Further protection studies using recombinant forms of Haemonchus contortus cysteine proteinases

Significant levels of protection against Haemonchus contortus have been achieved in sheep by vaccination with a cysteine proteinase-enriched fraction (TSBP) isolated from the gut of adult parasites. Protection is associated with three cathepsin B-like cysteine proteinases (hmcp 1, 4 & 6). Lambs vaccinated with these proteinases, expressed in bacteria as glutathione S-transferase fusion proteins, had significantly reduced (38%) worm burdens compared to challenge controls although, intriguingly, egg output was unaffected. Here, a repeat trial with similar results is reported and protection obtained compared to that induced by vaccination with the predicted mature forms of hmcp1, 4 and 6 expressed in bacteria as non-fusion proteins. Sheep immunized with a cocktail of these non-fusion proteins had reduced faecal egg counts of 27% (P = 0.17) and worm burdens of 29% (P = 0.01) compared to controls. High levels of host serum IgG were detected in GST-hmcp and non-fusion hmcp-immunized animals, although no correlation with protection could be determined. Sera from these groups bound to the microvillar surface of the gut of H. contortus.