Molecular cloning and characterization of a novel Schistosoma japonicum "irradiated vaccine-specific" antigen, Sj14-3-3

Proteomic analysis of schistosomiasis japonica vaccine candidate antigens recognized by UV-attenuated cercariae-immunized porcine serum IgG2

Many studies have showed that the radiation-attenuated cercariae (RAC) vaccine could induce the high protection of laboratory animals to resist the schistosoma infection by cellular and humoral mechanism. Here, we aimed to identify possible vaccine antigens by using specific IgG2 antibody from RAC-vaccinated pigs or vaccination and challenge pigs. The antigens from the schistosomal soluble worm antigen preparation (SWAP) recognized by the porcine IgG2 antibody were obtained using immunoprecipitation technique. These antigens were separated by 2-D electrophoresis, and 116 spots were successfully identified by MALDI-TOF MS from about 400 putative spots in gels. Among these spots, 113 spots could match to the Schistosoma japonicum. These identified proteins in four groups were classified by Gene Ontology (Go) database, and the mainly functions of these proteins were involved in binding, catalytic activity (thioredoxin peroxidase-2, et al.), signal transduction class (MAP Kinase, et al.), cell process (the heat shock 70-kDa protein 9B, et al.), and the intracellular component (tektin, et al.). Our methods suggested that it was possible to pull-down the interesting proteins recognized by specific antibodies. Our results may provide new clues for exploring the mechanism of high protection induced by RAC and shed some light on the research for anti-schistosomiasis japonica vaccine.

Differential recognition patterns of Schistosoma haematobium adult worm antigens by the human antibodies IgA, IgE, IgG1 and IgG4

Schistosoma haematobium antigen recognition profiles of the human isotypes IgA, IgE, IgG1 and IgG4 were compared by image analysis of western blots. Adult worm antigens separated by two-dimensional gel electrophoresis were probed with pooled sera from Zimbabweans resident in a S. haematobium endemic area, followed by the identification of individual antigenic parasite proteins using mass spectrometry. Overall, IgG1 reacted with the largest number of antigens, followed by IgE and IgA which detected the same number, while IgG4 detected the fewest antigens. IgE recognized all antigens reactive with IgG4 as well as an additional four antigens, an isoform of 28-kDa GST, phosphoglycerate kinase, actin 1 and calreticulin. IgG1 additionally recognized fatty acid–binding protein, triose-phosphate isomerase and heat shock protein 70, which were not recognized by IgA. Recognition patterns varied between some isoforms, e.g. the two fructose 1-6-bis-phosphate aldolase isoforms were differentially recognized by IgA and IgG1. Although the majority of S. haematobium adult worm antigens are recognized by all of the four isotypes, there are clear restrictions in antibody recognition for some antigens. This may partly explain differences observed in isotype dynamics at a population level. Differential recognition patterns for some isoforms indicated in the study have potential importance for vaccine development.

Application of signaling protein 14-3-3 and 26 kDa glutathione-S-transferase to serological diagnosis of Schistosomiasis japonica

Schistosomiasis japonica is currently one of the most serious parasitic diseases and over 670000 people are infected in China by the end of 2006. In order to establish an effective diagnostic method, the gene coding for Sj14-3-3 and Sj26kDa GST were cloned and expressed separately in Escherichia coli as fusion protein with His-tag. The rSj14-3-3 and 26kDa rSjGST were combinedly used as antigens for enzyme-linked immunosorbent assays (ELISA) to diagnose acute and chronic S. japonica. Our results showed that the sensitivity in diagnoses of both acute and chronic schistosomiasis was 94.4% (67/71) and 80.7% (96/119), respectively. The specificity was 94.7% applying 132 sera from people living in S. japonicum-free areas. The data also showed that the recombinant proteins cross-react with Clonorchis sinensis and hookworms at a rate of 11.8% and 5.3% respectively. Parallel tests were conducted among ELISA, indirect hemagglutination assay (IHA) and circular ovum precipitin test (COPT) to determine anti-S. japonicum antibodies in sera of patients with schistosomiasis, healthy control, and those infected with other parasites and the results showed no significant difference in sensitivity for acute schistosomiasis between ELISA and IHA assays (chi(2)=1.33, P>0.05), but significant between ELISA and COPT assays (chi(2)=6.72, P<0.01). Our results also revealed significant difference in positive rate between ELISA and IHA (chi(2)=24.74, P<0.005), as well as between ELISA and COPT (chi(2)=58.14, P<0.005). These results suggest that the rSj14-3-3 and r26kDa SjGST would be effective diagnostic antigens for detection of antibodies to S. japonicum in human. Due to the easy production, high sensitivity and specificity, the recombinant proteins tested in this study can be considered as candidate reagent for immunological diagnosis of human schistosomiasis.

