Serodiagnostic comparison between two methods, ELISA and surface plasmon resonance for the detection of antibody titres of Mycoplasma hyopneumoniae

A protein chip based on surface plasmon resonance (SPR) was developed for measuring the Mycoplasma hyopneumoniae antibody titres using a recombinant 30-kDa fragment of P97 adhesin as an antigen. The diagnostic potential of this SPR assay, for detecting the antibody titres to the M. hyopneumoniae 30-kDa protein, was compared with that of conventional ELISA using 70 pig serum samples taken from six pig farms. The SPR assay was found to be highly specific and sensitive. Moreover, there was a strong positive correlation between the SPR and ELISA titres (n = 70, r = 0.898, P < 0.01). Therefore, this recombinant 30-kDa protein can be used as an antigen for serological studies, and the SPR, which is a label-free method, is expected to be a valuable and reproducible tool in the serodiagnosis of M. hyopneumoniae infection.     

A novel 57-kDa merozoite protein of Babesia gibsoni is a prospective antigen for diagnosis and serosurvey of canine babesiosis by enzyme-linked immunosorbent assay

We isolated a novel single copy gene encoding a 57-kDa merozoite protein of Babesia gibsoni (BgP57). The nucleotide sequence of the cDNA was 2387 bp with an open reading frame (ORF) of 1644 bp encoding a 57-kDa predicted polypeptide having 547 amino acid residues. The recombinant BgP57 (rBgP57) without a predicted signal peptide was expressed in Escherichia coli as a soluble glutathione S-transferase (GST) fusion protein. Western blotting showed that the corresponding native protein was 57-kDa, consistent with molecular weight of predicted mature polypeptide. An indirect enzyme-linked immunosorbent assay (ELISA) using the rBgP57 detected specific antibodies in the sequential sera from a dog experimentally infected with B. gibsoni. Moreover, the antigen did not cross-react with antibodies to B. canis sub-species and closely related apicomplexan parasites indicating that the rBgP57 was a specific antigen for B. gibsoni antibodies. The diagnostic performance of ELISA based on rBgP57 using 107 sera from B. gibsoni-naturally infected dogs was the same as the previously identified rBgP32 but performed better than the previously studied rBgP50. Although, seminested PCR detected higher proportions (82%) of positive samples than the ELISAs, the Mcnemar's chi-square test showed that there was no significant difference in relative effectiveness of rBgP57-ELISA and seminested PCR (chi(2)=2.70; P=0.1003) in identifying positive samples. The rBgP57-ELISA when used in combination with rBgP32-ELISA and rBgP50-ELISA appeared to improve sensitivity of the rBgP57-ELISA for detection of B. gibsoni antibodies. Overall, the rBgP57-ELISA and seminested PCR when used in combination, could improve epidemiological surveys and clinical diagnosis of B. gibsoni infection.     

Diagnostic potential of recombinant protein of hexahistidine tag and infectious bursal disease virus VPX expressed in Escherichia coli

The current method to detect antibody titre against infectious bursal disease virus (IBDV) in chickens is based on enzyme-linked immunosorbent assay (ELISA) using whole virus as coating antigen. Coating the ELISA plates requires a purified or at least semi-purified preparation of virus as antigen, which needs special skills and techniques. In this study, instead of using whole virus, recombinant protein of hexahistidine tag (His 6 tag) and VPX protein of IBDV expressed in E. coli was used as an alternative antigen to coat the ELISA plates. There was a good correlation coefficient (R2 = 0.972) between the results of the ELISA using plates coated with monoclonal antibody against His 6 tag and those of the commercial IBDV ELISA kit. Hence, His 6 tag and VPX recombinant protein expressed in E. coli has the potential for the development of ELISA for the measurement of IBDV-specific antibody.     

猪乙型脑炎病毒囊膜E蛋白间接ELISA诊断方法的建立与初步应用

本研究利用纯化的原核表达乙型脑炎囊膜E蛋白作为包被抗原,建立了乙型脑炎间接ELISA诊断方法。对检测的各种条件进行了优化,优化反应条件后确定的抗原最适包被浓度为2μg/mL,抗原最佳包被条件为37℃包被2 h,血清的最适稀释度为1∶160,酶标抗体最适稀释度为1∶5000,最佳封闭条件为1%BSA,阴阳性临界值判定标准为D492 nm=0.254。该方法不与猪瘟、猪繁殖与呼吸综合征、猪圆环病毒2型、猪伪狂犬病毒阳性血清反应,其D492 nm0.254,说明该方法具有良好的特异性。采用该方法对150份疑似乙型脑炎血清样品进行检测,结果显示,与某猪乙型脑炎试剂盒相比符合率为90.77%,表明建立的间接ELISA方法具有较高的敏感性和特异性,因此,本研究成功建立了能特异性检测抗乙型脑炎血清抗体的ELISA检测方法。     

