Leishmania (Leishmania) major-infected rhesus macaques (Macaca mulatta) develop varying levels of resistance against homologous re-infections

Seven rhesus macaques were infected intradermally with 10(7) promastigotes of Leishmania (Leishmania) major. All monkeys developed a localized, ulcera tive, self-healing nodular skin lesion at the site of inoculation of the pa rasite. Non-specific chronic inflammation and/or tuberculoid-type granuloma tous reaction were the main histopathological manifestations of the disease . Serum Leishmania-specific antibodies (IgG and IgGl) were detected by ELIS A in all infected animals; immunoblot analyses indicated that numerous anti gens were recognized. A very high degree of variability was observed in the parasite-specific cell-mediated immune responses [as detected by measuring delated-type hypersensitivity (DTH) reaction, in vitro lymphocyte prolifer ation, and gamma interferon (IFN-gamma) production] for individuals over ti me post challenge. From all the recovered monkeys (which showed resolution of the lesions after 11 weeks of infection), 57.2% (4/7) and 28.6% (2/7) an imals remained susceptible to secondary and tertiary infections, respective ly, but the disease severity was altered (i.e. lesion size was smaller and healed faster than in the primary infection). The remaining monkeys exhibit ed complete resistance (i.e. no lesion) to each rechallenge. Despite the in ability to consistently detect correlates of cell-Mediated immunity to Leis hmania or correlation between resistance to challenge and DTH, lymphocyte t ransformation or IFN-gamma production, partial or complete acquired resista nce was conferred by experimental infection. This primate model should be u seful for measuring vaccine effectiveness against the human disease.