Proteome approach for identification of schistosomiasis japonica vaccine candidate antigen

Experimental vaccination with radiation-attenuated cercariae (RAC) confers possible practical levels of resistance to challenge infection by humoral and by cellular mechanism. Here, we aimed to identify possible vaccine antigens by using specific IgG antibody from RAC vaccinated miniature pig. Two milligrams of soluble egg antigen (SEA) or schistosomal worm antigen preparation (SWAP) was fractionated using two dimensional liquid chromatography (proteome PF 2D) consisted of high performance chromatofocusing (HPCF) and high resolution reversed phase chromatography (HPRP). Of the 42 HPCF fractions of SEA or SWAP, 26 (61.9%) or 15 (35.7%) showed positive dot blot reaction with RAC vaccinated serum respectively. The dot blot positive fractions were applied to the second HPRP column. One hundred and seven out of 26 x 96 of SEA fractions and 18 out of 15 x 96 SWAP fractions reacted with RAC vaccinated serum. From the positive fractions we chose 17 of SEA and 10 of SWAP that had no reactivity with normal cercariae infected (NCI) sera and had single peak of 214 nm; and automated N-terminal amino acid sequence based on in situ Edman Reaction was conducted. Four sequences were obtained and applied to the homology search in NCBI database. A total of eight candidate genes were listed up and their cDNA clones from schistosomula stage were obtained. Two of the recombinant proteins (AAW27472.1 and AXX25883.1) showed strong reactivity with the RAC vaccinated serum but marginal with NCI serum. This protocol using proteome PF 2D could be applicable in identifying immunoreactive proteins from crude extract for the development of vaccines or for diagnostics.

The Schistosoma bovis Sb14-3-3ζ recombinant protein cross-protects against Schistosoma mansoni in BALB/c mice

Current control programs against schistosomiasis could be reinforced through the use of an effective vaccine. Schistosome 14-3-3 proteins have been proposed as candidates for vaccine against the respective infections, and were seen to elicit high protection levels against Schistosoma bovis in a previous work done by our group. We have therefore investigated the protective capacity of the 14-3-3 protein from S. bovis - Sb14zeta - against Schistosoma mansoni in mice. In addition, we have addressed the influence of the co-administration of three different immunomodulators with the 14-3-3 polypeptide. Protection was high when the Sb14zeta protein was combined in two independent experiments with the AA2829 and PAL immunomodulatory molecules as regards both the reduction of worm numbers (mean: 64.8%) and egg loads in liver (mean: 73.9%) or intestine (mean: 71.5%). In contrast, the degree of protection achieved with the Sb14zeta-CpG vaccine was very low (14.9% reduction in worm numbers, and 46.6% and 32% reduction in liver and intestinal egg loads). The immune responses observed in the vaccinated animals showed that the production of IFNgamma and the absence of IL-4, accompanied by a strong humoral response, are insufficient to elicit protection against S. mansoni.

