Trichinella spiralis: Knockdown of gamma interferon inducible lysosomal thiol reductase (GILT) results in the reduction of worm burden

Trichinella spiralis is mammalian skeletal muscles parasite which may cause trichinellosis in animals and humans. Gamma interferon inducible lysosomal thiol reductase (GILT) is a widespread superfamily which plays key role in processing and presentation of MHC class II restricted antigen by catalyzing disulfide bond reduction. There are no reports about GILT in T. spiralis. In present study, GILT from T. spiralis (Tsp-GILT) was cloned, analyzed by multiple-sequence alignment, and predicted by 3D structure model. Recombinant Tsp-GILT (about 46 kDa) was efficiently expressed in Escherichia coli and thiol reductase activity suggested that in acidic environment the addition of a reducing agent is needed. Soaking method was used to knockdown expression of Tsp-GILT using small interference RNA (siRNA). Immunofluorescence assay confirmed the transformation of siRNA into muscle larva (ML) and new born larva (NBL). Quantitative real time-PCR (QRT-PCR) analysis revealed that transcription level of Tsp-GILT mRNA can be up-regulated by stimulation of mouse IFN-γ and down-regulated by siRNA2 in vitro. NBLs soaked with siRNA2 showed 32.3% reduction in the generation of MLs. MLs soaked with siRNA2 showed 26.2% reduction in the next generation of MLs, but no significant effect was observed on adult worms or NBLs. These findings concluded that GILT may play important roles in the development of T. spiralis parasite.

Trichinella spiralis is the most important pathogen causing trichinellosis of animals and humans. Reports in mammal animals showed that gamma interferon inducible lysosomal thiol reductase (GILT) play key roles in processing and presentation of MHC class II restricted antigens. However, there were no reports about GILT in nematode T. spiralis. In this study, GILT gene from T. spiralis (Tsp-GILT) was cloned and analyzed. The predicted 3D structure of Ts-GILT protein was found similar with that of Homo sapiens and Sus scrofa. To further evaluate the roles of Tsp-GILT in T. spiralis development, a soaking method was used to knockdown the expression of Tsp-GILT gene by siRNA. It was found that NBLs soaked with siRNA showed 32.3% reduction in the generation of MLs, and MLs soaked with siRNA showed 26.2% reduction in the next generation of MLs. Current study concluded that siRNA knockdown of gamma interferon inducible lysosomal thiol reductase from Trichinella spiralis significantly reduce the larval infectivity, development and survival.

Binding of elastase-1 and enterocytes facilitates Trichinella spiralis larval intrusion of the host's intestinal epithelium

Elastase-1 is one member of serine protease family, distributes in organisms widely and plays a crucial role in the invasion and development of Trichinella spiralis. In order to identify the binding of T. spiralis elastase-1 (TsEla) with host's intestinal epithelial cells (IECs) and its role in Trichinella larval intrusion, TsEla gene was cloned and expressed in our previous study. The recombinant TsEla (rTsEla) has the enzymatic activity to degrade specific peptide substrate. A specific binding between rTsEla and IECs was detected by Far Western blot and ELISA. In an in vitro invasion assay, rTsEla promoted the larval intrusion, whereas anti-rTsEla serum inhibited the larval penetration. The larval intrusion was also suppressed after the silencing of TsEla by siRNA. Silencing of TsEla gene by siRNA-291 meditated RNA interference suppressed TsEla protein expression, reduced the worm infectivity, development and reproductive capacity. These results indicated that TsEla plays an important role in the T. spiralis intrusion of host's intestinal epithelia, and it could be a prospective vaccine molecular target against T. spiralis infection.

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.

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.

Functional analysis of Trichinella spiralis serine protease 1.2 by siRNA mediated RNA interference

A T. spiralis serine protease 1.2 (TsSP1.2) was identified in the muscle larvae (ML) and intestinal larvae surface/excretory-secretory (ES) proteins by immunoproteomics. The aim of this study was to determine the TsSP1.2 function in the process of T. spiralis intrusion, growth and reproduction by using RNA interference (RNAi). RNAi was used to silence the expression of TsSP1.2 mRNA and protein in the nematode. On 2 days after the ML were electroporated with 2 µM of TsSP1.2-specific siRNA 534, TsSP1.2 mRNA and protein expression declined in 56.44 and 84.48%, respectively, compared with untreated ML. Although TsSP1.2 silencing did not impair worm viability, larval intrusion of intestinal epithelium cells (IEC) was suppressed by 57.18% (P < 0.01) and the suppression was siRNA-dose dependent (r = 0.976). Infection of mice with siRNA 534 transfected ML produced a 57.16% reduction of enteral adult burden and 71.46% reduction of muscle larva burden (P < 0.05). Moreover, silencing of TsSP1.2 gene in ML resulted in worm development impediment and reduction of female fertility. The results showed that silencing of TsSP1.2 by RNAi inhibited larval intrusion and development, and reduced female fecundity. TsSP1.2 plays a crucial role for worm invasion and development in T. spiralis life cycle, and is a potential vaccine/drug target against Trichinella infection.

Molecular characterization of a Trichinella spiralis aspartic protease and its facilitation role in larval invasion of host intestinal epithelial cells

BACKGROUND

T. spiralis aspartic protease has been identified in excretion/secretion (ES) proteins, but its roles in larval invasion are unclear. The aim of this study was to characterize T. spiralis aspartic protease-2 (TsASP2) and assess its roles in T. spiralis invasion into intestinal epithelial cells (IECs) using RNAi.

METHODOLOGY/PRINCIPAL FINDINGS

Recombinant TsASP2 (rTsASP2) was expressed and purified. The native TsASP2 of 43 kDa was recognized by anti-rTsASP2 serum in all worm stages except newborn larvae (NBL), and qPCR indicated that TsASP2 transcription was highest at the stage of intestinal infective larvae (IIL). IFA results confirmed that TsASP2 was located in the hindgut, midgut and muscle cells of muscle larvae (ML) and IIL and intrauterine embryos of the female adult worm (AW), but not in NBL. rTsASP2 cleaved several host proteins (human hemoglobin (Hb), mouse Hb, collagen and IgM). The proteolytic activity of rTsASP2 was host-specific, as it hydrolyzed mouse Hb more efficiently than human Hb. The enzymatic activity of rTsASP2 was significantly inhibited by pepstatin A. The expression levels of TsASP2 mRNA and protein were significantly suppressed by RNAi with 5 μM TsASP2-specific siRNA. Native aspartic protease activity in ML crude proteins was reduced to 54.82% after transfection with siRNA. Larval invasion of IECs was promoted by rTsASP2 and inhibited by anti-rTsASP2 serum and siRNA. Furthermore, cell monolayer damage due to larval invasion was obviously alleviated when siRNA-treated larvae were used. The adult worm burden, length of adult worms and female fecundity were clearly reduced in mice challenged using siRNA-treated ML relative to the PBS group.

CONCLUSIONS

rTsASP2 possesses the enzymatic activity of native aspartic protease and facilitates T. spiralis invasion of host IECs.

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.

