Proteomic analysis of the changed proteins of Trichinella spiralis infective larvae after co-culture in vitro with intestinal epithelial cells

Characterization of a novel aminopeptidase P from Trichinella spiralis and its participation in the intrusion of intestinal epithelial cells

Aminopeptidases P are metalloproteases belonging to the M24 peptidase family. It specifically hydrolyzes the N-terminus of polypeptides free of acidic amino acids, and plays an important role in the nutrition, metabolism and growth of parasites. The aim of this study was to characterize a novel Trichinella spiralis aminopeptidase P (TsAPP) and to investigate its functions in the invasion of T. spiralis. TsAPP contained two domains of creatinase (a creatinase N and creatinase N2) and a domain of peptidase M24C and APP. The complete TsAPP sequence was cloned and expressed in Escherichia coli BL21 cells. The recombinantly produced TsAPP was used to raise polyclonal antibodies that were subsequently used to detect the expression of the protein in the different life stages of T. spiralis. TsAPP was expressed in various T. spiralis stages. TsAPP was primarily localized in the cuticle, stichosome and intrauterine embryos of this nematode. rTsAPP has an enzymatic activity of a natural aminopeptidase P to hydrolyze the substrate H-Ala-Pro-OH. rTsAPP promoted the larval intrusion of intestinal epithelium cells (IECs). The results showed that TsAPP is involved in the T. spiralis intrusion of IECs and it might be a potential candidate vaccine target against Trichinella infection.

Molecular characterization and determination of the biochemical properties of cathepsin L of Trichinella spiralis

Cathepsin L is an important cysteine protease, but its function in T. spiralis remains unclear. The aim of this research was to explore the biological characteristics of T. spiralis cathepsin L (TsCatL) and its role in T. spiralis-host interactions. Bioinformatic analysis revealed the presence of the cysteine protease active site residues Gln, Cys, His and Asn in mature TsCatL, as well as specific motifs of cathepsin L similar to ERFNIN and GYLND in the prepeptide of TsCatL. Molecular docking of mature TsCatL and E64 revealed hydrophobic effects and hydrogen bonding interactions. Two domains of TsCatL (TsCatL2) were cloned and expressed, and recombinant TsCatL2 (rTsCatL2) was autocatalytically cleaved under acidic conditions to form mature TsCatL. TsCatL was transcribed and expressed in larvae and adults and located in the stichosome, gut and embryo. Enzyme kinetic tests showed that rTsCatL2 degraded the substrate Z-Phe-Arg-AMC under acidic conditions, which was inhibited by E64 and PMSF and enhanced by EDTA, L-cysteine and DTT. The kinetic parameters of rTsCatL2 were a Km value of 48.82 μM and Vmax of 374.4 nM/min at pH 4.5, 37 °C and 5 mM DTT. In addition, it was shown that rTsCatL2 degraded haemoglobin, serum albumin, immunoglobulins (mouse IgG, human IgG and IgM) and extracellular matrix components (fibronectin, collagen I and laminin). The proteolytic activity of rTsCatL2 was host specific and significantly inhibited by E64. rTsCatL2 possesses the natural activity of a sulfhydryl-containing cysteine protease, and TsCatL is an important digestive enzyme that seems to be important for the nutrient acquisition, immune evasion and invasion of Trichinella in the host.

Proteases secreted by Trichinella spiralis intestinal infective larvae damage the junctions of the intestinal epithelial cell monolayer and mediate larval invasion

The intestinal epithelium is the first natural barrier against Trichinella spiralis larval invasion, but the mechanism of larval invasion of the gut epithelium is not fully elucidated. The aim of this study was to investigate whether the excretory/secretory proteins (ESPs) of T. spiralis intestinal infective larvae (IIL) degrade tight junction (TJ) proteins, to assess the main ESP proteases hydrolysing TJ proteins using various enzyme inhibitors and to define the key invasive factors in IIL invasion of the gut epithelium. The results of immunofluorescence, Western blot and Transwell assays showed that serine proteases and cysteine proteases in the ESPs played main roles in hydrolysing occludin, claudin-1 and E-cad and upregulating claudin-2 expression. Challenge infection results showed that IIL expulsion from the gut at 12 hpi was significantly higher in mice which were infected with muscle larvae (ML) treated with a single inhibitor (PMSF, E-64, 1,10-Phe or pepstatin) or various mixtures containing PMSF and E-64 than in mice in the PBS group or the groups treated with an inhibitor mixture not containing PMSF and E-64 (P < 0.0001). At 6 days post-infection, mice which were infected with ML treated with PMSF, E-64, 1,10-Phe or pepstatin exhibited 56.30, 64.91, 26.42 and 31.85% reductions in intestinal adult worms compared to mice in the PBS group (P < 0.0001). The results indicate that serine proteases and cysteine proteases play key roles in T. spiralis IIL invasion, growth and survival in the host and that they may be main candidate target molecules for vaccines against larval invasion and development.

Oral immunization with attenuated Salmonella encoding an elastase elicits protective immunity against Trichinella spiralis infection

Elastase belongs to the serine protease family. Previous studies showed that Trichinella spiralis elastase (TsE) was highly expressed in intestinal infective larvae (IIL). Recombinant TsE (rTsE) promoted the larval intrusion of enteral epithelium cells (IECs), whereas anti-rTsE antibodies and siRNA impeded larval intrusion. Subcutaneous vaccination of mice with rTsE showed a partial protective immunity, suggesting that TsE might be a promising vaccine target against Trichinella infection. In this study, complete TsE cDNA sequence was cloned into pcDNA3.1, and the rTsE DNA was transformed into attenuated S. typhimurium strain ΔcyaSL1344. Oral vaccination of mice with TsE DNA elicited a systemic Th1/Th2/Treg mixed immune response and gut local mucosal sIgA response. Immunized mice exhibited a significant immune protection against T. spiralis larval challenge, as demonstrated by a 52.48% reduction of enteral adult worms and a 69.43% reduction of muscle larvae. The protection might be related to the TsE-induced production of intestinal mucus, specific anti-TsE sIgA and IgG, and secretion of IFN-γ, IL-2, IL-4 and IL-10, which protected gut mucosa from larval intrusion, suppressed worm development and impeded female reproduction. The results demonstrated that attenuated Salmonella-delivered TsE DNA vaccine provided a prospective strategy for the control of Trichinella infection in food animals.

