Development and application of a double-antigen sandwich enzyme-linked immunosorbent assay for detection of antibodies to porcine circovirus 2

A double-antigen sandwich enzyme-linked immunosorbent assay (ELISA) is described for detection of porcine circovirus 2 (PCV2) antibodies using the well-characterized recombinant PCV2 capsid protein. In a comparative test of 394 pig sera against an indirect immunofluorescence (IIF) test and a commercial ELISA kit (also based on the recombinant PCV2 capsid protein), the results showed that the diagnostic sensitivity, specificity, and accuracy of the assay were, respectively, 90.61, 94.02, and 91.62% compared with IIF and 94.38, 95.28, and 94.67% compared with the commercial ELISA kit. Assay of 12 PCV-free pigs over a 5-week period produced only PCV2-negative titers by all 3 methods. These results and the seroprofiles of 4 pig farms obtained by both the commercial ELISA kit and the double-antigen sandwich ELISA indicate that the sandwich ELISA is a reliable method for detection of antibodies to PCV2. Additionally, the method described here permits the use of undiluted test serum samples simultaneously loaded with horseradish peroxidase (HRP)-conjugated antigen into the test well, and the complete test procedure can be performed in less than 90 min. This double-antigen sandwich ELISA should be a useful tool to aid swine industry professionals in deciding the intervention strategies for the control of PCV2-associated diseases.     

Development and evaluation of serological assays for detection of Hantaanvirus-specific antibodies in human sera using yeast-expressed nucleocapsid protein

Indirect and capture enzyme-linked immunosorbent assays (ELISAs) for detection of Hantaan virus (HTNV)-specific immunoglobulins G (IgG) and M (IgM) in human serum samples were developed on the basis of recombinant yeast-expressed nucleocapsid (N) protein of HTNV. The sensitivities and specificities of the indirect and capture ELISAs were evaluated by comparing the reactivity of sera from patients with hemorrhagic fever with renal syndrome (HFRS) from China with that of a commercial IgG/IgM kit. The sensitivity of the indirect IgG and IgM ELISA tests was both 100% and the specificity of the indirect IgM and IgG ELISA test was 98% and 99%, respectively. The sensitivity and specificity of the capture IgM ELISA was 100% and 97%, respectively. The novel assays were found to detect HTNV-specific antibodies in acute phase sera from suspected HFRS patients in China. The results indicate that these novel ELISAs are suitable for the diagnosis of HTNV and for sero-epidemiological studies.     

双抗体间接夹心ELISA法检测乳腺癌患者外周血MUC1蛋白水平的评价

目的优化双抗体间接夹心ELISA试剂盒,并探讨其在乳腺癌患者中检测MUC1黏蛋白水平的应用价值。方法用基因重组MUC1-GST和MUC1-MBP融和蛋白免疫家兔和大鼠,获得抗MUC1血清,并对其纯化,获得纯化的家兔抗人及大鼠抗人MUC1多克隆抗体;经不同的筛选确立了以家兔抗人MUC1抗体作为包被抗体、大鼠抗人MUC1抗体作为检测抗体的双抗体间接夹心试剂盒,敏感度可达到0.2 ng/ml。结果应用建立的试剂盒对40例乳腺癌,18例乳腺良性疾病和120健康对照者血清中MUC1蛋白水平的进行检测,检测结果绘制ROC曲线,分析得出以2.75 ng/ml为乳腺癌患者与乳腺良性疾病患者的临界值,以1.86 ng/ml为乳腺疾病与正常人为临界值,检测结果表明本研究对乳腺癌诊断的阳性率高达97.5%,乳腺良性疾病的阳性率为66.7%,正常人特异性为96.7%。对于乳腺癌同一病例样本用酶联免疫法CA15-3诊断试剂盒进行对比检测,其检出率为3.33%,特异度为100%。绘制ROC曲线对比显示,本研究所建立的双抗体夹心ELISA方法对乳腺癌诊断的准确度明显高于CA15-3试剂盒。结论本研究成功建立了特异性强,灵敏度良好的双抗体间接夹心ELISA试剂盒,有望开发为临床辅助诊断的常规试剂盒,尤其有望应用于乳腺癌的大规模筛查及早期诊断。     

抗HBx IgM的检测及临床应用

利用羊抗人IgM,基因工程表达的乙型肝炎X抗原和酶标抗-HBx单克隆抗体,建立了检测血清中抗-HBx IgM充体的ELISA双夹心法,并进行了初步应用。实验结果表明,此方法的特异性强,稳定性及重复性好(批内变异系数8.64％,批间变异系数10.60％,重复率为100％),且不受血清中抗-HBc IgM、抗-HAV IgM及类风湿因子的影响。由于目前国内外都没有抗-HBx IgM标准品,故对方法的敏感性没有报道。     

