Comparing Montanide ISA 720 and 50-V2 adjuvants formulated with LmSTI1 protein of Leishmania major indicated the potential cytokine patterns for induction of protective immune responses in BALB/c mice

•Immunization with LmSTI1+ Montanides (Ag-M720, Ag-M50) result in protection against leishmaniasis.•At week 8 after challenge lesion size was significantly smaller in Ag-M720 compared to Ag-M50.•Ag-M720 and Ag-M50 groups produce comparable levels of IFN-γ.•Ag-M720 showed higher IL-10/IL-17 ratio compared to Ag-M50; which accompanied with less pathology.•IL-10/IL-17 ratio might be an indicator of pathology in cutaneous leishmaniasis.

Adjuvants have a key role in subunit vaccine formulations to generate protective immune responses. Herein, we present results of a comparative study on mice immunized with E. coli-derived rLmSTI1 antigen formulated with Montanide ISA 720 (Ag-M720) and ISA 50-V2 (Ag-M50) adjuvants against Leishmania major (L. major). Groups of BALB/c mice were immunized with either Ag-M720 or Ag-M50 by 3 subcutaneous injections with 3-week intervals. Three weeks after the last injection mice were challenged by L. major promastigotes. Immune responses were evaluated before, 3 weeks, and 8 weeks after challenge. Results indicated lower parasite and lesion size in vaccinated mice (the lowest for Ag-M720 indicating the best protection) which correlated with higher IFN-γ induction in immunized groups (Ag-M720 and Ag-M50) compared to control (PBS/adjuvant alone) group. Immune assays showed comparable IFN-γ, total IgG, IgG1 and IgG2a levels for Ag-M720 and Ag-M50 immunized mice but higher induction of IL-4, IL-10 and IL-17 in Ag-M50 and the highest IL-10/IL-17 ratio in Ag-M720 group followed by Ag-M50 and control groups. Altogether, results indicated that lower induction of IL-4, IL-10 and IL-17 cytokines (and/or higher ratio of IL-10/IL-17) despite comparable IFN-γ might be the reason for the superior protection in Ag-M720 group.