新孢子虫dNcSRS2重组蛋白间接ELISA的建立及其应用

利用新孢子虫体外重组表面蛋白dNcSRS2蛋白作为包被抗原，对各项条件进行优化，确定判定标准，建立了检测新孢子虫血清抗体的间接ELISA方法。经对多例血清检测表明，所建立的诊断试剂盒重复性好、特异性强、灵敏度高，与进口的IFAT及两种商品化ELISA试剂盒的检测结果相比较，符合率均达到92％以上。应用建立的ELISA方法对236份奶牛血清的新孢子虫抗体进行检测，阳性率为22％。这是国内首次利用重组蛋白建立的诊断试剂盒，该方法的建立将为牛新孢子虫病的诊断与流行病学调查提供有效的技术手段。     

基于E^rns蛋白的猪非典型瘟病毒间接ELISA检测方法的建立

猪非典型瘟病毒(APPV)是新近发现的仔猪先天震颤的病原体,其血清学检测方法亟待建立.E^rns蛋白是APPV诱导机体产生中和抗体的重要保守性抗原,是血清学检测的特异性靶标之一.本研究制备了猪非典型瘟病毒原核表达的Erns蛋白,以其作为包被抗原,建立了间接ELISA检测方法.结果表明,最佳抗原包被浓度为8μg/mL,最佳血清稀释度为1:10,阴阳性临界值D450=0.318,灵敏度达到1:64,特异性好,与猪瘟、猪伪狂犬、猪繁殖与呼吸障碍综合征、猪流感及圆环病毒病的阳性血清均不发生交叉反应.该检测方法重复性好,批内变异系数最大值为7.84%,批间变异系数最大值为8.57%.利用建立的间接ELISA方法对50份猪临床血清样本进行了检测,其阳性率为10%.基于Erns蛋白间接ELISA检测方法的建立为APPV的流行病学调查和临床诊断提供了有效的工具.     

口蹄疫病毒结构蛋白基因vp1的表达与应用研究

体外克隆口蹄疫病毒vp1基因，构建重组表达载体pET28a-vp1。将此重组质粒转化到受体菌BL21（DE3）中，进行诱导表达，SDS-PAGE和蛋白质印迹分析表明，诱导5h后表达量达到最高，表达产物大小约为33Ku-40Ku，表达蛋白能与口蹄疫病毒阳性血清产生特异性免疫反应。经HPLC纯化后，以重组蛋白为抗原，建立检测VP1蛋白抗体的ELISA方法，检测猪牛血清样品，免疫抗体检测结果与口蹄疫液相阻断ELISA检测结果呈正相关，能反映出免疫抗体动态变化，对临床样品口蹄疫病毒血清抗体检测，两种方法有一定相关性，但不显著。所以以重组VP1蛋白为检测抗原的ELISA方法有望用于口蹄疫免疫抗体监测。     

Characterization of antibody response to porcine reproductive and respiratory syndrome virus ORF5 product following infection and evaluation of its diagnostic use in pigs.

The sensitivity and specificity of recombinant open reading frame 5 products used in the Western blotting assay for confirmation of porcine reproductive and respiratory syndrome virus (PRRSV) serologic status were evaluated. The recombinant antigen-based assays were specifically compared with a commercial enzyme-linked immunosorbent assay (ELISA) for PRRSV antibodies using 1) PRRSV antibody-negative reference sera (n = 30), 2) naturally infected pig sera (n = 40), 3) sequential sera obtained from 24 experimentally infected pigs, and 4) sera submitted to 3 state diagnostic laboratories (n = 200). The recombinant antigen assay yielded an average increased sensitivity of 10% over the commercial PRRSV ELISA. The negative controls (group 1 sera) showed no difference between the 2 assays. This comparison confirmed that the recombinant antigen-specific assay was more sensitive than the commercial ELISA and is well suited for routine confirmation of the presence of PRRSV antibodies.     

