Sphingomyelin Liposomes Containing Soluble Leishmania major antigens Induced Strong Th2 Immune Response in BALB/c Mice

Soluble Leishmania antigens (SLA) provide suitable protection against leishmaniasis in murine model when delivered by an appropriate delivery system. Liposomes have been shown to be suitable vaccine delivery systems against leishmaniasis, however, the phospholipase-A (PLA) activity of SLA is a drawback to prepare a stable liposomal SLA. One strategy to overcome this problem might be using a lipid which is resistant to PLA activity of SLA such as sphingomyelin (SM). The aim of this study was to evaluate the effect of stable SM liposomes containing SLA on the immune response induced against leishmaniasis in BALB/c mice. BALB/c mice were immunized subcutaneously, three times with 2-week intervals, with SLA, SM-liposome-SLA, empty liposome or buffer. As criteria for protection, footpads swelling at the site of challenge and foot parasite loads were assessed. The immune responses were also evaluated by determination of IgG subtypes and the level of IFN-γ and IL-4 in cultured splenocytes. The group of mice receiving SM-liposome-SLA, showed a significant large footpad swelling, higher parasite burden in foot and higher IL-4 level compared to the group immunized with buffer. In terms of IgG and IgG isotypes, there was no significant difference between the mice receiving SM-liposome-SLA and the mice that received buffer. Moreover, the immune response induced by SM-liposome-SLA showed no significant difference compared with the one caused by SLA alone. It is concluded that SM-liposome-SLA is not an appropriate strategy to induce Th1 immune response and protect the mice against Leishmaniasis; however, SM-liposomes could be suitable vaccine delivery systems when a Th2 response is needed.