Immunogenicity and protection effects of cationic liposome containing imiquimod adjuvant on leishmaniasis in BALB/c mice

Protection against leishmaniasis, in the murine model, is dependent on developing a potent CD4+ mediated Th1 type response. Liposomes can be applied as immunoadjuvants to stimulate immune responses to different antigens. In the present study, it was investigated whether DOTAP liposomes having SLA and imiquimod adjuvant, can induce a Th1 response and protect against Leishmania major challenge in BALB/c mice. Liposomes were provided applying the lipid film procedure. BALB/C mice were subcutaneously immunized, three times with 2-week intervals, with various formulations. Assessment of lesion development and parasite burden in the foot and spleen after challenge with L. major, assessment of Th1 cytokine (IFN-γ), and titration of IgG isotypes assessed the type of generated immune reaction and the protection extent. The mice immunized with Liposome DOTAP+imiquimod+SLA showed smaller footpad swelling which was meaningfully different (P<0.05) compared with other groups. The highest level of IgG2a was observed with Lip DOTAP+imiquimod+SLA more than the control (P<0.001). Mice immunized with Lip DOTAP+SLA+imiquimod demonstrated the least number of live parasites in the footpad and spleen. Cytokine assay showed that the greatest IFN- γ secretion was seen in the splenocytes of mice immunized with all formulations as compared to the control group (P<0.0001). In contrast, the lowest IL-4 production was detectable in Lip+imiquimod+SLA spleen, which was not significantly different compared with other groups. The results of this study show that liposome DOTAP+SLA+imiquimod formulation generates a cellular immune response that is protective against challenge against L. major.