Vaccination of mice with recombinant novel aminopeptidase P and cathepsin X alone or in combination induces protective immunity against Trichinella spiralis infection

Trichinella spiralis is a major foodborne zoonotic parasitic nematode which has a serious threat to meat food safety. Development of anti-Trichinella vaccine is requisite for control and elimination of Trichinella infection in food animals to ensure meat safety. Aminopeptidase P (TsAPP) and cathepsin X (TsCX) are two novel proteins identified in T. spiralis intestinal infectious L1 larvae (IIL1). The objective of this study was to investigate the protective immunity elicited by immunization with TsAPP and TsCX alone and TsAPP-TsCX in combination in a mouse model. The results demonstrate that subcutaneous vaccination of mice with rTsAPP, rTsCX or rTsAPP + rTsCX elicited a systemic humoral response (high levels of serum IgG, IgG1/IgG2a and IgA) and significant local gut mucosal sIgA responses. The vaccination with rTsAPP, rTsCX or rTsAPP + rTsCX also induced a systemic and local mixed Th1/Th2 response, as demonstrated by clear elevation levels of IFN-γ and IL-4 in vaccinated mice. Vaccination of mice with rTsAPP+rTsCX exhibited a 63.99 % reduction of intestinal adult worms and 68.50% reduction of muscle larva burdens, alleviated inflammation of intestinal mucosal and muscle tissues, and provided a higher immune protection than that of vaccination with rTsAPP or rTsCX alone. The results demonstrated that TsAPP and TsCX might be considered novel candidate target molecules for anti-Trichinella vaccines.

Molecular characterization of a novel cathepsin L from Trichinella spiralis and its participation in invasion, development and reproduction

Cathepsin L is one member of cysteine protease superfamily and widely distributed in parasitic organisms, it plays the important roles in worm invasion, migration, nutrient intake, molting and immune evasion. The objective of this study was to investigate the biological characteristics of a novel cathepsin L from Trichinella spiralis (TsCL) and its role in larval invasion, development and reproduction. TsCL has a functional domain of C1 peptidase, which belongs to cathepsin L family. The complete TsCL sequence was cloned and expressed in Escherichia coli BL21. The rTsCL has good immunogenicity. RT-PCR and Western blotting analysis showed that TsCL was transcribed and expressed at different T. spiralis phases (e.g., muscle larvae, intestinal infectious larvae, adult worms and newborn larvae). Immunofluorescence test revealed that TsCL was principally localized in the cuticle, stichosome, midgut and female intrauterine embryos of the nematode. rTsCL has the capacity to specially bind with intestinal epithelial cells (IECs) and the binding sites was located in the cytoplasm. rTsCL promoted larval penetration into IEC, while anti-rTsCL antibodies inhibited the invasion. The silencing of TsCL gene by specific dsRNA significantly reduced the TsCL expression and enzyme activity, and also reduced larval invasive ability, development and female reproduction. The results showed that TsCL is an obligatory protease in T. spiralis lifecycle. TsCL participates in worm invasion, development and reproduction, and may be regarded as a potential candidate vaccine/drug target against T. spiralis infection.

Characterization of a Novel Glutamine Synthetase From Trichinella spiralis and Its Participation in Larval Acid Resistance, Molting, and Development

Trichinella spiralis is a major foodborne parasite worldwide. After the encapsulated muscle larvae (ML) in meat are ingested, the ML are liberated in the stomach of the host and activated into intestinal infectious larvae (IIL), which develop into adult worm after molting four times. A novel glutamine synthetase (TsGS) was identified from T. spiralis IIL at 10 h post-infection, but its biological role in T. spiralis life cycle is not clear. The aim of this study was to investigate the biological characteristics of TsGS and its functions in larval acid resistance, molting, and development. TsGS has a glutamine synthetase (GS) catalytic domain. Complete TsGS sequence was cloned and expressed in Escherichia coli BL21. rTsGS has good immunogenicity. qPCR and Western blotting showed that TsGS was highly expressed at IIL stage, and immunofluorescence revealed that TsGS was principally localized at the cuticle and intrauterine embryos of this nematode. rTsGS has enzymatic activity of natural GS to hydrolyze the substrate (Glu, ATP, and NH₄⁺). Silencing of TsGS gene significantly reduced the IIL survival at pH 2.5, decreased the IIL burden, and impeded larval molting and development. The results demonstrated that TsGS participates in T. spiralis larval acid resistance, molting and development, and it might be a candidate vaccine target against Trichinella molting and development.

Characterization of a Trichinella spiralis cathepsin X and its promotion for the larval invasion of mouse intestinal epithelial cells

The aim of this study was to ascertain the characteristics of a Trichinella spiralis cathepsin X (TsCX) and its role on larval invasion of intestinal epithelial cells (IECs). The full-length of TsCX cDNA sequence was cloned and expressed in Escherichia coli BL21. The results of RT-PCR, IFA and Western blot revealed that TsCX was expressed at T. spiralis muscle larvae (ML), intestinal infective larvae, adult worm and newborn larvae, and it was located in whole worm section. The results of Far western and confocal microscopy demonstrated that there was a specific binding of rTsCX and IEC, and the binding site was located within the IEC cytoplasm. rTsCX promoted T. spiralis larval invasion of mouse IECs while anti-rTsCX antibody inhibited larval invasion into the IECs. Silencing TsCX by specific siRNA reduced the TsCX expression and larval invasive capacity. These results indicated that TsCX specifically binds to IECs and promotes larval invasion of intestinal epithelia, and it might be a potential target of vaccines against enteral stages of T. spiralis.

Characterization of a novel cysteine protease in Trichinella spiralis and its role in larval intrusion, development and fecundity

The aim of this study was to investigate the biological properties of a novel gut-specific cysteine protease in Trichinella spiralis (TsGSCP) and its role in larval intrusion, development and fecundity. TsGSCP has a functional C1 peptidase domain; C1 peptidase belongs to cathepsin B family. The TsGSCP gene cloned and expressed in Escherichia coli BL21 showed intensive immunogenicity. qPCR and Western blotting revealed that TsGSCP mRNA and protein were expressed at various T. spiralis stages, but their expression levels in intestinal infectious larvae (IIL) were clearly higher than those in muscle larvae (ML), adult worms (AWs) and new-born larvae (NBL). Indirect immunofluorescence (IIF) analysis showed that TsGSCP was primarily located at the outer cuticle and the intrauterine embryos of this parasite. rTsGSCP showed the ability to specifically bind with IECs, and the binding site is within the IEC cytoplasm. rTsGSCP accelerated larval intrusion into host intestinal epithelial cells (IECs), whereas anti-rTsGSCP antibodies suppressed larval intrusion; the acceleration and suppression was induced by rTsGSCP and anti-rTsGSCP antibodies, respectively, in a dose-dependent manner. When ML were transfected with TsGSCP-specific dsRNA, TsGSCP expression and enzymatic activity were reduced by 46.82 and 37.39%, respectively, and the capacity of the larvae to intrude into IECs was also obviously impeded. Intestinal AW burden and adult female length and fecundity were significantly decreased in the group of mice infected with dsRNA-transfected ML compared to the control dsRNA and PBS groups. The results showed that TsGSCP plays a principal role in gut intrusion, worm development and fecundity in the T. spiralis lifecycle and might be a candidate target for vaccine development against Trichinella intrusion and infection.

