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  1. Toxoplasma gondii excretory secretory antigenic proteins of diagnostic potential
    Saadatnia G, Mohamed Z, Ghaffarifar F, Osman E, Moghadam ZK, Noordin R
    APMIS, 2012 Jan;120(1):47-55.
    PMID: 22151308 DOI: 10.1111/j.1600-0463.2011.02810.x
    Infection with Toxoplasma gondii is widespread and important in humans, especially pregnant women and immunosuppressed patients. A panel of tests is usually required for diagnosis toxoplasmosis. Excretory secretory antigen (ESA) is highly immunogenic, and thus it is a good candidate for investigation into new infection markers. ESA was prepared from tachyzoites of RH strain of T. gondii by mice intraperitoneal infection. Sera were obtained from several categories of individuals who differed in their status of anti-Toxoplasma IgM, IgG and IgG avidity antibodies. The ESA was subjected to SDS-PAGE, two-dimensional gel electrophoresis and Western blot analysis. Antigenic bands of approximate molecular weights of 12, 20 and 30 kDa, when probed with anti-human IgM-HRP and IgA-HRP, showed good potential as infection markers. The highest sensitivity of the bands was 98.7% with combination of IgM and IgA blots with sera of patients with anti-Toxoplasma IgM+ IgG+. The specificities were 84% and 70% with sera from other infections and healthy controls in IgM blots and IgA blots respectively. By mass spectrometry, the 12 kDa protein was identified as thioredoxin. The two top proteins identified for 20 kDa molecule were microneme protein 10 and dense granule protein 7; whereas that for 30 kDa were phosphoglycerate mutase 1 and phosphoglycerate mutase.
  2. Recombinant proteins in the diagnosis of toxoplasmosis
    Kotresha D, Noordin R
    APMIS, 2010 Aug;118(8):529-42.
    PMID: 20666734 DOI: 10.1111/j.1600-0463.2010.02629.x
    Toxoplasma gondii is an important human pathogen with a worldwide distribution. It is primarily of medical importance for pregnant women and immunocompromised patients. Primary infection of the former is often associated with fetal infection, which can lead to abortion or severe neonatal malformation. Immunocompromised patients are at risk of contracting the severe form of the disease that may be fatal. Thus, detection of T. gondii infection with high sensitivity and specificity is crucial in the management of the disease. Toxoplasmosis is generally diagnosed by demonstrating specific immunoglobulin M (IgM) and IgG antibodies to toxoplasma antigens in the patient's serum sample. Most of the commercially available tests use T. gondii native antigens and display wide variations in test accuracy. Recombinant antigens have great potential as diagnostic reagents for use in assays to detect toxoplasmosis. Thus in this review, we address recent advances in the use of Toxoplasma recombinant proteins for serodiagnosis of toxoplasmosis.
  3. Comparison of IgG-ELISA and IgG4-ELISA for Toxocara serodiagnosis
    Noordin R, Smith HV, Mohamad S, Maizels RM, Fong MY
    Acta Trop, 2005 Jan;93(1):57-62.
    PMID: 15589798
    Diagnosis of human toxocariasis, caused by Toxocara canis or Toxocara cati, normally relies on a combination of the presence of clinical signs and symptoms backed by positive serology. The use of Toxocara excretory-secretory antigen (TES) in ELISA assays increases the test specificity. However, in tropical countries where soil-transmitted helminths are endemic, cross-reactivity from antibodies to these intestinal parasites poses a significant limitation for Toxocara serodiagnosis. To increase the specificity of serodiagnosis, we compared the use of IgG-ELISA to the use of IgG4-ELISA using commercially manufactured TES-coated plates. The sensitivity of the IgG-ELISA was 97.1%, while that of the IgG4-ELISA was 45.7%; the specificities were 36.0 and 78.6%, respectively. The study shows that employing both assays can improve the serodiagnosis of toxocariasis. An IgG4 immunoassay would also be useful in the secondary screening of antigen clones in the effort to develop improved serological tests for toxocariasis.
  4. A new antigen detection ELISA for the diagnosis of Strongyloides infection
    Balachandra D, Rahumatullah A, Lim TS, Mustafa FH, Ahmad H, Anuar NS, et al.
    Acta Trop, 2021 Sep;221:105986.
