Immunization against Taenia taeniaeformis in mice: Identification of oncospheral antigens in polyacrylamide gels by western blotting and enzyme immunoassay

Abstract

Oncospheral antigens of Taenia taeniaeformis were fractionated using polyacrylamide gel electrophoresis (PAGE) in the presence of sodium deoxycholate (DOC PAGE) under conditions in which their ability to vaccinate mice against infection was not destroyed. A gel cut-out fraction (DOC PAGE FII) was shown to be effective in vaccinating against infection with larvae. DOC-PAGE analysis of radioactivity using ¹²⁵I-labelled antigen indicated that FII represented 11% of the original labelled protein. Antigens from DOC PAGE FII were eluted from gel cut-outs and shown to retain their ability to vaccinate mice against infection. In sodium dodecyl sulphate PAGE (SDS PAGE) the eluted DOC PAGE FII components were shown to contain a restricted subset of polypeptides over a wide range of molecular weight. Specific oncospheral antigens were identified on western blots from DOC PAGE using enzyme immunoassay. Sera used included sera collected from mice protected against infection with larvae by vaccination with oncosphere antigen and sera from mice 28 days post infection (28 DPI) which had been shown to contain antibodies capable of passively transferring protection against infection. Four major antigens were visualized within the FII region using sera from mice vaccinated with complete oncosphere antigen or DOC PAGE FII. The principal antigen detected using 28 DPI sera was not within the FII region although a single weak antigen was detected with 28 DPI sera in FII. Using low acrylamide concentration gels (5% monomer) the four antigens within FII were widely separated and used as gel cut-outs for immunizing mice. No fractions were effective in protecting against infection with larvae. Vaccination with cut-outs from 5% acrylamide gels containing all four FII antigens stimulated only marginal protection as did a gel cut-out from an area in which major antigens were not identified. Loss of vaccination efficacy as oncosphere antigens are fractionated in DOC PAGE suggests that other techniques will have to be used for identifying host-protective antigens from oncospheres beyond DOC PAGE FII. A polyclonal rabbit antiserum against DOC PAGE FII will now be used in screening expression libraries of T. taeniaeformis cDNA in further attempts to obtain host-protective antigens.