Primary assessment of a T. spiralis putative serine protease for early serological detection of experimental trichinellosis

A putative serine protease of T. spiralis (TsSP) was expressed in Escherichia coli and its potential as a diagnostic antigen was primarily assessed in this study. Anti-Trichinella IgG in serum samples from T. spiralis different animal hosts (mice, rats, pigs and rabbits) were detected on Western blot analysis with rTsSP. Anti-Trichinella antibodies were detected in 100% (30/30) of experimentally infected mice by rTsSP-ELISA. Cross-reactions of rTsSPELISA were not found with sera from mice infected with other parasites (S. erinaceieuropaei, S. japonicum, C. sinensis, A. cantonensis and T. gondii) and sera from normal mice. There was no statistical difference in antibody detection rate among mice infected with the encapsulated Trichinella species (T. spiralis, T. nativa, T. britovi, and T. nelsoni) (P>0.05). The results of rTsSP-ELISA showed that serum specific antibody IgG in mice infected with 100 or 500 T. spiralis muscle larvae (ML) were detectable early at 7-8 dpi, but not detected by ML ES antigen-ELISA prior to 10-12 dpi. Specific anti-Trichinella IgG was detected in 100% (18/18) of infected pigs by rTsSP-ELISA and ES-ELISA, but no specific antibodies was not detected in 20 conventionally raised normal pigs by two antigens. The results showed the rTsSP had the potential for early serodiagnosis of animal Trichinella infection, however it requires to be assayed with early infection sera of swine infected with Trichinella and other parasites.

Molecular cloning of enolase from Trichinella spiralis and the protective immunity in mice

Trichinella spiralis, the main pathogen of trichinosis, infects a wide range of mammalian hosts and is one of the most widespread parasites worldwide. For parasites, glycolysis is the most important way to generate energy. Previous studies showed that some enzymes involved in the glycolytic pathway play roles in regulation the host immunity. In this paper, enolase from T. spiralis was cloned and the protective potentials were studied. One hundred and sixty ICR mice were divided into four groups and vaccinated with recombinant enolase (pET-ENO), eukaryotic recombinant plasmid encoding enolase (pVAX1-ENO) and negative controls (pVAXl and PBS), respectively. Two weeks after the second immunization, each mouse was challenged orally with 200 muscle larvae (MLs) of T. spiralis. Results showed that mice vaccinated with pET-ENO and pVAX1-ENO induced specific antibodies of IgG, IgA, IgM, but no IgE. Subclasses of IgG antibodies showed that mice immunized with recombinant protein and recombinant plasmids induced a Th1/Th2 immune response. Concentrations of serum cytokines were detected and showed significant increase of IFN-γ, IL-4 and TGFβ1, while IL-17 in each group was not significantly different. Flow cytometric analysis showed significant increase of CD4+ and CD8+ T lymphocytes in the groups immunized with recombinant protein and recombinant plasmids. Challenge infection demonstrated that immunized groups had a reduced number of worm burdens. The reductions of larvae per gram muscle (LPG) in pET-ENO and pVAX1-ENO group were 17.7% and 15.8% when compared with PBS control.

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.

Characterization of a putative glutathione S-transferase of the parasitic nematode Trichinella spiralis

The aim of this study was to identify the biological characteristics and functions of a putative Trichinella spiralis glutathione S-transferase (TspGST). The results of real-time PCR and immunofluorescent test (IFT) showed that the TspGST gene was expressed at all of T. spiralis different developmental stages (muscle larvae, intestinal infective larvae, adult worms and newborn larvae). When anti-rTspGST serum, mouse infection serum, and pre-immune serum were added to the medium, the inhibition rate of the larvae penetrated into the intestinal epithelial cells (IECs) was 25.72%, 49.55%, and 4.51%, respectively (P < 0.01). The inhibition of anti-rTspGST serum on larval invasion of IECs was dose-dependent (P < 0.05). Anti-rTspGST antibodies killed T. spiralis newborn larvae by an ADCC-mediated mechanism. Our results showed that the TspGST seemed to be an indispensable protein for T. spiralis invasion, growth and survival in host.

[Nuclease activity of the recombinant plancitoxin-1-like proteins with mutations in the active site from Trichinella spiralis]

Although there are 125 predicted DNase Ⅱ-like family genes in the Trichinella spiralis genome, plancitoxin-1-like (Ts-Pt) contains the HKD motif, a typical conserved region of DNase Ⅱ, in N- and C-terminal. It is generally believed that histidine is the active site in DNase Ⅱ. To study the nuclease activity of recombinant Ts-Pt with mutations in the active site from T. spiralis, different fragments of the mutated Ts-Pt genes were cloned using overlap PCR technique and inserted into the expressing vector pET-28a(+), and transformed into Escherichia coli Rosseta (DE3). The fusion proteins were purified by Ni-NTA affinity chromatography and SDS-PAGE. Nuclease activity of the recombinant proteins was detected by agarose gel electrophoresis and nuclease-zymography. The recombinant plasmids harboring the mutated Ts-Pt genes were constructed and expressed as inclusive body in a prokaryotic expression system. After renaturation in vitro, the recombinant proteins had no nuclease activity according to agarose gel electrophoresis. However, the expressed proteins as inclusive body displayed the ability to degrade DNA after renaturation in gel. And the nuclease activity was not affected after subjected to mutation of active site in N- and C-termini of Ts-Pt. These results provide the basis to study the relationship between DNase Ⅱ-like protein family and infection of T. spiralis.

DsRNA-mediated silencing of Nudix hydrolase in Trichinella spiralis inhibits the larval invasion and survival in mice

The aim of this study was to investigate the functions of Trichinella spiralis Nudix hydrolase (TsNd) during the larval invasion of intestinal epithelial cells (IECs), development and survival in host by RNAi. The TsNd-specific double-stranded RNA (dsRNA) was designed to silence the expression of TsNd in T. spiralis larvae. DsRNA were delivered to the larvae by soaking incubation or electroporation. Silencing effect of TsNd transcription and expression was determined by real-time PCR and Western blotting, respectively. The infectivity of larvae treated with dsRNA was investigated by the in vitro larval invasion of IECs and experimental infection in mice. After being soaked with 40 ng/μl of dsRNA-TsNd, the transcription and expression level of TsNd gene was inhibited 65.8% and 56.4%, respectively. After being electroporated with 40 ng/μl of dsRNA-TsNd, the transcription and expression level of TsNd gene was inhibited 74.2% and 58.2%, respectively. Silencing TsNd expression by both soaking and electroporation inhibited significantly the larval invasion of IECs in a dose-dependent manner (r1 = -0.96798, r2 = -0.98707). Compared with the mice inoculated with untreated larvae, mice inoculated with larvae soaked with TsNd dsRNA displayed a 49.9% reduction in adult worms and 39.9% reduction in muscle larvae, while mice inoculated with larvae electroporated with TsNd dsRNA displayed a 83.4% reduction in adult worms and 69.5% reduction in muscle larvae, indicating that electroporation has a higher efficiency than soaking in inhibiting the larval development and survival in mice. Our results showed that silencing TsNd expression in T. spiralis inhibited significantly the larval invasion and survival in host.