Double-antigen sandwich ELISA for detection of antibodies to SARS-associated coronavirus in human serum

The study presented here was conducted to evaluate the performance of a double-antigen sandwich ELISA to detect antibodies in human serum against the coronavirus associated with severe acute respiratory syndrome (SARS). A recombinant partial nucleocapsid protein of SARS-associated coronavirus was used as a serodiagnostic antigen in the ELISA. A total of 2892 clinical serum samples were tested with the ELISA kit, which positively identified 25 of 35 (71.4%) samples of patients with confirmed SARS infection, 286 of 407 (70%) samples of patients suspected of having SARS, 229 of 302 (75.8%) samples of convalescent SARS patients, and 0 of 544 samples obtained from healthcare workers; only 1 of 1604 clinical samples obtained from patients with other diseases demonstrated a weakly positive result. These results indicate that the double-antigen sandwich ELISA is an effective screening method for the serodiagnosis of SARS-associated coronavirus.     

HIV-1 gp41重组抗原的表达及其免疫反应性检测

为了在大肠杆菌中表达具有良好免疫反应性的HIV-1gp41重组抗原,本实验运用基因工程技术,经PCR扩增gp41的主要抗原表位序列,BamHⅠ、XhoⅠ双酶切后与E3质粒连接,转化克隆宿主菌DH5α,再提取重组质粒进一步转化表达宿主菌BL21(DE3),经IPTG诱导表达重组蛋白,纯化后标记HRP,通过双抗原夹心酶联免疫方法检测其免疫反应性和特异性。结果表明,获得的HIV-1gp41重组抗原能够与相应抗体特异性结合,与多种无关抗体间无交叉反应,对825份HIV阴性标本检测无错检。检测结果说明该重组抗原具有良好的免疫反应性,在HIV-1抗体诊断试剂中具有潜在的应用价值,为进一步研究gp41抗原奠定了基础。     

Preparation and evaluation of recombinant severe fever with thrombocytopenia syndrome virus nucleocapsid protein for detection of total antibodies in human and animal sera by double-antigen sandwich enzyme-linked immunosorbent assay

The recent emergence of the human infection confirmed to be caused by severe fever with thrombocytopenia syndrome virus (SFTSV) in China is of global concern. Safe diagnostic immunoreagents for determination of human and animal seroprevalence in epidemiological investigations are urgently needed. This paper describes the cloning and expression of the nucleocapsid (N) protein of SFTSV. An N-protein-based double-antigen sandwich enzyme-linked immunosorbent assay (ELISA) system was set up to detect the total antibodies in human and animal sera. We reasoned that as the double-antigen sandwich ELISA detected total antibodies with a higher sensitivity than traditional indirect ELISA, it could be used to detect SFTSV-specific antibodies from different animal species. The serum neutralization test was used to validate the performance of this ELISA system. All human and animal sera that tested positive in the neutralization test were also positive in the sandwich ELISA, and there was a high correlation between serum neutralizing titers and ELISA readings. Cross-reactivity was evaluated, and the system was found to be highly specific to SFTSV; all hantavirus- and dengue virus-confirmed patient samples were negative. SFTSV-confirmed human and animal sera from both Anhui and Hubei Provinces in China reacted with N protein in this ELISA, suggesting no major antigenic variation between geographically disparate virus isolates and the suitability of this assay in nationwide application. ELISA results showed that 3.6% of the human serum samples and 47.7% of the animal field serum samples were positive for SFTSV antibodies, indicating that SFTSV has circulated widely in China. This assay, which is simple to operate, poses no biohazard risk, does not require sophisticated equipment, and can be used in disease surveillance programs, particularly in the screening of large numbers of samples from various animal species.     

用ELISA法检测丙型肝炎病毒IgM抗体试剂盒的研究

市售丙型肝炎检测试剂盒仅能检测丙肝ＩｇＧ抗体，本工作建立的丙型肝炎病毒ＩｇＭ抗体检测方法稳定性强，重复性好，检出率高，具有高度特异性，与甲、乙、丁型肝炎及ＣＭＶ、ＥＢＶ患者无交叉反应。健康人血中不含丙肝ＩｇＭ抗体，我们用该方法检测了１０９例输血后肝炎患者，发现３７例急性肝炎中３６例丙型肝炎病毒ＩｇＭ抗体阳性（９７％），其中１６例患者在起病后４个月内随病情好转而ＩｇＭ抗体阴转，７２例慢性输血后肝炎患者中４３例ＡＬＴ明显异常，４３例中有３６例（８３７％）丙肝ＩｇＭ抗体阳性，而２９例ＡＬＴ正常患者仅有５例阳性，Ｐ＜０．０１，说明慢性肝炎丙肝ＩｇＭ抗体阳性多伴有肝病活动。     

