Biomedical Engineering Reference
In-Depth Information
(not recombinant protein) protects lambs against naturally acquired infection
in a field setting, further highlighting the ecacy of this protein as a vaccine; 44
however, numerous attempts by different labs to replicate the vaccine ecacy of
native H11 using recombinant (enzymatically active) H11 has proven unsuc-
cessful (J. Zawadzki, pers. comm.), implying that the protective epitopes on
parasite-derived H11 might be glycan residues.
A leucine aminopeptidase purified from detergent-soluble extracts of F.
hepatica (LAP) was used to vaccinate sheep and resulted in an 89% reduction in
fluke burden compared to non-vaccinated animals, and antisera from vaccinees
inhibited the enzymatic activity of LAP. 45 Furthermore, vaccination with a
recombinant form of the enzyme afforded a 78% decrease in worm numbers
relative to controls. 46 Both S. mansoni and S. japonicum express a gene
encoding a leucine aminopeptidase, and immunolocalization studies show that
these proteins are synthesized in the gastrodermal cells surrounding the gut
lumen. 47 Given their perceived involvement in the Hb digestion process, they
merit investigation as targets for vaccine intervention.
8.3 Proteases of Larval-Stage Hookworms
Helminth infection of a host often occurs from penetration of the skin by an
immature larva followed by migration through host tissue into the vasculature.
This is a largely chemical process that is mediated by the release of a range of
proteolytic enzymes from specialized larval glands. Secretions of the larval
stage of N. americanus possess enzymatic activity belonging to all the known
major mechanistic classes of proteases and have the ability to degrade the
connective tissue substrates collagen, fibronectin, laminin, and elastin. Fur-
thermore, larval skin penetration was significantly neutralized only by pep-
statin A, an inhibitor of aspartic proteases, implicating the importance of these
enzymes in the infection process. 26 This activity may be at least partially due to
the aspartic protease and human hookworm vaccine antigen, Na-APR-1, due
to its ability to digest skin macromolecules and its presence in larval parasites. 48
One of the best-characterized proteases in larval ES products is Ac-MTP-1,
an astacin-like zinc metalloprotease from the dog hookworm, A. caninum. 49,50
Ac-MTP-1 aids larval migration through skin and tissue by degrading fibro-
nectin, laminin, and collagen. The metalloprotease inhibitor 1,10 phenan-
throline inhibited larval skin penetration by up to 61% and antiserum against
recombinant Ac-MTP-1 neutralized migration of larvae through tissue in vitro
by 75%, 50 highlighting the importance of this enzyme in the infective process.
Furthermore, dogs vaccinated with Ac-MTP-1 and then challenged with
A. caninum larvae showed a statistically significant inverse association between
anti-Ac-MTP-1 IgG2 antibody titres and both intestinal adult hookworm
burden and faecal egg counts. 51 In addition, a recent vaccine trial conducted in
hamsters indicated that recombinant MTP-1 reduced worm burden by up to
29% compared to the control group which received adjuvant alone, 20 sug-
gesting that this molecule offers promise as a component of a recombinant
vaccine cocktail.
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