Immunological studies on the protective immune response against Taeniid Cestode parasites
Document TypeMasters Research thesis
Access StatusOpen Access
© 2017 Julia Annette Lackenby
Taeniid cestodes have a lifecycle involving two mammalian hosts. Some species such as Taenia solium and Echinococcus granulosus infect humans and cause morbidity and mortality. T. solium is the aetiological agent of neurocysticercosis, the cause of substantial neurological disease in the non-Islamic regions of the developing world, including Africa, Asia and Latin America. Recombinant vaccines, derived from the larval oncosphere stage, have been developed against T. solium and several cestode parasites for use in livestock animals to prevent parasite transmission to humans. This study investigated antigenic cross-reactivity between the host-protective, recombinant oncosphere proteins with the aim of identifying a surrogate species for T. solium and E. granulosus as the target in in vitro oncosphere killing assays. Investigations into antigenic cross-reactivity were undertaken by comparative analyses of the amino acid sequence of the recombinant host-protective oncosphere antigens. Immunological assays including Indirect ELISA, Inhibition ELISA and Western blot were used to determine immunological cross-reactivity between the recombinant oncosphere antigens. Antigenic cross-reactivity between oncosphere antigens and different Taeniid species was also examined via in vitro oncosphere killing assays. Analysis of amino acid sequences of twelve recombinant oncosphere antigens identified four homology groups, To16, To18, To45 (from Taenia ovis) and EG95 (from E. granulosus) with the nomenclature based on the first recombinant antigen isolated for each group. Examination of the amino acid sequences determined high levels of sequence identity among oncosphere proteins within homology groupings, not with antigens from within a species. Limited immunological cross-reactivity was identified by Indirect ELISA and Inhibition ELISA as well as Western blot. This was in contrast to the close sequence relationship observed between several of the antigens. Detectable immunological cross-reaction was observed for the Taenia multiceps antigens TM16 and TM18 with all Taeniid proteins from within the To16 and To18 homology groups, with the exception of TSOL18 (from T. solium). Substantial antigenic cross-reactivity was detected between TM16 and TM18 in both Indirect ELISA and Inhibition ELISA, while a weak reaction was detected in Western blot, despite amino acid sequence identity being 15%. In contrast, To18 and TSOL18 share 60% amino acid sequence identity, yet no cross-reaction was detected in immunological assays or in vitro oncosphere killing assays. The lack of cross-reactivity with TSOL18 was unexpected given the high amino acid sequence identity it shares with other proteins of the To18 homology group. These studies investigated the potential to identify a surrogate Taeniid species (more amenable to laboratory manipulation) from assessment of protective immune responses raised by TSOL18 in vaccinated pigs. Oncosphere killing assays were also utilised as an in vitro method to assess antigenic cross reactivity between proteins from different Taeniid species. Oncosphere killing assays determined that anti TSOL18 sera induced significant killing of T. saginata oncospheres. None of the cross-reactions observed in immunological assays or amino acid sequence analysis was reflected in oncosphere killing assays. These studies have revealed that detectable levels of antigenic cross-reactivity exist between some of the recombinant oncosphere antigens. The successful killing of a heterologous species indicated that the use of a surrogate target Taeniid species, to monitor immune responses in vaccinated animals, is feasible. The findings here limit the potential for development of in vitro methods for assessment of host-protective immune responses induced by the vaccines. Further investigation is required in order to identify a Taeniid species with significant cross-reactive capabilities and a lifecycle that is maintainable in a laboratory setting.
Keywordsparasitology; cestode; Taenia; antigenic cross-reacitvity; ELISA; oncopshere killing
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