Surface and excretory/secretory antigens of fourth-stage larvae and adult Ostertagia circumcincta

Abstract

With the use of an enzyme-linked immunosorbent assay (ELISA), it was revealed that surface antigens of both adult and fourth-stage larvae (L 4) of Ostertagia circumcincta induced high levels of serum IgG antibodies, while serum IgA antibody levels were low but increased significantly ( P <0.01) after infection. Immunofluorescence studies on the surface of viable L 4 and adult nematodes showed that the IgG response was stage-specific only in animals vaccinated with adult surface extracts. The results of Western blot analysis using these antibodies suggested that at least eight polypeptides were shed from the L 4 surface to the environment and that infection induced (or boosted) IgG antibody against a further four polypeptides. A comparison of reactivity of pre- and post-infection sera of sheep vaccinated with adult nematode surface antigens suggested that only one of the antigens stripped from the nematode surface was immunogenic and/or present in a concentration sufficient to induce an IgG response following parenteral vaccination. Infection boosted the IgG antibodies to a further four polypeptides. Only one polypeptide of 63 kDa seems to be shed in vivo from the adult nematode surface. Ten to eleven antigens were recognised in adult excretory/secretory products by serum IgG of multiple-infected sheep.