Porcine Interleukin-2 Expression in Insect Cells and Its Enhancement of Pig Immunity to Swine Influenza Virus Inactivated Vaccine

Mature porcine interleukin-2 （pIL-2） gene was amplified by PCR from the plasmid pGEM-T-pIL2 and cloned into the baculovirus pFastBacTM Dual vector of the Bac-to-Bac baculovirus expression system under the control of the PH promoter. Recombinant plL-2 （rpIL-2） expressed in Sf9 insect cells was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunofluorescence assay. Western blot analysis confirmed that the rpIL-2 protein had a molecular mass of 20 kDa, which was larger than the molecular mass of the mature protein predicted based on its peptide sequence. The rpIL-2 protein induced in vitro proliferation of ConA-stimulated porcine splenocytes and enhanced in vivo protective immune responses induced by vaccinating the pigs with inactivated oil emulsion vaccine against swine influenza virus. The results showed that the rpIL-2 expressed in Sf9 insect cells has immunoenhancement effects; the finding lays the foundation for the preparation of a specific recombinant IL-2 protein and the development of a novel immune adjuvant of vaccines against various infectious porcine pathogens to increase the immunoprotective efficacy of vaccines.

A survey on porcine circovirus type 2 infection and phylogenetic analysis of its ORF2 gene in Hangzhou,Zhejiang Province,China

Porcine circovirus type 2 (PCV2) is closely related to the postweaning multisystemic wasting syndrome (PMWS). In this study, the pig serum and tissue samples collected from different regions of Hangzhou District in Zhejiang Province of China between 2003 and 2005 were analyzed by enzyme-linked immunosorbent assay (ELISA) for PCV2 antibody and by polymerase chain reaction (PCR) for ORF2 gene. The results show that out of 1250 randomly collected serum samples, 500 sera (40%) were seropositive for PCV2. PCR results demonstrate that Hangzhou PCV2 with more than 50% Chinese PCV2 strains and French PCV2 formed Cluster A. Only one PCV2 from Hangzhou belonged to Cluster B with some other Chinese PCV2 and Netherlands’s isolates. Cluster C consisted of PCV2 isolates from China, US, Canada, UK and Germany. The results indicate that the PCV2 infection was widespread in Hangzhou.

Development of a Loop-Mediated Isothermal Amplification Assay for Porcine Circovirus Type 2

In this study, the loop-mediated isothermal amplification (LAMP) method was used to develop a rapid and simple detection system for porcine circovirus type 2 (PCV2). According to the PCV2 sequences published in GenBank, multiple LAMP primers were designed targeting conserved sequences of PCV2. Using the DNA extracted from PCV2 isolates HUN-09 and SD-09 as the template, LAMP reactions in a PCV2 LAMP system was performed, the amplification products were detected by adding SYBR Green I and could be observed directly by the naked eye. The results showed highly-efficient and specific amplification in 30 min at 63°C with a LAMP real-time turbidimeter. Furthermore, PCV2 DNA templates, with a detection limit of 5.5×10-5 ng of nucleic acid, indicated that this assay was highly sensitive. The results obtained with the naked eye after SYBR Green I staining were consistent with those detected by the real-time turbidimeter, showing the potential simplicity of interpretation of the assay results. The LAMP assay appeared to have greater accuracy than PCR and virus isolation for the analysis of 18 clinical samples. In addition it offers higher specificity and sensitivity, shorter reaction times and simpler procedures than the currently available methods of PCV2 detection. It is therefore a promising tool for the effective and efficient detection of PCV2.

Genetic Diversity of Intragenomic Rearrangement of Porcine Circovirus Type 2 in vitro and in vivo

We characterized the genome sequences of defective-interfering(DI) particle DNA of porcine circovirus type 2(PCV2) by sequencing and bioinformatics analyses. DI particles were both generated by serial passage of PCV2 in PK15 cells and obtained from sera of pigs with postweaning multisystemic wasting syndrome(PMWS). These subviral isolates ranged from 358 nt to 1 125 nt genomes. Investigating the complexity and diversity of PCV2 DI in vivo and in vitro can help elucidating the evolutionary history of PCV2.

