[The nematode Haemonchus contortus: antigenic characterization and immune response in rabbits and sheep]

Abstract

In the first part of the study, various tissues of L3 larvae and adult Haemonchus contortus were examined by indirect fluorescence to investigate their antigenicity. L3 larvae were studied in immunoblots as well. The following tissues contained antigens: the sheath and cuticle of L3 larvae; and the cuticle, muscles, epithelium and glandular tissue of the oesophagus and sheath of the spicules of adult nematodes. On the cuticle of exsheathed L3 larvae, we detected by light-microscope slightly raised patches: places where the cuticle differs from the surrounding cuticular morphology. We suggest that the patches are comparable to those found on exsheathed L3 larvae of the horse. Whether the patches produce excretory or secretory antigens or both is unknown, however. Somatic soluble extracts of L3 and adult worms were found to be complex mixtures of proteins by polyacrylamide gel electrophoresis. Results in immunoblots of L3 larvae suggested that the region between the 42 kDa protein and the 18 kDa protein may contain antigens specific for H. contortus. We injected rabbits with the 42-25 kDa fraction of the L3 larvae. The rabbit sera were probed in immunoblots with the total somatic soluble L3 extract for the presence of antibodies. Antibodies reacted with antigens in the 42-25 kDa fraction, however, cross-reactions occurred with antigens in the L3 fractions that were not injected into the rabbits. We found that antibodies against phosphorylcholine were induced and suggest that these cause some of the cross-reactions. In the second part of the study sheep were infected orally with H. contortus and their lymphocyte responses towards L3 antigen and mitogen were measured in a lymphocyte stimulation test. Lymphocyte responses to L3 antigen are expressed in a stimulation index. Two groups of worm-free raised sheep were inoculated (sheep older than 1 year and lambs that were 4 to 6 months old) as well as a group of hyperimmunized sheep. Some sheep were inoculated only once; others were inoculated and then challenged. Lymphocytes of sheep that were hyperimmunized replicated rapidly in the test resulting in significantly higher stimulation indices than those recorded for the lymphocytes of all other sheep. After inoculation the enhanced response further increased. We explain these lymphocyte responses as a result from the immunological memory induced during the hyperimmunization. Lymphocytes of sheep over 1 year old only respond in the test when sheep are infected.(ABSTRACT TRUNCATED AT 400 WORDS)