    PMID: 34058161 DOI: 10.1016/j.actatropica.2021.105986
    Serodiagnosis is an essential component of the laboratory diagnosis of Strongyloides infection and is usually performed using an indirect IgG antibody test. A direct antigen detection method can complement the IgG assay, particularly for detecting early infection and post-treatment follow-up. In the present study, a recombinant scFv monoclonal antibody against NIE recombinant protein (rMAb23) that we had previously produced was used to develop a Strongyloides antigen detection ELISA (SsAg-ELISA). The assay is based on detecting immune complexes of circulating NIE antigens bound to Strongyloides-specific IgG antibodies. The optimized ELISA parameters were 10 µg/mL of rMAb23 coated on microtitre plate wells, 2% skim milk as blocking reagent, 1:100 serum dilution, and 1:1000 goat anti-human IgG F(ab')2 conjugated to horseradish peroxidase. Four groups of serum samples were used, i.e., Strongyloides-positive serum samples categorized into Groups IA and IB; the former were from probable chronic infections and the latter from probable early/acute infections. Strongyloides-negative samples comprising Groups II (healthy samples) and III (other infections); the latter were from eleven different types of other parasitic infections. The receiver operating characteristic (ROC) curve showed an area under the curve (AUC) of 1.00, cut-off optical density (OD405) of 0.5002, and 100% diagnostic sensitivity and specificity. The results of the commercial IgG-ELISA and SsAg-ELISA from Group IA were found to be moderately correlated (r = 0.416; p 
  5. Parallel ELISAs using crude soluble antigen and excretory-secretory antigen for improved serodiagnosis of amoebic liver abscess
    Wong WK, Foo PC, Olivos-Garcia A, Noordin R, Mohamed Z, Othman N, et al.
    Acta Trop, 2017 Aug;172:208-212.
    PMID: 28506795 DOI: 10.1016/j.actatropica.2017.05.017
    Crude soluble antigen (CSA) produced from Entamoeba histolytica trophozoite is conventionally used for serodiagnosis of invasive amoebiasis. However, high background seropositivities by CSA-assay in endemic areas complicate the interpretation of positive result in clinical settings. Instead, incorporating a second assay which indicates active or recent infection into the routine amoebic serology could possibly complement the limitations of CSA-assay. Hence, the present study aimed to evaluate the diagnostic efficacies of indirect ELISAs using CSA and excretory-secretory antigen (ESA) for serodiagnosis of amoebic liver abscess (ALA). Reference standard for diagnosis of ALA at Hospital Universiti Sains Malaysia is based on clinical presentation, radiological imaging and positive indirect haemagglutination assay (titer ≥256). Five groups of human serum samples collected from the hospital included Group I - ALA diagnosed by the reference standard and pus aspirate analysis using real-time PCR (n=10), Group II - ALA diagnosed by the reference standard only (n=41), Group III - healthy control (n=45), Group IV - other diseases control (n=51) and Group V - other infectious diseases control (n=31). For serodiagnosis of ALA serum samples (Group I and II), CSA-ELISA showed sensitivities of 100% for both groups, while ESA-ELISA showed sensitivities of 100% and 88%, respectively. For serodiagnosis of non-ALA serum samples (Group III, IV and V), CSA-ELISA showed specificities of 91%, 75% and 100%, respectively; while ESA-ELISA showed specificities of 96%, 98% and 100%, respectively. Indirect ELISAs using CSA and ESA have shown distinct strength for serodiagnosis of ALA, in terms of sensitivity and specificity, respectively. In conclusion, parallel analysis by both assays improved the overall efficacies of amoebic serology as compared to either single assay.
  6. Lateral flow dipstick antigen assay for human cystic echinococcosis
    Khanbabaie S, Riazi M, Chang CH, Yunus MH, Noordin R
    Acta Trop, 2019 Feb;190:171-176.
    PMID: 30458123 DOI: 10.1016/j.actatropica.2018.11.018
    Cystic echinococcosis (CE) is a neglected zoonotic disease with a worldwide distribution and is a major public health problem in some areas. Diagnosis of CE is mainly based on clinical symptoms, imaging and serological testing, however, improvement in serodiagnosis is still needed. This study was aimed at detecting circulating Echinococcus antigen in CE patients using a lateral flow dipstick (LFD) assay. Three types of hydatid antigens i.e. hydatid cyst fluid (HCF), native antigen B (nAgB) and recombinant antigen B (rAgB) were prepared and polyclonal rabbit antiserum was raised against each antigen. Purified IgG fractions were prepared and a portion was conjugated to gold nanoparticles. After a series of optimizations, a final antigen detection LFD assay was developed using a combination of anti-nAgB-IgG and gold-conjugated anti-HCF-IgG. Evaluation of the assay showed that 27 out of 35 (77%) serum samples from CE patients gave positive results. Meanwhile, the test showed a diagnostic specificity of 82% when tested with sera from 38 healthy individuals and 13 patients with other parasitic diseases. In conclusion, the antigen detection LFD assay seemed to be useful for diagnosis of CE and possibly for post-treatment follow-up, and merit further evaluation studies. We foresee that it may improve serodiagnosis of CE when used in tandem with an antibody detection test.
