Cloning, expression and characterisation of a type II cystatin from Schistosoma japonicum, which could regulate macrophage activation.

Cystatin play an important role in parasite immune evasion. It is involved in many immune responses processes regulations such as inhibiting antigen presentation, modifying cytokines production and macrophage polarization. In recent years, more and more cystatins were used in treating some inflammatory diseases such as asthma and inflammation bowel diseases; however, cystatins from Schistosoma japonicum were rarely studied. In the present study, we have cloned a cystatin from the adult stage of Schistosoma japonicum, named as SjCystatin, and its sequence shares conserved domains with other type II family cystatins. It was further verified by enzyme inhibition assays. SjCystatin retained its inhibitory activity under a wide range of pH values and temperatures, can maintain its inhibitory activity at pH 6.5-7.5 and 37 °C, respectively. Then, we investigated the effects of SjCystatin on the lipopolysaccharide (LPS)-induced activated RAW264.7. Results showed that SjCystatin inhibit LPS-induced nitric oxide production in a dose-dependent manner. LPS-induced TNF-α and IL-6 production began to be inhibited at least 6 h after SjCystatin stimulation. SjCystatin significantly increased IL-10 production at 6 h after stimulation and its effect on IL-10 production diminished quickly. These results imply that SjCystatin can induce M2 macrophage polarization and can be expected to serve as a potential drug source for the medication of inflammatory disorders like other cystatins.

A field survey for Wolbchia and phage WO infections of Aedes albopictus in Guangzhou City, China.

Wolbachia are maternal endosymbiotic bacterium, which infect a diverse range of arthropods, ranging from 20 to 76% in nature. They are capable of inducing a wide range of reproductive abnormalities to their hosts, such as cytoplasmic incompatibility (CI), which has been proposed to be used as a tool to modify mosquitoes that are resistant to the development of pathogen, as an alternative vector control strategy. Here, we evaluated the prevalence of Wolbachia and phage WO infections in the field population of Aedes albopictus in Guangzhou City via polymerase chain reaction (PCR) assay using the Wolbachia specific Wolbachia surface protein (wsp) and phage WO orf7 gene primers. Based on the results of PCR and phylogeny analysis, we found that A. albopictus in Guangzhou City were infected with two Wolbachia strains, wAlbA and wAlbB. Phage WO, the virus-infected Wolbachia, was also detected in A. albopictus. One hundred and ten female individuals were screened via PCR, with 109 super-infected with Wolbachia and one sample single-infected with wAlbB strain. And 104 of 113 male individuals were both infected with wAlbA and wAlbB, and nine male samples were found to be infected with wAlbA strain only. The infection rates of phage WO in female and male individuals were 82.73 and 46.02%, respectively. These results showed that the natural Wolbachia and phage WO infections in A. albopictus population in Guangzhou were at a higher frequency at present, indicating that Wolbachia appear to be a better candidate nature resource for biological control insect vectors to reduce vector-borne diseases.

[Protein interaction site of Toxoplasma gondii microneme protein 6 and aldolase determined by site-directed mutagenesis].

