Identification of antigenic genes in Trichinella spiralis by immunoscreening of cDNA libraries

A novel Trichinella spiralis serine proteinase disrupted gut epithelial barrier and mediated larval invasion through binding to RACK1 and activating MAPK/ERK1/2 pathway

BACKGROUND

Gut epithelium is the first natural barrier against Trichinella spiralis larval invasion, but the mechanism by which larval penetration of gut epithelium is not completely elucidated. Previous studies showed that proteases secreted by T. spiralis intestinal infective larvae (IIL) degraded tight junctions (TJs) proteins of gut epithelium and mediated larval invasion. A new T. spiralis serine proteinase (TsSPc) was identified in the IIL surface proteins and ES proteins, rTsSPc bound to the intestinal epithelial cell (IECs) and promoted larval invasion of IECs. The aim of this study was to characterize the interacted proteins of TsSPc and IECs, and to investigate the molecular mechanisms of TsSPc mediating larval invasion of gut mucosa.

METHODOLOGY/PRINCIPAL FINDING

IIFT results showed natural TsSPc was detected in infected murine intestine at 6, 12 hours post infection (hpi) and 3 dpi. The results of GST pull-down, mass spectrometry (MS) and Co-IP indicated that rTsSPc bound and interacted specifically with receptor for activated protein C kinase 1 (RACK1) in Caco-2 cells. rTsSPc did not directly hydrolyze the TJs proteins. qPCR and Western blot showed that rTsSPc up-regulated RACK1 expression, activated MAPK/ERK1/2 pathway, reduced the expression levels of gut TJs (occludin and claudin-1) and adherent protein E-cad, increased the paracellular permeability and damaged the integrity of intestinal epithelial barrier. Moreover, the RACK1 inhibitor HO and ERK1/2 pathway inhibitor PD98059 abolished the rTsSPc activating ERK1/2 pathway, they also inhibited and abrogated the rTsSPc down-regulating expression of occludin, claudin-1 and E-cad in Caco-2 monolayer and infected murine intestine, impeded larval invasion and improved intestinal epithelial integrity and barrier function, reduced intestinal worm burdens and alleviated intestinal inflammation.

CONCLUSIONS

rTsSPc bound to RACK1 receptor in gut epithelium, activated MAPK/ERK1/2 pathway, decreased the expression of gut epithelial TJs proteins and disrupted the epithelial integrity, consequently mediated T. spiralis larval invasion of gut epithelium. The results are valuable to understand T. spiralis invasion mechanism, and TsSPc might be regarded as a vaccine target against T. spiralis invasion and infection.

Immunomodulatory in vitro effects of Trichinella cystatin-like protein on mouse splenocytes

Trichinella parasites have developed specific mechanisms allowing successful completion of their life cycle. These mechanisms are in a great part involved in immunomodulation and studying them may provide a valuable insight into the functioning of the immune system. Trichinella products may be also used as potential therapeutic agents to treat immune diseases. This study investigates the immunomodulatory potential of recombinant multi cystatin-like protein (CLP) derived from T. britovi to determine whether CLP has anti-inflammatory properties in vitro. CLP is a highly antigenic glycoprotein present in Trichinella excetory-secretory (ES) products. AlphaFold structure prediction confirms that it consists of three type-two cystatin-like domains. Mouse splenocytes were stimulated in vitro with lipopolysaccharide (LPS) and co-stimulated with recombinant CLP. The culture supernatants were collected and tested for secreted cytokine levels using ELISA. CLP was found to reduce LPS-induced secretion of inflammatory cytokines TNFα and IL-6. On the contrary, in some experimental groups, co-stimulation with CLP resulted in increased secretion of the regulatory cytokine IL-10. The obtained results indicate that CLP has anti-inflammatory properties and future research on its function is advisable, specifically in the context of the therapy of inflammatory disorders.

Trichinella-induced immunomodulation: Another tale of helminth success

Trichinella spiralis is a unique parasite in that both the adults and larvae survive in two different intracellular niches in the same host. The immune response, albeit intense, is highly modulated to ensure the survival of both the host and the parasite. It is skewed to T helper 2 and regulatory arms. Diverse cells from both the innate and adaptive compartments of immunity, including dendritic cells, T regulatory cells, and alternatively activated macrophages are thought to mediate such immunomodulation. The parasite has also an outstanding ability to evade the immune system by several elaborate processes. The molecules derived from the parasites including Trichinella, particularly the components of the excretory-secretory products, are being continually identified and explored for the potential of ameliorating the immunopathology in animal models of diverse inflammatory and autoimmune human diseases. Herein we discuss the various aspects of Trichinella-induced immunomodulation with a special reference to the practical implications of the immune system manipulation in alleviating or possibly curing human diseases.

Recombinant cystatin-like protein-based competition ELISA for Trichinella spiralis antibody test in multihost sera

Objectives

Trichinella spiralis is a zoonotic parasite with a complex parasitic life cycle and exposed to animals or humans by infectious meat. To control transmissions of T. spiralis through the food chain to humans, sensitive and selective multihost sera-diagnosis is urgent needed for monitoring T. spiralis exposure.