  7. A point-of-care cassette test for detection of Strongyloides stercoralis
    Noordin R, Osman E, Kalantari N, Anuar NS, Gorgani-Firouzjaee T, Sithithaworn P, et al.
    Acta Trop, 2022 Feb;226:106251.
    PMID: 34808116 DOI: 10.1016/j.actatropica.2021.106251
    Strongyloides stercoralis is a parasite that causes strongyloidiasis worldwide. It may lead to a life-long infection in immunocompetent people and hyperinfection in immunosuppressed patients. A point-of-care (POC) rapid test is helpful for patient diagnosis in resource-limited settings and as a detection tool in elimination/control programs. Previously, we reported a rapid IgG4 dipstick test (Ss Rapid®) for Strongyloides suitable for a laboratory setting. A POC cassette format of the test, which is field-applicable, has since been developed. Here, we report on a laboratory-based evaluation of the Ss Rapid® cas sette test on 285 sera. We assessed the diagnostic sensitivity of the Ss Rapid® cas sette with 32 sera, comprising samples from larval and/or DNA positive individuals from three countries. Additionally, we also tested samples from 33 seropositive endemic areas residents. We evaluated the diagnostic specificity of the test using 220 samples, comprising sera from other infections (n = 101), allergy cases with high IgE antibodies (n = 4), and blood donors (n = 115). The test showed high diagnostic sensitivity (97%, 31/32), and all sera of the seropositive endemic residents were reactive. It also showed high diagnostic specificity (94.5%, 208/220), and all false-positive samples tested negative after sera adsorption using recombinant NIE-coated microsphere beads. Additionally, we showed that the test worked with spiked whole blood samples. The study results showed that the SsRapid® cas sette test merits further laboratory and field evaluations.
  8. Soil-transmitted helminthic vaccines: Where are we now?
    Wong MTJ, Anuar NS, Noordin R, Tye GJ
    Acta Trop, 2023 Mar;239:106796.
    PMID: 36586174 DOI: 10.1016/j.actatropica.2022.106796
    It has been tested and proven that vaccination is still the best strategy to combat infectious diseases. However, to date, there are still no vaccines against human soil-transmitted helminthic diseases, despite their high prevalence globally, particularly in developing countries and rural areas with tropical climates and poor sanitation. The development of vaccines against helminths is riddled with obstacles. Helminths have a complex life cycle, multiple stages within the same host with stage-specific antigen expression, and the ability to regulate host immune reactions to evade the immune response. These elements contribute to the main challenge of helminthic vaccines: the identification of effective vaccine candidates. Therefore, this article reviews the current progress and potential future direction of soil-transmitted helminthic vaccines, particularly against Trichuris trichiura, Ascaris lumbricoides, Strongyloides stercoralis, Necator americanus and Ancylostoma duodenale. The study design employed was a systematic review, using qualitative meta-summary synthesis. Preclinical studies and clinical trials on the development of protein subunit vaccines against the five soil-transmitted helminths were searched on PubMed and Scopus. Effectiveness was indicated by a reduction in worm burden or larval output, an increase in specific IgG levels, or an increase in cytokine production. Our findings show that only the hookworm vaccine against N. americanus is in the clinical trial phase, while the rest is still in exploratory research and pre-clinical development phase.
  9. Generation of IgG antibodies against Strongyloides stercoralis in mice via immunization with recombinant antigens A133 and Ss-IR
    Wong MTJ, Anuar NS, Noordin R, Tye GJ
    Acta Trop, 2024 Mar;251:107122.
