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Peptide vaccines constitute an interesting alternative to classical vaccines due to the possibility of selecting specific epitopes, easy of production and safety. However, an inadequate design may render these peptides poorly immunogenic or lead to undesirable outcomes (e.g., formation of B neoepitopes). As an approach to vaccine development, we evaluated the antibody response to chimeras composed of two or three known B epitopes from Trichinella and Fasciola, and several linkers (GSGSG, GPGPG and KK) in species as different as mice, sheep and turbot. All these species could mount an effective immune response to the short chimeric peptides. Nevertheless, this response depended on several factors including a favorable orientation of B-cell epitopes, adequateness of linkers and/or probability of formation of T neoepitopes. We also observed that, at least in mice, the inclusion of a decoy epitope may have favorable consequences on the antibody response to other epitopes in the chimera., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A clone, designated L20h-Ts3, was selected by immunoscreening of cDNA libraries of Trichinella spiralis worms collected 14h, 20h and 48h post-infection (p.i.) from mice intestines. L20h-Ts3 encodes the full-length of a conserved hypothetical protein of 13.1kDa involving putative interaction with the immune system. PCR analysis showed that L20h-Ts3 mRNA is constitutively expressed throughout T. spiralis life cycle and not restricted to intestinal stages. The L20h-Ts3 fusion protein was obtained in an Escherichia coli expression system and purified by Ni-affinity chromatography before inoculation into mice in order to produce polyclonal antibodies. Then, immunohistochemical study and Western blot analysis revealed its presence within the stichosome of T. spiralis and in excretory/secretory products strengthening a putative fundamental role for the parasite's survival such as host tissue invasion or modification of the host muscular cell phenotype. L20h-Ts3 fusion protein was recognized in Western blot as soon as 15-20 days p.i. by sera from pigs experimentally infected with 20,000 muscle larvae (ML) of T. spiralis. Thus, an indirect L20h-Ts3 ELISA was designed and evaluated using sera from experimentally infected pigs by comparison with the only ELISA currently available for trichinellosis purposes. A gain of precocity from 7 up to 14 days and detection up to 25 weeks p.i. was possible with the L20h-Ts3 ELISA offering a large window for trichinellosis detection. The L20h-Ts3 ELISA was less effective in the case of low infections in pigs. Nevertheless, these results show that the L20h-Ts3 ELISA has a real interest due to its precocity and stability of detection in time. The association of the L20h-Ts3 fusion protein with other antigenic proteins identified previously could appreciably improve the serological test and facilitate its standardization., (Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.)

Parasite-induced and parasite-regulated larval capsule formation and host immunosuppression are two major characteristics that are unique in Trichinella spp. infections, but the molecule(s) and mechanism(s) that mediate these processes remain largely unknown. Trichinella pseudospiralis and Trichinella spiralis, are obviously different with respect to these two characteristics. A comparative study of these two species, in particular their antigen expression profiles at different developmental stages (the main molecules involved in the cross-talk or interaction between each parasite and its host), may help us better understand the parasite molecules and mechanisms involved. Here, we constructed cDNA libraries from T. pseudospiralis adults (Ad), newborn larvae (NBL) and muscle larvae (ML) mRNA and screened them with pig anti-T. pseudospiralis serum collected 26, 32 and 60 days post-infection (p.i.). The most abundant antigens were found to vary among life-cycle stages. Pyroglutamy peptidase 1-like and 6-phosphogluconolactonase-like genes predominated in the Ad stage and a serine protease (SS2-1-like gene) predominated in NBL similar to that observed in T. spiralis. Muscle larvae expressed proteasome activator complex subunit 3-like and 21 kDa excretory/secretory protein-like genes. This study indicated that parasites of two species may utilise different molecules and mechanisms for larvae capsule formation and host immunosuppression during their infections. Proteins of antigenic genes identified in this study may be also good candidates for diagnosis, treatment or vaccination for T. pseudospiralis infection, and also for the differential diagnosis of two species' infections., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The 53-kDa proteins in larval excretory and secretory (E-S) products were expressed from five Trichinella species (T. spiralis, T. britovi, T. nativa, T. pseudospiralis, and T. papuae), using the Escherichia coli expression system, and the antibody responses to the 53-kDa recombinant proteins in mice infected with Trichinella spp. were analyzed by Western blotting. The 53-kDa protein is conserved among the five Trichinella species, with >60% similarity in amino acid sequences. The 53-kDa recombinant proteins of T. spiralis and T. pseudospiralis reacted to sera from mice infected with T. spiralis and T. pseudospiralis at 8 days postinfection (p.i.), respectively. An antibody against the 53-kDa recombinant protein of T. spiralis recognized the 53-kDa protein in the crude extracts from adult worms and 30-day p.i. muscle larvae and E-S products from muscle larvae of T. spiralis but did not recognize any proteins from T. pseudospiralis. The sera from the mice infected with T. spiralis strongly reacted with the 53-kDa recombinant protein of T. spiralis but did not react with the 53-kDa recombinant proteins of T. britovi, T. nativa, T. pseudospiralis, and T. papuae. Similarly, the sera from mice infected with T. britovi, T. nativa, T. pseudospiralis, or T. papuae strongly reacted with the 53-kDa recombinant proteins of T. britovi, T. nativa, T. pseudospiralis, or T. papuae, respectively. These results showed that the 53-kDa recombinant proteins provide early and species-specific antibody responses in mice infected with Trichinella spp.

