Echinococcus granulosus: Cloning and Functional in Vitro Characterization of an Actin Filament Fragmenting Protein

Evaluation of the sensitivity and specificity of GST-tagged recombinant antigens 2B2t, Ag5t and DIPOL in ELISA for the diagnosis and follow up of patients with cystic echinococcosis

Cystic echinococcosis (CE) is a neglected zoonotic disease caused by Echinococcus granulosus sensu lato. Diagnosis and monitoring of CE rely primarily on imaging while serology is used as a confirmatory test. However, imaging is not always conclusive and currently available serological assays have suboptimal sensitivity and specificity, lack standardization, and are not useful for patients´ follow-up. Seroassays for CE are usually based on hydatid fluid (HF), a complex, variable antigenic mixture, and cross-reactivity exists especially with alveolar echinococcosis. Recombinant proteins based on immunogenic antigens most abundant in HF, such as AgB1, AgB2 and Ag5, have been used to overcome these limitations. None of them so far showed potential to replace HF; however, their performance have been largely tested on a limited number of samples, and comparison of different antigens using the same cohort has been rarely performed. The combination of several immunogenic epitopes in a single recombinant protein could enhance test sensitivity. For the diagnosis and follow-up of patients with CE, we compared the performance of the crude HF, previously described recombinant 2B2t antigen, and GST-tagged version of 2B2t, and novel designed recombinants (GST-Ag5t and the GST-DIPOL chimera containing AgB1, AgBB2 and Ag5 epitopes) by IgG-ELISA format. Samples belong to a retrospective cohort of 253 well-characterized patients with CE, previously described for the evaluation of the 2B2t antigen, 92 patients with alveolar echinococcosis, and 82 healthy donors. The reference standard for CE diagnosis was the presence of a CE lesion as diagnosed by ultrasonography. The highest sensitivity was obtained with HF [86.7%, 95% confidence interval (CI): 81.2–91.0], followed by GST-2B2t (70.0%, 95% CI: 63.1–76.2), 2B2t (65.5%, 95% CI: 58.5–72.0), GST-Ag5t (64.5%, 95% CI: 57.5–71.1) and GST-DIPOL (63.1%, 95% CI: 56.0–69.7). The GST-2B2t had the best specificity (95.8%, 95% CI: 88.3–99.1) and the lowest cross-reactivity (38.7%, 95% CI: 27.6–50.6). Good response to treatment also correlated to negative test results in the GST-2B2t ELISA. While none of the tested recombinant antigen appears suitable to replace HF for the diagnosis of CE, GST-2B2t should be further explored as a confirmation test, based on its high specificity and low cross-reactivity, and for the follow-up after treatment in those patients with positive serology for this antigen.

Cystic echinococcosis (CE) is a neglected parasitic zoonosis. Its diagnosis and follow-up require evaluation with imaging. Currently available serological tests are applied to confirm the diagnosis in doubtful cases, although having limitations in diagnostic accuracy, and they are not useful for patients’ follow-up. Seroassays for CE are usually based on hydatid fluid (HF) obtained from infected animals, with consequent problems of heterogeneity and low specificity. The use of semi-purified HF derivatives or recombinant antigens has been attempted to improve these aspects, but with an unacceptable loss in sensitivity. Most newly developed antigens have been tested on a limited number of samples, not always well characterized, and have been rarely compared using the same samples cohort. Here, we tested and compared three recombinant antigens (2B2t, GST-2B2t and GST-Ag5t), and a recombinant chimeric antigen (DIPOL) based on three highly immunogenic components of HF (B1, B2 and Ag5), in an attempt to increase the sensitivity of recombinant antigen-based seroassays for the diagnosis and follow-up of patients with CE. We found that GST-2B2t had higher sensitivity than the other antigenic preparations, but still not as high as HF, and that GST-2B2t and GST-DIPOL had statistically higher specificity than any of the other tested antigens. GST-2B2t also showed potential for the follow-up of patients with CE after drug treatment.