The Sb14-3-3ζ recombinant protein protects against Schistosoma bovis in BALB/c mice

Schistosoma bovis is a trematode parasite mainly affecting cattle and sheep. Evidences about the arise of drug resistance and the high rates of re-infection of animals in endemic areas have pointed out the need of developing new control tools, e.g., effective vaccines. Schistosomes 14-3-3 proteins have been defined as vaccine candidates against respective infections. We have therefore investigated the protective capacity of the 14-3-3 protein from S. bovis - Sb14zeta - against S. bovis in mice. In addition, we have addressed the influence of the co-administration of four different immunomodulators with the 14-3-3 polypeptide. The values of protection against S. bovis were statistically significant when the Sb14zeta was combined in two independent experiments with the AA0029 (61.0% and 40.31%), AA2829 (49% and 36.3%) and PAL (49% and 40.075%) immunomodulatory molecules. Immune responses from vaccinated animals showed that the highest protection rates do not necessarily match with a dominant Th1-type response.

Molecular and immunological characterization of encoding gene and 14-3-3 protein 1 in Fasciola gigantica

A cDNA encoding Fg14-3-3 protein 1 was cloned by immunoscreening of an adult-stage Fasciola gigantica cDNA library using a rabbit antiserum against tegumental antigens of the parasite. The protein has a deduced amino acid sequence of 252 residues and a calculated molecular weight of 28.7 kDa. It shows sequence identity values between 57.6 and 58.1% to the human 14-3-3 beta, zeta, theta, and eta proteins and is in a phylogenetic cluster with the 14-3-3 protein 1 of Schistosoma spp. Nucleic acid analyses indicate that the Fg14-3-3 protein 1 is encoded by a single copy gene and that this gene is expressed as a transcript of 1250 nucleotides. In adult and 4-week-old parasites the gene's transcriptional and translational products were localized in the gut epithelium, parenchyma, tegument cells, and in the reproductive organs. An antiserum against recombinant Fg14-3-3 protein 1 detected a slightly smaller 14-3-3 protein in the parasite's excretion/secretion material and showed cross-reactivity with 14-3-3 proteins in extracts of other trematodes and mouse. Antibodies against Fg14-3-3 protein were detected in the sera of rabbits as early as 2 weeks after infection with metacercariae of F. gigantica and the antibody titre increased continuously over a 10-week observation period.

Development of a vaccine against Schistosoma japonicum in China: a review

Significant progress has been made over the past 50 years in the control of schistosomiasis japonica in China. However, recent data suggest that the disease is re-emerging. By the end of 2003, Schistosoma japonicum was still endemic in 110 counties in seven provinces in the southern part of China where the long-term reduction of the disease has been replaced by an increase in the number of people infected and areas infested by the intermediate host snail, i.e. Oncomelania hupensis. Explanations are multifactorial, including the construction of the Three Gorges dam, major flooding events, recovery of the Dongting Lake and the possible impact of climate change. An efficacious vaccine against S. japonicum would represent a significant addition to the current arsenal of control tools, particularly in the framework of an integrated control approach. The vaccine could be targeted either towards the prevention of infection or towards the reduction of parasite fecundity. Although progress in this field has been relatively slow, encouraging results have been obtained in recent years using defined native and recombinantly derived S. japonicum antigens. These findings suggest that development of a safe and efficacious vaccine is feasible. This paper reviews the progress in the development of a vaccine against S. japonicum in China, and includes also data from foreign researchers who are engaged in collaborative work with Chinese scientists.

A DNA-prime/protein-boost vaccination regimen enhances Th2 immune responses but not protection following Schistosoma mansoni infection

