Genomic Sequencing and Molecular Characteristics of A Very Virulent Strain of Infectious Bursal Disease Virus Isolated in China

[Objective] The paper was to determine the genomic sequence of a very virulent strain of infectious bursal disease virus（IBDV）,and study its molecular characteristics.[Method] A very virulent strain（vvIBDV）（HLJ-0504） of infectious bursal disease virus（IBDV） with special characters was isolated in China and its genome was sequenced.[Result] Sequence analysis showed that segment A of HLJ-0504 was derived from vvIBDV,while segment B was from a distinct ancestor.The morbidity and mortality of HLJ-0504 was 100% and 86.7%to SPF chickens,respectively.[Conclusion] vvIBDV with distinct segment B were still circulating and the evolution of IBDV was diversified in China.Besides,it is hard to imagine that the virulence of IBDV is determined solely by segment A or B.

Effect of Astragalus polysaccharides on Erythrocyte Immune Adherence of Chickens Inoculated with Infectious Bursal Disease Virus

Two hundred and forty specific pathogen free leghorn chickens were randomly divided into four groups and reared in isolated pens. The tested chickens were negative to infectious bursal disease virus （IBDV） at 25 d old. Group 1 was treated with saline, whereas Groups 2, 3, and 4 were inoculated with 0.3 mL IBDV suspension intranasally the next day. Groups 3 and 4 were also administered with Astragalus polysaccharides （APS） intramuscularly twice daily at 5 or 10 mg kg-1 BW, respectively, until 31 d old. The erythrocyte-C3b receptor rosette rate （E-C3bRR） and the erythrocyte-C3b immune complex rosette rate （E-ICRR） were measured at 25, 29, 32, 35, and 38 d old. The results showed that IBDV significantly reduced E-C3bRR and E-ICRR when compared with the control group （P 〈 0.05）, while simultaneous administration of APS with 1BDV maintained E-C3bRR at similar levels to the control group （P 〉 0.05） and increased E-ICRR when compared with the control group and the group non-treated with APS （P 〈 0.05）. APS treatment reduced the morbidity and mortality of chickens inoculated with IBDV （P 〈 0.05）. The results suggest that APS may enhance the immune adherence of chickens erythrocytes by affecting the activity and/or the number of complement receptors on the erythrocyte membrane. These findings can be beneficial in providing an understanding of the basic mechanisms required for the rational application of APS in modern medicine.

Immunogenicity of formaldehyde and binary ethylenimine inactivated infectious bursal disease virus in broiler chicks

Infectious bursal disease virus (IBDV) was inactivated by two different chemicals—formaldehyde and binary ethylenimine (BEI). Formaldehyde was used at 0.1% and 0.2%, while BEI was used at concentrations of 0.001 and 0.002 mol/L. These four vaccines were tested for their efficiency in generating humoral immune response in different groups of broiler chicks. Both BEI-inactivated vaccines gave relatively higher antibody titers and were almost twice as efficient as formaldehyde-inactivated ones.

Inactivation of infectious bursal disease virus by binary ethylenimine and formalin

In this experiment conducted to study the inactivation dynamics of infectious bursal disease virus （IBDV） by binary ethylenimine （BEI） in comparison with formalin, IBDV was isolated from the bursa of infected chickens and its confirmation was done by agar gel precipitation test. Viral suspensions were subjected to inactivation with BEI and formalin for pre-set time in- tervals. BEI was employed at concentrations of 0.001 and 0.002 mol/L while formalin was used at 0.1% and 0.2%. Sampling was done at 6, 12, 24, 36 and 48 h of incubation and samples were tested for their inactivation status in 9-day-old embryonated eggs and 3-week-old broiler chickens. IBDV was completely inactivated by 0.001 and 0.002 mol/L BEI after 36 h of incubation at 37℃, whereas formalin at 0. 1% and 0.2% concentrations inactivated IBDV in 24 h.