Recent Advances in Epidemiology of Porcine Circovirus Type 2 and Diagnosis of Porcine Circovirus-Associated Diseases

Porcine cimovirus （PCV） is the smallest animal virus so far and has two serotypes. PCV1 is nonpathogenic, but PCV2 is pathogenic and causes post-weaning multisystemic wasting syndrome （ PMWS）. Factors to induce PMWS include immunity and infection status of sows, infec- tion time, mixed infection, PCV2 variants, physical status of gilts, and feeding management. For final diagnosis, histopathological changes and ex- istence of PCV2 in lymphoid tissues are professional standards, because fluorescence quantitative RT-PCR is not enough specific or sensitive. The commemial PCV2 vaccines can reduce occurrence of PMWS and PCV-related diseases. This paper reviews recent advances in epidemiology of PCV2 as well as diagnosis and control of PMWS.

Phylogenetic Relationship Analysis of the Complete Genomes of Porcine Circovirus Type 2( PCV2) Strains Isolated from Hainan Province

[ Objective] This study aimed to investigate the molecular characteristics of porcine circovirus type 2 （PCV2） strains isolated from Hainan Province. [ Method] The complete genome of PCV2 was amplified from PMWS-suspected samples by PCR for sequence analysis. [ Result] A total of eight PCV2 strains were isolated and identified. All the eight isolates belonged to genotype PCV2b, among which seven isolates belonged to subgenotype PCV2b-1 C, and one isolate be- longed to subgenotype PCV2b-IA/1B. ORF2 gene of PCV2 isolates from Hainan Province was 705 bp in length, encoding 234 amino acids. Antigenic epitopes of Cap protein exhibited certain changes. Nucleotide sequences and deduced amino acid sequences of ORF2 gene shared 95.3% -99.7% and 93.6% - 100% simi- larities among eight PCV2 isolates from Hainan Province, respectively. Moreover, nucleotide sequences and deduced amino acid sequences of ORF2 gene of PCV2 isolates from Hainan Province shared 91.0% -99.9% and 91.0% -99.6% similarities with other PCV2 strain isolated from China （AY682994, AF381175, JX945577, JX682407, AY180397 ）, respectively; nucleotide sequences and deduced amino acid sequences of ORF2 gene of PCV2 isolates from Hainan Province shared 90.0% - 97.0% and 88.0% -97.9% similarities with PCV2 isolates from other countries （ NC_005148, JQ994268, KJ187306, AF201307, AF454546, AY＂/Sd020）, respectively; nucleotide sequences and deduced amino acid sequences of ORF2 gene of PCV2 isolates from Hainan Province shared 98.2% -100% and 94.9% -100% similarities with vaccine strain SH, respectively; nucleotide sequences and deduced amino acid sequences of ORF2 gene of PCV2 isolates from Hainan Province shared 90.6% -91.7% and 89.7% - 91.0% similarities with vaccine strain LG, respectively. [ Conclusion] This study provided theoretical hasis for the prevention and control of PCV2 and selection of vaccine strains in Hainan Province.

An Immunochromatographic Strip Test for Rapid Detection of Antibodies against Porcine Circovirus Type 2

Porcine cimovirus type 2 (PCV2) infection causes huge economic losses, but no serological method is available for batch detection of field samples. The aim of the study was to develop a method for large-batch detection of PCV2 infection. Colloidal gold-labeled staphylococcal protein A (SPA) was sprayed on glass fibers to prepare a conjugate pad. The recombinant ORF2 protein of PCV2 was blotted on the test line of the nitrocellulose (NC) membrane, and pig IgG was streaked on the control line of the NC membrane. Then, the immunochromatographic strip was used for detection of antibodies against PCV2. The results show that the strip test was simple and the results could be determined within 10 min with naked eyes. The test strip was highly specific for pig serum against PCV2 and no cross-reaction with pig serum against other pathogens was observed. The test strip had close similarity with ELISA. Storage at RT for 6 months did not affect the specificity and sensitivity obviously. A total of 324 clinical pig sera were detected by both ELISA and the developed test strip, and the coincidence was 98.77%. Therefore, the developed immunochromatographic strip is specific, sensitive, stable, fast and simple, and it is suitable for on-site detection of antibodies against PCV2.

