HETEROLOGOUS PROTECTION BY LEISHMANIA-DONOVANI FOR LEISHMANIA-MAJOR INFECTIONS IN THE VERVET MONKEY MODEL OF THE DISEASE

Heterologous protection by Leishmania donovani for Leishmania major in fections in the vervet monkey model of the disease. Experimental Paras itology 85, 109-116. The study was aimed at analyzing immunological cr oss-reactivity between Leishmania major and Leishmania donovani and po ssible cross-protection between the two parasite species in the vervet monkey model of the disease. Nine vervet monkeys (Cercopithecus aethi ops) from the institute animal colony were sued in the study. Five of the animals had been previously infected with L. donovani but had rema ined asymptomatic while the other four animals were naive and comprise d the control group. Immunological responses to both L. major and L. d onovani antigens in the five animals with prior exposure to L. donovan i were examined before challenge. High antibody titers to the two anti gens were demonstrated in an enzyme-linked immunosorbent assay, but th e antibody titers to L. donovani were significantly higher than those to L. major (P < 0.005). Positive in vitro peripheral blood leucocyte (PBL) proliferation to L. major and L. donovani antigens was also demo nstrated, but there wa no significant difference in the response to th e two antigens (P > 0.1). High and varying levels of interferon gamma (IFN-gamma) were secreted in PBL from the five vervet monkeys when sti mulated with L. major antigen, but vervet monkey 1296 secreted margina l levels of IFN-gamma. When the animals were challenged intradermally with 1 x 10(5) virulent L. major. promastigotes mixed with sandfly vec tor salivary gland lysate all four vervet monkeys in the control group developed nodules of varying sizes at the inoculation sites that even tually ulcerated. However, nodule formation and ulceration occurred at different times among these animals. The other five animals (animals with prior exposure to L. donovani) did not pick up the infection at a ll, but one animal from this group, vervet monkey 1296, developed a tr ansient lesion that healed within 9 weeks, the same animal that had be en shown to secrete low levels of IFN-gamma. The results demonstrate h igh cross-reactivity between L. donovani and L. major and that L. dono vani protects against L. major infections. This finding is important f or vaccine development studies against leishmaniasis. (C) 1997 Academi c Press.