Proteomic analysis of hydrolytic proteases in excretory/secretory proteins from Trichinella spiralis intestinal infective larvae using zymography combined with shotgun LC-MS/MS approach

The critical step of Trichinella spiralis infection is that the muscle larvae (ML) are activated to intestinal infective larvae (IIL) which invade the intestinal columnar epithelium to further develop. The IIL excretory/secretory (ES) proteins play an important role in host-parasite interaction. Proteolytic enzymes are able to mediate the tissue invasion, thereby increasing the susceptibility of parasites to their hosts. The aim of the current study was to screen and identify the natural active proteases in T. spiralis IIL ES proteins using Western blot and gel zymography combined with liquid chromatography tandem mass spectrometry (LC-MS/MS). The T. spiralis ML and IIL ES proteins were collected from the in vitro cultures and their enzymatic acitvities were examined by gelatin zymography and azocasein degradation. The protease activities were partially inhibited by PMSF, E-64 and EDTA. Three protein bands (45, 118 and 165 kDa) of T. spiralis IIL ES proteins were identified by shotgun LC-MS/MS because they have hydrolytic activity to gelatin compared to the ML ES proteins. Total of 30 T. spiralis proteins were identified and they are mainly serine proteinases (19), but also metalloproteinases (7) and cysteine proteinases (3). The qPCR results indicated that transcription levels of four T. spiralis protease genes (two serine proteases, a cathepsin B-like cysteine proteinase and a zinc metalloproteinase) at IIL stage were obviously higher than at the ML stage. These proteolytic enzymes are directly exposed to the host intestinal milieu and they may mediate the worm invasion of enteral epithelium and escaping from the host's immune responses. The results provide the new insights into understanding of the interaction of T. spiralis with host and the invasion mechanism.

Molecular characterization of a Trichinella spiralis serine proteinase

The aim of this study was to investigate the biological characteristics and functions of a Trichinella spiralis serine proteinase (TsSerp) during larval invasion and development in the host. The full-length TsSerp cDNA sequence was cloned and expressed in Escherichia coli BL21. The results of RT-PCR, IFA and western blotting analyses showed that TsSerp was a secretory protein that was highly expressed at the T. spiralis intestinal infective larva and muscle larva stages and primarily located at the cuticle, stichosome and intrauterine embryos of the parasite. rTsSerp promoted the larval invasion of intestinal epithelial cells (IECs) and the enteric mucosa, whereas an anti-rTsSerp antibody impeded larval invasion; the promotion and obstruction roles were dose-dependently related to rTsSerp and the anti-rTsSerp antibodies, respectively. Vaccination of mice with rTsSerp elicited a remarkable humoral immune response (high levels of serum IgG, IgG1/IgG2a, IgE and IgM), and it also triggered both systemic (spleen) and local intestinal mucosal mesenteric lymph node (MLN) cellular immune responses, as demonstrated by a significant elevation in Th1 cytokines (IFN-γ) and Th2 cytokines (IL-4) after the spleen and MLN cells from vaccinated mice were stimulated with rTsSerp. Anti-TsSerp antibodies participated in the killing and destruction of newborn larvae via ADCC. The mice vaccinated with rTsSerp exhibited a 48.7% reduction in intestinal adult worms and a 52.5% reduction in muscle larvae. These results indicated that TsSerp participates in T. spiralis invasion and development in the host and might be considered a potential candidate target antigen to develop oral polyvalent preventive vaccines against Trichinella infection.

Molecular cloning and characterization of a novel peptidase from Trichinella spiralis and protective immunity elicited by the peptidase in BALB/c mice

In our previous studies, a novel T. spiralis peptidase (TsP) was identified among the excretory/secretory (ES) proteins of T. spiralis intestinal infective larvae (IIL) and T. spiralis at the adult worm (AW) stage using immunoproteomics, but the biological function of TsP in the life cycle of T. spiralis is not clear. The objective of this study was to investigate the biological properties and functions of TsP in larval intrusion and protective immunity induced by immunization with rTsP. The complete TsP cDNA sequence was cloned and expressed. The results of RT-PCR, indirect immunofluorescence assay (IIFA) and western blotting revealed that TsP is a surface and secretory protein expressed in T. spiralis at different stages (muscle larvae, IIL, AWs and newborn larvae) that is principally localized at the epicuticle of the nematode. rTsP facilitated the larval intrusion of intestinal epithelial cells (IECs) and intestinal mucosa, whereas anti-rTsP antibodies suppressed larval intrusion; these facilitative and suppressive roles were dose-dependently related to rTsP or anti-rTsP antibodies. Immunization of mice with rTsP triggered an obvious humoral immune response (high levels of IgG, IgG1/IgG2a, and sIgA) and also elicited systemic (spleen) and intestinal local mucosal (mesenteric lymph node) cellular immune responses, as demonstrated by an evident increase in the cytokines IFN-γ and IL-4. Immunization of mice with rTsP reduced the numbers of intestinal adult worms by 38.6% and muscle larvae by 41.93%. These results demonstrate that TsP plays a vital role in the intrusion, development and survival of T. spiralis in hosts and is a promising candidate target molecule for anti-Trichinella vaccines.

Vaccination of Mice with a Novel Trypsin from Trichinella spiralis Elicits the Immune Protection against Larval Challenge

Trichinella spiralis is a major foodborne parasite and has a serious threat to meat safety. Development of anti-Trichinella vaccines is prospective to eliminate Trichinella infection in food animal. The aim of this study was to assess the biological properties of a novel T. spiralis trypsin (TsT) and its elicited immune protection against larval challenge. The cDNA sequence of TsT gene was cloned and expressed. Western blotting showed rTsT was identified by infection serum and anti-TsT serum. RT-PCR results revealed that TsT gene was transcribed at diverse T. spiralis lifecycle stages. The IIFT results showed that natural TsT was principally expressed at epicuticle of 5-6 day adult worms, indicating that TsT is a worm somatic antigen and adult-stage specific surface antigen. Vaccination of mice with rTsT triggered an evident humoral immune response (high levels of serum IgG, IgG1/IgG2a, and enteral sIgA), and it also induced the systemic and enteral local cellular immune response, demonstrated by an significantly elevation of cytokines IFN-γ and IL-4. The mice vaccinated with rTsT exhibited a 33.17% reduction of enteral adult worms and a 37.80% reduction of muscle larvae after larval challenge. The results showed that TsT might be considered as a candidate target antigen for anti-T. spiralis vaccines.

Characterization of a Trichinella spiralis aminopeptidase and its participation in invasion, development and fecundity

A Trichinella spiralis aminopeptidase (TsAP) has been identified in intestinal infectious larvae (IIL) and adult worms (AW), but its biological function in the T. spiralis life cycle is unknown. The aim of this study was to characterize TsAP and ascertain its functions in the invasion, development and fecundity of T. spiralis. Recombinant TsAP (rTsAP) was expressed and purified. rTsAP has strong immunogenicity. qPCR and western blotting show that TsAP was transcribed and expressed at all T. spiralis lifecycle stages, but the expression level of TsAP mRNA and proteins at IIL and AW stages was obviously higher than those in muscle larvae (ML) and newborn larvae (NBL). The IFT results reveal that TsAP was principally located at the cuticle and the intrauterine embryos of this nematode. rTsAP had the enzymatic activity of natural aminopeptidase to hydrolyze the substrate Leu-pNA with an optimal temperature of 50 °C and optimal pH of 8.0. rTsAP promoted the larval penetration into intestinal epithelial cells, whereas anti-rTsAP antibodies suppressed the larval intrusion; the promotion and suppression was dose-dependently related to rTsAP or anti-rTsAP antibodies. TsAP protein expression level and enzymatic activity were reduced by 50.90 and 49.72% through silencing of the TsAP gene by specific siRNA 842. Intestinal AW and muscle larval burdens, worm length and female reproductive capacity were significantly declined in mice infected with siRNA-transfected ML compared to the control siRNA and PBS group. These results indicate that TsAP participates in the invasion, development and fecundity of T. spiralis and it might be a candidate target for anti-Trichinella vaccines.