检测抗丙型肝炎病毒总抗体的双抗原夹心法的建立

以丙型肝炎病毒（ＨＣＶ）结构区和非结构区基因工程表达抗原及人工合成多肽包被酶标板，用辣根过氧化物酶标记抗原，建立了检测血清中抗－ＨＣＶ总抗体的双抗原夹心法。与普遍采用的检测抗－ＨＣＶＩｇＧ的间接酶联免疫吸附试验（ＥＬＩＳＡ）比较，其灵敏度（１∶１２８）稍高于间接法（１∶６４），特异性相同，均为１００％。该法可同时检测抗－ＨＣＶ各类抗体，使检出率提高１０％。     

用重组结构区抗原检测抗丙型肝炎病毒IgM抗体方法？…

目的 检测抗丙型肝炎病毒（ＨＣＶ）结构区蛋白ＩｇＭ抗体。方法 采用丙型肝炎病毒Ｃ，Ｅ１、Ｅ２区重组抗原混合包被和分别包被酶标板；用兔抗人γ链血清处理人血清标本，再用固相包被羊抗兔抗体吸附兔抗人γ链－人ＩｇＧ复合物，建立了抗－ＨＣＶＩｇＭ检测方法。结果 对７６例现型肝炎病人血清进行抗－ＨＣＶ ＩｇＭ检测，同时与逆转录－巢式聚合酶链反应（ＲＴ＋ＰＣＲ）检测结果进行比较，再会得具有相关性（Ｐ〈０．００５     

前列腺特异性抗原EIA试剂盒的研制及应用

目的 建立可定量测定人血清中前列腺特异性抗原（ＰＳＡ）含量的夹心ＥＬＩＳＡ法,研制ＰＳＡ－ＥＩＡ检测试剂盒。方法 从健康男性精液中提取并纯化ＰＳＡ,分别免疫Ｂａｌｂ／ｃ小鼠和山羊制备特异性单克隆抗体和多克隆抗体,并以纯化的ＰＳＡ为标准品,建立可定量测定血清中ＰＳＡ含量的夹心ＥＬＩＳＡ法。在此基础上组装ＰＳＡ－ＥＩＡ试剂盒,对该试剂盒的特异性、灵敏度、精密度、正确性和稳定性等多项指标进行评价。应用该     

Prevalence of hepatitis-C virus infection in children with chronic post-transfusion hepatitis.

The prevalence of hepatitis-C virus (HCV) infection was investigated in a group of children with chronic post-transfusion hepatitis using a first- and second-generation HCV-antibody ELISA, 2 confirmatory tests (a second-generation recombinant immunoblot assay and a line immunoassay) as well as an HCV-polymerase chain reaction (PCR). In 33% of the children, clear discrepancies were observed between the 4 different HCV-antibody detection assays, indicating that the serological diagnosis of HCV infection is still problematic. HCV RNA was detectable by PCR in only 69% of the antibody positive patients, which may be due to a fluctuation of viraemia during the course of infection. Such a fluctuation was demonstrated in 6 patients from whom serum samples drawn at different times were investigated. In contrast, in 8 of the 15 seronegative patients, HCV infection was identified only by PCR, although the hepatitis had already persisted for more than 2 years. Antibody assays and PCR together detected HCV infection in about 90% of the patients with chronic hepatitis. When markers of hepatitis B infection were also investigated, only 6% of the cases remained undiagnosed.     

重组人源细胞珠蛋白单抗制备及检测方法建立

目的制备重组人源细胞珠蛋白（recombinanthumanCytoglobin,rhCygb）单克隆抗体,并建立检测该蛋白双抗体夹心ELISA法,为下一步研究rhCygb药代动力学做准备。方法用纯化的rhCygb免疫BALB/c小鼠,采用甲基纤维素半固体培养基法获得抗rhCygb的单克隆抗体杂交瘤细胞,间接ELISA法筛选制备单克隆抗体,建立双抗体夹心ELISA法。结果筛选获取了稳定分泌单克隆抗体的杂交瘤细胞株,通过抗原表位相加法实验获得5株表位不同的细胞株,Western-blotting验证能与rhCygb特异性结合,间接ELISA法验证其不与本实验室制备的其它PET28a-BL21蛋白及BL21裂解液发生交叉反应。本方法灵敏度为1.25ng/ml,在浓度为10～1250ng/ml时,线性关系良好,相关性达0.9931,实验内和实验间平均变异系数分别为6.2%和10.92%。结论成功建立了灵敏度好、特异性高的双抗体夹心法,为下一步研究rhCygb药代动力学奠定了基础。     