Development of recombinant nucleocapsid protein based IgM-ELISA for the early detection of distemper infection in dogs

An IgM-ELISA based on a 16-kDa recombinant protein produced for the conserved and functional middle region of nucleocapsid protein of Canine distemper virus was developed. Out of 70 serum samples from distemper-suspected and vaccinated dogs analyzed, 34 serum samples (49%) were positive. The specificity of this ELISA was confirmed by blocking and adsorption experiments. The IgM-ELISA based on the recombinant nucleocapsid protein showed a strong correlation (r=0.857, p<0.0001 at 95% CI) and good agreement (kappa=0.714) with the conventional Vero cell culture distemper antigen based IgM-ELISA. The percent positivity was more in dogs with systemic signs (62%) by recombinant nucleocapsid protein IgM-ELISA. Out of 70 clinical serum samples, 69 samples were used along with 4 control sera used in the IgM-ELISA for the detection of viral RNA by Slot blot hybridization and 26 of them (36%) were positive. Fifty-one percent agreement was observed between the recombinant nucleocapsid protein IgM-ELISA and Slot blot hybridization. The analysis of clinical history of the dogs with systemic signs supported the application of IgM-ELISA over Slot blot hybridization in the early detection of distemper infection.     

Production of a baculovirus-derived gp50 protein and utilization in a competitive enzyme-linked immunosorbent assay for the serodiagnosis of pseudorabies virus.

The pseudorabies virus (PRV) gp50 envelope glycoprotein gene was cloned and expressed in a recombinant baculovirus. An anti-gp50 Mab (1842) recognized a protein of approximately 40 kDa in immunoblotting assays from infected insect cell lysates, while this product was not present in cells infected with wild-type baculovirus. The recombinant protein was purified by lectin affinity chromatography, utilizing lectins specific for O-linked oligosaccharides (Artocarpus integrifolia and Glycine max). Competitive (c) ELISAs, using either crude or lectin-purified antigen, were devised for the detection of antibodies to PRV in sera, and were capable of monitoring sero-conversion by day 14 post-infection. Furthermore, a specificity of 100% and sensitivity of 98% (crude lysate antigen) or 96% (lectin-purified antigen) was found for a panel of 80 swine sera, using the cELISA, as compared to a serum neutralization (SN) test. These studies demonstrated that recombinant PRV gp50 protein shows promise as a cELISA antigen, for serodetection of PRV.     

Serodiagnostic comparison between two methods, ELISA and surface plasmon resonance for the detection of antibodies of classical swine fever

A protein chip based on surface plasmon resonance (SPR) was developed to measure the antibody (Ab) titers of classical swine fever virus (CSFV) using the recombinant gp55 protein as an antigen. The diagnostic potential of this SPR assay for detecting the Ab titers to CSFV gp55 was compared that of the enzyme-linked immunosorbent assay (ELISA) using 170 serum samples from 14 pig farms. The SPR assay was highly specific and sensitive, and there were no cross-reactions detected. There was a strong positive correlation between the SPR and ELISA titers (n=170, r=0.869, p<0.01). Therefore, the SPR label-free method is a valuable tool in the serodiagnosis of CSFV infection and determining Ab titers after vaccination.     

Serodiagnostic comparison of enzyme-linked immunosorbent assay and surface plasmon resonance for the detection of antibody to Porcine circovirus type 2

This paper describes the cloning and expression of the capsid protein of Porcine circovirus type 2 (PCV2) in an Escherichia coli expression system that was used to produce a fusion protein for subsequent immunologic studies: enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR). Polymerase chain reaction was used to amplify the gene encoding the capsid protein from the DNA of PCV2. The protein was then cloned into a pRSET prokaryotic expression vector. Western blot analysis revealed that the recombinant protein gave strong signals on a polyvinylidene difluoride membrane when exposed to the serum from a pig infected with PCV2. The expressed protein was purified and used as an antigen for the ELISA and SPR study. A protein chip based on SPR was developed, and the diagnostic potential of SPR was compared with that of ELISA with the use of 70 serum samples obtained from 6 pig farms. There was a strong positive correlation between the ELISA and SPR titers (r = 0.877, P < 0.01). Therefore, this recombinant capsid protein can be used as an antigen for serologic studies, and the SPR, a label-free method, appears to be a valuable and reproducible tool in the serodiagnosis of a PCV2 infection.     

