An Immunochemical Study of D. viviparus Infective Larvae

The bovine lungworm Dictyocaulus viviparus induces a highly effective immune response in infected cattle and a vaccine, consisting of radiation attenuated infective larvae, has been successfully used for over thirty years. In spite of this notable success, there is little understanding of natural or vaccine-induced immunity to this parasite. Since the infective larva is a potential source of important antigens and can be obtained in relatively large quantities, an immunochemical study of this stage formed the basis of the work presented in this thesis. An investigation of the mouse as a potential immunological model of D.vivipants infection revealed that larvae migrate to the lungs but are expelled without undergoing significant development. Although mice were capable of mounting an immune response to invading larvae, the results suggested the mouse was of limited value as an immunological model for this parasite. No polypeptides were detected by surface biotinylation of exsheathed L3 but several molecules were revealed by labelling sheathed L3. The generation of monoclonal antibodies and lectin binding studies on the L3 cuticular surface demonstrated the presence of phosphorylcholine and carbohydrate epitopes respectively. Lectin binding studies suggested that carbohydrate was not exposed on the external surface of the L3 sheath but was present on the internal surface. The generation of monoclonal antibodies revealed a 29-40kDa antigen on the externzil surface of the L3 sheath which appeared to be highly immunogenic and responsible for the marked antibody response produced to this surface by immunised cattle. These monoclonal antibodies also bound to the surface of the L3 sheath of numerous other nematodes from the order Strongylida, although the molecular weight of the detected antigen varied between some of the species. The antigen was located on a surface coat overlying the sheath epicuticle and was also found to be present in the somatic tissues of the L3. The stage specificity and immunochemical properties of this antigen were examined. In vitro culture of L3 revealed partial development to the L4 with the production of several antigens which were detected by immune bovine serum. An L3 cDNA expression library was produced but screening with immune bovine serum or the monoclonal antibodies failed to detect any positive recombinant clones