Performance of immunoglobulin G (IgG) and IgM enzyme-linked immunosorbent assays using a West Nile virus recombinant antigen (preM/E) for detection of West Nile virus- and other flavivirus-specific antibodies

Focus Technologies developed an indirect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) and a mu-capture IgM ELISA for the detection of West Nile virus (WNV)-specific antibodies based on a WNV preM/E protein recombinant antigen. Normal and disease state serum panels were used to assess the performance characteristics of the two WNV ELISA kits. Totals of 807 and 1,423 sera were used to assess the IgG ELISA and IgM ELISA kits, respectively. The Focus Technologies IgG ELISA had a sensitivity of 97.6% and a specificity of 92.1% (excluding non-WNV flavivirus sera). The comparative method for WNV IgG may lack sensitivity in detecting IgG in early WNV infection, so the specificity of the Focus IgG ELISA may be higher than 92.1%. When sera from patients either infected with or vaccinated against other flaviviruses were tested on the WNV IgG assay, 35% of the sera reacted as positive for WNV IgG. Yellow fever and Japanese encephalitis vaccinees were less reactive in the IgG ELISA than St. Louis and dengue fever patients. The Focus Technologies IgM ELISA had a sensitivity and a specificity of 99.3% (excluding the non-WNV flavivirus sera). The overall cross-reactivity for the IgM ELISA to flavivirus sera was 12%, with 31% of St. Louis encephalitis patients found to be WNV IgM positive and no yellow fever vaccinees found to be WNV IgM positive. In a selected population of 706 sera, 15 false-positive WNV IgM sera were identified. The use of a background subtraction method for the IgM ELISA eliminated all 15 false-positive results, giving a specificity of 100% for the Focus IgM ELISA.     

Microenzyme-linked immunosorbent assay for detection of immunoglobulin G and immunoglobulin M antibodies to Legionella pneumophila

The microenzyme-linked immunosorbent assay (ELISA) for the detection of immunoglobulin M and G (IgM, IgG) antibodies to Legionella pneumophila serogroup 1 antigens was evaluated. IgM antibodies were measured by both double-sandwich and single-sandwich techniques. These assays were compared with the previously standardized indirect immunofluorescence test in four groups of subjects: (i) pneumonia patients with culture-proven Legionnaires disease with serogroup 1 isolates, (ii) pneumonia patients with serogroup 1 organisms detected by direct immunofluorescence testing of respiratory secretions but without culture confirmation, (iii) pneumonia patients with negative culture and direct immunofluorescence tests, and (iv) healthy hospital employees. In addition, the sensitivity and specificity of the IgG ELISA were evaluated with larger groups of controls and Legionnaires disease patients. The ELISA was more sensitive than the indirect immunofluorescence test. However, it detected antibody rises in pneumonia patients without culture or direct immunofluorescence evidence of L. pneumophila serogroup 1 infection, thereby suggesting that the specificity of the ELISA was slightly lower than that of the indirect immunofluorescence test. The double-sandwich ELISA was a sensitive method for detecting IgM antibodies and, as previously reported, appeared to be free from interference by rheumatoid factor. IgM anti-Legionella antibodies detected by the ELISA appeared earlier and were less persistent than IgG antibodies. In addition, the IgM ELISA was useful in detecting antibodies in necropsy serum samples obtained from patients dying acutely of Legionnaires disease. The data presented show that the ELISA is a reliable method for the detection of specific anti-Legionella antibodies.     

Recognition of multiple classes of hepatitis C antibodies increases detection sensitivity in oral fluid.

Paired serum-oral fluid samples from 127 hepatitis C virus (HCV)-positive and 31 HCV-negative patients were tested for the presence of anti-HCV using the Ortho HCV 3.0 ELISA. Using the immunoglobulin G (IgG)-specific detection antibody provided with the HCV 3.0 ELISA we attained 100% sensitivity and specificity with serum samples; however, sensitivity in oral fluid samples was only 81%. By modifying the HCV 3.0 ELISA to utilize a secondary antibody cocktail that recognizes not only IgG but IgA and IgM as well, we attained 100% specificity and sensitivity with oral fluid samples.     

