Surface-associated proteins and host IgG on early and late metacestode stages of Taenia pisiformis.

125I-labelled proteins associated with the surface of the oncosphere and metacestode stages of Taenia pisiformis were investigated, together with the presence of host immunoglobulin G on the parasite surface. Rabbit IgG was detected by enzyme-linked immunosorbent assay (ELISA) in the acid washes (pH 3.0) of viable 3-week migratory metacestodes and 8-week mature cystic metacestodes from the liver and peritoneal cavity, respectively, of rabbits orally infected with eggs of T. pisiformis. However, specific anti-T. pisiformis IgG antibodies could not be detected in these washes using ELISA. When intact and washed hatch-activated oncospheres and 3-week and 8-week metacestode stages were iodinated with Bolton-Hunter 125I reagent and examined by SDS-PAGE and autoradiography, there appeared to be a marked loss and/or reduction of labelled proteins on the mature cystic metacestode compared to the oncosphere and 3-week juvenile metacestode stages. Six-week post-infection rabbit sera strongly immunoprecipitated a 43 kD iodinated protein from oncospheres together with others including a 65 kD polypeptide. Only the 65 kD polypeptide, which is the major iodinated protein on 3-week liver metacestodes, was immunoprecipitated from these juvenile or the mature metacestode stages. The results are discussed in relation to survival of metacestodes in the host, and as to how acquired resistance might result from both frequent egg challenge and concomitant immunity.