The role of liposome size on the type of immune response induced in BALB/c mice against leishmaniasis: rgp63 as a model antigen.

To develop an efficient liposomal vaccine delivery system, the size of liposomes is critical to their adjuvant activities. In the present study, liposomes with different sizes (100, 400, 1000 nm) containing recombinant major surface glycoprotein of Leishmania (rgp63) were prepared, characterized, and inoculated subcutaneously into BALB/c mice to evaluate the rate of protection and the type of immune response generated against leishmaniasis. The lowest footpad lesion size and splenic parasite burden were seen in the mice immunized with large size (≥400 nm) liposomes after challenge with Leishmania major. The production of IFN-γ was only elevated in the spleen cells of mice immunized with large size (≥400 nm) liposomes. The highest IgG2a/IgG1 ratio was also seen in the sera of the mice immunized with large size (≥400 nm) liposomes before and 14 weeks after challenge. The results showed that immunization with small size (100 nm) liposomes induces a Th2 response, whereas immunization with large size (≥400 nm) liposomes induces a Th1 type of immune response. There was no significant difference in the type of induced immune response between the mice immunized with liposomes of 400 nm and those immunized with liposomes of 1000 nm or unextruded. The results of the current study demonstrated that the size of liposomes plays a significant role in the type of generated immune response.