OBJECTIVE: To identify the protein interaction site of Toxoplasma gondii microneme protein 6 (MIC6) and aldolase by using site-directed mutagenesis. METHODS: Based on Toxoplasma gondii MIC6 gene sequence (GenBank Accession No. AF110270), the specific primers were designed. Tryptophan (W)-348 of MIC6 C terminus (MIC6C) was mutated to valine (V) via site-directed mutagenesis. MIC6C W/V gene was obtained from cDNA library by PCR amplification and subcloned into pGEX-4T-1. The mutant protein GST-MIC6C W/V was expressed in E. coli, induced by 0.8 mmol/L IPTG, and purified by affinity chromatography. Glutathione sepharose beads were incubated with GST-MIC6C W/V and GST-MIC6C, respectively, and then incubated with T. gondii tachyzoites lysate, and bound proteins were eluted using sample buffer. Bound products were resolved by SDS-PAGE and Western blotting. Glutathione sepharose beads were incubated with GST-MIC6C W/V and GST-MIC6C, respectively, and then incubated with aldolase-His6. After incubation, the resin was washed and subjected to SDS-PAGE. RESULTS: The MIC6C W/N gene was obtained, and the recombinant plasmid MIC6C W/V/pGEX-4T-1 was successfully constructed. The mutant protein GST-MIC6C W/V was expressed and purified in vitro. SDS-PAGE analysis indicated that GST-MIC6C was co-precipitated with aldolase from T. gondii tachyzoites lysate or aldolase-His6, whereas GST-MIC6C W/V failed to precipitate aldolase from T. gondii tachyzoites lysate or aldolase-His6. Western blotting analysis using anti-aldolase antibody indicated that GST-MIC6C could pull-down aldolase from T. gondii tachyzoites lysate. CONCLUSION: Tryptophan (W348) was the interaction site of MIC6 and aldolase in T. gondii.

Laccase2 is required for sclerotization and pigmentation of Aedes albopictus eggshell.

Laccase (EC 1.10.3.2) is a member of multicopper oxidases that have been found in higher plants, fungus, bacterium, and insects. Two types of laccase genes have been detected in many species of insects: laccase1 and laccase2. It has been identified that laccase2 enzyme may play a key role in sclerotization and pigmentation of insect cuticle. But few attentions were given to the biological role of laccase2 in the synthesizing of similar structures, such as oothecae, eggshell, or silk cocoons. We cloned laccase2 gene from Aedes albopictus, one main mosquito vector of dengue virus in China. An upregulation of laccase2 gene was observed after a blood meal in female adult mosquitoes, suggesting that laccase2 gene may have an involvement in the development of ovary. RNA interference experiment was performed by using adult female mosquitoes. Female mosquitoes were injected with 20 ng of double-strain RNA into the thorax. Pigmentation of mosquito eggshell was blocked that these eggs never became dark. And the incomplete sclerotization of eggshell weakened the stability and flexibility of the eggs. These eggs without enough protection were deformed and died in water. These results demonstrate that laccase2 plays a critical role in the development of eggs of A. albopictus. Laccase2 may provide a novel target for mosquito control and management.

Molecular cloning, expression, and characterization of a putative activation-associated secreted protein from Angiostrongylus cantonensis.

Activation-associated secreted protein (ASP) had been found in many helminthes, which was associated with pathogenesis and stage transition. A complementary DNA (cDNA) sequence encoding a putative two-domain ASP was obtained from an Angiostrongylus cantonensis fourth-stage larvae cDNA library, which we designated as AgASP. The cDNA of AgASP contains an open reading frame encoding 424 amino acids, the first 19 residues being a putative secretion signal. The expression pattern of this protein was investigated by real-time polymerase chain reaction and Western blot. We found that this protein expressed most highly in the brain-stage larvae (Lbr) of this parasite and existed in the excretory/secretory products of this stage. Immunofluorescence showed it existed in the lumen of the Lbr. The recombinant protein can be recognized by the infection sera from mice (nonpermissive host), while it cannot be recognized by infection sera from rats (permissive host). The infiltration of neutrophils in infected nonpermissive host can be lessened by immunizing this host with this protein (immunized vs control group, 13.7 ± 10.2 vs 65.5 ± 19.2). These findings suggest that this protein plays a role in the pathogenesis of human angiostrongyliasis and is worthy of further study.

Cloning and characterization of a novel cathepsin B-like cysteine proteinase from Angiostrongylus cantonensis.

