Vaccination against Haemonchus contortus with denatured forms of the protective antigen H11

As part of a systematic examination of the protective epitopes on H11, groups of sheep were vaccinated with preparations of purified H11 used untreated (group A), or progressively denatured (linearized) by incubation with sodium dodecyl sulphate (SDS) (group B) or by boiling with SDS in the presence of dithiothreitol (group C). All the sheep developed antibodies which bound to the untreated H11. When challenged with 10 000 infective larvae of Haemonchus contortus the mean levels of protection relative to the mean values for adjuvant controls were 99.8%, 85% and 79% for faecal egg counts and 95%, 79% and 54% for worm burden at post‐mortem for groups A, B and C respectively. The H11‐specific antibodies inhibited the microsomal aminopeptidase activity of H11 in vitro up to 80%. The levels of inhibition by sera from individual animals correlated with levels of protection with r2, of 0.69–0.87.