Molecular Differentiation of Different Pathogenic Phenotypes of Infectious Bursal Disease Viruses by RT-PCR Combined with Restriction Fragment Length Polymorphism(RFLP) Assay

Accurate differentiation of the pathogenic phenotypes of infectious bursal disease viruses(IBDVs) will instruct effective vaccination programs and improve the study of the molecular epidemiology of IBDVs. In this study, an 833 bp hypervariable nucleotide region was identified in VP2 genes of known IBDVs with different virulences through multiple sequence alignment.Moreover, using NEBcutter software analysis, two restriction enzyme sites, SpeⅠ(generating 531 and 302 bp fragments) and StuⅠ(generating 242 and 591 bp fragments) were found presented in very virulent but not attenuated IBDVs. Moreover, the restriction enzyme site SacⅠ(generating 218 and 615 bp fragments) presented in attenuated IBDVs but not very virulent IBDVs. Therefore,a reverse-transcription(RT)-PCR combined with a restriction fragment length polymorphism(RFLP) assay was developed to differentiate attenuated and very virulent IBDVs. The RT-PCR assay was used to confirm 282 IBDV positive samples from 310 suspicious dead chicken samples. The 60 IBDV positive samples were used to evaluate the assay, followed by confirmation via gene sequencing and histopathological examinations of the bursas of Fabricius from chickens infected by these IBDVs. The results showed that 24 viral strains with SpeⅠand StuⅠsites were very virulent, causing severe pathological damage in the bursas of Fabricius, while36 viral strains with the SacⅠsite were attenuated IBDVs, exhibiting only slight pathological damage. The combined RT-PCR and RFLP assay provided a useful approach for differentiating the pathogenic phenotypes of IBDVs.

Analysis of the function of D279N mutation of VP2 of infectious bursal disease virus

Infectious bursal disease virus（IBDV）is responsible for the highly contagious infectious bursal disease of chickens.Further understanding the gene-function is necessary to design the tailored vaccine.The amino acid residue 279,located on strand P_F of VP2,is one of the three residues that have been reported to be involved in cell-tropism but with some inconsistency.In this study,to further clarify the amino acids involved in the cell tropism of IBDV,a series of mutations about residue 279were introduced into the VP2 of vv IBDV Gx strain.With the reverse genetic system,we found single mutation of D279N,double mutations of D279N/A284T or Q253H/D279N were not enough to adapt IBDV to chicken embryo fibroblast（CEF）cell.To evaluate whether residue 279 could influence the replication and virulence of IBDV,the virus r Gx HT-279 with three mutations（Q253H/D279N/A284T）was rescued and evaluated.Results showed that the mutation of residue 279 in VP2had no efficient effects on both the replication efficiency in vitro and the virulence to SPF chickens of IBDV.In summary,the results demonstrated that residue 279 of VP2 did not contribute efficiently to cell tropism,replication efficiency,and virulence of IBDV at least in some strains.These findings provided further information for understanding the gene function of IBDV.

Study on Propagation of Chicken Infectious Bursal Disease Virus on Vero Cells Using Microcarriers in Fermentor

It was in flask optimization tests proved that 2% serum, pH 7.0, 5:10 000 inoculation concentration of infectious bursal disease virus (IBDV) and 108 hours cultivation for IBDV harvest after its inoculation were the optimal conditions when IBDV was propagated on Vero cells. 250 ml self-made spinner bottle and 5 L stirring fermentor tests proved that IBDV could maintain higher liters for a long time and the highest liters of IBDV in a spinner bottle and a fermentor were 8.875 and 8.58 ( - lgTCID50/0.1 ml) respectively when IBDV was proliferated on Vero cells using 2 g/L microcarriers in a spinner bottle and a fermentor and was cultivated under the optimum conditions obtained from flask tests after Vero cells had developed a confluent monolayer on microcarriers, which were at least one titer higher than the highest titer in the traditional rolling bottle. All these results suggested that this technology could be applied to large scale production for IBDV.

鸡IL-18对IBDV多聚蛋白DNA疫苗的免疫增强作用研究

为进一步评价鸡IL-18的免疫增强作用,用鸡白细胞介素18(IL-18)的真核表达质粒(pCI-IL-18)与传染性法氏囊病病毒(IBDV)多聚蛋白DNA疫苗分别免疫SPF鸡,14日龄时首免,2周后二免,二免后5周用IBDV标准强毒株BC6/85攻击.研究发现,鸡IL-18能显著促进T、B淋巴细胞的增殖反应,增强IBDV多聚蛋白DNA疫苗诱导的中和抗体水平及其对强毒攻击的保护力.结果提示,鸡IL-18(200μg)对IBDV多聚蛋白DNA疫苗具有显著的免疫增强作用(P<0.05).

