Evaluation of the Effects of a New Formulation of Leishmania Major Antigen in Balb/C and Conventional White Laboratory Mice

BACKGROUND/PURPOSE: Leishmaniasis is currently a threat in 80 countries around the world, and cutaneous Leishmaniasis accounts for more than 5% of new cases. It is a problematic disease in Iran, and preparing a protective vaccine has been a major goal of medical investigations. The objective of this study was to compare the protective effects of a cocktail vaccine candidate encoding various Leishmania major antigens in highly susceptible (Balb/C, or type I mice) and resistant (laboratory small white, or type II) mice. METHODS: A new antigen formulation was evaluated in type I and II mice. Leishmania major promastigotes was cultured and harvested at different growth stages, and a cocktail made from the harvested organisms. The preparations were tested for sterility and contamination by endotoxin. Five different methods were utilized to produce a crude antigen preparation. The protein levels of the antigen preparations were measured using the Lowry method, and the antigens were intradermally injected using different protocols for type I and II mice. After 38 days, all mice were euthanized with diethyl ether, and spleens were removed. Histological sections were prepared, stained with hematoxylin and eosin and changes to the splenic white pulp (SWP) were studied microscopically. RESULTS: Compared with the control groups, there was a drastic change in white pulp structure. The size increases of the SWP were dependent on the injection group and mouse strain. There was a remarkable expansion of lymphoid follicles in the treated groups in both mice strains. CONCLUSION: The new antigen formulation was able to stimulate and expand the lymphoid constituents of spleen tissue. The SWP is where immune responses and antibodies are produced. Therefore, the effect of the antigen preparations on secondary immune responses, adaptive immunity, and antibody production is important in determining the susceptibility of mice to cutaneous Leishmaniasis and the induction of immunity.