Peptide epitopes of the Taenia solium antigen Ts8B2 are immunodominant in human and porcine cysticercosis

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.

Comparison of T24H-his, GST-T24H and GST-Ts8B2 recombinant antigens in western blot, ELISA and multiplex bead-based assay for diagnosis of neurocysticercosis

Background

Currently, the reference standard assay for the serodiagnosis of neurocysticercosis (NCC) is the lentil lectin-bound glycoproteins/enzyme-linked immunoelectrotransfer blot (LLGP-EITB). The main disadvantage of this technique is the complexity of obtaining and purifying the LLGP extract. This could be solved by replacement with highly specific recombinant antigens from Taenia solium. Based on previous studies, we selected and produced the recombinant Ts8B2 and T24H proteins and applied them to three diagnostic techniques: western blot (WB), enzyme-linked immunosorbent assay (ELISA) and the multiplex bead-based assay (MBA).

Methods

The Ts8B2 and T24H cDNA sequences were expressed in a prokaryotic system and the corresponding expression products purified; three recombinant proteins were further characterized: T24H-his, GST-T24H and GST-Ts8B2. The proteins on WB, ELISA and MBA were tested against 149 sera from patients with NCC confirmed by brain imaging, 40 sera from patients with other parasitic diseases, and 131 sera from US. individuals without evidence of neurocysticercosis (clinical/serological/brain imaging). The sensitivity and specificity of each antigen by WB were calculated by counting the number of true positive, false positive, true negative and false negative results. Using the receiver operating characteristic (ROC) curves, the cut-off values for the ELISA and MBA were established as well as the sensitivity and specificity of each assay.

Results

All three antigens showed a high sensitivity on WB in active NCC cases with two or more viable cysts and low sensitivity for cases with single viable cyst or calcified lesions and inactive NCC. WB showed the highest specificity and sensitivity out of the three diagnostic techniques. The recombinant T24H-his was the best diagnostic reagent in WB (100% sensitivity, 99.4% specificity), exhibiting similar results to the LLGP-EITB, against the same panel of NCC sera. The GST-T24H antigen worked better than the others in ELISA and MBA protocols (88.3 and 96.1% sensitivity, respectively and 96.5% specificity).

Conclusions

The sensitivity and specificity that we obtained were similar to results from a previous study using a similar recombinant antigen (rT24H), suggesting that recombinant antigens may be good alternatives to crude extracts in a variety of diagnostic techniques. Furthermore, these antigens can be applied in the development of point-of-care tests which would be useful in NCC field studies.

Expression, tissue localization and serodiagnostic potential of Taenia multiceps acidic ribosomal protein P2

BACKGROUND

The larval stage of Taenia multiceps, also known as coenurus, is the causative agent of coenurosis, which results in severe health problems in sheep, goats, cattle and other animals that negatively impact on animal husbandry. There is no reliable method to identify coenurus infected goats in the early period of infection.

METHODS

We identified a full-length cDNA that encodes acidic ribosomal protein P2 from the transcriptome of T. multiceps (TmP2). Following cloning, sequencing and structural analyses were performed using bioinformatics tools. Recombinant TmP2 (rTmP2) was prokaryotically expressed and then used to test immunoreactivity and immunogenicity in immunoblotting assays. The native proteins in adult stage and coenurus were located via immunofluorescence assays, while the potential of rTmP2 for indirect ELISA-based serodiagnostics was assessed using native goat sera. In addition, 20 goats were randomly divided into a drug treatment group and a control group. Each goat was orally given mature, viable T. multiceps eggs. The drug treatment group was given 10% praziquantel by intramuscular injection 45 days post-infection (p.i), and all goats were screened for anti-TmP2 antibodies with the indirect ELISA method established here, once a week for 17 weeks p.i.

RESULTS

The open reading frame (366 bp) of the target gene encodes a 12.62 kDa protein, which showed high homology to that from Taenia solium (93% identity) and lacked a signal peptide. Immunofluorescence staining showed that TmP2 was highly localized to the parenchymatous zone of both the adult parasite and the coenurus; besides, it was widely distributed in cystic wall of coenurus. Building on good immunogenic properties, rTmP2-based ELISA exhibited a sensitivity of 95.0% (19/20) and a specificity of 96.3% (26/27) in detecting anti-P2 antibodies in the sera of naturally infected goats and sheep. In goats experimentally infected with T. multiceps, anti-TmP2 antibody was detectable in the control group from 3 to 10 weeks and 15 to 17 weeks p.i. In the drug-treated group, the anti-TmP2 antibody dropped below the cut-off value about 2 weeks after treatment with praziquantel and remained below this critical value until the end of the experiment.