    PMID: 38246399 DOI: 10.1016/j.actatropica.2024.107122
    Strongyloidiasis, caused by the nematode Strongyloides stercoralis, remains a threat to global public health, and a vaccine would be useful to control the disease, especially in developing countries. This study aimed to evaluate the efficacy of recombinant proteins, A133 and Ss-IR, as potential vaccine candidates against strongyloidiasis by investigating the humoral and cellular immune responses in immunized mice. Respective antigens were adjuvanted with Complete Freund's Adjuvant (prime) and Incomplete Freund's Adjuvant (boost) and administered intraperitoneally (prime) and subcutaneously (boost) to female BALB/c mice. For antigen-only doses, only antigens were injected without adjuvants. Altogether, 1 prime dose, 4 booster doses, and 2 antigen-only doses were administered successively. ELISAs were conducted to assess the antibody responses, along with flow cytometry and cytokine ELISA to elucidate the cellular immune responses. Results showed that A133 and Ss-IR induced the production of IgG1 and IgG2a, with A133 generating more robust IgG2a responses than Ss-IR. Flow cytometry findings indicated that effector CD8+T-cells and memory B-cells activity were upregulated significantly for A133 only, whereas cytokine ELISA demonstrated that a Th1/Th2/Th17 mixed cell responses were triggered upon vaccination with either antigen. This preliminary study illustrated the good potential of recombinant A133 and Ss-IR as vaccine candidates against S. stercoralis. It provided information on the probable immune mechanism involved in host defence and the elicitation of protection against S. stercoralis.
  10. Serodiagnostic methods for diagnosing larval toxocariasis
    Noordin R, Yunus MH, Tan Farrizam SN, Arifin N
    Adv Parasitol, 2020;109:131-152.
    PMID: 32381194 DOI: 10.1016/bs.apar.2020.01.003
    Toxocariasis is a human infection primarily caused by larvae of Toxocara canis from dogs, and also by T. cati from cats. Children have a more significant risk of acquiring the infection due to their closer contact with pets, and greater chances of ingesting soil. Diagnosis of toxocariasis is based on clinical, epidemiological, and serological data. Indirect IgG ELISA is a widely used serodiagnostic method for toxocariasis, with native T. canis TES most commonly used as the antigen. Western blots, using the same antigen, can be used to confirm positive ELISA findings to reduce false-positive results. Improvements in Toxocara serodiagnosis include the use of recombinant TES antigens, simpler and more rapid assay formats, and IgG4 subclass detection. Also, incorporation of recombinant T. cati TES protein increases the diagnostic sensitivity. Development of antigen detection tests using polyclonal and monoclonal antibodies, nanobodies, or aptamers can complement the antibody detection assays, and enhance the effectiveness of the serodiagnosis.
  11. Antigenic proteins of Helicobacter pylori of potential diagnostic value
    Khalilpour A, Santhanam A, Wei LC, Saadatnia G, Velusamy N, Osman S, et al.
    Asian Pac J Cancer Prev, 2013;14(3):1635-42.
    PMID: 23679248
    Helicobacter pylori antigen was prepared from an isolate from a patient with a duodenal ulcer. Serum samples were obtained from culture-positive H. pylori infected patients with duodenal ulcers, gastric ulcers and gastritis (n=30). As controls, three kinds of sera without detectable H. pylori IgG antibodies were used: 30 from healthy individuals without history of gastric disorders, 30 from patients who were seen in the endoscopy clinic but were H. pylori culture negative and 30 from people with other diseases. OFF-GEL electrophoresis, SDS-PAGE and Western blots of individual serum samples were used to identify protein bands with good sensitivity and specificity when probed with the above sera and HRP-conjugated anti-human IgG. Four H. pylori protein bands showed good (≥ 70%) sensitivity and high specificity (98-100%) towards anti-Helicobacter IgG antibody in culture- positive patients sera and control sera, respectively. The identities of the antigenic proteins were elucidated by mass spectrometry. The relative molecular weights and the identities of the proteins, based on MALDI TOF/ TOF, were as follows: CagI (25 kDa), urease G accessory protein (25 kDa), UreB (63 kDa) and proline/pyrroline- 5-carboxylate dehydrogenase (118 KDa). These identified proteins, singly and/or in combinations, may be useful for diagnosis of H. pylori infection in patients.
  12. Fulltext Entamoeba histolytica acetyl-CoA synthetase: biomarker of acute amoebic liver abscess
    Huat LB, Garcia AO, Ning TZ, Kin WW, Noordin R, Azham SS, et al.
    Asian Pac J Trop Biomed, 2014 Jun;4(6):446-50.
    PMID: 25182945 DOI: 10.12980/APJTB.4.2014C1169
    To characterize the Entamoeba histolytica (E. histolytica) antigen(s) recognized by moribound amoebic liver abscess hamsters.
  13. Fulltext Detection of Entamoeba histolytica in experimentally induced amoebic liver abscess: comparison of three staining methods
    Ning TZ, Kin WW, Mustafa S, Ahmed A, Noordin R, Cheong TG, et al.