The siRNA-mediated silencing of Trichinella spiralis nudix hydrolase results in reduction of larval infectivity

Previous studies showed that Trichinella spiralis Nudix hydrolase (TsNd) bound to intestinal epithelial cells (IECs), and vaccination of mice with rTsNd or TsNd DNA produced a partial protective immunity against T. spiralis infection. In this study, three TsNd specific small interfering RNA (siRNA) were designed to silence the expression of TsNd in T. spiralis larvae. SiRNAs were delivered to the larvae by electroporation. Silencing effect of TsNd transcription and expression was determined by real-time PCR and Western blotting, respectively. The infectivity of the larvae treated with siRNA was investigated by the in vitro larval invasion of IECs and experimental infection in mice. The results showed that siRNAs were efficiently delivered into T. spiralis larvae through electroporation. Real-time PCR and Western blotting showed that transcription and expression level of TsNd gene was inhibited 73.3 and 76.7 %, respectively, after being electroporated with 2 μM of siRNA-275 for 1 day. Silencing TsNd expression inhibited significantly the larval invasion of IECs (P < 0.01) and was in a dose-dependent manner (r = -0.97941). The mice with infected larvae treated with TsNd siRNA displayed a 63.6 % reduction in intestinal adult worms and 68.8 % reduction in muscle larval burden compared with mice infected with control siRNA-treated larvae. Our results showed that silencing TsNd expression in T. spiralis significantly reduced the larval infectivity and survival in host.

Oral vaccination of mice with Trichinella spiralis nudix hydrolase DNA vaccine delivered by attenuated Salmonella elicited protective immunity

We have previously reported that Trichinella spiralis Nudix hydrolase (TsNd) bound to intestinal epithelial cells (IECs), and the vaccination of mice with recombinant TsNd protein (rTsNd) produced a partial protective immunity against challenge infection in mice. In this study, the full-length cDNA sequence of TsNd gene was cloned into the eukaryotic expression plasmid pcDNA3.1, and the recombinant TsNd DNA was transformed into attenuated Salmonella typhimurium strain ⊿cyaSL1344. Oral immunization of mice with TsNd/S. typhimurium elicited a significant local mucosal IgA response and a systemic Th1/Th2 immune response. Cytokine profiling also showed a significant increase in the Th1 (IFN-γ, IL-2) and Th2 (IL-4, 10) responses in splenocytes of immunized mice upon stimulation with the rTsNd. The oral immunization of mice with TsNd/S. typhimurium displayed a statistically significant 73.32% reduction in adult worm burden and a 49.5% reduction in muscle larvae after challenge with T. spiralis muscle larvae, compared with PBS control group. Our results demonstrated that TsNd DNA delivered by attenuated live S. typhimurium elicited a local IgA response and a mixed Th1/Th2 immune response, and produced a partial protection against T. spiralis infection in mice.

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.

Characterisation of a plancitoxin-1-like DNase II gene in Trichinella spiralis

Background

Deoxyribonuclease II (DNase II) is a well-known acidic endonuclease that catalyses the degradation of DNA into oligonucleotides. Only one or a few genes encoding DNase II have been observed in the genomes of many species. 125 DNase II-like protein family genes were predicted in the Trichinella spiralis (T. spiralis) genome; however, none have been confirmed. DNase II is a monomeric nuclease that contains two copies of a variant HKD motif in the N- and C-termini. Of these 125 genes, only plancitoxin-1 (1095 bp, GenBank accession no. XM_003370715.1) contains the HKD motif in its C-terminus domain.

Methodology/Principal Findings

In this study, we cloned and characterised the plancitoxin-1 gene. However, the sequences of plancitoxin-1 cloned from T. spiralis were shorter than the predicted sequences in GenBank. Intriguingly, there were two HKD motifs in the N- and C-termini in the cloned sequences. Therefore, the gene with shorter sequences was named after plancitoxin-1-like (Ts-Pt, 885 bp) and has been deposited in GenBank under accession number KF984291. The recombinant protein (rTs-Pt) was expressed in a prokaryotic expression system and purified by nickel affinity chromatography. Western blot analysis showed that rTs-Pt was recognised by serum from T. spiralis-infected mice; the anti-rTs-Pt serum recognised crude antigens but not ES antigens. The Ts-Pt gene was examined at all T. spiralis developmental stages by real-time quantitative PCR. Immunolocalisation analysis showed that Ts-Pt was distributed throughout newborn larvae (NBL), the tegument of adults (Ad) and muscle larvae (ML). As demonstrated by DNase zymography, the expressed proteins displayed cation-independent DNase activity. rTs-Pt had a narrow optimum pH range in slightly acidic conditions (pH 4 and pH 5), and its optimum temperature was 25°C, 30°C, and 37°C.

Conclusions

This study indicated that Ts-Pt was classified as a somatic protein in different T. spiralis developmental stages, and demonstrated for the first time that an expressed DNase II protein from T. spiralis had nuclease activity.

Deoxyribonuclease II (DNase II) is classified into a unique family of nucleases and mediates the degradation of DNA associated with apoptosis. Although DNase II activity was first observed in 1947, and has been studied biochemically and enzymatically since the 1960s, only recently has genetic information on the enzyme been reported. Compared with enzymes from other species, including C. elegans, the DNase II-like protein family of the parasitic nematode T. spiralis has expanded remarkably, with an estimated 125 genes found in the draft genome of T. spiralis. However, none of these proteins have been confirmed by biochemical studies. This study describes Ts-Pt, a DNase II protein that is expressed in different T. spiralis developmental stages. The recombinant protein purified via a prokaryotic expression system displayed in vitro nuclease activity, as determined by DNase zymography. The exact function and mechanisms of Ts-Pt should be further explored in vivo.

Molecular characterization of 45 kDa aspartic protease of Trichinella spiralis

In a previous study, we identified an aspartic protease gene (Ts-Asp) from the Trichinella spiralis muscle stage larva cDNA library. The gene sequence of Ts-Asp was 1281 bp long and was found to encode a protein consisting of 405 amino acids, with a molecular mass of 45.248 kD and a pI of 5.95. The deduced Ts-Asp has a conserved catalytic motif with catalytic aspartic acid residues in the active site, a common characteristic of aspartic proteases. In addition, the deduced amino acid sequence of Ts-Asp was found to possess significant homology (above 50%) with aspartic proteases from nematode parasites. Results of phylogenetic analysis indicated a close relationship of Ts-Asp with cathepsin D aspartic proteases. For production of recombinant Ts-Asp (rTs-Asp), the pGEX4T expression system was used. Like other proteases, the purified rTs-Asp was able to digest collagen matrix in vitro. Abundant expression of Ts-Asp was observed in muscle stage larva. Ts-Asp was detected in ES proteins, and was able to elicit the production of specific antibodies. It is the first report of molecular characterization of aspartic protease isolated from T. spiralis.