Establishment and Application of a Real-time Fluorescent Quantitative PCR Method for Detection of Porcine Circovirus Type 2

[ Objective ] To establish a real-time fluorescent quantitative polymerase chain reaction （PCR） method with SYBR Green I for the detection of porcine circovirus type 2 （PCV2）. [Methods] Specific primers were designed to amplify the conserved gene segments of PCV2 with a size of 177 bp by PCR. The ampli- fied gene was cloned into the vector of pMD 18-T and transformed into DHSct to screen positive clones. After being extracted and purified, the recombinant plasraids pMD 18-T-177 were taken as the standard DNA templates to establish the fluorescence quantitative PCR method for the detection of PCV2, and the PCR re- action conditions were optimized. [ Results] Ct value of the established PCR method showed a good linear relationship with the standard DNA templates within a viral load of 3.21 × 100 -4.16 × 108 copies/μL , the correlation coefficient was O. 998 8 and the slope was - 3.286. The method did not show any cress-reactions with the genomes of PRRSV, PCV1, CSFV, PRV, PPV and Escherichia coli. Sensitivity of this method was proved to be 3.21 × 10 copies/μL, which was 1 000 times higher as conventional PCR method. Variation coefficients of the repeated trims among same batch or different batches were both less than 3.00%. Positive rate of clinical samples detected by the established PCR method was 58.94%, which was significantly higher than the detection rate by conventional PCR. [ Conclusions ] A reM-time fluorescent quantitative PCR method with SYBR Green I for the detection of PCV2 was established, which was better for conducting the quan- titative analysis and the early diagnosis of PCV2 infection.

Isolation and Identification of Porcine Circovirus Type 2 in Taizhou

In September 2011, an infectious disease suspected to be postweaning multisystemic wasting syndrome （PMWS） broke out in some pig farm in Taizhou. The inguinal lymph node, liver and lung tissues were collected and grinded into tissue suspension. The suspension was subjected to PCR detection, and the positive product was sequenced. The suspension of positive samples was filtered with 0.22 μm filter membrane, and the filtrate was inoculated onto PK15 cells. After five generations of blind passages, the cell viral liquid was collected and extracted for DNA, which was subjected to PCR detection and indirect immunofluorescence. The results showed that the isolate was porcine circovirus type 2 （PCV2） and designated as TAIZ110926. The target sequence was committed to NCBI with a serial number： KF039888.

Inducible Expression on Multi-epitope of Porcine Circovirus Type 2 and Its Immunological Competence

In order to obtain induction expressed porcine circovirus type 2（PCV2）multi-epitope with good immunogenicity in vitro.Major epitopes of PCV2 were screened in the test,epitopes were composed sequentially,the c DNA sequences were artificially synthesized.Bam HⅠand SalⅠwere directionally cloned into prokaryotic expression vector PEGX-4T-1 multiple cloning site,then BL21 competent cells were transformed,positive clones were screened,IPTG inducible expression was conducted.Expression on target gene was analyzed by SDS-PAGE,fusion protein polypeptide was extracted and purified,immunocompetence of the expressed multi-epitope protein was identified by Westernblot.BALB/c mouse was immuned by fusion protein polypeptide,the antibody was determined by ELISA,immunogenicity was evaluated.Results showed that expression recombinant plasmid pEGX-4T-1-ep contained with seven PCV2 antigen epitopes had been constructed successfully.SDS-PAGE analysis showed that fusion protein polypeptide was expressed effectively in Escherichia coli（E.coli）,and the molecular weight was about 35ku,which existed in the form of solubility.Results of Westernblot showed that the extraction and purification of fusion protein polypeptide and PCV2 positive serum had good reactogenicity.Results of ELISA showed that the purified fusion protein polypeptide could stimulate the body to produce PCV2 specific antibody which had good immunogenicity.Results indicated that the constructed PCV2 multi-epitope had good expression characteristics in vitro,and the expression protein had good immunogenicity.The study provided a basic for the study on PCV2 epitope screening,functional identification and multi-epitope vaccine.

