Analysis of a calcium-binding EF-hand protein family in Fasciola gigantica.

Transcriptome data supports the notion of a Platyhelminthes-specific protein family that is characterized by combination of two N-terminal EF-hands and a C-terminal dynein light chain-like domain. Family members in schistosomes induce an IgE response that has been connected with resistance to reinfection in schistosomiasis and is considered as a marker of protection. In the present study, we have compared three homologs of the liver fluke Fasciola gigantica for their immunological properties in mouse. Antisera raised against the recombinant proteins detected the native proteins in tegumental type tissues and epithelial linings of excretory system and intestinal tract. The recombinant EF-hand domains induced strong IgG and IgE responses in immunised mice while only weak to moderate responses were observed against the complete recombinant proteins and their DLC-like domains. Parasite crude worm and tegumental extract antisera reacted predominantly with one isoform and its EF-hand domain. Sera of F. gigantica infected mice did not react with the recombinant proteins. The RNA products of the three genes were detected from the metacercarial up to the adult stage. These observations indicate that the investigated EF-hand proteins are not at the frontier of humoral host/parasite interaction in acute fascioliasis gigantica in mouse but are acting as intracellular proteins in tissues that interface with the parasite's environment or tubular tracts.