Methods

A competition enzyme-linked immunosorbent assay (cELISA) for T. spiralis infection diagnosis in multihost sera was developed based on recombinant cystatin-like protein (rCLP-cELISA) as well as monoclonal antibodies. The sensitivity and accuracy of the rCLP-cELISA were quantified using swine (n = 1316), mice (n = 189) and human (n = 157) serum samples. T. spiralis-antibody targeting test ability of the rCLP-cELISA in swine (n = 22) and human (n = 36), instead of other parasites or viruses antibodies, was evaluated.

Results

The rCLP-cELISA showed high agreement with commercial ELISA kits in field swine sera assessed by Cohen’s kappa value (κ = 0.7963). And it showed 100% specificity in human trichinellosis detection with sensitivity of 96.49%, no cross-reaction with other parasite or virus infections, and high positive detection rate of 87.5% in low-dose infected swine. Besides, the rCLP-cELISA exhibited potential in the detection of T. spiralis, T. nelsoni and Trichinella T8 infections.

Conclusions

The rCLP-cELISA can be used for T. spiralis-associated antibody test in multihost sera.

Infections with T. spiralis that lives in host muscles for long periods of time are commonly difficult to diagnosis without causing a strong immune response or symptoms. The habit of eating raw/undercooked pork meat accidentally introduces humans into the exposure of T. spiralis that circulates between herds and rodents. There is an urgent need for serological antibody test of T. spiralis to monitor the infection of humans as well as hosts in the food chain, which is restricted by the mixture type of current used antigens and species-specific secondary antibodies for different hosts. We developed a novel recombinant cystatin-like protein-based competition enzyme-linked immunosorbent assay (rCLP-cELISA) employing monoclonal antibody. The proposed method showed considerable sensitivity and specificity in filed swine sera and human serum samples with good versatility in mice. Taking advantage of its controllable quality stability, the rCLP-cELISA had potential applications for screening of T. spiralis infections for multihost sera in one test. With the development of monoclonal antibody modification strategies and the discovery of antigenic proteins from parasitic pathogens, the proposed competition ELISA also provides useful reference for the improvement of serological assay for monitoring the exposure of zoonotic parasites.

Adjuvanticity of β -Glucan for Vaccine Against Trichinella spiralis

In the past 30 years, few researches focus on the efficacy of adjuvant against Trichinella spiralis infection. Identifying new, improved vaccine adjuvants for T. spiralis infection are required. β-glucan are effective and safe as adjuvant for infectious diseases. In this paper, we first observed the adjuvanticity of β-glucan as adjuvant for defensing helminth T. spiralis in vivo. We showed that IgG and IgE were elevated in the mice immunized with β-glucan combined with recombinant T. spiralis serine protease inhibitor (rTs-Serpin), which is one of the vaccine candidates. Furthermore, in vitro, the combination of β-glucan and rTs-Serpin enhanced the maturation of bone marrow dendritic cells (BMDCs) compared to rTs-Serpin alone. We showed that β-glucan + rTs-Serpin –treated BMDCs secreted higher production of IL-12 and IL-10. Moreover, β-glucan + rTs-Serpin –treated BMDCs not only promoted the population of CD4⁺ IFN-γ⁺ T cells, but also enhanced the population of CD4⁺ IL-4⁺ T cells. These findings suggested that β-glucan, as an adjuvant, have the capacity to protect against T. spiralis infection via activating both Th1 and Th2 immune response.

Bioinformatic Prediction and Production of Four Recombinant Proteins from Different Developmental Stages of Trichinella spiralis and Testing of Their Diagnostic Sensitivity in Mice

Background:

Trichinellosis is a serious food-borne parasitic zoonosis, thus finding high quality antigens is the key to serodiagnosis of trichinosis. This article reports the characterization and sensitivity of four recombinant proteins expressed by four genes (Wn10, Zh68, T668, and Wm5) from different developmental stages of Trichinella spiralis for the diagnosis of trichinellosis in mice.

Methods:

This study was conducted in Jilin University and National Institute of Parasitic Diseases of Chinese Center for Disease Control and Prevention in 2017–2018. The structures and functions of the proteins encoded by four genes were predicted by bioinformatics analysis. The four genes were cloned and expressed, and the recombinant proteins were purified. Anti-Trichinella IgM and IgG antibodies in the sera of mice infected with T. spiralis from 1-45 d post-infection (dpi) were evaluated by ELISA.

Results:

The optimal antigen epitopes of four proteins (P1, P2, P3, and P4) encoded by the four genes from T- and B-cells were predicted, and four purified recombinant proteins (r-P1, r-P2, r-P3, and r-P4) were successfully produced. For IgM, the antibody levels detected by the four recombinant antigens were approximately equal to the cut-off value. Anti-Trichinella IgG antibodies were first detected by r-P1 at 8 dpi, followed by r-P2, r-P3, and r-P4 at 10 dpi, 14 dpi, and 16 dpi, respectively, and the antibody levels remained high until 45 dpi.

