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.