Cysteine protease plays a key role in host-parasite interactions. In this study, we identified a novel gene encoding a cathepsin B-like cysteine protease (AcCBL1) from the cDNA library of Angiostrongysus cantonensis fourth-stage larvae (L4) and characterized its biological role in the parasite. Sequence and phylogeny analysis showed that AcCBL1 is related to other cathepsin B family members with the conserved catalytic triad (Cys, His, Asn) and diagnostic occluding loop. In addition, the sequence contains a specific "hemoglobinase motif" and might have a hemoglobinase (Hb)-degrading function. The recombinant AcCBL1 (rAcCBL1) exhibited the protease activity by gelation SDS/PAGE assay; rAcCBL1 can cleave the fluorogenic substrate Z-Arg-Arg-AMC, and the optimum pH was 5.5. The enzyme can hydrolyse several host proteins including Hb and human IgG in acidic pH, but low levels of hydrolysis were observed in neutral pH. Reverse transcription polymerase chain reaction revealed that AcCBL1 expression was detected throughout various developmental stages, L3, L4, adult male and female worms. Western blotting analysis indicated that AcCBL1 was an excretory/secretory product of L4 in mature form of protease. Immunolocalization demonstrated that AcCBL1 was mainly localized in the intestine of L4. These results suggest that rAcCBL1 may play an important role in the parasite nutrition uptake.

Molecular cloning and characterization of a matrix metalloproteinase, from Caenorhabditis elegans: employed to identify homologous protein from Angiostrongylus cantonensis.

Matrix metalloproteinases (MMPs) are a class of zinc-binding endopeptidases mainly responsible for degrading extracellular matrix constituent components, which also serve as effectors of leukocyte recruitment, cytotoxicity, cytokine and chemokine processing, and defensin activation involved in multiple mechanisms of immunomodulation. MMPs are a conserved proteolytic enzyme family participating in normal physiological function. In the present study, we have cloned a gene named CEMMP62 from Caenorhabditis elegans, the putative 62-kDa protein that contained 579 residues with MMP-conserved catalytic domain known as ZnMc_MMP and showed high identities with MMPs from other nematodes, and demonstrated that the recombinant CEMMP62 (rCEMMP62) expressed and purified from Escherichia coli could have weak proteolytic activity on swine gelatin; Western blot analysis revealed that sera from BALB/c mice immunized by recombinant protein could recognize excretory-secretary antigens from Angiostrongylus cantonensis third-stage larvae (L3). Also, the antiserum can recognize larval soluble antigens of L4 coming from mice (nonpermissive host) infected with A. cantonensis while it cannot recognize larval soluble antigens of L4 coming from rats (permissive host) infected with A. cantonensis. The results implied that probably CEMMP62 has homologous proteins which exist in A. cantonensis, and the potential MMP may play an important role in A. cantonensis infection and pathogenic process.

Molecular characterization and immunolocalization of a protein disulfide isomerase from Angiostrongylus cantonensis.

Protein disulfide isomerases (PDIs), belonging to the thioredoxin superfamily, are oxidoreductases that catalyze the formation, reduction, and isomerization of disulfide bonds among cysteine residues of proteins. In this study, we report the cloning and characterization of a cDNA encoding a protein disulfide isomerase (AcPDI) from a cDNA library of fourth-stage larvae of Angiostrongylus cantonensis. The deduced amino acid sequence contains two thioredoxin domains and exhibits high identity to the homologues from other species. Quantitative real-time PCR (qRT-PCR) was performed at the third-stage larvae, fourth-stage larvae, and adult stage of A. cantonensis, and the results revealed that the AcPDI mRNA, while expressed at all three stages, is expressed at a significantly higher level in female adult worms. Results of immunohistochemical studies indicated that the AcPDI expression was specifically localized in the tegument and uterus wall of female adult worms. Biochemical analysis showed that recombinant AcPDI was biologically active in vitro and exhibited the typical biochemical functions of PDIs: oxidase/isomerase and reductase activities. Collectively, these results implied that AcPDI may be a female-enriched protein and associated with the reproductive development of A. cantonensis. In addition, considering its biochemical properties, AcPDI may be involved in the formation of the cuticle of A. cantonensis.