DNA immunization represents a promising vaccine strategy that has been reasonably successful, and will likely play an even greater role in vaccine development as these vaccines continue to be improved. We have developed a partially protective DNA vaccine against schistosome infection based on a 23-kDa integral membrane protein, Sm23. The focus of this study was to compare immunogenicity and efficacy of vaccination regimens utilizing Sm23 DNA vaccine alone vs. regimens that utilized both Sm23 DNA and Sm23 in recombinant protein form. We found that priming and boosting with the Sm23 DNA construct (Sm23-pcDNA) resulted in a significant level of protection against challenge infection (36-44%). In contrast, altering this protocol by changing the boost from Sm23 DNA to boosting with recombinant Sm23 protein (rSm23) formulated in aluminium hydroxide (alum) failed to induce a significant reduction in worm burdens. Similarly, mice primed and boosted with the rSm23 in alum also did not develop significant levels of protection against challenge infection. We hypothesize that the differences in the ability to drive protective immunity using the DNA prime-DNA boost strategy and the inability to do so when recombinant Sm23 in alum was substituted for Sm23 DNA is due to driving of different immune responses. In support of this, we found that mice primed and boosted with Sm23-pcDNA had Th1-type immune responses characterized by low anti-Sm23 IgG1 : IgG2a antibody isotype ratios, whereas mice boosted with rSm23 had higher IgG1 : IgG2a ratios. In addition, priming and boosting with rSm23 elicited mainly IgG1 antibodies with no detectable IgG2a, indicative of a polarized Th2-type immune response. Thus, similar to our earlier work, the results of this study show that protective vaccination using Sm23 is associated with a Th1 immune response, and efficacy is diminished using protocols that diminish this Th1 bias. In our study, this was likely due to the use of the Th2-driving adjuvant alum, and future studies are planned where we will compare the protective efficacy of rSm23 administered with Th1-type adjuvants.

14-3-3 proteins in Schistosoma mansoni; identification of a second epsilon isoform

A new member of the 14-3-3 protein family in Schistosoma mansoni has been identified. Sequence analysis demonstrated that this protein is a member of the epsilon sub-group and is the orthologue of Schistosoma japonicum 14-3-3epsilon. Since we had previously identified a 14-3-3epsilon protein from S. mansoni, we termed the original protein 14-3-3epsilon-1 and this second epsilon protein 14-3-3epsilon-2. Schistosoma mansoni encodes at least four different 14-3-3 isoforms: the two epsilon proteins and 14-3-3 protein 1 and protein 2, which are zeta-like isoforms. Phylogenetic analysis demonstrated the early divergence of the epsilon isoforms, and that schistosome proteins 1 and 2 are among the oldest non-epsilon 14-3-3 proteins yet identified. Schistosoma mansoni 14-3-3epsilon-1, 14-3-3epsilon-2, and protein 1 are stage specifically expressed in a similar manner, being absent in cercariae and schistosomula, and abundant in lung stage and adult male and female worms. Protein 2 transcript was not detected at any of the life cycle stages examined. All three detected 14-3-3 isoforms elicit an immune response during infection, with the greatest response directed against protein 1. Binding studies with S. mansoni receptor kinase-1 (SmRK1) and human Raf kinase revealed that the three 14-3-3epsilon isoforms exhibit a preference for target protein binding. Although all three isoforms do bind to both targets, 14-3-3 protein 1 interacts most strongly with Raf, whereas the 14-3-3-1 isoform binds SmRK1 preferentially. These results suggest that the individual 14-3-3 proteins may have evolved to play isoform-specific roles in the development and survival of S. mansoni within its host.

Direct identification of stylet secreted proteins from root-knot nematodes by a proteomic approach

The stylet secretions produced by plant parasitic root-knot nematodes are thought to be pathogenicity factors involved in the invasion of the root tissue and in the induction and maintenance of feeding cells. A new procedure was established that allowed the direct qualitative analysis of proteins secreted by Meloidogyne incognita infective juveniles. Purified proteins whose isoelectric point (pI) ranged from 5.0 to 7.5 were separated by two-dimensional (2D) electrophoresis and the seven most abundant proteins were identified by micro-sequencing. A calreticulin (CRT) was isolated and transcription of its gene in infective juveniles and adults was demonstrated. Moreover, evidence for expression of the CRT in the subventral oesophageal glands of infective juveniles was obtained. The potential roles of this secreted protein in pathogenesis and the advantages of developing this strategy to obtain new insights into plant-nematode interactions are discussed.