Conclusion:

The recombinant antigens r-P1, r-P2, r-P3, and r-P4 could be antigens that react with antibodies, they showed high sensitivity in the detection of anti-Trichinella IgG antibodies in mice. Among these proteins, r-P1 may be a candidate antigen for the detection of anti-Trichinella IgG antibodies in the early infection phase and exhibited the best sensitivity among the antigens.

Immunoproteomic analysis of Trichinella spiralis and Trichinella britovi excretory-secretory muscle larvae proteins recognized by sera from humans infected with Trichinella

The present study compares the immunogenic patterns of muscle larvae excretory-secretory proteins (ML E-S) from T. spiralis and T. britovi recognized by Trichinella-infected human sera. Samples were analyzed using two-dimensional electrophoresis (2-DE) coupled with 2D-immunoblot and liquid chromatography-tandem mass spectrometry LC-MS/MS analysis, two ELISA procedures and a confirmatory 1D-immunoblot test. Sera were obtained from nine patients with a history of ingestion of raw or undercooked meat who presented typical clinical manifestations of trichinellosis and from eleven healthy people. Specific anti-Trichinella IgG antibodies were detected in all samples tested with the Home-ELISA kits, but in only four samples for the commercially-available kit. The 1D-immunoblot results indicated that all nine serum samples were positive for T. spiralis ML E-S antigens, expressed as the presence of specific bands. In contrast, eight of the serum samples with T. britovi E-S ML antigens were positive, with one serum sample taken from a patient at 33dpi (days post infection) being negative. To identify immunoreactive proteins that are specifically recognized by host antibodies, both species of ML E-S proteins were subjected to 2D-immunoblotting with human serum taken at 49 dpi. The sera recognized 22 protein spots for T. spiralis and 18 for T. britovi in 2D-immunoblot analysis. Their molecular weights (MW) ranged from 50 to 60 kDa. LC-MS/MS analysis identified both common and specifically-recognized immunoreactive proteins: transmembrane serine protease 9, serine protease, antigen targeted by protective antibodies and Actin-1 partial were shared for both Trichinella species; hypothetical protein T01_7775 and P49 antigen, partial those specific to T. spiralis; deoxyribonuclease-2-alpha and hypothetical protein T03_17187/T12_7360 were specific to T. britovi. Our results demonstrate the value of 2-DE and 2D-immunblot as versatile tools for pinpointing factors contributing to the parasite-host relationship by comparing the secretomes of different Trichinella species.

The immune protection induced by a serine protease from the Trichinella spiralis adult administered as DNA and protein vaccine

Trichinellosis is caused by Trichinella spiralis (T. spiralis), which is an important public health problem. In this study, a gene encoding a serine protease from adult worms of T. spiralis (Ts-Adsp) was screened from a cDNA library of adult worms and was cloned and expressed in a prokaryotic expression system. The gene Ts-Adsp was subcloned into the eukaryotic expression vector pcDNA3.1(+), which was named pcDNA3.1(+)-Adsp. Previous studies have found that recombinant Ts-Adsp protein (rTs-Adsp) can elicit partial protection against T. spiralis infection in mice. Our aim was to explore the protective effect of combining a DNA vaccine with the rTs-Adsp protein against T. spiralis. One week after the last vaccination, the serum and spleen were obtained. The levels of IgG, IgG1 and IgG2a and cytokine production in serum and spleen cells were analyzed. The results showed that the levels of humoral and cell-mediated immune responses increased in the pcDNA3.1(+)-Adsp/rTs-Adsp group mice and demonstrated that a Th1/Th2 mixed immune response was induced by pcDNA3.1(+)-Adsp/rTs-Adsp after vaccination. Moreover, mice vaccinated with pcDNA3.1(+)-Adsp/rTs-Adsp displayed a 69.50% reduction in muscle larvae burden. This study suggested that mixed immunity could improve the muscle larvae reduction rate.

Lentinan improved the efficacy of vaccine against Trichinella spiralis in an NLRP3 dependent manner

There is an urgent need for the development of new, improved vaccine adjuvants against T. spiralis infection. Polysaccharides are effective, safe, and biodegradable as adjuvant. In our study, we first observed the protective efficacy of lentinan as adjuvant against helminth T. spiralis infection. Recombinant T. spiralis Serpin (rTs-Serpin) immunoscreened from a cDNA library of T. spiralis, as a vaccine, protect host against Trichinella infection. The reduction rate of helminth burden of rTs-Serpin+lentinan–immunized mice was significantly increased compared with rTs-Serpin+FCA -immunized mice. rTs-Serpin+lentinan induced IgG1-dominant immune response and higher levels of IFN-γ and IL-4. rTs-Serpin+lentinan displayed a lower reduction rate of parasite burden in NLRP3^-/- mice than that in WT mice and lower level of IgG1 than that in WT mice. The level of IL-4, but not IFN-γ, from NLRP3^-/- mice immunized by rTs-Serpin+lentinan was significantly lower than that from WT mice, suggesting that NLRP3 is associated with rTs-Serpin+lentinan -triggering Th2 protective immunity against T. spiralis infection. In summary, we revealed that lentinan was a novel adjuvant against T. spiralis infection via NLRP3. NLRP3 therefore represents an important target for adjuvant discovery and the control of T. spiralis infection.