Phosphoantigen-activated V gamma 2V delta 2 T cells antagonize IL-2-induced CD4+CD25+Foxp3+ T regulatory cells in mycobacterial infection.

Although Foxp3(+) T regulatory cells (Tregs) are well documented for their ability to suppress various immune cells, T-cell subsets capable of counteracting Tregs have not been demonstrated. Here, we assessed phosphoantigen-activated Vgamma2Vdelta2 T cells for the ability to interplay with Tregs in the context of mycobacterial infection. A short-term IL-2 treatment regimen induced marked expansion of CD4(+)CD25(+)Foxp3(+) T cells and subsequent suppression of mycobacterium-driven increases in numbers of Vgamma2Vdelta2 T cells. Surprisingly, activation of Vgamma2Vdelta2 T cells by adding phosphoantigen Picostim to the IL-2 treatment regimen down-regulated IL-2-induced expansion of CD4(+)CD25(+)Foxp3(+) T cells. Consistently, in vitro activation of Vgamma2Vdelta2 T cells by phosphoantigen plus IL-2 down-regulated IL-2-induced expansion of CD4(+)CD25(+)Foxp3(+) T cells. Interestingly, anti-IFN-gamma-neutralizing antibody, not anti-TGF-beta or anti-IL-4, reduced the ability of activated Vgamma2Vdelta2 T cells to down-regulate Tregs, suggesting that autocrine IFN-gamma and its network contributed to Vgamma2Vdelta2 T cells' antagonizing effects. Furthermore, activation of Vgamma2Vdelta2 T cells by Picostim plus IL-2 treatment appeared to reverse Treg-driven suppression of immune responses of phosphoantigen-specific IFNgamma(+) or perforin(+) Vgamma2Vdelta2 T cells and PPD-specific IFNgamma(+)alphabeta T cells. Thus, phos-phoantigen activation of Vgamma2Vdelta2 T cells antagonizes IL-2-induced expansion of Tregs and subsequent suppression of Ag-specific antimicrobial T-cell responses in mycobacterial infection.

Specific detection of Angiostrongylus cantonensis in the snail Achatina fulica using a loop-mediated isothermal amplification (LAMP) assay.

Angiostrongylus cantonensis, a rat lungworm, can cause eosinophilic meningitis and angiostrongyliasis in humans following ingestion of contaminated foods or intermediate/paratenic hosts with infective larvae. The snail Achatina fulica is one of the important intermediate hosts of A. cantonensis and is commonly eaten by humans in some countries. In the present study, we developed a loop-mediated isothermal amplification (LAMP) method for the specific detection of A. cantonensis in Ac. fulica. Primers for LAMP were designed based on the first internal transcribed spacer (ITS-1) of nuclear ribosomal DNA (rDNA) of A. cantonensis. Specificity tests showed that only the products of A. cantonensis were detected when DNA samples of A. cantonensis and the heterologous control samples Anisakis simplex s.s, Trichuris trichiura, Toxocara canis, Trichinella spiralis and Ascaris lumbricoides were amplified by LAMP. Sensitivity evaluation indicated that the LAMP assay is 10 times more sensitive than the conventional polymerase chain reaction (PCR) assay. The established LAMP assay is rapid, inexpensive and easy to be performed. It can be used in clinical applications for rapid and sensitive detection of A. cantonensis in snails, which has implications for the effective control of angiostrongyliasis.

Epidemiological survey of Angiostrongylus cantonensis in the west-central region of Guangdong Province, China.