    Asian Pac J Trop Biomed, 2012 Jan;2(1):61-5.
    PMID: 23569836 DOI: 10.1016/S2221-1691(11)60191-3
    To compare the efficacy of three different tissue stains, namely haematoxylin and eosin (H&E), periodic-acid Schiff (PAS) and immunohistochemical (IHC) stains for detection of Entamoeba histolytica (E. histolytica) trophozoites in abscessed liver tissues of hamster.
  14. Isolation and genotyping of Toxoplasma gondii from free-range ducks in Malaysia
    Puvanesuaran VR, Noordin R, Balakrishnan V
    Avian Dis, 2013 Mar;57(1):128-32.
    PMID: 23678741
    Toxoplasma gondii is a parasitic protozoan that infects nearly one-third of humans. The present study was performed to isolate and genotype T. gondii from free-range ducks in Malaysia. Sera, heads, and hearts from 205 ducks were obtained from four states in Peninsular Malaysia, and 30 (14.63%) sera were found to be seropositive when assayed with the modified agglutination test (MAT > or = 1:6). All the positive samples were inoculated into mice, and T. gondii was successfully isolated from four individual duck samples (1.95%), which were initially found to be strongly seropositive (MAT > or = 1:24). The isolates were subjected to PCR-RFLP analysis, and two T. gondii strains were identified: type I and type II. This is the first reported study on the genetic characterization of T. gondii isolates from free-range farm animals in Southeast Asia.
  15. Fulltext In vitro anti-Toxoplasma gondii activity of root extract/fractions of Eurycoma longifolia Jack
    Kavitha N, Noordin R, Chan KL, Sasidharan S
    BMC Complement Altern Med, 2012;12:91.
    PMID: 22781137 DOI: 10.1186/1472-6882-12-91
    Toxoplasma gondii infection causes toxoplasmosis, an infectious disease with worldwide prevalence. The limited efficiency of drugs against this infection, their side effects and the potential appearance of resistant strains make the search of novel drugs an essential need. We examined Eurycoma longifolia root extract and fractions as potential sources of new compounds with high activity and low toxicity. The main goal of this study was to investigate the anti-T. gondii activity of crude extract (TACME) and four fractions (TAF 273, TAF 355, TAF 191 and TAF 401) from E. longifolia, with clindamycin as the positive control.
  16. Fulltext Production of recombinant Entamoeba histolytica pyruvate phosphate dikinase and its application in a lateral flow dipstick test for amoebic liver abscess
    Saidin S, Yunus MH, Zakaria ND, Razak KA, Huat LB, Othman N, et al.
    BMC Infect Dis, 2014 Apr 04;14:182.
    PMID: 24708664 DOI: 10.1186/1471-2334-14-182
    BACKGROUND: Amoebic liver abscess (ALA) is the most common clinical manifestation of extraintestinal amoebiasis especially in developing countries, causing up to 100 000 fatal cases annually. Accurate and early diagnosis is important to prevent the disease complications, however its diagnosis still poses many challenges due to the limitations of the available detection tools. Pyruvate phosphate dikinase (PPDK), an excretory-secretory protein of E. histolytica, has been reported as a potential diagnostic marker for ALA, hence it may be exploited in the development of a new test for ALA.

    METHODS: Recombinant PPDK (rPPDK) was expressed, purified and evaluated by Western blot. In parallel, recombinant galactose-and-N-acetyl-D-galactosamine inhibitable lectin (Gal/GalNAc lectin) was produced and tested similarly. The protein identity was confirmed by analysis using MALDI-TOF/TOF. A lateral flow dipstick (LFD) test using rPPDK was subsequently developed (rPPDK-LFD) and evaluated for serodiagnosis of ALA.

    RESULTS: rPPDK was expressed as soluble protein after 4 hours of induction with 1 mM isopropyl β-D-1-thiogalactopyranoside (IPTG) at 30°C. Purification using nickel-nitrilotriacetic acid (Ni-NTA) resin yielded 1.5 mg of rPPDK from 1 L of culture with estimated molecular mass of 98 kDa on SDS-PAGE. Western blots using sera from patients with ALA, healthy individuals and other diseases probed with anti-human IgG4-HRP showed the highest sensitivity (93.3%) and specificity (100%); as compared to blots using IgG and IgG1 as secondary antibodies. Moreover, rPPDK showed better specificity when compared to rGal/GalNAc lectin. In the development of the LFD test, the optimum amount of rPPDK was 0.625 μg per dipstick and the optimum working concentration of colloidal gold conjugated anti-human IgG4 was optical density (OD) 5 (1.7 μg of anti-human IgG4). Evaluation of rPPDK-LFD using ALA patients and controls serum samples showed 87% diagnostic sensitivity and 100% specificity.

