Sphingomyelin liposome bearing whole Leishmania lysate antigens induce strong Th2 immune response in BALB/c mice

Whole Leishmania lysate antigens (WLL) has been shown to be effective to tackle leishmaniasis in murine models. Although liposomes can be considered as promising vaccines, the activity of phospholipase-A (PLA) in WLL, breeds difficulties to preparing stable liposomal WLL. One strategy to overcome this shortcoming is to use lipids such as sphingomyelin (SM) which is resistant against PLA. This study aim is formulating stable SM liposomes containing WLL and comparing their adjuvant effects with another first generation vaccine , i.e. solube Leishmania Antigen (SLA) liposomes in BALB/c mice.

BALB/c mice were immunized subcutaneously, three times with 2-week intervals, with Empty-liposome (E-lipo), Particulate WLL, Liposome-WLL, Liposome-SLA and control Buffer, three times every 2-week. Protection was assessed through measuring the swollen footpads and the load of parasites in the spleen. Other factors were used to assess the response of immune system by means of IgG subclasses, IL-4 and IFN-γ levels and intracellular cytokine assay in cultured splenocytes.

Although liposomal WLL were stable in terms of physicochemical properties, mice received Liposome-WLL did not reduce footpad swelling. The load of parasites in spleen and levels of IL-4- were also higher compared to other immunized groups. In terms of IgG isotypes, no considerable difference observed in mice received Liposome-WLL or other formulations.  

Liposome-WLL could be a suitable vaccine delivery system when a Th2 response is desired. Also, further studies are warranted to fully understand the role of sphingomyelin in inducing an immune response.