Trichinella spp., pathogenic agents of trichinellosis, is foodborne zoonotic nematodes cause huge economic burden to the livestock industry. The potential of new adjuvants for improving veterinary vaccines remains largely unexploited to trigger safe and long-lasting immunity in large animals, including livestock. Polysaccharides are effective, safe, and biodegradable as adjuvant. We first observed the protective efficacy of lentinan as a novel adjuvant against helminth T. spiralis infection. NLRP3 is associated with lentinan -triggering Th2 protective immunity against T. spiralis infection. NLRP3 therefore represents an important target for adjuvant discovery and the control of T. spiralis infection.

Effect of recombinant serine protease from adult stage of Trichinella spiralis on TNBS-induced experimental colitis in mice

Inflammatory bowel disease (IBD), which includes ulcerative colitis (UC) and Crohn's disease (CD), is a chronic autoimmune disease. At present, worms and their products has been shown to have protective effects on immune-mediated diseases. Therefore, we aimed to investigate the effect of the recombination Trichinella spiralis (T. spiralis, Ts) adult serine protease-like protein rTs-ADSp-7 on a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced CD mouse model. Colitis was induced by intrarectal administration of a TNBS solution. The disease activity index (DAI), which included weight loss, diarrhoea, and bloody stool, was measured. Colon segments were stained with haematoxylin and eosin (H.E.) for histopathological score. Cytokine release in the serum was analysed by meso scale discovery (MSD). Cytokine release in the colon was detected by ELISA. Splenocytes were separated, and the cytokine profiles of Th1 (IFN-γ), Th2 (IL-4), Th17 (IL-17A) and Treg cells were analysed by flow cytometry. Our result showed that rTs-ADSp-7 reduced the clinical disease activity of TNBS-induced colitis in mice. In addition, we found that rTs-ADSp-7 reduced the production of Th1- and Th17-related cytokines while upregulating the expression of Th2- and Treg-related cytokines in TNBS-induced colitis mice. rTs-ADSp-7 also increased the population of Th2 and Treg cells in TNBS-induced colitis mice. rTs-ADSp-7 alleviated the severity of TNBS-induced colitis while balancing the CD4⁺ T cell immune response. rTs-ADSp-7 has therapeutic potential for colitis treatment and can be used as a helminth-derived protein therapy for CD or other Th1 immunity-mediated diseases.

Evaluation of a cystatin-like protein of Trichinella spiralis for serodiagnosis and identification of immunodominant epitopes using monoclonal antibodies

An antigenic cystatin-like protein (Ts-CLP) selected from cDNA library of intestinal infective larvae at 6 h post-infection, was expressed by prokaryotes in the form of a histidine-tagged protein (rTs-CLP). The fusion protein was purified by an on-column refolding procedure using Ni-NTA affinity chromatography. An indirect rTs-CLP ELISA was developed using 270 known negative serum samples from commercial swine maintained under non-special pathogen free conditions. Based on the distribution of the signal-to-positive (S/P) ratio, a cut-off value was set at 0.30. Using this cut-off value, rTs-CLP ELISA was evaluated using sera from swine experimentally infected with 1000 and 50,000 muscle larvae of Trichinella spiralis. Specific IgG antibodies were detectable by rTs-CLP ELISA as soon as 17 days post-infection (dpi), but the commercial ELISA kit based on excretory-secretory (ES) antigens did not permit detection before 21 dpi. Three monoclonal antibodies (McAbs) against Ts-CLP (designated 1H9, 6B5 and 7F8) were obtained by screening with both rTs-CLP ELISA and ES ELISA methods. Two dominant epitopes recognized by McAbs were determined by analysis with overlapping fusion peptides and synthetic peptides. One epitope ³⁹ HEALFSSDLKQESGV ⁵³ was recognized by 1H9 and 6B5, and the other epitope ¹⁷⁸ REALFSSDSKEQSGV ¹⁹² was recognized by 7F8. The generation of McAbs against Ts-CLP and the characterization of the two dominant epitopes provide a foundation for the development of a specific early serodiagnostic strategy for T. spiralis infection.

Development of genome-wide polymorphic microsatellite markers for Trichinella spiralis

Background

Trichinella nematodes are globally distributed food-borne pathogens, in which Trichinella spiralis is the most common species in China. Microsatellites are a powerful tool in population genetics and phylogeographic analysis. However, only a few microsatellite markers were reported in T. spiralis. Thus, there is a need to develop and validate genome-wide microsatellite markers for T. spiralis.

Methods

Microsatellites were selected from shotgun genomic sequences using MIcroSAtellite identification tool (MISA). The identified markers were validated in 12 isolates of T. spiralis in China.