In vitro expression of the 50-kDa and 30-kDa fragments of the P97 adhesin of Mycoplasma hyopneumoniae in Escherichia coli and their use for serodiagnosis

This article reports the cloning and expression of 2 fragments of the P97 adhesin of Mycoplasma hyopneumoniae for use in serodiagnosis: a 50-kDa fragment (including the N-terminal cleavage site) and a 30-kDa fragment (including the C-terminal R1 and R2 repeats, which are essential for adherence). The genes encoding the fragments were amplified, cloned, and expressed in the Escherichia coli expression system BL21 (DE3)pLysS. Antiserum against the purified recombinant proteins reacted with the mycoplasmal 97-kDa intact protein and the 66-kDa major cleavage fragment, confirming that both cloned fragments could induce antigen-specific antibodies in mice. Of 70 serum samples from nonvaccinated pigs, 26 (37%) were seropositive when the 30-kDa fragment was used as an antigen for enzyme-linked immunosorbent assay, suggesting that natural mycoplasmal infection is quite common in Korea. However, only 4 samples were seropositive when the 50-kDa fragment was used; this fragment was therefore deemed unsuitable for serodiagnosis. The 30-kDa fragment protein might be useful for measuring antibody response to vaccination and for detecting mycoplasmal infection.     

A 38-kDa protein from Babesia gibsoni and its antibody response in an experimentally infected dog

A cDNA encoding the Babesia bovis 12D3 antigen homologue was obtained by immunoscreening the expression library prepared from Babesia gibsoni merozoite mRNA. The complete nucleotide sequence of the gene was 1406 bp. Computer analysis suggested that the sequence contains an open reading frame of 1052 bp encoding an expected protein with a molecular weight of 36kDa. Based on homology analysis, this putative protein was designated as the B. gibsoni 12D3 antigen (Bg12D3). The Bg12D3 gene was expressed in the Escherichia coli BL21 strain, and the chronically infected dog serum reacted with the recombinant protein. The antiserum against the recombinant Bg12D3 protein can recognize a 38-kDa native protein, which is consistent with its expected size. Moreover, the purified recombinant proteins were used as the antigen to detect the antibody response in an experimentally infected dog by the enzyme-linked immunosorbent assay (ELISA). Our results indicated that the Bg12D3 protein was recognized by the host immune system and that it induced an antibody response in chronic B. gibsoni infection. These results allowed us to identify a new member of the 12D3 antigens and its characteristic immune response in canine B. gibsoni infection.     

猪沙波病毒抗体间接ELISA检测方法的建立及初步应用

以原核表达重组蛋白作为抗原建立了猪沙波病毒(SaV)抗体的间接ELISA检测方法。使用矩阵滴定法确定抗原包被浓度为6.4μg/mL,血清稀释倍数为1∶50。试验选用1%BSA作为封闭液,血清和二抗的最佳作用时间分别为60 min和40 min。选择无致癌的TMB为底物,确定TMB最佳反应时间为10 min。通过对20份猪阴性血清样品的检测,计算阳性判定值为0.203。通过交叉试验、批内和批间重复性试验证明,本研究建立的SaV间接ELISA检测方法具有特异性高,重复性好的特点,可用于猪沙波病毒抗体的检测。     

猪蓝耳病病毒抗体双抗原夹心ELISA方法的建立及初步应用

根据PRRSV VR-2332株序列设计了1对扩增PRRSV N蛋白基因的特异性引物,从PRRSV北方株感染细胞中提取总RNA,通过RT-PCR获得长约372 bp的N蛋白编码基因片段。将其克隆到pGEX-6p-1质粒,构建了原核表达载体pPRRS-N。重组基因在大肠杆菌中表达出相对分子质量约为41 000的融合蛋白,目的蛋白表达量约占菌体蛋白的28.5%。利用此重组融合N蛋白建立了一种检测PRRSV特异性抗体的双抗原夹心ELISA,并通过与商品化试剂盒的应用比较对本方法进行了系统评价。分析了来自北京、山东、河南、河北4省区13个养猪场的260份血清,结果表明,本方法的敏感性和特异性分别为93.5%和86.7%,与IDEXX PRRSV抗体检测试剂盒检测结果的符合率达到91.5%。     

一株牛蛙源虹彩病毒的分离及鉴定

用鲤鱼表皮瘤细胞系(epithelioma papulosum cyprini cell line,EPC)从福建省某美洲牛蛙养殖场分离到一株病毒FJ049。感染病毒的EPC呈现细胞圆缩、颗粒增多、脱落等特征性病变。间接免疫荧光检测结果表明,感染FJ049的EPC细胞与虹彩病毒单克隆抗体反应并出现特异性的胞浆荧光。采用PCR对虹彩病毒主衣壳蛋白(major capsid protein,MCP)基因保守区域进行扩增,扩增出531 bp的特异性基因片段。MCP基因同源性和遗传进化分析结果表明分离株FJ049与沼泽绿牛蛙虹彩病毒RGV9808的核苷酸同源性最高,为99.8%,属于虹彩病毒科蛙病毒属。     

