Aspartyl proteases from the intestinal brush border of Haemonchus contortus as protective antigens for sheep

SUMMARY A novel pepsin‐like aspartyl protease was identified as a component of Haemonchus galactose‐containing glycoprotein (H‐gal‐GP), which is an integral membrane glycoprotein complex located on the intestinal cells of Haemonchus contortus, and a highly protective antigen for sheep. This molecule, designated HcPEP2, showed 50% sequence identity with a previously described aspartyl protease from H‐gal‐GP known as HcPEP1. Fractions of H‐gal‐GP, either containing both HcPEP1 and 2 or other lower molecular weight components of the complex, were evaluated as protective antigens in immunization – challenge trials in sheep. When separated from the rest of the complex by gel filtration in 8 m urea, the HcPEP1 and 2 fraction significantly reduced H. contortus egg counts by 48% and worm numbers by 36%, but the lower molecular weight components were not significantly protective. However, the HcPEP1 and 2 fraction did not protect if electro‐eluted from SDS‐dissociated H‐gal‐GP, nor did bacterially expressed recombinant HcPEP1, suggesting that conformational epitopes are important for inducing immunity.