Molecular cloning of Taenia taeniaeformis oncosphere antigen genes

Abstract

Infection of mice with the cestode Taenia taeniaeformis exhibits several important features common to other cestode infections, including the ability to vaccinate with crude antigen mixtures [1]. Partial purification of the protective oncosphere antigens has been reported with a cutout from deoxycholate (DOC) acrylamide gels; this cutout was called fraction II (FII), and comprises approximately 10% of total DOC-soluble oncosphere antigen. Western blots of DOC gels probed with anti-FII antisera revealed a series of 3–5 discrete bands within the FII region [2]. Further fractionation of the FII antigens on DOC gels was impractical due to limitations in supply of oncospheres, so a cDNA library was constructed from 150 ng of oncosphere mRNA and screened with α-FII antisera. Two distinct clone families were identified, oncA and oncB. Antibodies affinity-purified on either of two representative members, oncA1 and oncB1, recognised all the FII bands. Individual FII bands excised from a DOC gel resolved into an overlapping series of molecules when re-run on SDS-PAGE, indicating that each FII band consisted of several polypeptides of differing molecular weight. Immunoprecipitates resolved on SDS-PAGE revealed that α-FII recognised 3 major oncosphere antigens, of 62, 34 and 25 kDa; antisera against oncB precipitated both the 34- and 25-kDa antigens, whereas α- oncA antisera precipitated the 62-kDa antigen. We conclude that oncA and oncB encode the major antigens in the FII complex. The 62-kDa antigen encoded by oncA1 was the only common antigen precipitated by anti-FII and two other antisera raised against different protective extracts, suggesting that it may be a protective component in all three. Southern blot results indicate that oncA and oncB are distinct genes present at low copy number in the genome. Evidence is also presented suggesting that some cestode mRNAs, including oncA, may use variant polyadenylation signals.