Results

A total of 93,140 microsatellites were identified by MISA from 9267 contigs in T. spiralis genome sequences, in which 16 polymorphic loci were selected for validation by PCR with single larvae from 12 isolates of T. spiralis in China. There were 7–19 alleles per locus (average 11.25 alleles per locus). The observed heterozygosity (H_O) and expected heterozygosity (H_E) ranged from 0.325 to 0.750 and 0.737 to 0.918, respectively. The polymorphism information content (PIC) ranged from 0.719 to 0.978 (average 0.826). Among the 16 loci, markers for 10 loci could be amplified from all 12 international standard strains of Trichinella spp.

Conclusions

Sixteen highly polymorphic markers were selected and validated for T. spiralis. Primary phylogenetic analysis showed that these markers might serve as a useful tool for genetic studies of Trichinella parasites.

The Immunological Properties of Recombinant Multi-Cystatin-Like Domain Protein From Trichinella Britovi Produced in Yeast

Trichinellosis is a globally-distributed zoonotic parasitic disease caused by nematode worms of the genus Trichinella. One of the most common species of Trichinella known to affect human health is T. britovi; however, it is relatively poorly investigated. A thorough knowledge of the proteins expressed by Trichinella is important when developing immunological detection methods and vaccines and studying its interactions with the host. The present study uses the Pichia pastoris expression system to produce a soluble TbCLP antigen which induces strong antibody responses in the host during natural infection. Our results demonstrate the feasibility of TbCLP antigen production in yeasts, which are able to carry out post-translational modifications such as glycosylation and disulfide bond formation; they also indicate that the glycosylated TbCLP antigen had immunogenic effects in the tested mice and induced a mixed Th1/Th2 response, and was associated with a reduced larval burden after challenge with T. britovi. Subsequent in vitro stimulation of mice splenocytes revealed that TbCLP most likely possesses immunomodulatory properties and may play a significant role in the early phase of infection, affecting host immunological responses.

Characterization of an antigenic serine protease in the Trichinella spiralis adult

Serine proteases have been identified as important molecules that are involved in many parasitic infections, and these molecules have also been suggested to play important roles in Trichinella spiralis infections. In the present study, the antigenic serine protease gene Ts-ADSp-7, which was screened from a cDNA library of Trichinella spiralis Adults at 3 days post-infection (p.i.), was cloned and expressed in Escherichia coli. The encoded protein, Ts-ADSp-7, revealed a potential trypsin-like serine protease domain but lacked substrate banding site at position 227 and protease activity. Transcription could be detected in the Adult and muscle larval stage but not in the newborn larval stage, where no fluorescent signal was detected. Western blot analysis revealed that the 3 days p.i. Adults and muscle larvae could secrete Ts-ADSp-7. Interestingly, strong fluorescent signal of Ts-ADSp-7 could be detected in the nucleoli of the enlarged muscle cell nuclei from 12 to 16 days p.i. and in the β-stichosomes of the muscle larvae from 16 to 35 days p.i.. The coagulation assay indicated that Ts-ADSp-7 could inhibit intrinsic coagulation pathway. Regarding the putatively important function of the serine protease in the helminth infection to hosts, a total of 81 serine proteases were found in the parasite and mainly comprised eight subfamilies. These subfamilies exhibited high similarity to transmembrane serine protease, coagulation factor XI, lipocalin, guanylin, ceropin, kallikrein, and plasminogen. Moreover, stage specificity was detected in several subfamilies. In summary, the putatively inactive serine protease-like protein Ts-ADSp-7 could inhibit blood coagulation, and the protein is located in the enlarged nuclei of nurse cells during capsule formation. Furthermore, members of the serine protease family in the parasite might be important molecules in the parasite-host interaction.

Identification and Preliminary Evaluation of a Novel Recombinant Protein for Serodiagnosis of Strongyloidiasis

Strongyloides stercoralis is a human parasite that can cause a long-term infection. In immunosuppressed patients, strongyloidiasis may be fatal when there is overwhelming autoinfection resulting in the migration of large numbers of larvae through many organs. Definitive diagnosis is still a challenge, and a combination of symptoms, microscopic identification, and serology test results are often used to arrive at a clinical decision. However, intermittent larval excretion, low parasite burden, and occult infections are challenges with parasitological diagnosis of infection with S. stercoralis. Meanwhile, serologic tests using immunoglobulin G and parasite antigen extract have problems of cross-reactivity with other helminthic infections. Recombinant antigen-based serodiagnosis is a good alternative to overcome the laboratory diagnostic issues. Herein, we report on the isolation of cDNA clone encoding an antigen of potential diagnostic value identified from immunoscreening of a S. stercoralis cDNA library. The translated protein had highest similarity to Strongyloides ratti immunoglobulin-binding protein 1. The recombinant antigen produced, rSs1a, was assessed using western blot and enzyme-linked immunosorbent assay. The latter showed 96% diagnostic sensitivity and 93% specificity; thus, rSs1a has good potential for use in serodiagnosis of human strongyloidiasis.

