We have examined the immunological response to Leishmania donovani promastigote derived exo- antigen in a mouse model without any adjuvant. The topical application of Leishmania exo-antigen to the intact skin, nasal, or buccal mucous membranes of naïve BALB/c mice elicited antibody and cytokine production to levels that were detectable in plasma for up to five or six weeks post sensitization. Remarkably, these antigen specific immune responses observed did not require co-administration of adjuvant and were detectable after only one or two applications of 50 to 80μg of product. The most effective sensitization route for antibody production was through contact with the buccal mucosa when significant levels of IgG1 and IgG2a subtypes were measured. More importantly, a single injection of 100μg

of exo-antigen subcutaneously in mice elicited the protective helper T-cell (Th-1) phenotype manifested by high levels of IFN-g (8 to 10x) and no IL-4 production. This highly desirable profile was not observed with experimental infections or when exposure to exo-antigens took place through contact with the skin, nasal, or buccal mucosa. This finding of a novel parasite antigen which selectively induces the protective Th-1 phenotype when administered subcutaneously into a murine host without the co-administration of an adjuvant is unusual. Here is a way to induce protective immune response against Leishmania Parasites with L. donovani Exo-antigen. This approach is promising for future experiments/immunizations in humans, on the development of potent vaccination against leishmaniasis and possibly other infectious organisms.