CONCLUSION

The indirect ELISA method developed in this study has the potential for detection of T. multiceps infections in hosts.

Cysticercus cellulosae antigens in the serodiagnosis of neurocysticercosis

Neurocysticercosis (NCC) is difficult to diagnose clinically because of its varied clinical presentation. However, an accurate diagnosis is possible only after suspicion on epidemiological grounds, proper interpretation of the clinical data, analysis of the findings on imaging studies, and specific immunological tests on the serum and cerebrospinal fluid (CSF). The diagnosis of NCC by any single parameter thus continues to remain difficult. In the past, detection of NCC was based on autopsy studies and histological confirmation. In recent times, the advent of imaging methods such as computed tomography and magnetic resonance imaging have provided excellent non-invasive tools for easy detection of NCC. Nevertheless, an imaging technique of the brain, although useful, is not considered as a gold standard for the diagnosis of NCC. Serological tests are being increasingly used in adjunct with imaging techniques, to aid the diagnosis of NCC. Immunodiagnostic techniques include detection methods for specific antibodies and for circulating parasite antigens in the serum and CSF. Currently, many of the immunodiagnostic tests, including the enzyme-linked immunosorbent assay and enzyme immunotransfer blot, use purified native antigens for the immunodiagnosis of NCC. Nevertheless, the main problem with the use of native cysticercal antigens is that the native proteins often show cross reactions with sera from humans infected with other parasites. The preparation of native antigens also demand a constant supply of parasitic material from the intermediate host pig. In order to overcome the problems in using native antigens, the recombinant antigens or synthetic peptides, which can be produced under stable conditions, are being evaluated for the serodiagnosis of NCC.

Immunological and molecular diagnosis of cysticercosis

Cysticercosis, the infection with the larval stage of Taenia solium, is a cause of neurological symptoms including seizures, affecting the quality of life of patients and their families. Diagnosis focuses on brain imaging and serological tests are mostly used as confirmatory tools. Most cases, however, occur in poor endemic areas, where both kinds of diagnostic tools are poorly available. Development of point of care diagnostic tests is one of the most important priorities for cysticercosis researches today. The ideal point of care test would require detection of viable cysticercosis and hopefully identify cases with severe or progressive forms of neurocysticercosis, leading to referral of the patient for specialized medical attention. This manuscript describes the evolution of the serological diagnosis of cysticercosis over time, and the characteristics of the most common currently available tools, their advantages and disadvantages, and their potential use in future diagnostic tests.

Diagnostic epitope variability within Taenia solium 8 kDa antigen family: implications for cysticercosis immunodetection

To study diagnostic epitopes within the Taenia solium 8 kDa antigen family, six overlapping synthetic peptides from an 8 kDa family member (Ts8B2) were synthesized and evaluated by ELISA and MABA with sera from patients with neurocysticercosis (NCC), from infected pigs and from rabbits immunized with recombinant Ts8B2 protein. The pre-immune rabbit sera and the Ts8B2 recombinant protein served as negative and positive controls, respectively. A similar analysis was done with the already described antigenic peptides from another member of the 8 kDa family, highly similar to Ts8B2, the CyDA antigen. Surprisingly, neither the Ts8B2 peptides nor the CyDA peptides were recognized by infected human and porcine sera. However, the entire Ts8B2 recombinant, as well as amino and carboxy-terminal halves were recognized by the positive serum samples. The observed lack of recognition of linear Ts8B2 peptides suggests that the principal serological response to the Ts8B2 family is focused on conformational epitopes in contrast to the previously observed antigenicity of the CyDA peptides. This differential antigenicity of 8 kDa family peptides could be related with parasite antigenic variability. The fact that rabbits experimentally immunized with Ts8B2 did make anti-peptide antibodies to peptides Ts8B2-6 and CyDA-6, located in the carboxy-terminal region demonstrated that the Ts8B2 peptides are not intrinsically non-immunogenic.