Current Research of Trichinellosis in China

Trichinellosis, caused by Trichinella, is an emerging or re-emerging zoonotic parasitic disease, which is distributed worldwide with major socio-economic importance in some developing countries. In particular, it has been calculated that more than 40 million people are at risk of Trichinella infection in China. This review summarizes the current information on the epidemiology, laboratory diagnosis and vaccines of trichinellosis in China. Moreover, study of the treatment potential of using Trichinella for immune-related diseases and cancer, as well as the transcription and post-transcription modification of Trichinella were also collected, providing viewpoints for future investigations. Current advances in research will help us to develop new strategies for the prevention and control of trichinellosis and may potentially yield biological agents for treating other diseases.

Influence of adjuvant formulation on inducing immune response in mice immunized with a recombinant serpin from Trichinella spiralis

Nematodes of the genus Trichinella are one of the most widespread zoonotic pathogens on the world, and they can still cause major public health problems in many parts of the world. Vaccination against the helminth nematode Trichinella could be a good strategy to reduce the risk of human and animal infection. It was our aim to evaluate three adjuvants, which could be used as an efficient vaccine for animals in combination with rTs-Serpin antigen. In this study, BALB/c mice were vaccinated by an intramuscular route with rTs-Serpin antigen from the parasite Trichinella spiralis in combination with three different adjuvant formulations: Montanide ISA201, Montanide IMS 1313 N PR VG and Freund's complete adjuvant/Freund's incomplete adjuvant (FCA/FIA). The dynamics of IgG, IgM, IgE and cytokine production from spleen cells and worm reduction rate of the vaccinated mice were analysed. The results showed that rTs-serpin can induce partial protection against Trichinella larvae challenge in mice, when compared to the FCA-/FIA-formulated vaccination, the IMS1313 plus rTs-serpin mixture showed higher humoral immunity and similar levels of cellular immunity and worm reduction rate. The study suggested that Montanide IMS nanoparticles 1313 are as effective as FCA but less toxic; thus, Montanide IMS nanoparticles 1313 can be used as a good candidate of adjuvant for developing vaccine against Trichinella spiralis.

Partially protective immunity induced by the 14-3-3 protein from Trichinella spiralis

Trichinellosis, a widespread zoonosis, is considered to be an emerging or re-emerging infectious parasitic disease. The development of vaccines to prevent Trichinella infection in domestic animals and humans is important for disease control. In a previous study, we identified Ts14-3-3 as an immunodominant protein from Trichinella spiralis (T. spiralis) adult worms recognized by early infection sera from pigs and mice. In this study, we further confirmed that Ts14-3-3 mRNA is expressed in both adult worms and in the larval stages of T. spiralis. Immunostaining with anti-Ts14-3-3 mouse sera further confirmed that native Ts14-3-3 is highly expressed on the surface of T. spiralis muscle larvae. The immune recognition by infected sera, its expression in both adult and larval stages and its exposure on the surface of the parasite led us to explore Ts14-3-3 as a vaccine antigen. Recombinant Ts14-3-3 formulated with an ISA50v2 adjuvant produced strong total IgG and balanced IgG1 and IgG2a responses in vaccinated mice and stimulated mouse splenocytes to produce high levels of Th1 (INF-γ, IL-2) and Th2 (IL4, IL5) cytokines. These results indicate that Ts14-3-3 is highly immunogenic and is able to induce balanced Th1/Th2 immune responses. These vaccine-induced immune responses resulted in a reduction in muscle larvae of up to 46.2% in vaccinated mice upon subsequent larval challenge relative to the number of larvae in mice received PBS control. The significant reduction in muscle larvae in vaccinated mice suggests that Ts14-3-3 is a promising vaccine target for potential use in domestic pigs to prevent trichinellosis transmission.

Proteomic analysis of differentially expressed proteins in the three developmental stages of Trichinella spiralis

Trichinella spiralis, an intracellular parasitic nematode, can cause severe foodborne zoonosis, trichinellosis. The life cycle of T. spiralis consists of adult (Ad), muscle larvae (ML) and newborn larvae (NBL). The protein profiles in different developmental stages of the parasite remain unknown. In the present study, proteins from lysates of Ad, ML and NBL were identified by isobaric tags for relative and absolute quantitation (iTRAQ). A total of 4691 proteins were identified in all the developmental stages, of which 1067 proteins were differentially expressed. The number of up-regulated proteins in NBL was higher than that of the other two groups. The protein profiles from Ad, ML and NBL were compared in pairs. The identified proteins were involved in various functions of T. spiralis life cycle, including sexual maturity, metabolism, utilization of carbohydrates, lipids and nucleotides, and other crucial developmental processes that occur at distinct stages. Further investigation of the transcriptional levels of major sperm protein, serine protease, zinc finger protein, etc. from the different protein profiles using quantitative RT-PCR showed identical results to the iTRAQ analysis. The differentially expressed proteins that are involved in developmental regulation and host-parasite interactions should be further studied.

