Antibodies from sheep immunized against Haemonchus contortus with H-gal-GP inhibit the haemoglobinase activity of this protease complex.

Highly protective intestinal cell membrane antigens have been prepared from Haemonchus contortus, an important blood feeding nematode which parasitizes sheep and goats. One such antigen, H-gal-GP, is a glycoprotein complex containing predominantly digestive proteases. This study showed that H-gal-GP readily digested ovine haemoglobin and albumin, the two most abundant proteins in the parasite's blood meal. It was found that adding protective antibodies from H-gal-GP immunized sheep to the H-gal-GP catalysed haemoglobin digestion reaction, reduced the rate by 70-90% at pH 5·0. This reduction was only 30% when nonprotective IgG from sheep immunized with denatured H-gal-GP was added and IgG from worm-free sheep had no effect. These results support the theory that the mechanism of protection in sheep vaccinated with H-gal-GP is by specific antibodies impairing the parasites ability to digest its blood meal.

Attempts to immunize sheep against Haemonchus contortus using a cocktail of recombinant proteases derived from the protective antigen, H-gal-GP.

The objective of this study was to determine whether an antigen cocktail containing recombinantly expressed versions of most of the protective proteases of H-gal-GP, a known protective antigen from Haemonchus contortus, would confer any protection to lambs in a vaccine-challenge trial. Haemonchus contortus metalloendopeptidases, MEP1, MEP3 and MEP4, were expressed as soluble recombinant proteins in insect cells, but attempts to express the H. contortus aspartyl proteases, PEP1 and PEP2, by the same techniques were not successful. Recombinant H. contortus PEP1 was therefore expressed in Escherichia coli and refolded. Groups of sheep were immunized thrice with either native H-gal-GP, a cocktail of recombinantly expressed proteins (rMEP1, rMEP3, rMEP4 and rPep1), or adjuvant only (QuilA in PBS). All sheep were challenged with 5000 infective larvae 1 week after the final vaccination. High levels of serum antibodies that recognized H-gal-GP were detected in both the native antigen and recombinant cocktail-immunized groups by the time of challenge, but protective immunity was only observed in the group immunized with native H-gal-GP.