Mechanisms of protective immunity in experimental cutaneous leishmaniasis of the guinea-pig. I. Lack of effects of immune lymphocytes and of activated macrophages.

Leishmania enriettii is an obligatory intracellular protozoan parasite which infects guinea-pigs and resides in macrophages. Subcutaneous inoculation produces a skin infection which heals spontaneously and leaves the animal immune to reinfection. Experiments have been performed to explore the mechanisms of parasite destruction in the recovering and immune animal. Using quantitative techniques to assess parasite survival it was found that L. enriettii is not killed in vitro in macrophages from immune guinea-pigs. Inocubation of monolayers of parasitized macrophages with lymphocytes from Leishmania-immune animals had no effect on the intracellular parasites. Finally, macrophages activated to destroy Listeria monocytogenes did not impair intracellular survival of L. enriettii. The possible significance of these findings in explaining the course of infection is discussed.