VACCINATION OF SHEEP AGAINST FASCIOLA-HEPATICA WITH GLUTATHIONE-S-TRANSFERASE - IDENTIFICATION AND MAPPING OF ANTIBODY EPITOPES ON A 3-DIMENSIONAL MODEL OF THE ANTIGEN

The glutathione S-transferases (FhGST) of the liver fluke Fasciola hep atica have been identified as novel vaccine candidates that protect sh eep against a fluke infection. With the use of overlapping peptides co vering the predicted amino acid sequences of four FhGST cDNAs, we have defined the linear epitopes recognized by polyclonal antibody from sh eep vaccinated with FhGST. Dominant and minor epitopes were found to b e present on all four of the sequences although some epitopes were sho wn to be specific to particular FhGST. A high percentage of the FhGST peptides were found to be antigenic although considerable variability in response to the peptides was observed among the animals. This analy sis was extended to the IgG1 and IgG2 response at the peptide level. B ased on the recently solved crystal structure of the rat mu-class GST 3-3, a three-dimensional model of one of the FhGST sequences was gener ated that allowed the predicted spatial localization of defined epitop es. Most epitopes were localized on regions of high flexibility and ac cessibility. A comparison of epitopes on FhGST with the B cell epitope s on Sm28, a 28-kDa GST from Schistosoma mansoni, has found few simila rities. There was no correlation between an antibody response to linea r peptide epitopes and the level of protection induced in sheep by vac cination with FhGST.