传染性法氏囊病毒HN株的分离鉴定及应用免疫荧光检测IBDV

河南郑州地区某养鸡场的三黄肉鸡出现精神沉郁,拉水样白色粪便,剖检可见法氏囊水肿、出血;肾脏出血肿大,有尿酸盐沉淀,呈花斑状;腿肌、胸肌有出血斑点;腺胃与肌胃交界处出血。经病毒分离、鸡胚接种、琼脂扩散试验和细胞接种试验,最后确诊为传染性法氏囊病。同时,采集病料,制备冰冻切片,建立一种检测病料中的IBDV免疫荧光检测方法。

抗IBDV VP2单克隆抗体制备及其免疫学鉴定

采用不连续蔗糖密度梯度离心法纯化的鸡传染性法氏囊病病毒弱毒Gt株,并与Tj强毒株共同免疫BALB/c小鼠。利用淋巴细胞杂交瘤技术,取其脾细胞与SP2/0骨髓瘤细胞进行融合,经过3次筛选克隆,获得8株具有分泌抗IBDV抗体的杂交瘤细胞系,并对8株单抗进行了分子生物学及免疫学方面的鉴定。间接ELISA显示获得的8株单抗只与IBDV有特异性的反应,Western-blotting表明,部分单抗能够特异地与Sf9细胞表达的VP2蛋白反应;中和试验表明8株单抗均具有中和活性,而且有3株中和效价在26以上。研究推测,8株单抗中有2株针对的表位为构象依赖性,其余6株单抗所针对的为线性中和性表位。

IBDVvp2基因高变区序列测定与进化分析

本实验采用来源于江苏地区的六株不同鸡传染性法氏囊病病毒(Infectious bursal disease virus,IBDV)毒株,应用 RT-PCR 法对 vp2 基因高变区进行了扩增,构建重组质粒 pMD18T- vp2,测序。与有代表性的 IBDV 毒株 VP2 基因高变区序列进行比较分析,以 ClustalX 软件进行序列比对,得到基因序列及氨基酸序列同源性,IBDVY3、P2G、P8G、SZ、Y5 和 W04(6 株)IBDV 与 D6984(荷兰)的同源性达到 99.0%以上,与其它一些超强毒株(very virulent IBDV,vvIBDV)的同源性也达到了 97.8%以上,并在关键氨基酸位点符合 vvIBDV 特征,采用Phylip3.5 软件分析作出进化树,其结果从分子水平说明六个毒株均为 vvIBDV,与欧洲和日本的超强毒株有较近的亲缘关系,而与美洲株的较远,从而为 IBDV 分子流行病学研究和疫苗的研制提供了科学依据。

靶向传染性法氏囊病病毒(IBDV)VP2有效miRNA的筛选

为筛选出能有效抑制传染性法氏囊病病毒(IBDV)VP2基因复制的miRNA,采用RT-PCR方法从病毒基因组中进行结构蛋白VP2的基因扩增与序列测定,构建融合表达载体pVP2-EGFP。根据VP2测序结果,借助genscript软件设计针对VP2的5条miRNA,分别命名为miVP2A、miVP2B、miVP2C、miVP2D和miVP2E,将合成的5条miRNAs分别插入到pRFPRNAiC中形成miVP2s表达载体,这些载体分别与pVP2-EGFP共转染DF-1细胞系,通过NortheringBlotting方法检测miVP2s的表达,利用荧光共聚焦显微镜定性、流式细胞术定量的方法进行有效miVP2s的筛选。结果显示:miVP2s能成功表达;转染miVP2s表达载体组的绿色荧光蛋白(GFP)强度和数量都明显弱于或少于阴性对照组;miVP2s对VP2的抑制效率为59.7%到78.5%。表明所设计的miRNAs对VP2均有抑制作用,其中miVP2A和miVP2E效果最为显著。

荧光定量RT-PCR鉴别IBDV超强毒株与经典疫苗毒株

鸡传染性法氏囊病病毒(IBDV)超强毒株的出现给该病的防控带来了新的困难,有效鉴别IBDV超强毒株对IBD的防控有着积极意义。根据IBDV VP4基因的保守序列,设计了一对通用引物RPa/RPb,特异性扩增IBDV VP4基因720bp的目的片段。根据超强毒株和经典毒株VP4基因序列的差异,分别合成了FAM标记的超强毒荧光探针和JOE标记的经典毒荧光探针,建立了实时荧光RT-PCR鉴别IBDV超强毒株与经典疫苗毒株的方法。检测超强毒和经典毒的敏感性分别可达420和320个拷贝数。建立的实时荧光RT-PCR方法敏感性高、特异性强,可用于临床样品中IBDV超强毒和经典毒的鉴别诊断。