Protective immunity in mice vaccinated with a novel elastase-1 significantly decreases Trichinella spiralis fecundity and infection

Trichinella spiralis is an important foodborne parasitic nematode that represents an enormous threat to the food safety of pork meat. The development of a preventive vaccine is valuable for the prevention and control of Trichinella infection in domestic pigs to ensure pork safety. Elastase is a trypsin-like serine protease that hydrolyzes the host's diverse tissue components and participates in parasite penetration, and it might be a novel vaccine target molecule. The aim of this study was to assess the protective immunity produced by vaccination with a novel Trichinella spiralis elastase-1 (TsE) in a mouse model. The results demonstrate that subcutaneous vaccination of mice with rTsE elicited a systemic humoral response (high levels of serum IgG and subclass IgG1/IgG2a and IgA) and significant local enteral mucosal sIgA responses. Anti-rTsE IgG recognized the native TsE at the cuticle, stichosome of intestinal infective larvae and adult worm (AW), and intrauterine embryos of female AW. The rTsE vaccination also produced a systemic and local mixed Th1/Th2 response, as demonstrated by clear elevation levels of Th1 cytokines (IFN-γ, IL-2) and Th2 cytokines (IL-4, IL-10) after spleen, mesenteric lymph node and Peyer's patch cells from immunized mice were stimulated with rTsE. The immunized mice exhibited a 52.19% reduction in enteral AW and a 64.06% reduction in muscle larvae after challenge infection. The immune response triggered by rTsE vaccination protected enteral mucosa from larval intrusion, suppressed larval development and reduced female fecundity. The results indicate that TsE may represent a novel target molecule for anti-T. spiralis vaccines.

Interaction of a Trichinella spiralis cathepsin B with enterocytes promotes the larval intrusion into the cells

Cathepsin B is one member of cysteine protease family and widely distributed in organisms, it plays an important function in parasite penetrating, migrating, molting and immune escaping. The aim of this work was to investigate whether exist interaction between a Trichinella spiralis cathepsin B (TsCB) and mouse intestinal epithelium cells (IECs), and its influence in the process of larva cell invasion. The results of ELISA, indirect immunofluorescence assay (IIFA), confocal microscopy and Far western blotting showed that there was a strong specific binding of rTsCB and IEC proteins, and the binding positions were located in cytoplasm and nuclei of IECs. The results of the in vitro larva penetration test revealed that rTsCB facilitated the larva invasion of IECs, whereas anti-rTsCB antibodies impeded partially the larva intrusion of enterocytes, this promotive or inhibitory roles were dose-dependent of rTsCB or anti-rTsCB antibodies. Silencing TsCB by siRNA mediated RNA interference reduced the TsCB expression in T. spiralis larvae, and markedly inhibited the larva penetration of enterocytes. The results indicated that TsCB binding to IECs promoted larva penetration of host's enteral epithelia, and it is a promising molecular target against intestinal invasive stages of T. spiralis.

Molecular characterization of a Trichinella spiralis elastase-1 and its potential as a diagnostic antigen for trichinellosis

BACKGROUND

Trichinella spiralis muscle larval (ML) excretion/secretion (ES) antigen is the most widely used diagnostic antigen of trichinellosis, but preparation of ES antigen requires collecting worms from infected animals, and detection of specific IgG against ML ES antigen may result in a false negative at the early stage of infection. The aim of the study was to characterize T. spiralis elastase-1 (TsEla) and to evaluate its potential as diagnostic antigen for trichinellosis.

METHODS

The complete cDNA sequences of the TsEla gene were cloned and expressed, and recombinant (rTsEla) was purified. TsEla transcription and expression in different T. spiralis life-cycle stages was investigated by qPCR and western blotting, and its location in the nematodes was evaluated using an immunofluorescence assay (IFA). The antigenicity of rTsEla was investigated by western blotting analysis and ELISA. Anti-Trichinella IgG, IgM and IgE of experimentally infected mice and specific IgG antibodies of trichinellosis patients were assayed by rTsEla-ELISA and ES-ELISA.

RESULTS

The results of the qPCR and western blotting showed that TsEla was expressed in various T. spiralis life stages. Natural TsEla was detected in the soluble proteins and ES proteins of different life stages. IFA revealed that TsEla was identified in the whole nematodes of various stages, especially in the cuticle, stichosome and genital primordium of the parasite. Serum anti-Trichinella IgM, IgG and IgE in infected mice was first detected by rTsEla-ELISA at 6, 10 and 12 days post-infection (dpi), and reached 100% at 8, 14 and 14 dpi, respectively. When rTsEla-ELISA and ES-ELISA were used to detect anti-Trichinella IgG in sera of trichinellosis patients, the sensitivity was 97.37% (37/38) and 89.74% (34/38) (P > 0.05), and the specificity was 99.10% (220/222) and 98.20% (218/222), respectively (P > 0.05). The rTsEla cross-reacted with only one serum sample out of 20 samples from paragonimiasis patients and 7 samples from clonorchiasis patients.

CONCLUSIONS

rTsEla is valuable to early diagnosis of trichinellosis and could be an alternative diagnostic antigen to the ML ES antigens.

Vaccination of mice with a recombinant novel cathepsin B inhibits Trichinella spiralis development, reduces the fecundity and worm burden

BACKGROUND

Trichinella spiralis is a major zoonotic tissue-dwelling nematode, which is a public health concern and a serious hazard to animal food safety. It is necessary to exploit an anti-Trichinella vaccine to interrupt the transmission of Trichinella infection among animals and from animals to humans. The purpose of the present study was to characterize the novel T. spiralis cathepsin B (TsCB) and to evaluate the immune protection elicited by immunization with recombinant TsCB (rTsCB).

METHODS

The complete cDNA sequences of the TsCB gene were cloned, expressed and purified. The antigenicity of rTsCB was investigated by western blot analysis and ELISA. Transcription and expression of TsCB at various T. spiralis life-cycle stages were analyzed by RT-PCR and indirect immunofluorescent assay (IIFA). The mice were subcutaneously immunized with rTsCB, and serum level of TsCB-specific IgG (IgG1 and IgG2a) and IgE antibodies were assayed by ELISA. Immune protection elicited by vaccination with rTsCB was investigated.