Porcine Circovirus 2:Immunopathogenesis and Recent Developments in Vaccines

Porcine circovirus 2 (PCV2) is currently considered an important etiologic agent of swine and its infection has potentially serious economic impact on the swine industry worldwide. This virus is frequently associated with postweaning multisystemic wasting syndrome (PMWS), and also with other clinical conditions such as porcine dermatitis and nephropathy syndrome (PDNS), late-term abortions, reproductive failure in sows, proliferative and necrotizing pneumonia and congenital tremors. The term porcine circovirus-associated disease (PCVAD) is currently used to refer to any of these diseases when they are associated with PCV2 infection. The PCV2 was recognized as a pathogen in 1997, and many questions regarding its biology and pathogenesis remain unanswered. Currently, some studies have shown the production of new vaccine candidates and field efficacy testing of commercial vaccines. This review discusses some major points concerned with immunopathogenesis and vaccines for PCV2 infection.

猪圆环病毒2型疫苗及其效力评价方法比较研究

为探索对不同猪圆环病毒2型(Porcine circovirus type2,PCV2)疫苗产品进行统一质量评价的可行性,对国内该类疫苗产品及其现有效力评价方法进行了归纳和比较研究。结果发现,目前猪圆环病毒2型疫苗类产品种类有25个,且疫苗毒株数量多达10余个,效力检验方法包括传统的免疫攻毒法、血清学方法和多种不同的替代方法,但尚没有统一的效力评价体系。本研究可为进一步完善PCV2疫苗效力评价方法、统一评价疫苗效力、提高产品质量提供参考。

保育仔猪猪圆环病毒2型和副猪嗜血杆菌混合感染的诊疗

为查清山西省吕梁市中阳县某猪场从山东购买的保育仔猪大量出现的急性死亡、关节发炎、呼吸困难、高热等症状的病原,无菌采集病猪并带回实验室进行临床剖检,随后采集血液、淋巴结、肺、肾脏和脾脏进行实验室诊断,做出初步判断,制定综合防治策略,病情得到控制。本研究采用灵敏度和准确度较高的实时荧光PCR技术定性检测病料样品中的猪繁殖与呼吸综合征病毒(PRRSV)、非洲猪瘟病毒(ASFV)、猪圆环病毒2型(PCV2)、猪瘟病毒(CSFV)、猪伪狂犬病毒(PRV)和副猪嗜血杆菌(HPS)。结果表明:中阳县某猪场保育仔猪为PCV2与HPS混合感染。基于诊断结论对保育猪免疫治疗程序和消毒进行合理调整,综合防治13 d后,猪群无新增发病率和新增死亡率,最大程度地减少了经济损失。本研究为猪场后续的治疗与预防提供了诊断依据。

猪圆环病毒2型ORF1部分位点突变对病毒复制能力的影响

猪圆环病毒2型(PCV2)可引起断奶仔猪多系统衰竭综合征,导致仔猪逐渐消瘦。PCV2 ORF1表达的Rep蛋白及其剪切体Rep′是PCV2复制所需的重要蛋白。为了研究PCV2 ORF1部分位点对PCV2复制能力的影响,本试验通过构建PCV2 ORF1区域点突变双拷贝感染性克隆质粒,在无PCV2污染的PK-15细胞中进行病毒拯救,使用荧光定量PCR检测不同位点突变病毒培养不同代次上清液的Ct值。结果:将PCV2 Rep的17 aa、19 aa、20 aa和21 aa突变为丙氨酸后病毒无法成功拯救,2 aa突变后严重影响病毒的复制能力,3 aa、5 aa和18 aa突变后病毒的复制能力增强且细胞病毒载量高于PCV2原毒株,推测17 aa、19 aa、20 aa和21 aa是影响PCV2复制的关键作用位点。本研究结果为未来PCV2复制相关研究提供了试验依据。

