Molecular cloning of Taenia taeniaeformis oncosphere antigen genes

cDNA cloning of galectins from third stage larvae of the parasitic nematode Teladorsagia circumcincta

A monoclonal antibody raised to a Teladorsagia circumcincta 31-33 kDa doublet antigen was used to immunoscreen a T. circumcincta cDNA expression library. Sheep antibodies eluted from the proteins expressed by two clones immunopositive with the monoclonal antibody specifically recognised the doublet antigen on Western blots of third stage larval extract, confirming that these clones coded for the antigen. Database searches revealed high levels of similarity with beta-galactoside-binding lectin-like proteins (Ga1BPs or galectins) from Caenorhabditis elegans and Onchocerca volvulus. By analogy with these sequences, both T. circumcincta cDNA clones contain the full-length protein coding region. The native doublet proteins could be preferentially extracted from homogenates of third stage larvae with lactose and could be affinity purified on an asialofetuin column, confirming the identity of these bands as galectins. Reverse transcriptase-polymerase chain reaction amplification using a primer based on the C. elegans Spliced Leader SL1 sequence showed that the corresponding T. circumcincta mRNAs are also trans-spliced at their 5' ends. While there are considerable nucleotide differences between the two clones, the majority are located in the non-coding regions. Within the coding region there are 87 nucleotide differences but only three of these result in amino acid substitutions.

Immunocharacterization of Taenia solium oncosphere and metacestode antigens

A partial immunocharacterization of oncosphere and metacestode antigens of Taenia solium was carried out and compared to antigens from other taeniid species. The results indicated that T. solium metacestode antigen contained epitopes cross reactive with rabbit anti-sera to adult and oncospheral stages of the parasite. Oncospheres, however, consisted largely of stage specific antigens. Western blot analysis indicated that T. solium and T. pisiformis shared several oncospheral antigens; however, this was not the case with T. solium and T. hydatigena. Western blot analysis showed a time-related increase in the number of molecules recognized by antibodies to T. solium oncosphere and metacestode antigens in pigs experimentally infected with T. solium eggs. Oncosphere specific antibodies were detected in pig sera one month after experimental infection whereas antibodies to cystic stage antigens were not present until the 3rd to 5th month post infection. Sera from neurocysticercotic patients as well as naturally infected cysticercotic pigs recognized high molecular weight antigens in the oncospheres.

Vaccination against hydatidosis using a defined recombinant antigen

Echinococcus granulosus is the causative agent of hydatid disease in humans and animals. Natural transmission of the parasite occurs between dogs as definitive hosts and animal intermediate hosts. There is an urgent need for improved methods to control the parasite's transmission. Here we describe the development of a vaccine based on a cloned recombinant antigen from the parasite egg (oncosphere). Sheep-vaccinated with the antigen, designated EG95, are protected (mean 96-98%) against hydatidosis developing from an experimental challenge infection with E. granulosus eggs. The vaccine will provide a valuable new tool to aid in control of transmission of this important human pathogen. It also has the potential to prevent hydatid disease directly through vaccination of humans.

Identification and cDNA cloning of two novel low molecular weight host-protective antigens from Taenia ovis oncospheres

Oncosphere antigens of Taenia ovis were solubilised in sodium dodecyl sulphate and separated by electrophoresis in polyacrylamide gels (SDS-PAGE). Antigen-containing gel fractions cut from the region covering 18-12 kDa were shown to be highly immunogenic in sheep challenge experiments. Specific antisera against 2 candidate antigens at 18 and 16 kDa were used to screen a cDNA library prepared from T. ovis oncosphere mRNA. Recombinant proteins selected with antibody to the 16 and 18 kDa native antigens were expressed as GST fusion proteins. Vaccination trials using either of the 2 fusion proteins To16.17-GST and To18-GST, revealed that each was capable of inducing high levels of immunity in sheep against challenge infection with T. ovis eggs. Antibodies induced by vaccination with the recombinant antigens reacted specifically with their respective 18 or 16 kDa native oncosphere antigens. There was no apparent homology between the T. ovis cDNA coding for To18 and To16.17, or with another host-protective antigen, To45W, described previously. These additional host-protective antigens should prove a valuable adjunct to To45W and permit the development of effective vaccination strategies.

Identification and characterization of myophilin, a muscle-specific antigen of Echinococcus granulosus

A muscle-specific gene of Echinococcus granulosus has been identified and characterized. A lambda gt11 clone (10P1), containing an incomplete copy of the gene, was originally isolated from a larval E. granulosus cDNA library by serum antibodies from dogs infected with the parasite. The full-length cDNA sequence was obtained by PCR amplification of cDNA from an adult E. granulosus lambda gt22A library. Southern blot analysis indicated the presence of the gene as a single copy in the genome of E. granulosus and also detected homologous genes in genomic DNA of E. multilocularis and Taenia saginata. The 21.2-kDa protein deduced from the complete cDNA sequence contains two regions of 12 amino acids with similarity to the EF-hand motif of calcium binding proteins. Antibodies raised against the purified 10P1-GST fusion protein detected a 22-kDa antigen in the E. granulosus developmental stages examined. Immunoelectron microscopy localized the native protein in the muscle of the parasite. The amino-acid sequence of the E. granulosus protein shows significant homology to the muscle proteins mp20 of Drosophila melanogaster, chicken SM22 alpha and mammalian calponin, and also to the neuronal protein NP25 of rats. A conserved carboxy-terminal motif of 17 amino acids is present in all the homologous proteins and is proposed to be the characteristic feature of a novel protein family. The term myophilin is proposed for the E. granulosus protein due to its localization and homology to other muscle proteins.

A developmentally regulated gene of Echinococcus granulosus codes for a 15.5-kilodalton polypeptide related to fatty acid binding proteins

A stage-specific expressed gene has been isolated from a cDNA expression library of Echinococcus granulosus protoscolices. The isolated clone contains the complete coding sequence. The corresponding protein (EgDf1) has a molecular weight of 15.5 kDa and is expressed at the tegumental level in the protoscolices, being undetectable in the germinal layer of the metacestode. This protein shares an important homology with a family of low-molecular weight proteins involved in the binding of hydrophobic ligands. This family includes a protein of Schistosoma mansoni (Sm 14) that has immunoprotective activity in rodents. Histochemical and metabolic data already reported for E. granulosus suggest that EgDf1 could be a molecular marker for early events in the process of protoscolex differentiation.