RESULTS

The TsCB was transcribed and expressed in four T. spiralis life-cycle stages (adult worm, AW; newborn larvae, NBL; muscle larvae, ML; and intestinal infective L1 larvae), it was primarily located in the cuticle and stichosome of the parasitic nematode. Vaccination of mice with rTsCB produced a prominent antibody response (high level of specific IgG and IgE) and immune protection, as demonstrated by a 52.81% AW burden reduction of intestines at six days post-infection (dpi) and a 50.90% ML burden reduction of muscles at 35 dpi after oral larva challenge. The TsCB-specific antibody response elicited by immunization with rTsCB also impeded intestinal worm growth and decreased the female fecundity.

CONCLUSIONS

TsCB might be considered as a novel potential molecular target to develop vaccines against T. spiralis infection.

Molecular characterization of a Trichinella spiralis enolase and its interaction with the host's plasminogen

The binding and activation of host plasminogen (PLG) by worm surface enolases has been verified to participate in parasite invasion, but the role of this processes during Trichinella spiralis infection has not been clarified. Therefore, the expression and immunolocalization of a T. spiralis enolase (TsENO) and its binding activity with PLG were evaluated in this study. Based on the three-dimensional (3D) molecular model of TsENO, the protein interaction between TsENO and human PLG was analysed by the ZDOCK server. The interacting residues were identified after analysis of the protein–protein interface by bioinformatics techniques. The key interacting residues were confirmed by a series of experiments. The qPCR analysis results demonstrated that Ts-eno was transcribed throughout the whole life cycle of T. spiralis. The immunofluorescence assay (IFA) results confirmed that TsENO was distributed on the T. spiralis surface. The binding assays showed that recombinant TsENO (rTsENO) and native TsENO were able to bind PLG. Four lysine residues (90, 289, 291 and 300) of TsENO were considered to be active residues for PLG interaction. The quadruple mutant (Lys90Ala + Lys289Ala + Lys291Ala + Lys300Ala) TsENO, in which the key lysine residues were substituted with alanine (Ala) residues, exhibited a reduction in PLG binding of nearly 50% (45.37%). These results revealed that TsENO has strong binding activity with human PLG. The four lysine residues (90, 289, 291 and 300) of TsENO play an important role in PLG binding and could accelerate PLG activation and invasion of the host’s intestinal wall by T. spiralis.

In vitro silencing of a serine protease inhibitor suppresses Trichinella spiralis invasion, development, and fecundity

In a previous study, immunoproteomics was used to identify a serine protease inhibitor (TsSPI) of T. spiralis excretory/secretory (ES) proteins that exhibited an inhibitory effect on trypsin enzymatic activity, but the precise role of TsSPI on worm infection and development in its host is not well understood. The objective of the present study was to use RNA interference to ascertain the function of TsSPI in larval invasion and growth. TsSPI-specific small interference RNAs (siRNAs) were delivered to muscle larvae (ML) to silence TsSPI expression by electroporation. Four days after electroporation, the ML transfected with 2 μM siRNA-653 exhibited a 75.75% decrease in TsSPI transcription and a 69.23% decrease in TsSPI expression compared with control ML. Although the silencing of TsSPI expression did not decrease worm viability, it significantly suppressed the larval invasion of intestinal epithelium cells (IEC) (P < 0.01), and the suppression was siRNA dose-dependent (r = 0.981). The infection of mice with siRNA-653-treated ML produced a 63.71% reduction of adult worms and a 72.38% reduction of muscle larvae. In addition, the length of the adults, newborn larvae, and ML and the fecundity of female T. spiralis from mice infected with siRNA-treated ML were obviously reduced relative to those in the control siRNA or PBS groups. These results indicated that the silencing of TsSPI by RNAi suppressed larval invasion and development and decreased female fecundity, further confirming that TsSPI plays a crucial role during the T. spiralis lifecycle and is a promising molecular target for anti-Trichinella vaccines.

Intranasal immunization with recombinant Trichinella spiralis serine protease elicits protective immunity in BALB/c mice

The aim of this study was to observe the intestinal mucosal/systemic responses triggered by intranasal vaccination using recombinant Trichinella spiralis serine protease (rTsSP) and its capacity to elicit immune protection against larva challenge in a murine model. rTsSP coupled with cholera toxin B subunit (CTB) was used to vaccinate mice via intranasal route. The results revealed that intranasal vaccination with rTsSP plus CTB elicited significantly intestinal local sIgA response and a TsSP-specific systemic antibody response in vaccinated mice. Furthermore, more goblet cells/acidic mucins and IgA-secreting cells were observed in jejunum from vaccinated mice. Anti-rTsSP immune serum strongly recognized the cuticle of various worm stages (muscle larva, intestinal infective larva and adult worm). The level of IFN-γ, IL-4 and IL-10 of rTsSP-vaccinated mice was significantly elevated relative to CTB and PBS control groups. The vaccinated mice exhibited a 71.10% adult reduction at 9 days pi and a 62.10% muscle larva reduction at 42 days pi following larva challenge. Additionally, vaccination with rTsSP also dampened intestinal T. spiralis development and decreased the female fecundity. Our results showed that intranasal vaccination using rTsSP adjuvanted with CTB triggered significantly local sIgA response and systemic concurrent Th1/Th2 response that induced an obvious protection against Trichinella infection.

Molecular characterization of a 31 kDa protein from Trichinella spiralis and its induced immune protection in BALB/c mice

Background

Trichinella spiralis is an important foodborne zoonotic parasite and it is necessary to develop a vaccine in order to interrupt transmission from animals to humans. A 31 kDa protein from T. spiralis (Ts31) is an antigen targeted by protective antibodies, and Ts31 contains a domain of trypsin-like serine protease that might have the function of serine protease. The purpose of this study was to investigate the molecular characteristics of Ts31 and its induced immune protection.

Methods

Expression and localization of Ts31 in various T. spiralis phases were investigated using qPCR and immunofluorescent test (IFT). The specific binding between Ts31 and intestinal epithelium cells (IECs) was analyzed by Far-Western blotting, ELISA and IFT, and the cellular localization of binding sites was examined on confocal microscopy. The mice were subcutaneously vaccinated with recombinant Ts31 protein (rTs31), serum specific IgG was determined by ELISA, and immune protection induced by immunization with rTs31 was evaluated. Inhibition of anti-rTs31 IgG on IL1 invasion of IECs and ADCC-mediated killing of newborn larvae (NBL) was also determined.

Results

Ts31 was expressed at different life-cycle stages and located principally at the stichosome and cuticle of this parasite. rTs31 was capable to specially bond to IECs, and binding site was located in the cytoplasm of IECs. Immunization of mice with rTs31 elicited a significant humoral response and protection, as demonstrated by a 56.93% reduction of adult worms at 6 days post-infection (dpi) and a 53.50% reduction of muscle larvae at 42 dpi after larval challenge. Anti-rTs31 antibodies impeded T. spiralis penetration of enterocytes in a dose-dependent pattern, and participated in the destruction of NBL by an ADCC-mediated manner.

Conclusions

Ts31 facilitated the T. spiralis penetration of intestinal epithelium, which could make it a vaccine candidate target molecule against Trichinella infection.