[Effect in vitro of albendazole on the kinetics of cytosolic glutathione transferase from the rat liver]

INTRODUCTION

Since the idea of multifunctional mode of action of anthelmintics is considered and in experimental trichinellosis in vivo albendazole seems to act as an allosteric activator of cytosolic GST from mice muscles, in this study a termosensitivity after in vitro incubation with albendazole of purified commercial cytosolic glutathione transferase (GST) from the rat liver was investigated.

METHODS

Two extremal temperatures: -80 degrees C and +30 degrees C were used to destroy the dimer in quaternary structure of this enzyme.

RESULTS

In control preparations both extremal temperatures destroy this structure, so the Michaelis-Menten kinetic curves of substrate saturation show the typical hyperbolic shape. After a long (15 h) freezing at -80 degrees C or heating (up to 14 h at +30 degrees C) the kinetics of substrate saturation of GST after incubation with albendazole show the sigmoidal or "double sigmoidal" shape, pointing out the quaternary GST structure as a complex of "frozen subunits". Drug inhibits about 6-times the total activity of GST after incubation at +30 degrees C. We conclude that albendazole in vitro influences the structure of cytosolic GST from the rat liver and inhibits its activity, but, in opposite to in vivo study in mouse muscles infected with Trichinella spiralis larvae, does not act as an activator of this enzyme.

Binding and repression of translation of the cognate mRNA by Trichinella spiralis thymidylate synthase differ from the corresponding interactions of the human enzyme

Thymidylate synthase (TS) of Trichinella spiralis, a parasitic nematode causing trichinellosis, was found to bind its own mRNA and repress translation of the latter, similar to its human counter-part [Chu, Koeller, Casey, Drake, Chabner, Elwood, Zinn and Allegra (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 8977-8981]. However, in striking contrast with human TS, the parasite enzyme's interaction with mRNA was not affected by any of the substrate (deoxyuridylate or N(5,10)-methylenetetrahydrofolate) nor by the inhibitor (fluorodeoxyuridylate; used alone or in the presence of N(5,10)-methylenetetrahydrofolate) similar to that shown for the bifunctional enzyme from Plasmodium falciparum [Zhang and Rathod (2002) Science 296, 545-547]. Moreover, repression of the translation of the parasite enzyme was enhanced by the same ligands that were shown by others (Chu et al., 1991) to prevent human TS from impairing its translation. On comparing the capacity of TS to bind to its cognate mRNA, relative to its ability to inhibit its translation, the same enzyme preparation was active as translational repressor at a considerably lower protein/mRNA ratio, suggesting the two phenomena to be disconnected. Of interest is the fact that the presence of the enzyme protein N-terminal methionine proved to be critical for binding, but not for repression of its translation, indicating that mRNA binding requires a methionine or an adduct (i.e. methionine-histidine) at the N-terminus of TS, but that the translational repression effect does not. Notably, chicken liver dihydrofolate reductase, which is incapable of binding to T. spiralis TS mRNA, repressed the translation of TS.

Characterisation of a secreted N-acetyl-β-hexosaminidase from Trichinella spiralis

A thorough investigation was conducted for glycoside hydrolase activities in the secreted proteins of Trichinella spiralis. The data demonstrated that the only secreted glycosidase with significant activity was an exo-beta-hexosaminidase with catalysis of the substrates N-acetyl-beta-D-glucosamine, N-acetyl-beta-D-galactosamine and N-acetyl-beta-D-glucosamine-6-sulphate proceeding with an efficiency similar to the human isozyme beta-hexosaminidase A (Hex A). The hydrolysis of N-acetyl-beta-D-glucosamine followed Michaelis-Menten kinetics with a K(m) of 0.187+/-0.025 mM, and catalysis was inhibited competitively by both N-acetyl-beta-d-glucosamine and N-acetyl-beta-D-galactosamine, with K(i) values of 15.75+/-0.99 and 1.17+/-0.24 mM, respectively. The enzyme was maximally active at pH 4.4, had a temperature optimum at 54 degrees C and was thermolabile. We observed no cleavage of N-acetylglucosamine beta1-4 linkages in N-acetylchitooligosaccharides, but significant hydrolysis of N-acetylglucosamine beta1-2 linked to mannose in glycans was detected indicating that the secreted enzyme is linkage specific. The enzyme was partially purified and identified by SDS-PAGE and Western blotting as a protein with an apparent molecular mass of 50 kDa. We established that the protein was glycosylated and showed that the glycan was decorated with tyvelose (3,6-dideoxy-D-arabino-hexose). Matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) analysis demonstrated that the carbohydrate moeity was a tyvelose capped tetra-antennary N-glycan corresponding to the structure Tyv(4)Fuc(5)HexNAc(10)Hex(3). All our studies suggest that this is a novel variant of a secreted N-acetyl-beta-hexosaminidase.

Cloning and analysis of a cDNA encoding a putative serine protease comprising two trypsin-like domains of Trichinella spiralis

The cDNA encoding a putative serine protease, TsSerP, was cloned by degenerative polymerase chain reaction and screening of the cDNA library from Trichinella spiralis adult-newborn larvae stage. Sequence analysis revealed the presence of two trypsin-like serine protease domains flanking a hydrophilic domain, with the catalytic triad residue histidine in the alpha domain substituted by an arginine residue. Southern blots indicated that this was a single copy gene in the parasite genome. Northern blots demonstrated a single 2.3-kb transcript during the muscle larvae and adult stages of T. spiralis. The recombinant protein from the TsSerP beta domain (betaSerP) was produced but not recognised by T. spiralis-infected swine serum. An anti-betaSerP polyclonal serum detected a 69-kDa polypeptide in the soluble antigens of T. spiralis muscle larvae. Immunolocalisation analysis located TsSerP on the inner layer of the cuticle and oesophagus of the parasite, suggesting a potential role in its moulting and/or digestive functions.

Parasite nucleotide-metabolizing enzymes and host purinergic signalling

Tissue damage results in a variety of molecular signals that activate elements of the immune system. Recent years have seen a growing awareness that key regulators of these events are extracellular nucleotides that signal through purinergic receptors. Haematophagous insects and ticks secrete enzymes in their saliva that degrade nucleotides, thus inhibiting haemostasis and minimizing the ensuing pain and inflammatory reactions provoked by these mediators. The discovery of an enzymatic cascade of nucleotide-metabolizing enzymes in secreted products of Trichinella spiralis suggests that endoparasites use similar mechanisms to modulate host purinergic signalling.

Molecular cloning and functional expression of enolase from Trichinella spiralis

The cDNA library was constructed from muscle larvae of Trichinella spiralis, and immunoscreened with sera from mice infected with T. spiralis. A cDNA clone, designated as TsENO, encoded 2-phospho-D-glycerate hydro-lyase (enolase) that catalyzed a reversible conversion of 2-phospho-D-glyceric acid (2PGA) to phosphoenolpyruvate (PEP) in the glycolytic pathway. The recombinant TsENO protein was produced in an Escherichia coli expression system. The recombinant full-length TsENO protein had no activity in the conversion of 2PGA to PEP, but gained enolase activity after cutting off the signal peptide from the full-length protein. There was no meaningful difference in the expression level of TsENO gene at three distinct stages of T. spiralis. Also, antibody against the recombinant TsENO protein reacted with crude extract of muscle larvae, but not with the excretory and secretory products.