    CONCLUSION: The developed rPPDK-LFD showed good potential for rapid diagnosis of ALA, and merit further multicentre validation using larger number of serum samples.

  17. Fulltext Identification and real-time expression analysis of selected Toxoplasma gondii in-vivo induced antigens recognized by IgG and IgM in sera of acute toxoplasmosis patients
    Amerizadeh A, Khoo BY, Teh AY, Golkar M, Abdul Karim IZ, Osman S, et al.
    BMC Infect Dis, 2013;13:287.
    PMID: 23800344 DOI: 10.1186/1471-2334-13-287
    Toxoplasma gondii is an obligate intracellular zoonotic parasite of the phylum Apicomplexa which infects a wide range of warm-blooded animals, including humans. In this study in-vivo induced antigens of this parasite was investigated using in-vivo induced antigen technology (IVIAT) and pooled sera from patients with serological evidence of acute infection.
  18. Fulltext Evaluation of Entamoeba histolytica recombinant phosphoglucomutase protein for serodiagnosis of amoebic liver abscess
    Ning TZ, Kin WW, Noordin R, Cun ST, Chong FP, Mohamed Z, et al.
    BMC Infect Dis, 2013;13:144.
    PMID: 23514636 DOI: 10.1186/1471-2334-13-144
    Amoebic liver abscess (ALA) is the most frequent clinical presentation of extra-intestinal amoebiasis. The diagnosis of ALA is typically based on the developing clinical symptoms, characteristic changes on radiological imaging and serology. Numerous serological tests have been introduced for the diagnosis of ALA, either detecting circulating amoebic antigens or antibodies. However those tests show some pitfalls in their efficacy and/or the preparation of the tests are costly and tedious. The commercial IHA kit that used crude antigen was reported to be useful in diagnosis of ALA, however high antibody background in endemic areas may cause problems in its interpretation. Thus, discovery of well-defined antigen(s) is urgently needed to improve the weaknesses of current serodiagnostic tests.
  19. Fulltext Helicobacter pylori recombinant UreG protein: cloning, expression, and assessment of its seroreactivity
    Khalilpour A, Osman S, Yunus MH, Santhanam A, Vellasamy N, Noordin R
    BMC Res Notes, 2014;7:809.
    PMID: 25406411 DOI: 10.1186/1756-0500-7-809
    Helicobacter pylori is a human pathogen and during the process of infection, antigens from the bacterium elicit strong host humoral immune responses. In our previous report, native H. pylori UreG protein showed good reactivity with sera from H. pylori patients. This study was aimed at producing the recombinant form of the protein (rUreG) and determining its seroreactivities.
  20. Fulltext Theoretical investigation on structural, functional and epitope of a 12 kDa excretory-secretory protein from Toxoplasma gondii
    Tommy YB, Lim TS, Noordin R, Saadatnia G, Choong YS
    BMC Struct Biol, 2012 Nov 27;12:30.
    PMID: 23181504 DOI: 10.1186/1472-6807-12-30
    BACKGROUND: Toxoplasma gondii is an intracellular coccidian parasite that causes toxoplasmosis. It was estimated that more than one third of the world population is infected by T. gondii, and the disease is critical in fetuses and immunosuppressed patients. Thus, early detection is crucial for disease diagnosis and therapy. However, the current available toxoplasmosis diagnostic tests vary in their accuracy and the better ones are costly.

    RESULTS: An earlier published work discovered a highly antigenic 12 kDa excretory-secretory (ES) protein of T. gondii which may potentially be used for the development of an antigen detection test for toxoplasmosis. However, the three-dimensional structure of the protein is unknown. Since epitope identification is important prior to designing of a specific antibody for an antigen-detection based diagnostic test, the structural elucidation of this protein is essential. In this study, we constructed a three dimensional model of the 12 kDa ES protein. The built structure possesses a thioredoxin backbone which consists of four α-helices flanking five β-strands at the center. Three potential epitopes (6-8 residues) which can be combined into one "single" epitope have been identified from the built structure as the most potential antibody binding site.

    CONCLUSION: Together with specific antibody design, this work could contribute towards future development of an antigen detection test for toxoplasmosis.

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