The study was to understand the Angiostrongylus cantonensis infectious situation of rodent definitive host, snail intermediate host, and local residents in the west-central region of Guangdong Province in China. The snails Achatina fulica and Pomacea canaliculata collected from the survey place were digested with artificial gastric juice, and the third-stage larvae of A. cantonensis in the snails were examined under microscope. The heart and lung of rats captured from the survey place were taken to check the adult of A. cantonensis. The questionnaire surveys related to the infection of A. cantonensis were taken in local residents randomly selected, and the IgG antibody against A. cantonensis was tested in those residents with enzyme-linked immunosorbent assay (ELISA). A total of 1,391 rats including eight kinds of rats, such as Rattus norvegicus, Rattus flavipectus, Bandicota indica, Rattus sladeni, Mus musculus, Rattus rattoides, Suncus Murinus, and Rattus confucianus, were examined and 132 of them were infected by A. cantonensis, with an average infection rate of 9.49% and a mean intensity of A. cantonensis in infected rats was 9.39. A total of 3,184 snails A. fulica and 3,723 snails P. canaliculata were detected. The average infection rates of them were 25.03% (797/3,184) and 6.50% (242/3,723), respectively. There were 180 positive samples of IgG antibody against A. cantonensis in 1,800 serum samples of the residents, with a positive rate of 10.00%. The west-central region of Guangdong Province is the natural focus of A. cantonensis. In comparison with the investigation results in other regions of China, the infection rate of rat definitive host is at the middle level; in the intermediate host, the infection rate of snail A. fulica is above the middle level, and the infection rate of snail Pomacea canaliculata is below the middle level. Some local residents had already been infected by A. cantonensis or at the risk of being infected.

[Protein interaction between aldolase and actin of Toxoplasma gondii by GST pull-down].

OBJECTIVE: To identify the protein-protein interaction between aldolase and actin of Toxoplasma gondii by GST pull-down. METHODS: The aldolase and actin genes were obtained from cDNA library by PCR amplification, and subcloned respectively into pGEX-4T-1 and pET30a. The fusion protein GST-Aldolase and Actin-His6 were expressed in E. coli upon induction by 1 mmol/L IPTG and then purified with affinity chromatography. Fifteen rats were immunized intradermally with 200 microg Actin-His6 protein per rat at first time to produce the polyclonal antibodies. Then 100 microg Actin-His6 protein per rat on the 2nd-4th immunizations. Rats were immunized for 4 times with 7 days interval. The serum of rats was collected from heart at the fifth day after the final immunization. Glutathione sepharose beads were incubated with GST-Aldolase protein, then incubated with Actin-His6, and bound proteins were eluted using sample buffer. Eluants were resolved by SDS-PAGE and Western blotting. RESULTS: The aldolase and actin genes were obtained, and the recombinant plasmid aldolase/pGEX-4T-1, actin/pET30a were successfully constructed. Protein GST-Aldolase and Actin-His6 were expressed and purified in vitro. Serum samples were prepared from rats immunized with protein Actin-His6, and polyclonal antibody was purified with affinity chromatography. SDS-PAGE and Western blotting analysis of products from GST pull-down experiment showed that the protein bands on NC membrane were specifically recognized by anti-Aldolase-His6 and anti-Actin-His6 antibody. CONCLUSION: Aldolase interacts with Actin of Toxoplasma gondii.

Molecular cloning and characterization of cystatin, a cysteine protease inhibitor, from Angiostrongylus cantonensis.

Cystatins are thiol proteinase inhibitors ubiquitously present in mammalian body and serve various important physiological functions. In the present study, a novel cystatin molecule (AcCystatin) was cloned from a cDNA library of Angiostrongylus cantonensis fourth-stage larvae. The putative 14-kDa protein contained 120 residues with cystatin-conserved motifs known to interact with the active site of cysteine peptidases and showed high identities with cystatins from other nematodes. RT-PCR analysis revealed that the expression pattern of AcCystatin was equal at the time points of third-stage larvae, fourth-stage larvae, and adults of the parasite life cycle. The recombinant AcCystatin (rAcCystatin) expressed and purified from Escherichia coli has been demonstrated to possess an obvious inhibitory activity against cathepsin B and could significantly upregulate nitric oxide production from IFN-gamma activated RAW 264.7 macrophages. Sera from mice (non-permissive host) infected with A. cantonensis detected rAcCystatin by Western blot, while the sera from infected rats (permissive host) could not. The results implied that AcCystatin might be an immunoregulator in A. cantonensis infection.