A nucleotidase with unique catalytic properties is secreted by Trichinella spiralis

We have isolated and expressed a cDNA from the parasitic nematode Trichinella spiralis encoding a novel secreted nucleotidase which catalyses the hydrolysis of nucleoside 5'-diphosphates and 5'-monophosphates, but not 5'-triphosphates. The full length cDNA encodes a protein of 550 amino acids with an N-terminal signal peptide, but lacking a C-terminal signature sequence for addition of a glycosyl phosphatidylinositol (GPI) anchor. Expression in Pichia pastoris resulted in the secretion of an active enzyme with the catalytic properties of both a Mg2+-dependent diphosphohydrolase/apyrase and a 5'-nucleotidase. The protein sequence is homologous to 5'-nucleotidases from a wide variety of organisms but contains no sequences specifically conserved in apyrases, suggesting that it is a representative of a new class of secreted nucleotidase. The enzyme was essentially monospecific for AMP among the nucleoside 5'-monophosphates and catalysed the hydrolysis of nucleoside 5'-diphosphates in the order of UDP >> ADP. The diphosphatase activity was dependent on the presence of magnesium ions and a reducing agent, while the 5'-nucleotidase activity was enhanced by these additions. Kinetic analyses indicated that the enzyme exhibits allosteric behaviour. Determination of the number of active sites suggested that catalysis of the two different reactions occurs at the same active site. The data are discussed in terms of regulation of host purinergic signalling during infection.

Trichinella spiralis thymidylate synthase: cDNA cloning and sequencing, and developmental pattern of mRNA expression

The persistent expression of thymidylate synthase activity has previously been demonstrated not only in adult forms, but also in non-developing muscle larvae of Trichinella spiralis and T. pseudospiralis, pointing to an unusual pattern of cell cycle regulation, and prompting further studies on the developmental pattern of T. spiralis thymidylate synthase gene expression. The enzyme cDNA was cloned and sequenced, allowing the characterization of a single open reading frame of 307 amino acids coding for a putative protein of 35,582 Da molecular weight. The amino acid sequence of the parasite enzyme was analysed, the consensus phylogenetic tree built and its stability assessed. The aa sequence identity with thymidylate synthase was confirmed by the enzymatic activity of the recombinant protein expressed in E. coli. As compared with the enzyme purified from muscle larvae, it showed apparently similar Vmax value, but higher Km(app) values desscribing interactions with dUMP (28.8 microM vs. 3.9 microM) and (6RS,alphaS)-N(5,10)-methylenetetrahydrofolate (383 microM vs. 54.7 microM). With the coding region used as a probe, thymidylate synthase mRNA levels, relative to 18S rRNA, were found to be similar in muscle larvae, adult forms and newborn larvae, in agreement with muscle larvae cells being arrested in the cell cycle.

Characterization and cloning of metallo-proteinase in the excretory/secretory products of the infective-stage larva of Trichinella spiralis

Inhibitor sensitivity assays using azocaesin and FTC-caesin as substrates showed that the excretory/secretory (E/S) products of the infective-stage larvae of Trichinella spiralis contained serine, metallo-, cysteine and aspartic proteinases. The activity of the metallo-proteinase was zinc ion dependent (within a range of ZnSO(4) concentrations). Gelatin-substrate gel electrophoresis revealed two bands of molecular mass 48 and 58 kDa which were sensitive to the metallo-proteinase inhibitor EDTA. The former peptide was probably a cleavage product of the latter. The authenticity of the 58 kDa metallo-proteinase as an E/S product was confirmed by immunoprecipitation. Using PCR and RACE reactions, a complete nucleotide sequence of the metallo-proteinase gene was obtained. It comprised 2,223 bp with an open reading frame encoding 604 amino acid residues. The 3' untranslated region consisted of 352 bp, including a polyadenylation signal AATAA. A consensus catalytic zinc-binding motif was present. The conserved domains suggest that the cloned metallo-proteinase belongs to the astacin family and occurs as a single copy gene with 11 introns and 10 exons. Cluster analysis showed that the sequence of the metallo-proteinase gene of T. spiralis resembles those of Caenorhabdites elegans and Strongyloides stercoralis.

A family history of deoxyribonuclease II: surprises from Trichinella spiralis and Burkholderia pseudomallei

Deoxyribonuclease IIalpha (DNase IIalpha) is an acidic endonuclease found in lysosomes and nuclei, and it is also secreted. Though its Caenorhabditis elegans homolog, NUC-1, is required for digesting DNA of apoptotic cell corpses and dietary DNA, it is not required for viability. However, DNase IIalpha is required in mice for correct development and viability, because undigested cell corpses lead to lesions throughout the body. Recently, we showed that, in contrast to previous reports, active DNase IIalpha consists of one contiguous polypeptide. To better analyze DNase II protein structure and determine residues important for activity, extensive database searches were conducted to find distantly related family members. We report 29 new partial or complete homologs from 21 species. Four homologs with differences at the purported active site histidine residue were detected in the parasitic nematodes Trichinella spiralis and Trichinella pseudospiralis. When these mutations were reconstructed in human DNase IIalpha, the expressed proteins were inactive. DNase II homologs were also identified in non-metazoan species. In particular, the slime-mold Dictyostelium, the protozoan Trichomonas vaginalis, and the bacterium Burkholderia pseudomallei all contain sequences with significant similarity and identity to previously cloned DNase II family members. We report an analysis of their sequences and implications for DNase II protein structure and evolution.

Molecular cloning and characterization of a serine proteinase gene of Trichinella spiralis

A serine proteinase gene was isolated from a cDNA library of Trichinella spiralis muscle larvae at 30 days post-infection (PI). The library was immunoscreened with T. spiralis-infected sera. A clone, designated Ts23-2, contained a cDNA transcript of 1,445 bp that encoded a putative signal peptide of 27 amino acids, a proregion of 20 amino acids, and a predicted mature enzyme of 374 amino acids. The predicted molecular mass of the Ts23-2 mature protein was 42.3 kDa. The enzyme comprised 2 regions, a catalytic domain of 234 residues and a C-terminal domain. The closest homologues of the Ts23-2 mature protein were serine proteinases from a wide range of organisms. The catalytic domain of the Ts23-2 clone was expressed as a proform in Escherichia coli. The recombinant protein cleaved serine proteinase-specific synthetic peptide substrates, and class-specific inhibitors of serine proteinases inhibited the enzymatic activity. Antibody against the Ts23-2 recombinant protein stained proteins migrating at about 51 and 33 kDa in crude extracts from 30-day PI muscle larvae and 18-day PI muscle larvae, but it failed to stain any proteins in crude extracts from newborn larvae and adult worms or in excretory-secretory products from 30-day PI muscle larvae. Production of the mRNA transcript for the Ts23-2 gene was mainly restricted to the 30-day PI muscle larvae, suggesting stage-specific expression. Intense staining with the anti-Ts23-2 serum was found within the parasites at the muscle stage of 30 days PI.

