Tabriz University of Medical Sciences Advanced Pharmaceutical Bulletin 2228-5881 16 2 2026 06 15 PpSP42 and LmSTI1-PpSP42 Recombinant Proteins from Phlebotomus papatasi and Leishmania major Confer Protection Against Leishmania major Infection in BALB/c Mice 432 444 10.34172/apb.45925 EN Fariborz Bahrami https://orcid.org/0000-0001-9561-415X Touraj Miandoabi https://orcid.org/0000-0003-3538-8941 Vahideh Moein Vaziri https://orcid.org/0000-0001-8037-1458 Farhad Riazi-Rad https://orcid.org/0000-0002-5114-4173 Soheila Ajdary https://orcid.org/0000-0002-5052-2523 Journal Article 10.34172/apb.45925 2025 06 07 2026 03 23 Introduction: Cutaneous leishmaniasis (CL), a parasitic skin disease transmitted by sand flies, is characterized by complex interactions between Leishmania parasites and sand fly saliva, influencing both transmission and disease progression. This study investigated the immunogenicity of partial Phlebotomus papatasi salivary protein PpSP42 (or PP42 in short) and a novel recombinant fusion protein composed of Leishmania major stress-inducible protein 1 (LmSTI1) and PP42, produced in Escherichia coli. Methods: BALB/c mice were immunized subcutaneously with the fusion protein or with PP42 subunits separately, using resiquimod as an adjuvant, and subsequently challenged with L. major promastigotes and sand fly salivary gland homogenate. Lesion development and parasite burden as well as immune responses were evaluated by measuring key cytokines (IFN-γ, IL-4, IL-10, TNF-α) and antibodies (IgG, IgG1, IgG2a) up to eight weeks post-challenge. Results: Immunization with either PP42 or the fusion protein significantly attenuated lesion development (30-40% reduction in lesion size after 8 weeks; P<0.001) and parasite burden (∼100-fold lower after 8 weeks; P<0.05) compared to the PBS control. This protection was accompanied by significantly higher levels of IFN-γ and TNF-α (P<0.05 for both). Also, an elevated IgG2a/IgG1 ratio (P<0.01), indicative of a Th1-biased immune response was observed when the fusion protein was used for immunization. Conclusion: These findings suggest while immunization with PP42 protein alone resulted in lesion control and reduced parasite load, compared to the control group, these effects were less pronounced than those observed in the fusion protein group. Hence, LmSTI1-PP42 fusion protein warrants further investigation as a potential vaccine candidate against L. major infection.