Molecular cloning and characterization of a cathepsin L-like cysteine protease of Angiostrongylus cantonensis.

Angiostrongylus cantonensis is a parasitic nematode dwelling in the heart and pulmonary arteries of rats, which can cause angiostrongyliasis in human by accidental infections, manifested as eosinophilic meningitis or meningoencephalitis. Cysteine proteases are the major class of endopeptidases that are expressed at a high level in A. cantonensis, which suggests it may play key roles in pathogenesis of the disease. In this study, the biological properties of the cathepsin L-like peptidase (Ac-cathL) of A. cantonensis were investigated. The Ac-cathL gene was identified from the fourth stage cDNA library of A. cantonensis, and then cloned and characterized by bioinformatics analysis and heterologous expression. The open reading frame (ORF) of Ac-cathL (1068 bp) encodes a protein of 355 amino acids with an estimated molecular weight of 58.0 kDa. Sequence analysis and multiple sequence alignment demonstrated that Ac-cathL resembles members of cathepsin L family of other parasites and mammals. Stage-dependent mRNA expression analysis showed that Ac-cathL transcripts were expressed in all stages of A. cantonensis, with the highest expression in female stage. The recombinant Ac-cathL (rAc-cathL) expressed in Escherichia coli exhibited protease activity in acidic pH as demonstrated by gelatin zymography, as well as hydrolytic activity against natural substrates, including BSA, human IgG and human fibrinogen. Immunolocalization revealed that Ac-cathL is localized in tegument of the 18 days post infection stage and uterus of the female adult stage. Therefore, these results implied that the Ac-cathL plays important roles in host tissue migration, nutrition uptake and immune evasion.

Preliminary molecular characterization of the human pathogen Angiostrongylus cantonensis.

BACKGROUND: Human angiostrongyliasis is an emerging food-borne public health problem, with the number of cases increasing worldwide, especially in mainland China. Angiostrongylus cantonensis is the causative agent of this severe disease. However, little is known about the genetics and basic biology of A. cantonensis. RESULTS: A cDNA library of A. cantonensis fourth-stage larvae was constructed, and approximately 1,200 clones were sequenced. Bioinformatic analyses revealed 378 cDNA clusters, 54.2% of which matched known genes at a cutoff expectation value of 10(-20). Of these 378 unique cDNAs, 168 contained open reading frames encoding proteins containing an average of 238 amino acids. Characterization of the functions of these encoded proteins by Gene Ontology analysis showed enrichment in proteins with binding and catalytic activity. The observed pattern of enzymes involved in protein metabolism, lipid metabolism and glycolysis may reflect the central nervous system habitat of this pathogen. Four proteins were tested for their immunogenicity using enzyme-linked immunosorbent assays and histopathological examinations. The specificity of each of the four proteins was superior to that of crude somatic and excretory/secretory antigens of larvae, although their sensitivity was relatively low. We further showed that mice immunized with recombinant cystatin, a product of one of the four cDNA candidate genes, were partially protected from A. cantonensis infection. CONCLUSION: The data presented here substantially expand the available genetic information about the human pathogen A. cantonensis, and should be a significant resource for angiostrongyliasis researchers. As such, this work serves as a starting point for molecular approaches for diagnosing and controlling human angiostrongyliasis.

MIC6 associates with aldolase in host cell invasion by Toxoplasma gondii.

The transmembrane microneme protein MIC6 and its partner MIC1, MIC4 comprise an adhesive complex that play important roles in host cell attachment by the obligate intracellular parasite Toxoplasma gondii. Successful penetration of host cells by T. gondii depends on coordinated interactions between MICs complex and the parasite's cytoskeleton. We have identified that the carboxy-terminal cytoplasmic domain (C domain) of MIC6 interacts with aldolase and the parasite cytoskeleton. Our finding uncovers new features regarding MIC6-aldolase interactions in host cell invasion by T. gondii.