Characterisation of a high-frequency gene encoding a strongly antigenic cystatin-like protein from Trichinella spiralis at its early invasion stage

Background

The intestinal phase is the early invasion stage of Trichinella spiralis (T. spiralis), in which muscle larvae invade intestine epithelial cells and then develop into adult worms to breed newborn larvae. Thus, intestinal infective larvae are first exposed to the immune system of the host, and antigens from the worms may be the earliest marker in the diagnosis of trichinellosis and may contribute to vaccine development to prevent Trichinella infections in pigs.

Methods

A cDNA library of intestinal infective larvae of T. spiralis at 6 hours post infection (p.i.) was constructed and immunoscreened using serum collected from pigs that were infected with T. spiralis at 26 days p.i. T. spiralis cystatin-like protein (Ts-CLP) gene encoding a 45.9 kDa protein was cloned and expressed in Escherichia coli. The rabbit antisera were generated and used to determine the location of Ts-CLP in the parasite. Transcription levels of Ts-CLP in different developmental stages of T. spiralis were observed by RT-PCR. The potential application of recombinant Ts-CLP in diagnosis against T. spiralis infection was tested by ELISA. The immune protection of recombinant Ts-CLP protein against T. spiralis infection was evaluated in mice.

Results

Thirty-three positive clones were selected from cDNA library, among which 20 clones encoded the same novel cystatin-like protein (Ts-CLP). Immunolocalisation and real-time quantitative PCR revealed that native Ts-CLP was localised primarily to β-stichocytes and that the Ts-clp gene was transcribed and expressed in all developmental stages of T. spiralis. The recombinant protein rTs-CLP was recognised by pig antiserum as early as 15 days p.i., and could induce protective immunity in mice, with a 61.21% reduction in the number of muscle larvae.

Conclusions

These data preliminarily suggested that Ts-CLP may play an important role in the early infection of T. spiralis and that recombinant Ts-CLP protein is a candidate antigen for diagnosis and vaccine development in Trichinella infections.

Proteomic analysis of potential immunoreactive proteins from muscle larvae and adult worms of Trichinella spiralis in experimentally infected pigs

The present study was undertaken to identify potentially immunoreactive proteins of the muscle larvae (ML) and adult stage (Ad) of the nematode Trichinella spiralis Owen, 1835. To identify immunoreactive proteins that are specifically recognised by anti-Trichinella antibodies, ML and Ad crude extracts and their excretory-secretory (E-S) products were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot with serum samples from pigs experimentally infected with T. spiralis. A total of 18 bands were selected for final identification by liquid chromatography-tandem mass spectrometry. To further understand the functions of the proteins identified in this study, gene ontology terms were applied. Results showed that the specific antibodies against T. spiralis reacted with protein bands matching heat shock proteins, aminopeptidase, enolase, isocitrate dehydrogenase NADP-dependent, tropomyosin, P49 antigen, serine proteinase, secreted 5'-nucleotidase, antigen targeted by protective antibodies, 53 kDa E-S antigen, putative trypsin and paramyosin. Three proteins common for both adult stage and muscle larvae, including heat shock proteins, enolase and 5'-nucleotidase, might play important role during T. spiralis infection. These proteins are presumably presented to the host immune system and may induce humoral immune response. Thus, these proteins may be potential antigens for early diagnosis and the development of a vaccine against the parasite.

Primary characterization and assessment of a T. spiralis antigen for the detection of Trichinella infection in pigs

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.

An antigenic recombinant serine protease from Trichinella spiralis induces protective immunity in BALB/c mice

In this study, we report the cloning and characterization of a cDNA encoding a Trichinella serine protease gene (TspSP-1.3) from GenBank. The recombinant TspSP-1.3 protein (rTspSP-1.3) was expressed in an Escherichia coli expression system and purified with Ni-affinity chromatography. Real-time quantitative PCR analysis revealed that TspSP-1.3 was expressed at significantly higher levels in muscle larvae and adult worms than in newborn larvae. TspSP-1.3 was detected in excretory-secretory proteins of Trichinella spiralis with western blotting. Immunization with the rTspSP-1.3 antigen induced humoral immune responses, which manifested as elevated specific anti-rTspSP-1.3 IgG and IgE antibodies and a mixed Th1/Th2 response. To determine whether purified rTspSP-1.3 had good antigenicity and could be a vaccine candidate for the control of T. spiralis infection, we immunized BALB/c mice with rTspSP-1.3 and subsequently challenged the mice with T. spiralis larvae. The results showed that mice vaccinated with rTspSP-1.3 exhibited an average reduction in the muscle larvae burden of 39 % relative to the control group. These results suggest that TspSP-1.3 could be a novel vaccine candidate for controlling Trichinella infection.

