Differential expression and localization of saposin-like protein 2 of Fasciola hepatica

FhSAP2 is a novel antigen isolated from the adult fluke of Fasciola hepatica. Based on sequence similarity with amoebapores and other related proteins, it belongs to the saposin-like protein (SAPLIP) family. FhSAP2 has been shown to be highly immunogenic and capable of inducing protective immune responses in mice and rabbits challenged with F. hepatica. Moreover, FhSAP2 is also reactive with sera from humans with chronic fascioliasis. In the present study, we investigated the expression of FhSAP2 in various developmental stages of F. hepatica by qPCR and demonstrated that FhSAP2–mRNA species are up-regulated in undeveloped eggs, newly excysted juveniles, and adults, but down-regulated in the miracidium stage. Monoclonal antibodies against FhSAP2 were produced, and two clones that are positive to F. hepatica whole-body extract, but not reactive with extracts from other trematodes, were selected, expanded and used for histolocalization studies. Confocal immunofluorescence revealed the presence of native FhSAP2 in epithelial cells surrounding the gut, toward the outermost part of the tegument, and toward the tegumental cells of both adults and newly excysted juveniles.