表达CSFV E2线性表位的PCV2病毒样颗粒的制备及免疫原性研究

为制备携带猪瘟病毒(CSFV)E2蛋白的猪圆环病毒2型(PCV2)病毒样颗粒(VLP),并在小鼠体内评价其免疫原性,本研究采用PCR扩增PCV2 Cap基因,利用重叠延伸PCR将PCV2 Cap蛋白的诱饵表位(aa169~aa180)替换成编码两个连续的CSFV E2蛋白线性表位(aa829~aa837)的融合基因(PCV2-Cap^(169~180)-E2^(829~837))经测序鉴定正确后克隆至载体pET-32a(+)中,构建重组质粒p-Cap-E2并采用PCR方法鉴定正确后转化大肠杆菌BL21(DE3),经IPTG诱导表达重组蛋白(PCV2-Cap-E2),采用改良的镍亲和层析法纯化重组蛋白,并利用SDS-PAGE与western blot对重组蛋白的表达形式及反应原性鉴定;利用透射电镜观察纯化的重组蛋白能否形成VLP;利用本研究制备的VLP、PCV2及CSFV商品化疫苗分别免疫小鼠,采用ELISA方法检测免疫后不同时间小鼠体内的抗体水平及细胞因子含量。SDS-PAGE结果显示,在49 ku处出现目的条带,且重组蛋白主要以可溶性形式表达,纯化得到单一的目的蛋白;western blot结果显示,重组蛋白能够与猪源PCV2多克隆抗体(PAb)、猪源CSFV PAb及HRP标记的6×His-Tag小鼠单克隆抗体(MAb)发生特异性反应,在49 ku处出现特异性条带;电镜观察可见重组蛋白形成规则的VLP;抗体的ELISA结果显示,与PBS对照相比,VLP能够诱导小鼠产生较高的PCV2及CSFV抗体水平(P<0.01),与各商品化疫苗均无显著差异。细胞因子的ELISA结果显示,与PBS对照组相比,VLP能够诱导小鼠产生较高水平的细胞因子(P<0.01)。体外病毒中和试验结果显示,VLP免疫的小鼠血清中具有中和PCV2的活性。综上所述,本实验首次在大肠杆菌中可溶性表达并获得了纯化的重组蛋白(PCV2-Cap-E2),且其能够在体外自组装成VLP,并可刺激小鼠产生针对PCV2 Cap蛋白及CSFV E2蛋白的特异性抗体,为研制针对PCV2和CSFV的新型二联VLP疫苗提供了物质基础。

猪圆环病毒2型感染性克隆的构建及拯救病毒的双抗体夹心ELISA鉴定

旨在构建猪圆环病毒2型(PCV2)感染性克隆,并利用双抗体夹心ELISA对拯救病毒进行鉴定。通过PCR从阳性病料中扩增出PCV2两种基因型2b与2d的全基因组DNA,并分别克隆入pMD-19T载体,获得2个重组质粒,命名为p19T-PCV2b与p19T-PCV2d。利用SacⅡ酶切获得l 767 bp的PCV2全基因组,并在体外分别用T4连接酶连接而环化,将环状基因组转染至PK-15细胞,传至P6代,利用间接免疫荧光试验(IFA)对拯救病毒进行鉴定,结果表明PCV2b与PCV2d感染性克隆可拯救出病毒。利用PCV2单克隆抗体(单抗)作为捕获抗体,用辣根过氧化酶(HRP)标记的PCV2多抗作为检测抗体,建立检测PCV2病毒粒子的双抗体夹心ELISA方法,用于PCV2拯救病毒的鉴定。将该检测方法与IFA和半数组织细胞感染量(TCID_(50))结果进行对比分析,结果显示,ELISA检测值与Image-J所计算的IFA荧光强度及TCID_(50)的相关系数分别达到0.7和0.8以上,说明该方法与IFA及TCID_(50)检测结果均具有较强的一致性,可以用于PCV2拯救病毒的快速鉴定。