Recognition of antigens of three different stages of the Trichinella spiralis by antibodies from pigs infected with T. spiralis

Infective muscle larvae (ML), adults (Ad) and new born larvae (NBL) of Trichinella spiralis express many immunogenic proteins which can elicit a host protective response, and may be useful in the diagnosis of Trichinella infected humans and animals. The present study was carried out to identify T. spiralis antigens recognized by antibodies from pigs infected with T. spiralis. To that end, the crude extracts of ML, Ad, NBL and ML excretory-secretory (E-S) and Ad E-S proteins were analyzed by sodium dodecyl sulfate polycrystalline gel electrophoresis (SDS-PAGE). To identify antigens of T. spiralis that are recognized by host antibodies, crude extracts and E-S proteins were subjected to immunoblot with antisera derived from pigs experimentally infected with 200 or 20,000 T. spiralis ML. Searching for T. spiralis antigens with diagnostic potential, immunoblots showed that all T. spiralis antisera, regardless of the infective dose, recognized common proteins in each examined life stage with molecular weights around 20-27 kDa, 41 kDa and 197-105 kDa. Interestingly, all the common proteins were detected by T. spiralis sera throughout the infection, from 5 days post infection (dpi) to 60 dpi. These results extend our knowledge of specific antigenic components of T. spiralis. The finding of common components among all T. spiralis life stages may be useful in the preparation of parasite antigens for diagnostic use, as these antigens are relevant regardless of infection phase.

Screening of early antigen genes of adult-stage Trichinella spiralis using pig serum from different stages of early infection

The goal of this work was to identify novel, early antigens present in Trichinella spiralis. To this end, a cDNA library generated from 3-day old adult worms (Ad3) was immunologically screened using serum from a pig infected with 20,000 muscle larvae. The serum was obtained from multiple, time course bleeds coinciding with early worm development. Seventeen positive clones were isolated using serum obtained at 20 days post infection (dpi). All clones corresponded to one gene that exhibited high sequence identity with the T. spiralis ATP-dependent RNA helicase DDX19B which is involved in parasite growth and development. In addition, nine additional positive clones representing 5 unique genes were identified when the library was screened with 30 dpi serum; four of these five genes displayed high similarity with members of a putative T. spiralis serine protease family known to be involved in host invasion and host-parasite interactions. The remaining gene aligned with the T. spiralis hypothetical ORF 11.30. The identification of these antigens provides potential candidates for the early diagnosis of trichinellosis and for the development of a vaccine against this parasite.

Unique antigenic gene expression at different developmental stages of Trichinella pseudospiralis

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.

Vaccination of mice with an antigenic serine protease-like protein elicits a protective immune response against Trichinella spiralis infection

Trichinellosis has major economic impacts on animal husbandry and food safety, and the control and elimination of trichinellosis is a major objective of veterinary medicine. A gene encoding serine protease of Trichinella spiralis (Ts-Adsp) was identified by immunoscreening an adult T. spiralis cDNA library. In this study, the recombinant Ts-Adsp protein (rTs-Adsp) was cloned and expressed in a prokaryotic expression system and purified by Ni-affinity chromatography. To determine whether the purified rTs-Adsp is a potential vaccine candidate for the control of T. spiralis infection, we immunized BALB/c mice with this protein in combination with an alum adjuvant and subsequently challenged with T. spiralis larvae. The results showed that mice vaccinated with rTs-Adsp exhibited an average reduction in the muscle larvae burden of 46.5% relative to the control group. Immunization with the rTs-Adsp antigen induced both humoral and cellular immune responses, which manifested as elevated specific anti-rTs-Adsp IgG and IgE antibodies and a mixed Th1-Th2 response, as determined by Th1 (IFN-γ and IL-2) and Th2 (IL-4, IL-10, and IL-13) cytokine profiling, with the Th2 predominant. Thus, purified rTs-Adsp is able to limit the invasion of T. spiralis , and this protein could be an effective vaccine candidate for trichinellosis.

Identification of Trichinella spiralis early antigens at the pre-adult and adult stages

Three expression cDNA libraries from Trichinella spiralis worms 14 h, 20 h and 48 h post-infection (p.i.) were screened with serum from pigs experimentally infected with 20,000 T. spiralis muscle larvae. Twenty-nine positive clones were isolated from the 14 h p.i. cDNA library, corresponding to 8 different genes. A putative excretory-secretory protein similar to that of T. pseudospiralis was identified. Three clones corresponded to a T. spiralis serine proteinase inhibitor known to be involved in diverse functions such as blood coagulation and modulation of inflammation. Screening of the 20 h p.i. cDNA library selected 167 positive clones representing 12 different sequences. The clone with the highest redundancy encoded a small polypeptide having no sequence identity with any known proteins from Trichinella or other organisms. Fourteen clones displayed sequence identity with the heat shock protein (HSP) 70. HSPs are produced as an adaptive response of the parasite to the hostile environment encountered in the host intestine but their mechanism of action is not yet well defined. From the 48 h p.i. T. spiralis cDNA library, 91 positive clones were identified representing 7 distinct sequences. Most of the positive clones showed high similarity with a member of a putative T. spiralis serine protease family. This result is consistent with a possible major role for serine proteases during invasive stages of Trichinella infection and host-parasite interactions.