Characterization of a serine protease inhibitor from Trichinella spiralis and its participation in larval invasion of host's intestinal epithelial cells

Background

Trichinella spiralis serine protease inhibitor (TsSPI) was identified in ES proteins of adult worms (AW), the TsSPI gene was highly expressed at enteral stage worms (AW and newborn larvae), distributed mainly in the cuticle and stichosome of this nematode. Vaccination of mice with rTsSPI exhibited a 62.2% reduction of intestinal AW and a 57.25% reduction of muscle larvae after larval challenge. The aim of this study was to investigate the biological characteristics of TsSPI and its roles in the process of T. spiralis invasion of host’s intestinal epithelium cells (IECs).

Methods

The rTsSPI inhibition on trypsin enzymatic activity was detected by SDS-PAGE and spectrophotometry. The binding of rTsSPI with intestinal epithelium from normal mice and the primary cultured mouse intestinal epithelium cells (IECs) was examined by indirect immunofluorescent (IIF), the cellular localization of rTsSPI binding to IECs was observed by confocal microscopy. The inhibition of anti-rTsSPI serum on T. spiralis invasion of IECs was determined by an in vitro invasion assay. Anti-rTsSPI antibody cytotoxicity on the newborn larvae (NBL) was also determined.

Results

The rTsSPI had the inhibitory activity against porcine trypsin. The rTsSPI specifically bound to the intestinal epithelium from normal mice and primary cultured mouse IECs, and the binding sites were located in IEC membrane and cytoplasm. Anti-rTsSPI antibodies depressed the larval invasion of IECs with a dose-dependent mode. Anti-rTsSPI antibodies also participated in the destruction of T. spiralis NBL via an ADCC-mediated manner.

Conclusions

TsSPI might participate in the T. spiralis larval invasion of IECs and it is likely the potential vaccine target against T. spiralis enteral stages.

Molecular characterization of a putative serine protease from Trichinella spiralis and its elicited immune protection

In our previous work, a Trichinella spiralis putative serine protease (TsSP) was identified from ES products of T. spiralis intestinal infective larvae (IIL) and adult worms (AW) by immunoproteomics: it was highly expressed in IIL compared with muscle larvae (ML). In this study, the TsSP biological characteristics in larval invasion and growth were identified and its potential as a vaccine target against Trichinella infection were investigated. Expression of TsSP at various developmental phases (newborn larvae, ML, IIL, and AW) was detected by qPCR, immunofluorescent test and Western blotting. The rTsSP could specifically bind to the intestinal epithelial cell (IEC) membrane and enter into the cytoplasm. Anti-rTsSP serum suppressed the larval invasion of enterocytes in a dose-dependent mode, and killed newborn and ML of T. spiralis, decreased larval infectivity and development in the host by an ADCC-mediated mechanism. Immunization of mice with rTsSP produced a Th2 predominant immune response, and resulted in a 52.70% reduction of adult worms at 5 days post-infection (dpi) and a 52.10% reduction of muscle larvae at 42 dpi. The results revealed there was an interaction between TsSP and the host’s IEC; TsSP might be a pivotal protein for the invading, growing and parasiting of this nematode in the host. Vaccination of mice with rTsSP elicited immune protection, and TsSP is a potential target molecule for vaccines against enteral Trichinella infection.

Cloning, expression and characterisation of a cysteine protease from Trichinella spiralis

Cysteine protease is a superfamily of widespread proteolytic enzymes and plays a major role in larval invasion, migration, exsheathing, survival and immune evasion in parasites. In the present study, the gene coding cysteine proteinase of the nematode Trichinella spiralis (Owen, 1835) was cloned into pQE-80L and subsequently expressed in E. coli JM109. The rTsCP was purified and its antigenicity was identified by Western blot and ELISA. Using anti-rTsCP serum the native TsCP was identified in muscle larval crude proteins. The results of quantitative real-time PCR and immunofluorescence test demonstrated that the TsCP was expressed in all stages of T. spiralis and located mainly in cuticle, stichosome and reproductive organs. The immunisation of mice with rTsCP elicited Th2-predominant immune responses. Anti-rTsCP antibodies could partially inhibit the in vitro larval invasion of intestinal epithelial cells and kill the newborn larvae by an antibody-dependent cell-mediated dose-dependent cytotoxicity. The vaccinated mice exhibited a 54% reduction of adults and a 33% reduction of muscle larvae following challenge infection. The results suggested that the TsCP might be an indispensable protein in Trichinella invasion, development and survival of T. spiralis in hosts, and could be a potential vaccine target against infection.

Characterization of a Trichinella spiralis putative serine protease. Study of its potential as sero-diagnostic tool

Background

Trichinellosis is a serious zoonositc parasitosis worldwide. Because its clinical manifestations aren’t specific, the diagnosis of trichinellosis is not easy to be made. Trichinella spiralis muscle larva (ML) excretory–secretory (ES) antigens are the most widely applied diagnostic antigens for human trichinellosis, but the major drawback of the ES antigens for assaying anti-Trichinella antibodies is the false negative in the early Trichinella infection period. The aim of this study was to characterize the T. spiralis putative serine protease (TsSP) and to investigate its potential use for diagnosis of trichinellosis.

Methodology/Principal findings

The full-length TsSP sequence was cloned and expressed, and recombinant TsSP (rTsSP) was purified by Ni-NTA-Sefinose Column. On Western blotting analysis the rTsSP was recognized by T. spiralis-infected mouse serum, and the natural TsSP was identified in T. spiralis ML crude and ES antigens by using anti-rTsSP serum. Expression of TsSP was detected at various T. spiralis developmental stages (newborn larvae, muscle larvae, intestinal infective larvae and adult worms). Immunolocalization identified the TsSP principally in cuticles and stichosomes of the nematode. The sensitivity of rTsSP-ELISA and ES-ELISA was 98.11% (52/53) and 88.68% (47/53) respectively (P > 0.05) when the sera from trichinellosis patients were examined. However, while twenty-one serum samples of trichinellosis patients’ sera at 19 days post-infection (dpi) were tested, the sensitivity (95.24%) of rTsSP-ELISA was distinctly higher than 71.43% of ES-ELISA (P < 0.05). The specificity (99.53%) of rTsSP-ELISA was remarkably higher than 91.98% of ES-ELISA (P < 0.01). Only one out of 20 serum samples of cysticercosis patients cross-reacted with the rTsSP. Specific anti-Trichinella IgG in infected mice was first detected by rTsSP-ELISA as soon as 7 dpi and antibody positive rate reached 100% on 10 dpi, whereas the ES-ELISA did not permit detection of 100% of infected mice before 16 dpi.

Conclusions

The rTsSP is a potential early diagnostic antigen for human trichinellosis.