Nucleotidase cascades are catalyzed by secreted proteins of the parasitic nematode Trichinella spiralis

Extracellular nucleotides are signaling molecules whose receptor-mediated effects are involved in a variety of physiological responses in mammalian tissues. An overwhelming body of data indicate that inflammatory and other immune responses can be modulated by the availability and local concentrations of nucleotides via nucleotide receptor signaling, but this is only just beginning to be investigated in the context of infectious disease. Evidence is provided here that the parasitic nematode Trichinella spiralis can catalyze the conversion and thus modulate both the availability and concentration of extracellular nucleotides by means of the following secreted exoenzymes: apyrase, 5'-nucleotidase, and adenosine deaminase. These enzymes were characterized in terms of substrate specificity, kinetic behavior, pH, divalent cation preferences, and response to a series of compounds. The secreted 5'-nucleotidase was identified as a protein with an apparent molecular mass of 67 kDa after N-terminal amino acid sequencing of the purified protein. The presence of adenosine deaminase was confirmed in the secreted products by Western blotting with an antibody against a mammalian enzyme, as a protein with an apparent molecular mass of 38 kDa. These secreted proteins constitute an enzymatic cascade which catalyzes the degradation of extracellular nucleotides, with a potential physiological role in the regulation of purinergic signaling.

A putative serine protease among the excretory-secretory glycoproteins of L1 Trichinella spiralis

Trichinella spiralis first-stage larvae infect susceptible hosts by invading epithelial cells that line the small intestine. During this process the larva disgorges several glycoproteins that bear an unusual, highly antigenic sugar moiety, tyvelose (3,6-dideoxy arabinohexose). Monoclonal antibodies specific for tyvelose protect the intestine against infection, implicating tyvelose-bearing glycoproteins as mediators of invasion and niche establishment in the intestinal epithelium. In order to investigate these glycoproteins at the molecular level, we first prepared monoclonal anti-peptide antibodies. The antibodies bind a family of glycoproteins that are present in excretory-secretory products of first-stage larvae and are delivered to epithelial cells during invasion by T. spiralis. The major species present in an affinity purified fraction of crude T. spiralis antigens were subjected to tryptic peptide digestion. De novo amino acid sequencing of the peptides using Q-TOF tandem mass spectrometry, in combination with database searches and antibody screening of an L1 cDNA library, showed that the glycoproteins are variably glycosylated homologues of the serine protease family.

Comparison of cholinesterase activities in the excretion-secretion products of Trichinella pseudospiralis and Trichinella spiralis muscle larvae

The presence of cholinesterases (ChE) is reported in T. pseudospiralis excretion-secretion products (ESP) by spectrophotometric method, using acetylthiocholine (ATCI) and butyrilthiocholine (BTCI) as substrates. By inhibition assays, we found that T. pseudospiralis release both acetyl- and butiryl-cholinesterases (AchE and BchE, respectively). The sedimentation coefficientes of these enzymes were determined by sucrose density gradient. We studied the in vivo ChE secretion by immunoblot assays using AchE from Electrophorus (electric eel) and sera from normal or infected mice with T. pseudospiralis or T. spiralis. The presence of anti-AchE antibodies was only demonstrated in the sera from T. pseudospiralis infected mice. Moreover the in vivo secretion was corroborated by the high difference determinate between the ChE activity of the immuno complexes from T. pseudospiralis infected sera and the immunocomplexes from T. spiralis infected sera as well as normal sera. Finally, we analyzed the effect of the organophosphate Neguvón (metrifonate) on the ChE activity from the T. pseudospiralis ESP. The drug inhibits in part this activity. Moreover Neguvón (metrifonate) showed a high activity against the T. pseudospiralis viability.

Secreted variant of nucleoside diphosphate kinase from the intracellular parasitic nematode Trichinella spiralis

The molecular components involved in the survival of the parasitic nematode Trichinella spiralis in an intracellular environment are poorly characterized. Here we demonstrate that infective larvae secrete a nucleoside diphosphate kinase when maintained in vitro. The secreted enzyme forms a phosphohistidine intermediate and shows broad specificity in that it readily accepts gamma-phosphate from both ATP and GTP and donates it to all nucleoside and deoxynucleoside diphosphate acceptors tested. The enzyme was partially purified from culture medium by ATP affinity chromatography and identified as a 17-kDa protein by autophosphorylation and reactivity with an antibody to a plant-derived homologue. Secreted nucleoside diphosphate kinases have previously been identified only in prokaryotic organisms, all of them bacterial pathogens. The identification of a secreted variant of this enzyme from a multicellular eukaryote is very unusual and is suggestive of a role in modulating host cell function.

Estimating the genetic divergence and identification of three Trichinella species by isoenzyme analysis

Isoenzyme-based approach was applied to compare Trichinella spiralis, T. britovi and T. pseudospiralis species. Among 13 enzyme systems examined, esterase (EST), malic enzyme (ME) and phosphoglucomutase (PGM) have been found as fully diagnostic, with no common allele in species studied. Adenosine deaminase (ADA), adenylate kinase (AK), hexokinase (HK), peptidase leucyl-alanine (PEP-C) and fructose-bis-phosphatase (FBP) have been capable of distinguishing the two species from resulting profiles. In addition, ADA, AK and PGM displayed the enzyme expression in the lowest amounts of muscle larvae in systems tested (100 larvae/100 microliters of extracts). Based on allozyme data, T. pseudospiralis has been found as the most distinct species within the group of taxa. Only a subtle genetic variability was recorded for T. pseudospiralis in which solely phosphoglucomutase exhibited variant patterns. In addition to the study of reference isolates, T. spiralis from lowland fox in Eastern Slovakia has been evidenced by use of genetic markers. This finding has proved that T. britovi is not the exclusive species parasitizing in the sylvatic ecosystem of the Slovak region.

Proteolytic enzymes secreted by larval stage of the parasitic nematode Trichinella spiralis

Excretory/secretory products (ES), collected from in vitro cultures of muscle larvae (L1) of Trichinella spiralis (Owen, 1835) were examined for the presence of proteolytic enzymes. Several discrete proteinases in the size range of 25-55 kDa were identified by substrate gel electrophoresis and were characterised according to pH optima, substrate specificity and inhibitor sensitivity using azocasein assay. Serine, cysteine and metalloproteinases active at pH 5-7 were identified. The serine proteinases were found to predominate and some of them were found to be specific for the larval stage of the parasite. The results from the substrate analysis indicated the presence of collagenolytic and elastolytic activities. The proteinase activity was inhibited by IgG isolated from T. spiralis-infected mice, an observation of relevance to understanding host/parasite interactions and, ultimately, the development of anti-Trichinella vaccine.

A reversible protein phosphorylation system is present at the surface of infective larvae of the parasitic nematode Trichinella spiralis

Trichinella spiralis infective larvae have externally oriented enzymes catalysing reversible protein phosphorylation on their surface. Incubation of larvae with exogenous ATP resulted in phosphorylation of surface bound and released proteins. Exposure of the parasites to bile, a treatment which renders them infective for intestinal epithelia, resulted in increased release of protein and an altered profile of phosphorylation. Both serine/threonine and tyrosine phosphorylation and dephosphorylation reactions took place at the parasite surface. Examination of the structural characteristics of the larvae following exposure to bile showed that the non-bilayer surface coat was not shed but was structurally reorganised.