Linking murine resistance to secondary cystic echinococcosis with antibody responses targeting Echinococcus granulosus tegumental antigens

Successful establishment of a parasite infection depends partially on the host intrinsic susceptibility to the pathogen. In cystic echinococcosis (CE), a zoonotic disease caused by the cestode parasite Echinococcus granulosus, the infection outcome in the murine model of secondary CE varies according to the mouse strain used. In this regard, intrinsic differences in susceptibility to the infection were previously reported for Balb/c and C57Bl/6 mice, being C57Bl/6 animals less permissive to secondary CE. Induction of parasite-specific antibodies has been suggested to play relevant roles in such susceptibility/resistance phenomena. Here, we report an in deep comparison of antibody responses induced in both mouse strains. Firstly, only C57Bl/6 mice were shown to induce specific-antibodies with efficient anti-parasite activities during early secondary CE. Then, through ImmunoTEM and Serological Proteome Analysis (SERPA), an evaluation of specific antibody responses targeting parasite tegumental antigens was performed. Both strategies showed that infected C57Bl/6 mice -unlike Balb/c animals- narrowed their IgG recognition repertoire against tegumental antigens, targeting fewer but potentially more relevant parasite components. In this sense, tegumental antigens recognition between Balb/c and C57Bl/6 mice, either by natural and/or induced antibodies, was analyzed through SERPA and MALDI-TOF/TOF studies. A total of 13 differentially recognized proteins (DRPs) uniquely targeted by antibodies from C57Bl/6 mice were successfully identified, wherein a subset of 7 DRPs were only recognized by infection-induced antibodies, suggesting their potential as natural protective antigens. In this regard, immunoinformatic analyses showed that such DRPs exhibited higher numbers of possible T cell epitopes towards the H-2-IA^b haplotype, which is present in C57Bl/6 mice but absent in Balb/c animals. In summary, our results showed that the genetic predisposition to generate better T-dependent antibody responses against particular tegumental antigens might be a key factor influencing host susceptibility in the murine model of secondary CE.

Current status and future prospective of vaccine development against Echinococcus granulosus

Cystic echinococcosis (CE) is one of the most important zoonotic parasite diseases in human, livestock, and wildlife worldwide. Development of effective vaccines against CE appears to be the most promising strategy to control this infectious disease. Use of potential livestock and canine vaccines against the larval and adult stage of E. granulosus life cycle may be the key to the production of powerful vaccines. Some progress has been accomplished in the development of vaccines against hydatidosis using empirical approaches, while such immunotherapies often fail to induce adequate immune responses. Therefore, it is of great interest to identify antigens (Ags) with high immunogenicity and develop effective vaccines and adjuvant constructs against CE. To this end, various tools can be applied, including immune-based genomics and proteomics, immunoinformatics, systems vaccinology and mathematical/computational modeling. In this review, we aimed to provide comprehensive insights upon the current status of vaccination trials against E. granulosus, and also articulate some perspectives on the production of novel anti-CE vaccines. Use of novel prospective technologies is also discussed to highlight the importance of development and advancement of the next generation vaccines against E. granulosus.

Laboratory Diagnosis of Echinococcus spp. in Human Patients and Infected Animals

Among the species composing the genus Echinococcus, four species are of human clinical interest. The most prevalent species are Echinococcus granulosus and Echinococcus multilocularis, followed by Echinococcus vogeli and Echinococcus oligarthrus. The first two species cause cystic echinococcosis (CE) and alveolar echinococcosis (AE) respectively. Both diseases have a complex clinical management, in which laboratory diagnosis could be an adjunctive to the imaging techniques. To date, several approaches have been described for the laboratory diagnosis and followup of CE and AE, including antibody, antigen and cytokine detection. All of these approaches are far from being optimal as adjunctive diagnosis particularly for CE, since they do not reach enough sensitivity and/or specificity. A combination of several methods (e.g., antibody and antigen detection) or of several (recombinant) antigens could improve the performance of the adjunctive laboratory methods, although the complexity of echinococcosis and heterogeneity of clinical cases make necessary a deep understanding of the host-parasite relationships and the parasite phenotype at different developmental stages to reach the best diagnostic tool and to make it accepted in clinical practice. Standardization approaches and a deep understanding of the performance of each of the available antigens in the diagnosis of echinococcosis for the different clinical pictures are also needed. The detection of the parasite in definitive hosts is also reviewed in this chapter. Finally, the different methods for the detection of parasite DNA in different analytes and matrices are also reviewed.

