Molecular cloning of components of protective
antigenic preparations has suggested that related parasite
fatty acid-binding proteins could form the basis of the protective
immune crossreactivity between the parasitic trematode
worms Fasciola hepatica and Schistosoma mansoni. Molecular
models of the two parasite proteins showed that both
molecules adopt the same basic three-dimensional structure,
consisting of a barrel-shaped molecule formed by 10 antiparallel
(8-pleated strands joined by short loops, and revealed the
likely presence of crossreactive, discontinuous epitopes principally
derived from amino acids in the C-terminal portions
of the molecules. A recombinant form of the S. mansoni
antigen, rSml4, protected outbred Swiss mice by up to 67%
against challenge with S. mansoni cercariae in the absence of
adjuvant and without provoking any observable autoimmune
response. The same antigen also provided complete protection
against challenge with F. hepatica metacercariae in the same
animal model. The results suggest that it may be possible to
produce a single vaccine that would be effective against at least
two parasites, F. hepatica and S. mansoni, of veterinary and
human importance, respectively.