猪圆环病毒2型感染性克隆构建

基于PCV2滚环复制原理,在分析PCV2不同基因亚型代表毒株基因组结构和序列的基础上,设计2对引物用于PCR扩增PCV2基因组序列。以从收集到的疑似PCV2感染的10份猪血清样品中提取的DNA为模板,用设计的引物扩增目的片段,并进行测序分析,1株为PCV2a型,4株为PCV2b型,5株为PCV2d型。每种基因型毒株中各选取一个样本,利用上述2对引物进行PCR扩增,并将扩增产物克隆至pEASY-Blunt simple载体中,通过双酶切连接2个PCR片段,构建含有约1500 bp重叠序列的PCV2基因组的质粒。通过脂质体转染法将含PCV2全基因组的质粒转染至PK-15细胞进行病毒拯救,经PCR和IFA两种方法验证,证明成功拯救出3个基因型的PCV2毒株。通过对PCV2全基因组结构及序列分析,该方法同样适用于PCV2g、PCV2h基因型病毒的感染性克隆构建。本研究建立了一种基于反向遗传学技术的PCV2感染性克隆的构建方法,为开展PCV2的病原学研究提供了技术支持。

猪圆环病毒2型疫苗的应用和研发进展

猪圆环病毒2型(PCV2)是猪圆环病毒相关疾病(PCVAD)的主要病原,感染后会导致猪淋巴系统功能衰竭和免疫抑制,严重危害养猪业的正常生产。近年来,PCV2疫苗的研发一直备受关注,相关研究已取得一定进展,已上市了多种疫苗,包括灭活疫苗、亚单位疫苗、嵌合疫苗和合成肽疫苗等。此外,研究人员还在疫苗的免疫机制和接种策略方面进行了深入探讨,为疫苗的研发和应用提供了重要的理论支持。然而,目前PCV2疫苗的研究仍面临着诸多挑战,如临床流行的主要毒株从PCV2b逐渐转变为PCV2d,疫苗安全性、长期免疫效果等,现有疫苗的免疫效果仍需进一步研究证实。本文对PCV2及其现有疫苗的生产现状、新型疫苗的研发进展、佐剂在疫苗中的应用、疫苗对不同基因型的保护能力等进行了综述,以期为我国有效防控PCVAD提供科学参考。

猪圆环病毒2型、猪肺炎支原体和猪瘟疫苗不同免疫程序的免疫效果比较分析

为了评估不同免疫策略对猪场免疫效果和经济效益的影响,以确定最佳的疫苗免疫程序,本试验将处于产前1个月的四胎次健康三元母猪随机分为2个组,A组(联合免疫组)母猪于产前27 d联合免疫猪圆环病毒2型基因工程疫苗、猪肺炎支原体灭活疫苗和猪瘟活疫苗(圆柯欣+柯喘宁+稳柯健),其所产仔猪于21日龄联合免疫圆柯欣、柯喘宁和稳柯健;B组(对照组)母猪于产前34和27 d分别免疫稳柯健、猪圆环病毒疫苗和猪肺炎支原体疫苗二联疫苗(圆-支二联疫苗),其所产仔猪于14日龄免疫圆-支二联疫苗,28日龄免疫稳柯健。统计和分析免疫各组临床指标、生产性能和持续性抗体水平。结果显示,免疫疫苗后,2个组的母猪采食情况均正常;2个组的仔猪整体精神状态良好,哺乳情况正常,均未出现咳嗽和喘气等呼吸道疾病。在试验期间内,2个组的母猪的窝产健仔数和仔猪出生健仔均重并无差别。A组和B组的出生至23日龄死淘率、出生至50日龄死淘率分别为3.77%、5.11%和4.07%、5.43%,A组略优于B组。抗体监测结果显示,A组母猪的CSFV和PCV2抗体水平较B组无显著差异(P>0.05);A组仔猪的CSFV抗体阳性率与B组无明显差异(P>0.05),而PCV2抗体水平在免疫早期阶段(21日龄)明显高于B组(P<0.05)。结果表明,猪圆环病毒2型、猪肺炎支原体和猪瘟疫苗可以联合免疫,且免疫后相互之间不干扰。该联合免疫策略在确保免疫效果的同时,简化了疫苗免疫程序,为确定最佳的疫苗免疫程序提供了有价值的临床应用参考。