Molecular characterization of severin from Clonorchis sinensis excretory/secretory products and its potential anti-apoptotic role in hepatocarcinoma PLC cells

BACKGROUND

Clonorchiasis, caused by the infection of Clonorchis sinensis (C. sinensis), is a kind of neglected tropical disease, but it is highly related to cholangiocarcinoma and hepatocellular carcinoma (HCC). It has been well known that the excretory/secretory products of C. sinensis (CsESPs) play key roles in clonorchiasis associated carcinoma. From genome and transcriptome of C. sinensis, we identified one component of CsESPs, severin (Csseverin), which had three putative gelsolin domains. Its homologues are supposed to play a vital role in apoptosis resistance of tumour cell.

METHODOLOGY/PRINCIPAL FINDINGS

There was significant similarity in tertiary structures between human gelsolin and Csseverin by bioinformatics analysis. We identified that Csseverin expressed at life stage of adult worm, metacercaria and egg by the method of quantitative real-time PCR and western blotting. Csseverin distributed in vitellarium and intrauterine eggs of adult worm and tegument of metacercaria by immunofluorence assay. We obtained recombinant Csseverin (rCsseverin) and confirmed that rCsseverin could bind with calciumion in circular dichroism spectrum analysis. It was demonstrated that rCsseverin was of the capability of actin binding by gel overlay assay and immunocytochemistry. Both Annexin V/PI assay and mitochondrial membrane potential assay of human hepatocarcinoma cell line PLC showed apoptosis resistance after incubation with different concentrations of rCsseverin. Morphological analysis, apoptosis-associated changes of mitochondrial membrane potential and Annexin V/PI apoptosis assay showed that co-incubation of PLC cells with rCsseverin in vitro led to an inhibition of apoptosis induced by serum-starved for 24 h.

CONCLUSIONS/SIGNIFICANCE

Collectively, the molecular properties of Csseverin, a molecule of CsESPs, were characterized in our study. rCsseverin could cause obvious apoptotic inhibition in human HCC cell line. Csseverin might exacerbate the process of HCC patients combined with C. sinensis infection.

Mycobacterium tuberculosis heat-shock protein 70 impairs maturation of dendritic cells from bone marrow precursors, induces interleukin-10 production and inhibits T-cell proliferation in vitro

In different inflammatory disease models, heat-shock proteins (hsp) and hsp-derived peptides have been demonstrated to possess anti-inflammatory properties. While some studies have shown that hsp can directly interact with antigen-presenting cells, others report that bacterial hsp can induce specific T cells with regulatory phenotypes. Effective characterization of the immunomodulatory effects of hsp 70, however, has historically been confounded by lipopolysaccharide (LPS) contamination. In this study, we compared the effects of LPS-free Mycobacterial tuberculosis hsp 70 (TBhsp70) and its possible contaminants on dendritic cells (DC). We demonstrate herein that LPS-free TBhsp70 inhibits murine DC maturation in vitro, while LPS-contaminated TBhsp70 induces DC maturation. Mock recombinant preparations have no effect. In contrast to LPS, TBhsp70 does not induce tumour necrosis factor-alpha production by DC, but interleukin-10. In vivo, only LPS-contaminated TBhsp70 induces up-regulation of CD86 in splenic mature DC. Finally, TBhsp70 inhibited phytohaemagglutinin-induced T-cell proliferation. Our results support the hypothesis that TBhsp70 does not have inflammatory potential, but rather has immunosuppressive properties.

Recent advances in the immunology and diagnosis of echinococcosis

Echinococcosis is a cosmopolitan zoonosis caused by adult or larval stages of cestodes belonging to the genus Echinococcus (family Taeniidae). The two major species of medical and public health importance are Echinococcus granulosus and Echinococcus multilocularis, which cause cystic echinococcosis and alveolar echinococcosis, respectively. Both cystic echinococcosis and alveolar echinococcosis are serious diseases, the latter especially so, with a high fatality rate and poor prognosis if managed inappropriately. This review highlights recent advances in immunity to infection and vaccination against both parasites in their intermediate and definitive hosts and procedures for diagnosis of cystic echinococcosis and alveolar echinococcosis, including the value of immunodiagnostic and DNA approaches. There is discussion also of progress in genomics and related technologies that is providing valuable insights on the functional biology of the Echinococcus organisms. These studies will underpin future research that will reveal a better understanding of the Echinococcus-host interplay, and suggest new avenues for the identification of additional targets for diagnosis, vaccination and chemotherapy.

