Evaluation of immune response against autoclaved Leishmania major incorporated into positively charged liposomes in Balb/c mice

Background and aim: Efficacy of vaccines is mainly depending on the type of adjuvant used. Efficacy trials of first generation vaccine against leishmaniasis showed a limited efficacy due to lack of an appropriate adjuvant. The objective of this study was to investigate whether positively charged liposomes containing ALM could induce Th1 type immune response in susceptible Balb/c mice.Materials and methods: Liposomes containing ALM were prepared by dehydration-rehydration method. Female mice, 6-8 weeks old were immunized subcutaneously with prepared liposomes or as control with empty liposomes, ALM alone or PBS, 3 times, 3 weeks apart. Different groups of mice were challenged with virulent L. major. Immune responses of animals were evaluated in vivo by delayed type hypersensivity (DTH) and in vitro by titration of anti-Leishmania antibody isotypes using ELISA technique.Results: The results showed that footpad swelling in the group of mice immunized with DRV-PC/CHOL-ALM-DDAB was significantly smaller than the control groups (p<0.05). IgG2a titer was significantly higher in immunized mice with DRV-PC/CHOL-ALM-DDAB compared the control groups (p<0.001) and DRV-PC/CHOL-ALM (p<0.05). DTH response of groups received ALM incorporated into liposomes were significantly stronger than the control groups (p<0.001).Conclusion: Smaller lesion size, stronger DTH response and a high IgG2a titer are indicative of a Th1 response. It seems that positively charged liposomes might be used as an immunoadjuvant to induce a Th1 type of response.