[Epidemiological investigation of Angiostrongylus cantonensis in Jiangmen of Guangdong Province].

OBJECTIVE: To make an epidemiological survey on Angiostrongylus cantonensis in Jiangmen City of Guangdong Province. METHODS: From October 2006 to November 2007, the characteristics of A. cantonensis infection were investigated in Jiangmen district in various hosts, including the third stage larva infection in the snails Achatina fulica and Pomacea canaliculata by digestion method, and the adult A. cantonensis in rats by the dissection of heart and lungs. Relevant symptoms and dietary habits in Jiangmen residents who were randomly recruited were also investigated by questionnaire, and the specific IgG and IgM antibodies against A. cantonensis in their sera were detected by ELISA. RESULTS: 695 A. fulica and 720 P. canaliculata were examined. The infection rate of third stage larva of A. cantonensis were 45.0% and 1.8% respectively, with an infectivity of 53.74+/-147.30 and 5.23+/-8.51 respectively. Natural infection rate of A. cantonensis in all 229 rats was 4.4%. Among the 300 people surveyed, 11.3% had a history of eating raw or undercooked fish and shrimp, 5.3% directly or indirectly exposed to A. fulica or P. canaliculata. The positive rate of specific IgG antibody against A. cantonensis for serum samples among residents was 14.0% (42/300), and 5 serum samples in the 42 positive samples showed specific IgM antibody, with a positive rate of 1.7%. CONCLUSION: Jiangmen district is an endemic area of A. cantonensis, and the local residents are under the risk of infection.

[Pathological change in the brain of mice infected with Angiostrongylus cantonensis].

OBJECTIVE: To observe the pathological change in the brain of Angiostrongylus cantonensis-infected mouse. METHODS: Forty-eight mice were orally infected each with 40 third stage larvae of A. cantonensis, 3 mice were sacrificed at 7, 10, 13, 16, 19, 22, 25, 28 days postinfection respectively for worm recovery, and another 3 mice were for observing the histopathological change in tissue sections of the brain. RESULTS: Ten days postinfection, worms were found in the brain of the infected mice with a mean worm number of (7.0+/-1.7) per mouse. The highest number of worms was found at 16 days postinfection, with a mean of (23.7+/-4.9) per mouse. Notable symptoms of nervous system were seen on 15 days postinfection. Most mice died around 22 days postinfection. Histological examination revealed mechanical damages. Cavities and inflammation were observed in the brain parenchyma. Worms were seen in the subarachnoid space. Meningitis-like signs started at 13 days and aggravated then. CONCLUSIONS: Infection of A. cantonensis causes pathological change in mouse brain and the process is aggravating with postinfection time.

[Sequence analysis and expression of GRA7 gene of Toxoplasma gondii isolates in Escherichia coli].

OBJECTIVE: To analyze the difference of GRA7 gene of Toxoplasma gondii different isolated strains and express GRA7 in Escherichia coli. METHODS: The GRA7 gene was amplified from genomes of T. gondii isolates by PCR and was cloned into pGEX-4T-1. The recombinant plasmid was transformed into JM109 and sent to be sequenced. The sequence was analyzed with CLUSTALW (an internet tool). The recombinant plasmid was induced by IPTG to express the fusion protein,which was identified by SDS-PAGE and Western blot with positive sera. The protein was purified and used as a diagnostic antigen for ELISA to test serum samples. RESULTS: There was no difference among the sequences of T. gondii GRA7 gene from different isolates. The recombinant plasmid pGEX-4T-1/GRA7 induced by IPTG was expressed in E. coli. It was a GST fusion protein and could react with human and rabbit positive sera analyzed by Western blot. CONCLUSION: The GRA7 gene of T. gondii isolates is highly conservative. The GRA7 is expressed as a recombinant protein in Escherichia coli, which shows an immunoreactivity.