Structural analysis of an Echinococcus granulosus actin-fragmenting protein by small-angle x-ray scattering studies and molecular modeling

The Echinococcus granulosus actin filament-fragmenting protein (EgAFFP) is a three domain member of the gelsolin family of proteins, which is antigenic to human hosts. These proteins, formed by three or six conserved domains, are involved in the dynamic rearrangements of the cytoskeleton, being responsible for severing and capping actin filaments and promoting nucleation of actin monomers. Various structures of six domain gelsolin-related proteins have been investigated, but little information on the structure of three domain members is available. In this work, the solution structure of the three domain EgAFFP has been investigated through small-angle x-ray scattering (SAXS) studies. EgAFFP exhibits an elongated molecular shape. The radius of gyration and the maximum dimension obtained by SAXS were, respectively, 2.52 +/- 0.01 nm and 8.00 +/- 1.00 nm, both in the absence and presence of Ca2+. Two different molecular homology models were built for EgAFFP, but only one was validated through SAXS studies. The predicted structure for EgAFFP consists of three repeats of a central beta-sheet sandwiched between one short and one long alpha-helix. Possible implications of the structure of EgAFFP upon actin binding are discussed.

Characterization of various recombinant antigens from Echinococcus multilocularis for use in the immunodiagnosis

Using four clones isolated from Echinococcus multilocularis cDNA library with alveolar echinococcosis (AE) patient sera, various antigens were expressed as ThioHis tag-fused protein. Recombinant EmII/3 antigen was produced as the five fragments divided into the N-terminal (#5 and #5s), the central (#6 and #6s) and the C-terminal domain (#7). Immunoblot analysis revealed that the #7 showed significant reactivity whereas those of #5 and #5s were relatively low. The #6 and #6s also showed lower reactivity than that of #7, although the two minor bands of #6 reacted with every serum. These results suggested that an immunodominant region of EmII/3 locate within the C-terminal one third. The #8s recombinant antigen, Ser23-Glu176 of actin filament fragmenting protein (AFFP), apparently reacted with the AE patient sera, while the #1 antigen synthesized as a full-length antigen BI did not show such high reactivity. Thus, #7 and #8s antigens showed significant potential for use in immunodetection of AE. In addition, the specific antibodies against #7 and #8s reacted with specific antigens in crude extract of E. multilocularis cyst, indicating that these antigens retained antigenicity common to native EmII/3 and AFFP, respectively.

The Echinococcus granulosus antigen EgA31: localization during development and immunogenic properties

EgA31 is a fibrillar protein from Echinococcus granulosus that behaves as a potent antigen during infestation of dogs. The localization of this antigen during development of the parasite was investigated by immunohistochemistry in optical and electron microscopy. The protein is mostly abundant in the microtriches and subtegumental cells of the adult, whereas it is absent from protoscolex microtriches. Eggs, the periphery of calcareous corpuscles, and the germinal layer were other sites of accumulation. Immunogenicity of different domains of the protein was assessed during experimental infection of dogs. It was shown that the polypeptide encoded by the Pst I-Hind III fragment of the complete cDNA is the most antigenic during the infection. The uses of such polypeptide for infection diagnosis and as a candidate vaccine protein are discussed.

A set of recombinant antigens from Echinococcus granulosus with potential for use in the immunodiagnosis of human cystic hydatid disease

Several recombinant clones expressing antigens from Echinococcus granulosus were isolated previously from a parasite cDNA library using cystic hydatid disease (CHD) patients' sera or rabbit hyperimmune antiserum against a lipoproteic fraction from bovine cyst fluid. Six of these antigens were expressed in Escherichia coli and the purified recombinant proteins were tested in enzyme-linked immunosorbent assay (ELISA) for specific IgG with a panel of sera from patients with surgically confirmed (n = 58) or immunologically diagnosed (n = 71) CHD. Sera from clinically normal individuals (n = 203) and sera from individuals with other helminthic infections (n = 65) were assayed for the assessment of specificity. A cut-off value was determined by receiver-operating-characteristic plots for each antigen. A recombinant antigen B subunit (AgB8/2) presented the highest sensitivity (93.1%), considering the group of sera from patients with CHD surgically confirmed, and specificity (99.5%) and is proposed as the basis for an immunodiagnostic test. The other recombinant antigens tested presented sensitivities between 58.6% and 89.7%, and three of them were considered of complementary value. In subclass-specific ELISA, different IgG isotypes showed dominance in the response for each of the recombinant antigens. There was a clear predominance of IgG4 response for all antigens tested, indicating that this would be the subclass of choice to be assessed for these recombinant proteins.