ISOTYPE-SPECIFIC SERUM ANTIBODY-RESPONSES OF SHEEP TO HAEMONCHUS-CONTORTUS ANTIGENS

In total, 19 8-month-old Texel sheep were used to study the isotype-sp ecific serum antibody responses against infective larvae and adult wor ms of Haemonchus contortus. Group 1 sheep (n = 7) were infected with 2 0 000 L(3) larvae (Week 0), treated with ivermectin 6 weeks post-infec tion and subsequently challenged at Week 10 of the experiment. This ch allenge consisted of a trickle infection of 10 000 L(3) larvae per wee k for 5 weeks. Group 2 sheep (n = 7) received a single infection at We ek 10 of the experiment, and Group 3 (n = 5) served as a non-infected control group throughout the entire experiment. Individual blood and f aeces samples were collected at weekly intervals. The immune responses were monitored by ELISA and Western blotting. The secondary immune re sponse coincided with a significant reduction of the Haemonchus egg ou tput and reduction of worm counts. Both primary and challenge infectio ns induced humoral immune responses, and ELISA revealed that the most dominant serum antibody responses belong to the IgG1 isotype and to a lesser extent to IgG2. IgM and IgA responses were less dominant. Weste rn blotting experiments demonstrated that many antigens were commonly recognized by antibodies from both primary and challenge infected anim als. However, sera of immune animals specifically reacted with low mol ecular weight proteins. In particular, a 24 kDa antigen present in adu lt worms apl,eared to be specifically recognized.