Use of live attenuated Leishmania major parasites as a candidate vaccine against Leishmania major infections in BALB/c mice
Onyalo, Janet Achieng'
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Several studies have demonstrated that Leishmania and other protozoan parasites lose their infectivity and virulence when serially cultured in vitro for a long time. Serially cultured L. major parasites were used in this study as live attenuated vaccine candidate and its ability to induce protective immunity against cutaneous leishmaniasis in BALB/c mice was examined. Four experimental groups of 30 BALB/c mice each were used. The first group was immunized with live attenuated metacyclic promastigotes, the second one was immunized with heat killed whole parasites, third group was given soluble antigens derived from L. major metacyclic promastigotes while the last group was not immunized and served as the controls. The immunization was administered intravenously, four times at an interval of 7 days. Blood from all the animals was obtained through tail snipping and was used for the Enzyme-linked immunosorbet assay (ELISA) test to detect production of antibodies. Five animals from each group were kept separate from the others for 14 weeks; they were tested for delayed hypersensitivity test (DTH) reaction and then sacrificed. Their splenocytes were then used for lymphocyte proliferation assay to detect retention of immunological memory. The remaining immunized and control mice were challenged (infected) with 106 culture derived metacyclic L. major promastigotes on the left hind footpads (LHFP) while the right hind footpads (RHFP) were left as contraleteral controls. After every 7 days both (RHFP) and (LHFP) were measured and the difference between the two footpads of each mice was recorded as the lesion size. Fourteen weeks post-infection, all the mice were sacrificed. Impression smears and cultures of spleen and liver were prepared in order to determine the level of metastasis and visceral infections. Results obtained from the study showed that live attenuated parasites induced the best protection against the disease (ANOVA 1, P=0.000) compared to the other vaccines used. All the immunized mice produced significant level of antibodies, exhibited evidence for retention of immunological memory with T cell stimulation although non-produced DTH response. While live attenuated parasites did not cause lesion, mice immunized with them exhibited minimal lesion development upon challenge with virulent L. major parasites therefore it is possible to use them as a candidate vaccine against cutaneous leishmaniasis.
- MST-Zoological Sciences