| Summary: | The main aims of this study were to identify and characterise proteins from <i>T. circumcincta </i>that may induce a protective immune response in the host and to learn more about the biology of the worm. In order to identify possible protective antigens, a complementary DNA (cDNA) library prepared from adult worms was screened with serum from an animal that was protected against a single challenge infection after vaccination with a <i>T. circumcincta </i>protein fraction (S3 TSBP). Forty five immunopositive cDNA clones were identified, of which sixteen had homology to galectin. Of the remaining clones, the majority shared homology with two metabolic enzymes, methylmalonate semialdehyde dehydrogenase and 10-formyltetrahydrofolate dehydrogenase, that have not been characterised in nematodes. A single clone with homology to the antioxidant enzyme, catalase, was also identified. These three enzymes were selected for further investigation on the basis of their roles in nematode metabolism and therefore, their potential as vaccine candidates. Characterisation of <i>T. circumcincta </i>excretory/secretory material (ES) was also performed. L4 and adult worms were cultured <i>in vitro</i> and the proteins released were separated by 1D electrophoresis and analysed by Tandem Liquid Chromatography Mass Spectrometry and N-terminal sequencing. This identified proteins showing similarity to, amongst others, metabolic enzymes, structural components, antioxidants, globin-like proteins and cysteine proteases, present in online databases but not previously characterised in <i>T. circumcincta.</i> This study has identified several novel <i>T. circumcincta </i>proteins that may have potential as future vaccine or drug targets. It has also provided further information regarding the biology of the worm.
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