鼠源CD40L的原核表达及其对河豚毒素半抗原免疫增强效果分析

试验旨在通过大肠杆菌表达系统表达鼠源重组CD40L蛋白,探讨其对河豚毒素（tetrodotoxin,TTX）人工完全抗原在免疫BALB/c小鼠过程中的免疫增强作用。用Trizol试剂提取BALB/c小鼠脾脏总RNA并反转录成cDNA,根据CD40L CDS区设计引物,PCR扩增目的基因,构建pGEX4T-1重组载体,进行原核表达,并纯化重组CD40L蛋白;根据曼尼希反应原理,用甲醛法制备TTX免疫原TTX-BSA和检测原TTX-OVA;以人工重组蛋白CD40L佐剂组为试验组,弗氏佐剂组作为对照组,免疫BALB/c小鼠,用ELISA方法结合SPSS 19.0软件分析各组免疫效果,探讨重组CD40L蛋白在TTX-BSA免疫过程中对免疫效果的影响。结果显示,本试验成功扩增了783 bp的CD40L目的基因,原核表达并纯化了融合GST标签的55 ku鼠源CD40L重组蛋白;与人工制备的TTX-BSA协同免疫小鼠试验结果显示,在免疫初期与弗氏佐剂相比,CD40L具有极显著的免疫增强效果（P<0.01）。综上所述,重组蛋白CD40L与TTX-BSA完全抗原协同免疫小鼠,在免疫初期CD40L具有增强机体对半抗原的应答强度的作用,为进一步开发适于小分子半抗原抗体高效制备的免疫增强佐剂奠定基础。     

Development and evaluation of a MAb based competitive-ELISA using helicase domain of NS3 protein for sero-diagnosis of bovine viral diarrhea in cattle and buffaloes

The aim of this study was to develop a competitive inhibition ELISA (CI-ELISA) for detection of antibodies to bovine viral diarrhea virus (BVDV) using the helicase domain of NS3 (non-structural) protein and monoclonal antibody (MAb) against it and to estimate its sensitivity and specificity using two commercial ELISA kits as independent references. The 45-kDa helicase domain of NS3 protein of BVDV was expressed in Escherichia coli and 18MAbs were developed against it. MAb-11G8 was selected for use in CI-ELISA on the basis of maximum inhibition (90%) obtained with BVDV type 1 infected calf serum. Based on the distribution of percent inhibition of known negative sera (n=166), a cut-off value was set at 40% inhibition. In testing 914 field serum samples of cattle (810) and buffaloes (104), the CI-ELISA showed a relative specificity of 95.75% and 97.38% and sensitivity of 96% and 94.43% with Ingenesa kit and Institut Pourquier kit, respectively. This study proved that the use of helicase domain of NS3 (45-kDa) is equally good as the whole NS3 protein (80-kDa) used in commercial kits for detection of BVDV antibodies in cattle and buffaloes.     

猪繁殖与呼吸综合征病毒重组M蛋白间接ELISA抗体检测方法的建立及应用

为建立一种敏感、特异、快速、高通量的猪繁殖与呼吸综合征病毒(PRRSV)抗体血清学检测方法,本研究利用原核表达技术表达了PRRSV M蛋白,将纯化后的重组M蛋白作为包被抗原建立了检测PRRSV抗体的间接ELISA方法。参照已发表的PRRSV基因组M基因序列,设计合成1对特异性引物,RT-PCR扩增了长约435 bp的M基因片段,将目的片段亚克隆至pET32a(+)表达载体中,经IPTG诱导获得了以包涵体形式表达的重组M蛋白,重组蛋白纯化后,免疫印迹检测结果表明具有良好的抗原性和特异性。以重组M纯化蛋白为包被抗原,经间接ELISA反应条件的优化,建立了检测PRRSV抗体的间接ELISA方法,该方法检测猪瘟病毒(CSFV)、猪细小病毒(PPV)、猪乙型脑炎病毒(JEV)、猪伪狂犬病病毒(PRV)、猪传染性胃肠炎病毒(TGEV)、猪圆环病毒2型(PCV2)其他6种常见猪病病原的阳性血清均为阴性;该方法批内与批间重复性试验的变异系数分别小于5%和10%;该方法与商品化ELISA试剂盒的符合率为95.3%。本研究建立的M-ELISA检测方法将为猪群免疫PRRS疫苗后抗体水平监测及PRRSV野毒感染的快速诊断与流行病学调查等提供了一种简便易行、快速、高通量的血清学抗体检测方法。