A cDNA library was constructed from muscle larvae of Trichinella pseudospiralis. A cDNA clone, designated as Tp8 contained a cDNA transcript of 1326 bp length with a single open reading frame, which encoded 303 amino acid residues (34,187 Da, estimated molecular mass). The predicted amino acid sequence of the clone had an identity of approximately 60% to the Rcd1 (Required cell differentiation 1) -like proteins among a wide range of organisms. Real-time quantitative polymerase chain reaction results showed that the transcription level of Tp8 gene reached the highest value in adult worms, and that the transcription level in muscle larvae before stichosome formation was higher than in muscle larvae after stichosome formation. The recombinant Tp8 protein migrated at 37 kDa and reacted to antibody against T. pseudospiralis excretory-secretory (E-S) products and sera from mice infected with T. pseudospiralis. An antibody against the Tp8 recombinant protein could stain proteins migrating at approximately 34 kDa (which is the expected size from the sequence) on Western blotting of E-S products from muscle larvae. An immunocytochemical study showed that the Tp8 protein was present within the stichocyte of muscle larvae and adults worms.

This study investigates the heterogeneity and immunogenicity of the Trichinella TSL-1 antigen gp53. Western blotting analysis of several Trichinella isolates with the gp53-specific monoclonal antibodies (mAbs) US5 and US9, produced in Btkxid mice, revealed that gp53 from the species T. britovi, T. murrelli and genotype T8 had higher MW (60 kDa) than gp53 from T. spiralis, T. nelsoni and genotype T6 (53 kDa) and from T. nativa (55 kDa). mAb US5 reacted only with gp53 from T. spiralis. Experiments including immunoassays of gp53 binding by sera from T. spiralis-infected mice, in the presence of different potential inhibitors (recombinant gp53, US5, T. britovi-crude larval extract (CLE), and CLE N- and O-glycans), indicate (i) that gp53 from T. spiralis bears specific epitopes that induce antibody formation during infection; (ii) that the protein epitopes of gp53 are much more important (76 or 68% of total antibody reactivity in BALB/c and Swiss CD-1 mice, respectively) than the corresponding glycan epitopes including tyvelose (11 or 32% of total reactivity) for the induction of anti-gp53 circulating antibodies; and (iii) that the species-specific epitopes present on gp53 are differentially recognized in different mouse strains. Whereas in BALB/c mice US5- and non-US5-recognized species-specific epitopes on gp53 bind about 84% of circulating antibodies on day 80 post-infection, this percentage was only 38% in Swiss CD-1 mice. These data on the antigenicity of gp53 contrast with data for Trichinella CLE antigens, in that most circulating antibodies reactive with CLE antigens recognized tyvelose-containing epitopes (57% and 58% of circulating antibodies in BALB/c and Swiss CD-1 mice, respectively). Together these results demonstrate that gp53 is recognized during infection but is antigenically different from other Trichinella TSL-1 antigens.