Efficiency of various serological techniques for diagnosing Coxiella burnetii infection

An indirect immunofluorescence assay (IFA) using a recently developed commercial kit for detecting antibodies against Coxiella burnetii (C.b.), the etiological agent of Q fever, has been evaluated using human field serum samples. The IFA was compared with an ELISA and a complement fixation test (CFT). The IFA was based on the corpuscular C.b. phase I and phase II antigens specific to anti-C.b. phase I and II antibodies, respectively. Fifty sera from persons with symptoms of Q fever were examined in this study. The IFA compared with the ELISA showed the sensitivities of 97.7% and 87.2% for IgG and 66.7% and 60.0% for IgM phase II and I antibodies, respectively and the specificities of 100% and 90.0% for IgG and 75.9% and 64.7% for IgM phase II and phase I antibodies, respectively. Due to a limited number of sera positive in the IgA antibody testing, the data presented should be considered with caution. It appears that the IFA strikes a very good balance between high specificity and sensitivity with phase II and phase I IgG antibodies and a less satisfactory one with IgM antibodies. The CFT failed in one of the above aspects showing a good specificity but a poor sensitivity, especially for phase I antibodies. The study demonstrated that the IFA is suitable for diagnosing Q fever and its therapeutic follow-up and is a good candidate for screening sera in large numbers. A certain limitation, especially in testing early stages of the chronic disease, could be a low fluorescence intensity of the IgA positive control in comparison with the IgA negative one.     

Development and Evaluation of an Epstein-Barr Virus (EBV) Immunoglobulin M Enzyme-Linked Immunosorbent Assay Based on the 18-Kilodalton Matrix Protein for Diagnosis of Primary EBV Infection

A new immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA) based on the recombinant Epstein-Barr virus (EBV) matrix protein was developed. Compared to indirect immunofluorescence for the detection of IgM antibody to the EBV capsid antigen on clinical specimens, the sensitivity and specificity of the new IgM ELISA were 96 and 96%, respectively.     

Comparison of indirect double antibody and double antibody sandwich ELISA techniques with latex agglutination test for the diagnosis of human rotavirus infection

94 faecal samples from infants and children suffering of acute gastroenteritis were investigated for rotavirus by indirect double antibody sandwich ELISA kit (WHO, Geneva), Rotavirus ELISA kit (DAKOPATTS A/S, Copenhagen) and Rotalex latex-agglutination kit (Orion Diagnostica, Helsinki). The ELISA techniques gave almost identical results and seemed to be of same sensitivity and specificity. Rotalex agglutination had an overall agreement of 88% with ELISA. It is concluded that strongly positive reactions found by Rotalex may be regarded as true positive reactions, whereas samples producing weakly positive and/or negative reactions should be retested in a more specific and sensitive assay, such as enzyme linked immunosorbent-assay (ELISA).     

Serodiagnosis of Epstein-Barr Virus Infection by Using Recombinant Viral Capsid Antigen Fragments and Autologous Gene Fusion

Using recombinant 15- to 30-kDa fragments and fusion with glutathione S-transferase (GST), we investigated the seroreactivity of three large structural proteins of Epstein-Barr virus (EBV), p150 (BcLF1, capsid), p143 (BNRF1, tegument), and gp125 (BALF4, membrane) in Western blots. None of 13 fragments tested, however, was qualified for diagnostic application. In contrast, the two small viral capsid antigens (VCA), p18 (BFRF3) and p23 (BLRF2), demonstrated sensitive (100%) EBV-specific immunoglobulin G (IgG) reactivities. While p18 additionally showed maximum sensitivity for IgM detection, the IgM sensitivity of p23 was restricted (44%). An autologous fusion protein, p23-p18, which consists N-terminally of full-length p23, followed by the carboxy half of p18, was constructed. This antigen was subjected to indirect VCA enzyme-linked immunosorbent assays (ELISAs), for IgG and IgM, as well as to a micro-capture (microc) IgM ELISA. All assays were found to be 100% specific when EBV-negative sera were tested. Using sera from previously infected individuals, the p23-p18 fusion revealed an improved IgG sensitivity of 99% compared to sensitivities of 97 and 93% for the single antigens p18 and p23, respectively. The sensitivity and specificity of the indirect IgM ELISA with samples of primary and past infections, respectively, were 100%. The microc principle for IgM overcame completely the interference by rheumatoid factors. Compared to the specificity of the indirect IgM version, the specificity with sera collected from rheumatoid arthritis patients increased from 48 to 100%. In summary, the p23-p18 IgG and microc IgM ELISAs showed excellent performances and are promising new diagnostic tests for the detection of EBV-specific antiviral capsid antibodies.