Trichinellosis is an important parasitic zoonosis, and has a public health hazard and an economic impact on the safety of animal food. The diagnosis of trichinellosis is difficult and it is often misdiagnosed. There is an evident 2–3 week window stage between clinical manifestations and the anti-Trichinella IgG positive. Serine protease is a superfamily of proteolytic enzymes and exerts a major role in tissue invasion, larval development and survival of the parasites. A T. spiralis putative serine protease (TsSP) was characterized in ES proteins of T. spiralis intestinal infective larvae and adult worms by the immunoproteomics with early infection serum. In this study, the TsSP was expressed and purified. The results revealed that the TsSP was expressed at various T. spiralis stages (newborn larvae, muscle larvae, intestinal infective larvae and adult worms) and it was principally located in cuticle and stichosome of the nematode. The rTsSP was sensitive and specific for detection of anti-Trichinella IgG, and could be regarded as an early diagnostic marker of trichinellosis.

Immuno-proteomic analysis of Trichinella spiralis, T. pseudospiralis, and T. papuae extracts recognized by human T. spiralis-infected sera

The present study explored potentially immunogenic proteins of the encapsulated (Trichinella spiralis) and non-encapsulated (T. pseudospiralis, T. papuae) species within the genus Trichinella. The somatic muscle larval extracts of each species were subjected to immunoblotting analysis using human T. spiralis-infected serum samples. Fifteen reactive bands of all three species were selected for further protein identification by liquid chromatography-tandem mass spectrometry, and their possible functions were ascertained using the gene ontology. Our findings showed immunogenic protein patterns with molecular mass in the range of 33-67 kDa. Proteomic and bioinformatic analysis revealed a wide variety of functions of 17 identified proteins, which are associated with catalytic, binding, and structural activities. Most proteins were involved in cellular and metabolic processes that contribute in the invasion of host tissues and the larval molting processes. The parasite proteins were identified as actin-5C, serine protease, deoxyribonuclease-2, and intermediate filament protein ifa-1. This information may lead to alternative tools for selection of potential diagnostic protein markers or aid in the design of vaccine candidates for prevention and control of Trichinella infection.

Invasion by Trichinella spiralis infective larvae affects the levels of inflammatory cytokines in intestinal epithelial cells in vitro

As we all know, invasion of host intestinal epithelium is very important for T. spiralis to complete successfully their life cycle. However, the mechanisms that the intestinal infective larvae (IIL) invade and migrate in the intestinal epithailial cells (IECs) remain unclear until now. The related researches have been hindered since a readily operable in vitro normal model. In our earlier study, an in vitro normal IEC invasion model was established for the first time, and the abilities of the normal IECs to initiate mucosal inflammatory responses to invasion by the IIL in vitro were evaluated in this study. When the IIL were overlaid on the normal mouse IEC monolayers, they quickly within seconds invaded the monolayers and move within the IECs, leaving trails of damaged cells. Then the larvae were found to have started their molting at 12 h, and the complete cuticle was found at 24 h. The percentage of the first molt in the larvae was about 62.3%, and the percentage of the 2nd-4th molt was about 38.2% at 36 h. Real-time PCR showed that the mRNA levels of interleukin-1β (IL-1β), IL-8, epithelial neutrophil-activating peptide 78 (ENA-78), inducible nitric oxide synthase (iNOS), and monocyte chemotactic protein 2 (MCP-2) were elevated in the IECs after 7 h of infection after invasion by the IIL, and their levels were enhanced with the increase of larvae number. No changes in tumor necrosis factor-α (TNF-α) mRNA were observed after the IIL invasion. Secretion increases of IL-1β and IL-8 from the IEC monolayers invaded by T. spiralis were also detected by ELISA. Secretion increases of proinflammatory cytokines and inflammatory mediators in normal IECs can launch the acute inflammatory in response to the IIL invasion. This study would be helpful in further investigating the relationship between the host and T. spiralis, and the immune escape mechanisms of the niche established by T. spiralis.

Proteomic analysis and immunodetection of antigens from early developmental stages of Trichinella spiralis

Trichinella spiralis is an ubiquitous parasitic nematode that lives in muscle tissue of many hosts and causes trichinellosis in humans. Numerous efforts have been directed at specific detection of this infection and strategies for its control. TSL-1 and other antigens, mainly from muscle larvae (ML), have been used to induce partial protection in rodents. An improvement in protective immunity may be achieved by using antigens from other parasite stages. Further, identification of other parasite antigens may provide insights into their role in the host-parasite interaction. In this study, T. spiralis antigens from early developmental parasite stages, namely ML and pre-adult (PA) obtained at 6h, 18h and 30h post-infection, were identified by proteomic and mass spectrometry analyses. Our findings showed a differential expression of several proteins with molecular weights in the range of 13-224kDa and pI range of 4.54-9.89. Bioinformatic analyses revealed a wide diversity of functions in the identified proteins, which include structural, antioxidant, actin binding, peptidyl prolyl cis-trans isomerase, motor, hydrolase, ATP binding, magnesium and calcium binding, isomerase and translation elongation factor. This, together with the differential recognition of antigens from these parasite stages by antibodies present in intestinal fluid, in supernatants from intestinal explants, and in serum samples from mice infected with T. spiralis or re-infected with this parasite, provides information that may lead to alternatives in the design of vaccines against this parasite or for modulation of immune responses.

Trichinella spiralis: low vaccine potential of glutathione S-transferase against infections in mice

We have previously reported that Trichinella spiralis glutathione-S-transferase (TsGST) gene is an up-regulated gene in intestinal infective larvae (IIL) compared to muscle larvae (ML). In this study, the TsGST gene was cloned, and recombinant TsGST (rTsGST) was produced. Anti-rTsGST serum recognized the native TsGST by Western blotting in crude antigens of ML, adult worm (AW) and newborn larvae (NBL) of T. spiralis, but not in ML excretory-secretory (ES) antigens. Expression of TsGST was observed in all different developmental stages (IIL, AW, NBL and ML). An immunolocalization analysis identified TsGST in the cuticle, stichosome and genital primordium of the parasite. The rTsGST had GST enzymatic activity. After a challenge infection with T. spiralis larvae, mice immunized with rTsGST displayed a 35.71% reduction in adult worms and a 38.55% reduction in muscle larvae. The vaccination of mice with rTsGST induced the Th1/Th2-mixed type of immune response with Th2 predominant (high levels of IgG1) and partial protective immunity against T. spiralis infection.

Molecular identification and characterization of Trichinella spiralis proteasome subunit beta type-7

Background

Previous study showed that Trichinella spiralis proteasome subunit beta type-7 (Tspst) gene is an up-regulated gene in intestinal infective larvae (IIL) compared to muscle larvae (ML), which was screened by using suppression subtractive hybridization (SSH) and confirmed by real-time PCR. Tspst may be related to the larval invasion of intestinal epithelial cells (IECs). The aim of this study was to identify Tspst and to investigate its immune protection against intestinal T. spiralis infection.

Methods

The Tspst gene encoding a 29 kDa protein from T. spiralis infective larvae was cloned, and recombinant Tspst protein (rTspst) was produced in an Escherichia coli expression system. The rTspst was used to immunize BALB/c mice. Anti-rTspst antibodies were used to determine the immunolocolization of Tspst in the parasite. Transcription and expression of Tspst at T. spiralis different developmental stages were observed by RT-PCR and immunofluorescence test (IFT). The in vitro or in vivo immune protection of anti-rTspst serum or rTspst against intestinal T. spiralis infection in BALB/c mice was evaluated.