A study of proteases throughout the life cycle of Trichinella spiralis

In the present report we study the proteolytic activity of the excretion-secretion and crude extracts of different stages of Trichinella spiralis (Owen, 1835) Railliet, 1895, (muscle-stage larvae, adult worms before and after mating, and newborn larvae) using natural substrates (structural and hematic mammalian proteins). The analysis of the results allow us to set up a certain stage-specificity, as well as an important relationship between the protease patterns throughout the parasite life cycle and how the parasite may overcome both mechanical and humoral barriers within the host. Muscle-stage larvae present a great activity against structural proteins (collagen), while newborn larvae and adult worms degrade principally hematic proteins (hemoglobin, fibrinogen and immunoglobulin G).

Partial characterization of serine proteinases secreted by adult Trichinella spiralis

Serine proteinases secreted by adult Trichinella spiralis were isolated from excretory/secretory products (ES) of in-vitro-cultured parasites by affinity chromatography with p-benzamidine-celite. The purified enzymes had molecular weights of approximately 18, 40, and 50 kDa and displayed enzyme activity against a range of low-molecular-weight substrates, gelatin, and azocasein. The antigenicity of these parasite proteinases was demonstrated by the inhibition of enzymatic activity with IgG purified from infected hosts. The inactivation of major secreted proteinases of adult T. spiralis by immune antibody could presumably contribute to impairment of the survival of the parasite in sensitized hosts.

Trichinella spiralis and Trichinella pseudospiralis: developmental patterns of enzymes involved in thymidylate biosynthesis and pyrimidine salvage

Thymidylate synthase, dihydrofolate reductase and dUTPase specific activities were found to remain at a high and constant level in crude extracts from adult worms of Trichinella spiralis, as well as from muscle larvae of both Trichinella spiralis (isolated 1-24 months after infection) and Trichinella pseudospiralis (isolated 5.5-13 months after infection). The results obtained with Trichinella pseudospiralis muscle larvae isolated with the use of pepsin did not differ from those obtained when pepsin was not used. No thymidine kinase activity could be detected in muscle larvae of either species and thymidine phosphorylase could be found only in T. pseudospiralis larvae isolated without the use of pepsin. Muscle larvae of both species contained orotidylate phosphoribosyl transferase activity, pointing to a possibility of 5-fluorouracil activation. Uridine phosphorylase, another enzyme involved in 5-fluorouracil anabolism, was also present in T. pseudospiralis muscle larvae. Results of comparative studies on inhibition of purified T. spiralis and rat thymidylate synthases by substrate (4-thio-5-fluoro-dUMP, 2-thio-5-fluoro-dCMP and N4-hydroxy-dCMP) and cofactor (ZD 9331) analogues indicated only dUMP analogues to show feeble selectivity towards the parasite enzyme. A hypothesis is discussed, assuming high expression of thymidylate synthase in muscle larvae to be connected with their cells being arrested in the cell cycle.

Single-stranded endonuclease activity in the excretory--secretory products of Trichinella spiralis and Trichinella pseudospiralis

A novel acidic extracellular single-stranded endonuclease was demonstrated for the first time in the excretory-secretory (E-S) products of 2 species of Trichinella. Unlike the double-stranded endonuclease reported earlier, the single-stranded molecule is divalent cation independent and is detected in both T. spiralis and T. pseudospiralis E-S products. It hydrolysed single-stranded DNA and RNA at comparable rates. The single-stranded endonuclease was sensitive to inhibition by Zn2+ and to high concentrations of NaCl. Zymographic analysis indicated that it was encoded by at least 3 peptides of Mr approximately 50-60 kDa. The rate of hydrolysis of single-stranded targets by the E-S products was substantially higher than that of the double-stranded molecule. Due to the differences in peptide profile, divalent cation dependence, and species-specific expression, the single and double-stranded endonucleases are likely to be encoded by different proteins and may have different functions.

Characterization of endonuclease activity from excretory/secretory products of a parasitic nematode, Trichinella spiralis

Double-stranded endonuclease activity was demonstrated for the first time in the excretory/secretory (ES) products of a parasitic nematode, Trichinella spiralis, which can reorganize host muscle cells. The endonuclease introduced double-stranded breaks to the native DNA. The ES double-stranded endonuclease(s) was sequence nonspecific, with a pH optimum below 6, and required divalent cations as a cofactor. Its activity was inhibited by the Zn2+ ion. It was detected mainly in the ES products of the infective-stage larvae of T. spiralis collected at 37 degrees C and was present in much smaller amounts in samples collected at 43 degrees C and in the products of T. pseudospiralis, a nonencapsulated species. The activity of endonuclease was blocked by antibodies against ES products. Zymographic analysis showed that the endonuclease activity was associated with at least three molecular forms, designated approximately 25, 30 and 58 kDa, respectively.

Trichinella spiralis: proteinases in the larvae

Under in vitro conditions, muscle larvae of Trichinella spiralis secreted minute amounts of a cysteine proteinase into the outer environment from the stichosome. The proteinase hydrolyzed azocoll at pH 5.0 but not a number of synthetic N-blocked and N-unsubstituted proteinase substrates at this pH. The reducing compound dithioerythritol enhanced the enzyme activity, but the thiol-blocking reagent sodium-p-hydroxymercuribenzoate (0.1 mM) was without effect. Phenylmethylsulfonyl fluoride (PMSF) (2 mM) and leupeptin (100 mM) produced partial and complete inhibition, respectively, whereas soybean trypsin inhibitor, pepstatin A, and 1,10-phenanthroline were non-inhibitory. Calcium (1 mM) produced a slight decrease in the activity that was reversed by 1 mM EGTA. Although multiple proteinase activities were detected histochemically in the somatic muscles, stichosome, midgut, and genital primordium of the muscle larvae, none of these enzymes appeared to be the one secreted. Several histochemically demonstrable proteinases were also found in the cells of 48- to 72-h-old juveniles of the parasite. One was localized in the esophageal lumen and at or around the anterior esophagus of the larvae, where developing stichocytes are believed to occur. The proteinase hydrolyzed N-acetyl-L-methionine-L-naphthyl ester and was sensitive to the metal cation-complexing compound EGTA as well as to PMSF, an inhibitor of serine proteinases.

