Haemonchus contortus: identification of proteases with diverse characteristics in adult worm excretory-secretory products.

Host tissue penetration and feeding by helminth parasites may be mediated by both mechanical processes and histolytic products released by the parasites. To investigate potential histolytic products released by adult Haemonchus contortus worms, proteases in excretory-secretory (ES) products were analyzed. The optimum activity of ES proteases was at pH 5.0, although activity was observed over a wide range of pH tested (pH 3.0-9.0). Four protease bands were observed on gelatin-containing polyacrylamide gels, with estimated molecular weights (M(r)) of 32, 35, 38, and 40 kDa. Proteases of 32 and 35 kDa were active at pH 5.0-8.0, while activity of the 38- and 40-kDa proteases was inhibited at pH 8.0. Based on inhibitor studies, the four proteases identified on gelatin-containing polyacrylamide gels were classified as cysteine proteases. Evidence was also obtained that indicated the presence of aspartic and metalloprotease activities in ES products, but these activities were not detected in gels. The diversity of adult H. contortus ES proteases may indicate variable functional requirements for the proteases. Further characterization of ES proteases will facilitate evaluation of their potential application in immunotherapeuti control of disease.