抗鸡IBDV Gt株单克隆抗体制备及抗原表位初步分析

采用不连续蔗糖密度梯度离心法纯化的鸡传染性法氏囊病病毒Gt株免疫BALB／C小鼠，利用淋巴细胞杂交瘤技术，取其脾细胞与SP2／0骨髓瘤细胞进行融合，经过三次筛选克隆，获得具有分泌抗IBDV抗体的7D4、5D2两株杂交瘤细胞系，并对7D4及5D2株进行了特异性、稳定性等方面的鉴定。试验表明，两株分泌的抗体能够特异地与IBDV VP2蛋白反应。7D4株及5D2株杂交瘤细胞上清ELISA效价分别为1：250、1：50，腹水ELISA效价为6．4×10^6、5×10^3；并运用7D4、5D2介导的相加ELISA进行抗原表位的初步定位，这两株单抗针对不同的VP2抗原表位。

IBDV VP2/4/3-ChIL-2融合基因真核表达载体的构建及其在Vero细胞中的表达

构建含有传染性法氏囊病病毒(InfectiousBursalDiseaseVirus,IBDV)VP2/4/3和鸡白细胞介素2(ChickenInterleukin2,ChIL2)融合基因的真核表达载体pCIVP2/4/3IL2、pCIIL2VP2/4/3,并在Vero细胞中进行表达.应用重叠延伸剪切技术(splicingbyoverlappingextension),分别经3次PCR获得融合基因片段VP2/4/3IL2、IL2VP2/4/3,定向插入真核表达载体pCI中,获得重组质粒pCIVP2/4/3IL2、pCIIL2VP2/4/3,在脂质体介导下,分别转染Vero细胞.RTPCR检测证实导入的外源基因在Vero细胞中得到了转录;间接免疫荧光试验(IFA)和Westernblot检测证实重组质粒在Vero细胞中正确表达了插入的外源基因编码的融合蛋白,且表达的融合蛋白具有免疫反应性.重组真核表达载体pCIVP2/4/3IL2、pCIIL2VP2/4/3的成功构建及其在Vero细胞中的有效表达,为进一步探讨ChIL2作为分子免疫佐剂对IBDVDNA疫苗的特异性免疫增强作用奠定了基础.

IBDV超强毒株和弱毒株VP2基因同义密码子使用偏爱性研究

应用RT-PCR方法扩增并克隆了分离自河南省的30株IBDV超强毒和9株弱毒株VP2基因cDNA序列,研究IBDV超强毒和弱毒株的VP2高变区基因不同位点同义密码子的使用情况。结果表明,超强毒株和弱毒株除特定位点的特征性氨基酸不同外,在同义密码子的使用上也有明显的偏爱性。这预示着同义密码子的使用与VP2基因表达及其表达产物的空间结构有关,进而可能影响到IBDV的毒力。

IBDV单克隆抗体杂交瘤细胞株的建立及其应用

用经硫酸铵沉淀、高速离心并用蔗糖密度梯度离心提纯的鸡传染性法氏囊病病毒(IBDV)免疫BALB/C小鼠.取免疫鼠脾细胞与NS—1小鼠骨髓瘤细胞触合,共获11株阳性杂交瘤细胞.经3次克隆化和ELISA检测,筛选出3个(1B_1、5D_6、6D_8)能持续分泌抗IBDV单克隆抗体的杂交瘤细胞株.细胞上清液的ELISA效价为1B_1,3.2×10^(-2);5D_6,6.4×10^(-2);6D_8,3.2×10^(-2).腹水效价为1B_1,1.6×10^(-5);5D_6,8×10^(-4);6D_8,4×10^(-3).3株杂交瘤细胞的染色体数分别为105(1B_1),97(5D_6),85(6D_8).它们所产生的单抗皆为IgG1,所对抗的抗原决定簇不相同.3株McAb皆有沉淀特性.利用间接ELISA抑制试验,在诊断中进行了应用.