Vaccination of mice with a cocktail DNA vaccine induces a Th1-type immune response and partial protection against Schistosoma japonicum infection

Several defined vaccine candidate antigens of Schistosoma japonicum have shown promise in large animal vaccination experiments. However, vaccination of mice in the laboratory with either single recombinant antigens or DNA encoding forms of the individual antigens has so far failed to induce significant protection against S. japonicum cercarial challenge infection as judged by worm reduction, although specific antibodies were generated. This is in contrast to the results achieved using radiation-attenuated vaccines which are highly protective. Even in large animal vaccination experiments, the protection levels obtained with single defined antigens were far below those achieved using the attenuated vaccines. One possible interpretation is that the immune responses induced by single antigen vaccination may not be strong enough to combat the challenging infection. We, therefore, carried out mouse vaccination experiments using a cocktail DNA vaccine comprising four DNA plasmids encoding four different S. japonicum antigens, Sj62, Sj28, Sj23 and Sj14-3-3, respectively. We, also investigated whether co-injection of the mouse IL-12 encoding plasmid with the cocktail DNA vaccine was able to enhance the Th1 responses and hence the protective immunity. Three intramuscular injections of the cocktail DNA vaccine induced a significant Th1-type cellular response with high level of IFN-gamma production by splenocytes upon in vitro stimulation with recombinant antigens. Importantly, significant IgG antibody responses were also induced against crude worm antigens. In two out of three experiments, significant resistance (34-37 and 44-45%, respectively) was demonstrated while another experiment did not show any protection against S. japonicum cercarial challenge infection. Co-injection of the IL-12 encoding DNA did not further enhance these responses, nor the level of resistance, compared with the cocktail DNA alone.

The 14-3-3 protein as a vaccine candidate against schistosomiasis

We have previously reported on the cloning of the 14-3-3 protein of Schistosoma mansoni. Here, we evaluate the potential use of this protein as a vaccine candidate against infection by S. mansoni. Sm14-3-3 was expressed and purified either as a free protein or as a fusion protein to SjGST or MBP. Sera from mice infected with S. mansoni recognized both SjGST and 14-3-3, indicating that antibodies against these two proteins are induced in the course of the natural infection. Furthermore, mice immunized with either 14-3-3, GST or 14-3-3-GST, reacted with cercaria lysate. A cellular immune response was also detected, particularly in mice immunized with 14-3-3-GST. With respect to the effect on biological functions, antibodies to 14-3-3 and 14-3-3-GST caused 23-32% complement-mediated cytotoxcity of S. mansoni schistosomula compared to only 10-11% induced by either normal mouse serum, or GST alone. In challenge infection with S. mansoni, immunization with 14-3-3, either as a fusion protein or as a free protein, led to protection ranging from 25-46%, as determined by reduction of adult worm burden, while SjGST alone elicited only 0-8% protection and MBP alone did not elicit any protection.

Cloning of Schistosoma japonicum 14-3-3 epsilon (Sj14-3-3 epsilon), a new member of the 14-3-3 family of proteins from schistosomes

A new member of the 14-3-3 protein family from Schistosoma japonicum has been identified. Phylogenetic analysis showed that this member belongs to the epsilon subfamily of the 14-3-3 proteins, and it is therefore named Sj14-3-3 epsilon. Consistent with the findings for the previously reported S. japonicum 14-3-3 protein (Sj14-3-3), Southern analysis suggested the presence of more than one gene, and/or introns or allelic polymorphism in this epsilon isoform. By RT-PCR, Sj14-3-3 epsilon was shown to be stage-specifically transcribed, being abundant in adults, present in sporocysts but absent in cercariae. Furthermore, mRNA of the epsilon isoform seemed to be much less abundant in the sporocyst stage, compared with Sj14-3-3. This suggests varying requirements of the different 14-3-3 isoforms at different stages of the life cycle.