Protective role of secreted aspartyl proteinase in murine systemic candidiasis caused by non-albicans Candida species

Abstract

Abstract Non-albicans Candida species are increasingly becoming more prevalent globally and emergence of drug resistance is another cause of concern. We investigated the protective potential of secreted aspartyl proteinase (Sap2), a leading candidate vaccine antigen identified from research based on C. albicans, in murine systemic candidiasis caused by non-albicans Candida species. The Sap2 genes were successfully cloned and expressed as recombinant proteins from C. albicans, C. tropicalis and C. parapsilosis. Groups of Balb/c mice were immunized with individual rSap2 protein along with alum as adjuvant, followed by systemic infection with lethal dose of C. tropicalis. The protective potential of each rSap2 protein was evaluated using survival analysis and estimation of organ fungal burden. Mice immunized with rSap2 cloned from C. parapsilosis showed highest increase in survival time (p=0.02) and maximum reduction in organ fungal burden (spleen, kidneys, lungs, brain) (p<0.05); compared to sham immunized controls. Immunization with rSap2 cloned from C. albicans did not improve survival in non-albicans C. tropicalis infection, despite the protein having ~60% homology across species. Mice immunized with rSap2 cloned from C. parapsilosis also exhibited significantly higher levels of IFN gamma and IL-4 cytokine levels just before infection, which correlated with protection. The anti-Sap2 specific antibody titres were measured. No correlation was observed between level of Sap2-specific IgG titres and survival outcome. The IgG response was primarily Th2, belonging to IgG1 subtype. Further cellular and histological studies are in progress to characterize the murine rSap2-parapsilosis specific protective immune response in detail.