表达IBDV鸡源中和抗体的重组NDV的构建及免疫效果的探究

为研制预防新城疫病毒(NDV)和传染性法氏囊病毒(IBDV)两种病毒病的疫苗,本研究通过基因工程抗体和病毒反向遗传操作技术,以NDV LaSota株为载体,在病毒基因组的不同部位,分别或同时插入具有中和活性的鸡源IBDV抗体重链(H)或轻链(L)片段,构建并拯救出重组病毒,分别命名为rNDV-IRES-H-L(P/M)、rNDV-H(NP/P)-L(P/M)、rNDV-L(NP/P)-H(P/M)、rNDV-H(P/M)、rNDV-H(NP/P),并对其进行HA、TCID50、EID50、MDT、ICPI等试验以检测上述重组病毒的生物活性。结果显示,重组病毒不仅保持了其亲本病毒(NDV LaSota株)的感染能力而且还保持了其弱毒株的生物学特性。生长曲线结果显示,重组病毒与亲本NDV生长特性基本一致,表明外源基因的插入对病毒的复制能力无影响。ELISA和western blot结果显示rNDV-H(NP/P)、rNDV-H(P/M)中的H基因,rNDV-IRES-H-L(P/M)、rNDV-H(NP/P)-L(P/M)、rNDV-L(NP/P)-H(P/M)中的H和L基因均获得了表达,且rNDV-H(P/M)中的H基因和rNDV-L(NP/P)-H(P/M)中的H和L基因表达量高。用表达量高的重组病毒接种14日龄SPF鸡,分别检测其诱导SPF鸡NDV和IBDV抗体的产生情况。结果显示,在NDV抗体水平方面:HI实验结果表明重组病毒抗体效价均能在14 d达到保护临界值(4 log2);在IBDV抗体水平方面:ELISA结果表明重组病毒均能产生IBDV抗体。利用上述表达量高的重组病毒对人工感染IBDV(经典株BC6/85)的SPF鸡进行免疫保护试验,结果表明rNDV-H(P/M)的免疫保护效果要好于卵黄抗体和rNDV-L(NP/P)-H(P/M)。本研究获得了表达IBDV抗体的重组NDV即rNDV-H(P/M),为利用NDV载体表达本动物源抗体提供了实验依据。

A single mutation in the PBC loop of VP2 is involved in the in vitro replication of infectious bursal disease virus

To test whether amino acid mutations in the PBC and PHI loops of VP2 are involved in the replication and virulence of infectious bursal disease virus(IBDV), a pair of viruses, namely the moderately virulent IBDV(rG x-F9VP2) and the attenuated strain(rGt), were used. Residue mutations A222P(P_(BC)) and S330R(PHI), selected by sequence comparison, were introduced individually into r Gx-F9VP2 by using a reverse genetics system. In addition, the reverse mutation of either P222 A or R330 S was introduced into r Gt. The four modified viruses were then rescued and evaluated in vitro(CEF cells) and in vivo(SPF chickens). Results showed that A222 P elevated the replication efficiency of rG x-F9VP2 while P222 A reduced that of rG t in CEF cells. A mutation at residue 330 did not alter IBDV replication. In addition, animal experiments showed that a single mutation at either residue 222 or 330 did not significantly influence the virulence of IBDV. In conclusion, residue 222 in PBC of VP2 is involved in the replication efficiency of IBDV in vitro but does not affect its virulence in vivo, further facilitating our understanding of the gene-function of IBDV.

Generation of VP5 deficient mutant of infectious bursal disease virus strain HZ2

Infectious bursal disease virus (IBDV) is a bi-segmented, dsRNA virus of the Birnaviridae family. The nonstructural protein VP5 has been re- ported to be associated with virus-induced cell apoptosis and pathogenicity, but its role in viral rep- lication has not been unequivocally identified. Based on a PCR introduced mutagenesis strategy, the 33 bp of 96―129 bp located between ORF A1and ORF A2 of genomic segment A of IBDV strain HZ2 were de- leted, and an Nhe I (GcTaGc) site was inserted at 96―102 bp simultaneously. The mutated segment A was ligated into pCI, resulting in pCI-ANhe3. A chi- meric and deficient IBDV strain, named strain ANhe3, was recovered from chicken embryo fibroblast (CEF) cells by co-transfection with pCI-ANhe3 and pCI-mB, derived from the genomic segment B strain HZ2. The indirect fluorescent assay identified that strain ANhe3 could replicate on CEF cells without expression of VP5. Further examination showed that the patho- genesis of strain ANhe3 replicating on SPF chicken embryos was attenuated compared to strain HZ2. This paper provides a new rapid rescue strategy for gene-deleted virus. This strategy lays a basis for gene-deleted vaccine of IBDV.