against time, in the ability of mice infected with Leishmania tropica to inhibit the growth of a challenge inoculum of parasites. In addition, the development of T lymphocytes that mediate the acquired response was followed by adoptive immunization. It was found that acquired resistance developed rapidly and reached a maximum level at the time when the progressive multiplication of the parasites in the primary lesion stopped. Systemic immunity, however, as determined by the ability of splenic T cells to adoptively immunize normal recipients, did not develop fully until 4 weeks later. Acquired resistance is expressed systemically in the animal and probably nonspecifically, in that mice expressing resistance to a homologous challenge with L. tropica were also capable of destroying Listeria monocytogenes. These data, obtained from in vivo studies, are consistent with the hypothesis that the immunity which causes the destruction of L. tropica is mediated by T lymphocytes and expressed, nonspecifically, through macrophages.