Rapid purification and characterization of L-dopachrome-methyl ester tautomerase (macrophage-migration-inhibitory factor) from Trichinella spiralis, Trichuris muris and Brugia pahangi

Macrophage-migration-inhibition factor (MIF) is an essential stimulator of mammalian T-lymphocyte-dependent adaptive immunity, hence MIF orthologues might be expressed by infectious organisms as an immunosubversive stratagem. Since MIF actively catalyses the tautomerization of the methyl ester of l-dopachrome (using dopachrome tautomerase), the occurrence of MIF orthologues in several parasitic helminths was investigated by assaying and characterizing such activity. Evidence of MIF orthologues (dopachrome tautomerase) was found in the soluble fraction of the nematodes Trichinella spiralis (stage 4 larvae) and Trichuris muris (adults), and the filarial nematode Brugia pahangi (adults). The MIF orthologues of Tr. muris (TmMIF) and B. pahangi (BpMIF) were purified to homogeneity using phenyl-agarose chromatography, that of T. spiralis (TsMIF) required a further step: cation-exchange FPLC. Retention time on reverse-phase HPLC and Mr on SDS/PAGE of the nematode MIFs were similar to those of human MIF. N-terminal sequences (19 residues) of TsMIF and TmMIF showed 47 and 36% identity, respectively, with human MIF. The N-terminal sequence of BpMIF (14 residues) was identical to that of an MIF orthologue in the genome of B. malayi (Swiss-Prot, P91850) and showed 43% identity to either human or TsMIF. TsMIF had 10-fold higher dopachrome tautomerase activity than MIF from the other sources. The enzyme activities of TsMIF, BpMIF and TmMIF were less sensitive to inhibition by haematin (I50: >15 microM, >15 microM and 2.6 microM, respectively) than that of human MIF (I50 0.2 microM). Significant dopachrome tautomerase or phenyl-agarose-purifiable MIF-like protein was not detected in the soluble fraction of the nematodes Heligmosomoides polygyrus and Nippostrongylus brasiliensis, the cestode Hymenolepis diminuta, or the trematodes Schistosoma mansoni, S. japonicum and S. haematobium, or the free-living nematode, Caenorhabditis elegans, which does contain an MIF-related gene.

Developmental activation of infective Trichinella spiralis larvae

The initiation of further development is fundamental to the infectious processes of parasitic nematodes. We have examined early developmental activation of Trichinella spiralis larvae during host invasion, with particular emphasis on the timing of events. Using a novel approach, we have observed changes in tissue-specific transcriptional activity in live larvae during the infectious process with the fluorescent nucleic acid dyes SYTO12 and acridine orange. Simultaneously, the metabolic switch from anaerobic metabolism, characteristics of the infective stage, to aerobic metabolism, as found in the enteral stages, was tracked by measuring activities of the key regulatory enzymes phosphoenolpyruvate carboxykinase and pyruvate kinase, as well as isocitrate dehydrogenase (NADP) activity, and used as a co-indicator for developmental activation. Both metabolic enzyme activities and transcription patterns were found to change in response to host death, liberation from the nurse cell, and exposure to components of the host stomach environment. The results give a clear indication that the activation processes of T. spiralis infective larvae occur at a much earlier time than previously thought, and are stimulated upon liberation of the larvae from the nurse cell inside the host stomach.

Identification of serine/threonine protein kinases secreted by Trichinella spiralis infective larvae

Serine/threonine protein kinase activity was identified in excretory/secretory (ES) products of Trichinella spiralis infective larvae, via phosphorylation of exogenous and endogenous substrates. Protein kinase activity was identified as an authentic secretory product via blockade of release into culture medium by brefeldin A. Enzyme activity was reductant-dependent, and the relative resistance to a panel of inhibitors suggested that it could not be readily assigned to any of the major documented subfamilies of serine/threonine protein kinases. There was no evidence for protein tyrosine kinase activity in ES products. The major phosphorylated proteins in this compartment resolved at 50 and 55 kDa by SDS-PAGE, and are therefore designated pp50/55. These proteins contained mainly phosphoserine, and appear to represent differentially glycosylated variants of a 35 kDa polypeptide, modified via the addition of three and four N-linked oligosaccharides, respectively. An autophosphorylation assay following separation by SDS-PAGE identified two protein kinases of 70 and 135 kDa in ES products.

Hexosaminidase in Trichinella spiralis is a single protein with alpha- and beta-subunits catalytic activities

Beta-N-acetylhexosaminidase is expressed as a single protein in Trichinella spiralis and has catalytic properties similar to the alpha- and beta-subunits of human and mouse isoenzymes A and B. It can hydrolyze the artificial substrates, 4-methylumbelliferyl-beta-D-glucosamine and 4-methylumbelliferyl-beta-D-glucosamine-6-sulphate which are respectively hydrolyzed by the beta- and alpha-subunits. The enzyme is thermostable, has a basic isoelectric point, and thus is similar to the B isoenzyme. Northern blotting experiments indicate that the enzyme is encoded by a single gene. Hexosaminidase from Trichinella spiralis shows that the substrate specificities of alpha- and beta-subunits precede the duplication of their genes.

Immunological characteristics and localization of the Trichinella spiralis glutathione S-transferase

Trichinella spiralis glutathione S-transferase (TsGST) was isolated from crude extracts of L1 larvae by glutathione-affinity chromatography. Two closely migrating polypeptides with molecular masses of 28.5 and 28 kDa were identified by electrophoresis. Three isoforms of pI 5.6, 5.8, and 6.0 were detected by isoelectric focusing. Purified TsGST showed a low transferase activity as measured with 1-chloro-2,4-dinitrobenzene; glutathione peroxidase activity was also demonstrated using cumene hydroperoxide. A rabbit antiserum against TsGST reacted by western blot with crude extracts of Trichinella britovi and Trichinella nativa but not with extracts of Trichinella pseudospiralis, Fasciola hepatica, Schistosoma bovis, Schistosoma mansoni, Dirofilaria immitis, Toxocara canis, or Anisakis sp. TsGST was detected by western blot in extracts of T. spiralis adults, but not in newborn larvae or L1 excretory-secretory products; yet, an antiserum against T. spiralis excretory-secretory products reacted with TsGST. By immunoelectron microscopy, TsGST was found in the granules of the alpha- and beta-stichocytes of L1 larvae, as well as in some granules of the stichocytes of 72-hr adults. Rabbits experimentally infected with T. spiralis developed substantial levels of anti-TsGST antibodies. Moreover, circulating TsGST was detected in serum by a sandwich-enzyme-linked immunosorbent assay, isolated from serum by glutathione-affinity chromatography, and characterized as TsGST by western blot.

Trichinella spiralis thymidylate synthase: developmental pattern, isolation, molecular properties, and inhibition by substrate and cofactor analogues

Thymidylate synthase specific activity was found to remain at a constant level in crude extracts from muscle larvae, isolated (1-15 months after infection) by pepsin-HCI digestion, as well as from adult worms of Trichinella spiralis. The enzyme was purified and its molecular (monomer mol. wt 35 kD) and kinetic (sequential mechanism with the K(m) values 3.1 and 19 microM for dUMP and N5,10-methylenetetrahydrofolate, respectively) properties determined. 5-Fluoro-dUMP was a competitive, slow-binding inhibitor of the parasite enzyme. N5,10-methylenetetrahydrofolate analogues 10-propargy1-5,8- dideazafolate (CB3717), ZD1694, BW1843U89, and AG337 were weaker inhibitors of the parasite than regenerating rat liver enzyme. Inhibition by 10-propargyl-5,8-dideazafolate was strengthened by an increasing number of glutamate residues. Thymidine kinase activity could not be detected in the muscle larvae crude extracts.