Results

Anti-rTspst serum recognized the native Tspst protein with 29 kDa in ML crude antigens. Transcription and expression of gene was observed at all T. spiralis different developmental stages (IIL, adult worms, newborn larvae, and ML). An immunolocalization analysis identified Tspst in the cuticle and internal organs of the parasite. An in vitro invasion assay showed that, when anti-rTspst serum, serum of mice infected with T. spiralis or normal mouse serum were added to the medium, the invasion rate of the infective larvae in an IEC monolayer was 25.2%, 11.4%, and 79%, respectively (P < 0.05), indicating that anti-rTspst serum partially prevented the larval invasion of IECs. After a challenge infection with T. spiralis muscle larvae, mice immunized with rTspst conferred a 45.7% reduction in adult worm burden in intestines.

Conclusions

In the present study, Tspst was first identified and characterized. Tspst is an invasion-related protein of T. spiralis IIL and could be considered as a potential vaccine candidate antigen against intestinal T. spiralis infection that merits further study.

Molecular identification of Trichinella spiralis nudix hydrolase and its induced protective immunity against trichinellosis in BALB/c mice

BACKGROUND

Nudix hydrolases (Nd) is a widespread superfamily, which is found in all classes of organism, hydrolyse a wide range of organic pyrophosphates and has a 'housecleaning' function. The previous study showed that Trichinella spiralis Nd (TsNd) bound to intestinal epithelial cells (IECs), and the vaccination of mice with T7 phage-displayed TsNd polypeptides produced protective immunity. The aim of this study was to clone, express and identify the full-length TsNd and to investigate its immune protection against T. spiralis infection.

METHODS

The full-length cDNA sequence of TsNd gene encoding a 46 kDa protein from T. spiralis intestinal infective larvae (IIL) was cloned and identified. The antigenicity of rTsNd was analyzed by Western blot. Transcription and expression of TsNd at T. spiralis different stages were observed by RT-PCR and IFT. The levels of the specific total IgG, IgG1 and IgG2a antibodies to rTsNd were determined by ELISA. The immune protection of rTsNd against T. spiralis infection was investigated.

RESULTS

Sequence and phylogenetic analysis revealed that TsNd had a nudix motif located at 226-244aa, which had high homology and the closest evolutionary status with T. pseudospiralis. The rTsNd was obtained after expression and purification. Western blot analysis showed that anti-rTsNd serum recognized the native TsNd protein in crude antigens of muscle larvae (ML), IIL, adult worms (AW) and newborn larvae (NBL), and ES antigens of ML. Transcription and expression of TsNd gene was observed in all developmental stages of T. spiralis (ML, IIL, AW and NBL), with high level expression in IIL. An immunolocalization analysis identified TsNd in the cuticle, stichocytes and reproductive organs of the parasite. Following immunization, anti-rTsNd IgG levels were increased, and the levels of IgG1 were more significantly higher than that of IgG2a. After a challenge infection with T. spiralis, mice immunized with the rTsNd displayed a 57.7% reduction in adult worms and a 56.9% reduction in muscle larval burden.

CONCLUSIONS

TsNd induced a partial protective immunity in mice and could be considered as a novel candidate vaccine antigen against trichinellosis.

Proteomic analysis of surface proteins of Trichinella spiralis muscle larvae by two-dimensional gel electrophoresis and mass spectrometry

Background

Trichinella spiralis is a zoonotic tissue-dwelling parasitic nematode that infects humans and other mammals. Its surface proteins are recognized as antigenic in many infected hosts, being directly exposed to the host’s immune system and are the main target antigens that induce the immune responses. The larval surface proteins may also interact with intestinal epithelial cells and may play an important role in the invasion and development process of T. spiralis. The purpose of this study was to analyze and characterize the surface proteins of T. spiralis muscle larvae by two-dimensional gel electrophoresis (2-DE) and mass spectrometry.

Methods

The surface proteins of T. spiralis muscle larvae were stripped from the cuticle of live larvae by the cetyltrimethylammonium bromide (CTAB) and sodium deoxycholate. The surface protein stripping was examined by an immunofluorescent test (IFT). The surface proteins were analyzed by SDS-PAGE and Western blotting, and then identified by 2-DE and MALDI-TOF/TOF mass spectrometry analysis.

Results

The IFT results showed that the surface proteins-stripped larvae were not recognized by sera of mice immunized with surface antigens. Western blotting showed 7 of 12 protein bands of the surface proteins were recognized by mouse infection sera at 18 dpi and at 42 dpi. The 2-DE results showed that a total of approximately 33 proteins spots were detected with molecular weights varying from 10 to 66 kDa and isoelectric point (pI) from 4 to 7. Twenty-seven of 33 protein spots were identified and characterized to correlate with 15 different proteins. Out of the 14 proteins identified as T. spiralis proteins, 5 proteins (partial P49 antigen, deoxyribonuclease II family protein, two serine proteases, and serine proteinase) had catalytic and hydrolase activity. All of these 5 proteins were also associated with metabolic processes and 2 of the five proteins were associated with cellular processes.

Conclusions

In this study, T. spiralis muscle larval surface proteins have been identified, which will provide useful information to elucidate the host-parasite interaction, identify the invasion-related proteins, early diagnostic antigens and the targets for a vaccine.

Identification of differentially expressed genes of Trichinella spiralis larvae after exposure to host intestine milieu

Although it has been known for many years that T. spiralis muscle larvae (ML) can not invade intestinal epithelial cells unless they are exposed to the intestinal milieu and activated into intestinal infective larvae (IIL), which genes in IIL are involved in the process of invasion is still unknown. In this study, suppression subtractive hybridization (SSH) was performed to identify differentially expressed genes between IIL and ML. SSH library was constructed using cDNA generated from IIL as the ‘tester’. About 110 positive clones were randomly selected from the library and sequenced, of which 33 T. spiralis genes were identified. Thirty encoded proteins were annotated according to Gene Ontology Annotation in terms of molecular function, biological process, and cellular localization. Out of 30 annotated proteins, 16 proteins (53.3%) had binding activity and 12 proteins (40.0%) had catalytic activity. The results of real-time PCR showed that the expression of nine genes (Ts7, Ndr family protein; Ts8, serine/threonine-protein kinase polo; Ts11, proteasome subunit beta type-7; Ts17, nudix hydrolase; Ts19, ovochymase-1; Ts22, fibronectin type III domain protein; Ts23, muscle cell intermediate filament protein OV71; Ts26, neutral and basic amino acid transport protein rBAT and Ts33, FACT complex subunit SPT16) from 33 T. spiralis genes in IIL were up-regulated compared with that of ML. The present study provide a group of the potential invasion-related candidate genes and will be helpful for further studies of mechanisms by which T. spiralis infective larvae recognize and invade the intestinal epithelial cells.