Evaluation of Quillaja brasiliensis saponin-based nanoparticles combined with leucine aminopeptidases for immunoprotection of sheep against Fasciola hepatica

Abstract

Background: Fasciola hepatica causes important economic losses in ruminants with only pharmacological treatments currently available, which produces several secondary problems. Because of this, vaccines have become an interesting alternative. Leucine aminopeptidases (LAPs) are attractive vaccine targets against fasciolosis since they play essential roles in the parasite such as host invasion and nutrient acquisition. To characterize immune responses, we produced two recombinant F. hepatica LAPs (FhLAP1 and FhLAP2), formulated with ISCOM-matrices (IMXs) nanoparticles from Quillaja brasiliensis saponins. Methods: Forty female Corriedale sheep were assigned to four groups (n = 10): FhLAP1/IMX, FhLAP1/FhLAP2/IMX, IMX (control), and FhLAP1/Adj50 (Adjuvac 50). Animals received two subcutaneous immunizations at weeks 0 and 4 and were challenged orally with 200 metacercariae at week 6. Results: FhLAP1 and FhLAP1/FhLAP2 induced specific IgG responses, with the predominance of the IgG1 response. However, these responses were lower than those generated by FhLAP1 formulated with Adj50. A qPCR analysis revealed that FhLAP1/IMX stimulated a Th1-type response profile before the challenge, but this profile was not sustained after infection. The post-infection profile of FhLAP1/FhLAP2/IMX was more congruent with expected values despite not achieving a robust IFN-γ expression. No significant differences in the fluke burden were observed. Conclusions: Further research on the optimal antigen/adjuvant combination in ruminants is encouraged. For instance, a higher concentration of adjuvant in the formulation used in this work may enhance the strength and duration of the inflammatory response and improve protective immunity against fasciolosis.