Leishmania antigens are weak immunogens and need to be potentiated by various adjuvants and delivery systems. Alginate microspheres as antigen delivery system and Quillaja saponins (QS) as immunoadjuvant have been used to enhance the immune response against Autoclaved Leishmania major (ALM). Microspheres were prepared by an emulsification technique and characterized for size, encapsulation efficiency and release profile of encapsulates. BALB/c mice were immunized three times in 3-weeks intervals using ALM plus QS loaded microspheres [(ALM+QS)ALG], ALM encapsulated with alginate microspheres [(ALM)ALG], (ALM)ALG + QS, ALM + QS, ALM alone or PBS. The intensity of infection induced by L. major challenge was assessed by measuring size of footpad swelling. The strongest protection, showed by significantly (P < 0.05) smaller footpad, were observed in mice immunized with (ALM)ALG+QS. The (ALM+QS)ALG, ALM and PBS groups showed the least protection and highest swelling, while the (ALM)ALG and ALM+QS showed an intermediate protection with no significant difference. The mice immunized with (ALM+QS)ALG showed the highest IgG2a/IgG1 ratio (P<0.05). The highest IFN-γ and IL-4 production was seen in ALM+QS (P<0.01). It is concluded that QS adjuvant has a mixed Th1/Th2 effect and has increased both humoral and cellular immune responses.
Keywords: Alginate microsphere; Autoclaved Leishmania major (ALM); Quillaja saponin (QS); Vaccine.