A novel excretory-secretory (ES) protein of Trichinella pseudospiralis was produced. A cDNA library was constructed from mRNA of muscle larvae at 30 days post infection (p.i.) and immunoscreened with the antibody against ES products. A clone, designated Tp22-3, contained a cDNA transcript of 815 bp in length with a single open reading frame which encoded 244-amino acids (28407 Da in the estimated molecular mass). A database search revealed that no sequences had a homology to this predicted protein. The recombinant protein was produced in an Escherichia coli expression system. Stage specific expression of this protein was suggested from the following experiments. An antibody against the recombinant protein could stain proteins migrating at about 28 kDa (which is the expected size from the sequence) on Western blotting of crude extracts or ES products from 30 days p.i. muscle larvae, but failed to stain any proteins in crude extracts from newborn larvae or 15 days p.i. muscle larvae. The antibody reacted to the stichocytes of larvae at 30 days p.i., but did not react to 15 days p.i. muscle larvae. The production of an mRNA transcript for Tp22-3 gene was restricted largely to the 30 days p.i. muscle larvae and adult worms.

Hybrids between female Trichinella spiralis and male Trichinella britovi were constructed. Then, hybrid genotype was characterized by DNA markers including mitochondrial cytochrome c oxidase subunit I (CO I) gene, the gene encoding the 43-kDa excretory-secretory (ES) protein, and genomic DNA fragments specific for T. spiralis and T. britovi identified from random amplified polymorphism DNA (RAPD). PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of the mitochondrial CO I gene revealed that all hybrids carried a T. spiralis pattern. The same analysis of the gene encoding the 43-kDa ES protein showed that each hybrid carried both T. spiralis and T. britovi gene type simultaneously. In the analysis of genomic DNA using RAPD-derived PCR primers, some hybrids carried T. spiralis and T. britovi-specific RAPD markers, while others carried the RAPD marker of T. spiralis only.

A cDNA library for Trichinella pseudospiralis was constructed to study the expression of specific antigens. Four positive clones were identified using antibodies against the excretory/secretory (ES) products of the nematode as probe. Sequence analysis showed that they contained identical cDNA inserts of 606 bp, including a 5' non-translated region of 96 bp, a core translated segment of 408 bp and a poly(A)+ 3' terminus. It encoded a novel 136-amino-acid polypeptide. Southern blot analysis indicated that the cDNA did not cross-hybridize to the genomic digests of T. spiralis, mouse, or rat. A single copy only of its complementary sequence was found in the genome of T. pseudospiralis. Using the lambda ZAP expression system, the cDNA was induced to express a 23-kDa beta-galactosidase-fusion protein which did not cross-react with polyclonal and monoclonal antibodies against T. spiralis, heat shock proteins, or four heterologous species of nematodes. The antiserum against the fusion protein recognized a 15-kDa band from the ES products of T. pseudospiralis in immunoblotting. Immunocytolocalization demonstrated that the anti-fusion protein serum only recognized an epitope in the stichosome of T. pseudospiralis and not in T. spiralis. The protein can therefore serve as a specific antigen for the differential diagnosis of trichinellosis.

Reverse transcription-polymerase chain reaction (RT-PCR) was employed to amplify a cDNA encoding an excretory-secretory (ES) antigen with mol. wt 45-50 kDa by SDS-PAGE from T. spiralis muscle larvae. The PCR product was purified by electrophoresis and sequenced by thermal cycle sequencing with primer walking. The cDNA is 890 bp long and encodes a polypeptide of 255 amino acid (AA) residues. Using the same methods, we also recovered a corresponding cDNA from Trichinella T5, which is 891 bp long and encodes 255 AAs. Comparison of the 2 Trichinella species indicates approximately 2.6% and 2.4% differences between the 2 cDNA sequences and between the 2 deduced AA sequences, respectively.

Host antibody recognition of muscle larval (ML) antigens of Trichinella spiralis was examined. Monoclonal antibodies (MoAbs) to known host protective ML antigens have been produced in order to aid this examination. Eleven strains of mice with independent MHC haplotypes and seventeen T. spiralis infected human patients were all found to recognize the same three major antigens as the monoclonal antibodies; i.e., of mw 41, 46 and 55 kD. However all serum samples tested also recognized further ML antigens and this recognition varied with the individual or strain. This variation in antigen recognition also applied to the MoAb. Mutual inhibition studies demonstrated that even where the MoAb apparently recognized the same antigens, specific epitope recognition was disparate. Hence some of the major antigens recognized by hosts of T. spiralis, regardless of whether vaccinated or infected, correspond with antigens which have considerable host protective properties. There also appear to be a number of epitopes upon these antigens and the biological implications of this are discussed.

Complementary DNA (cDNA) encoding a 49-kDa antigen of Trichinella spiralis was cloned, characterized, and expressed in Escherichia coli by recombinant DNA methods. As a first step, 29 residues of N-terminal amino acid sequence were determined by direct analysis of highly purified antigen. Mixed-sequence primers based on the amino acid sequence were then synthesized and used as primers to generate a partial cDNA by the polymerase chain reaction (PCR). A nearly full-length cDNA was then obtained by PCR using a specific 5'-end primer and a non-specific 3'-end primer. Complete sequence of the 1133-bp cDNA was determined. Translation of this sequence predicts an N-glycosylated polypeptide of 322 amino acids. The cDNA was expressed as a fusion protein in bacteria which could be recognized in Western blots both by sera from mice immunized with purified native 49-kDa antigen and by sera from swine infected with the parasite. These findings suggest that recombinant P49 is a potentially valuable antigen both for vaccine development and immunodiagnosis.

A Trichinella spiralis cDNA expression library was constructed in lambda gt11 from muscle larvae mRNA and immunologically screened to identify genes encoding previously described immunodiagnostic excretory-secretory (ES) antigens. Screening the library with T. spiralis infection serum from swine or rabbit antiserum to T. spiralis ES antigen identified one clone, designated TsA-12, that contains a cDNA transcript 539 bp in length and codes for an apparent 123-kDa beta-galactosidase fusion protein that does not cross-react with Trichuris suis or Ascaris suum infection serum. Western blots of T. spiralis extracts and immunoperoxidase staining of tissue sections from muscle larvae using antibodies to purified TsA-12 demonstrate homology between TsA-12 and the 53 kDa diagnostic antigen from ES products (designated Ts.53) and localize the homologous native antigen to the stichocyte cells of the parasite. ELISA tests using TsA-12 as antigen, detected antibodies to T. spiralis in experimentally-infected mice as early as 14 days post-inoculation with maximum antibody titers being reached at 28 days post-inoculation. The TsA-12 dscDNA hybridizes to mRNA sequences expressed in both the muscle larvae and adult stages; however, concomitant expression of the native antigen is not observed within adult ES products. Southern blots of homologous and heterologous genomic DNAs probed with 32P-labeled TsA-12 dscDNA fragments verify TsA-12 as a T. spiralis specific sequence that is present in multiple copies within the parasite genome.

The gene encoding an antigenic polypeptide of Trichinella spiralis infective larvae was studied using recombinant DNA techniques. cDNA synthesized from poly(A)-rich mRNA from T. spiralis infective larvae was ligated into phage vector lambda gt11 DNA and packaged in vitro. The phages were propagated on Escherichia coli and a lambda gt11 expression library was constructed. A cDNA clone encoding a 46 kDa antigenic polypeptide was selected by immunoscreening of the library and identified by the epitope selection method. A clone containing nearly full-length cDNA for a 46 kDa protein was isolated. The gene encoding this 46 kDa antigenic polypeptide was characterized by DNA and RNA blot analysis using the cDNA as a probe. The gene was transcribed to mRNA with approximately 1400 nucleotides and translated to 46 kDa polypeptide. The antigenic polypeptide was excreted/secreted as a 46 kDa native antigen. The antigenic beta-galactosidase fusion protein synthesized by bacteria had no cross-reactivity with other parasite-infected sera.

Total RNA was extracted from packed infective larvae of Trichinella spiralis by centrifugation through a 5.7 M caesium chloride cushion. Polyadenylated messenger RNA was separated from total RNA in an oligothymidylic acid-cellulose gel column. The in vitro translation of the mRNA, isolated from infective larvae of T. spiralis, was carried out using the rabbit reticulocyte cell-free translation system. Incorporation of 35S-methionine into the trichloroacetic acid precipitates in the lysate containing mRNA was 5 times greater than that in control. The translation products were analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) followed by autoradiography. Many polypeptides with molecular weights of less than 100,000 were synthesized in the lysate. A T. spiralis positive mouse serum was mixed with translation products to form antigen-antibody complexes, which were then absorbed by Staphylococcus aureus Cowan 1 strain and analysed by autoradiography of SDS-PAGE. An antigenic polypeptide with a molecular weight of 48,000 was demonstrated to react specifically with IgG antibody in T. spiralis positive mouse serum. T. spiralis larvae were cultured in methionine-free medium containing 35S-methionine, and antigenic polypeptides in somatic extracts and ES products were compared with those in translation products by autoradiography of SDS-PAGE. Several polypeptides in ES products and somatic extracts reacted specifically with IgG antibodies in positive serum. Especially the polypeptide with a molecular weight of 48,000 in ES products strongly reacted with IgG antibody in positive serum.