Characterisation and separation of infectious bursal disease virus-like particles using aqueous two-phase systems

Infectious bursal disease(IBD)causes considerable economic losses in the commercial poultry industry worldwide.The principal way to control IBD virus(IBDV),the causative agent of IBD,is still through vaccination programs.Virus-like particles(VLPs)are recognised as a safe and potent recombinant vaccine platform.This research work explores the characterisation and separation of infectious bursal disease virus-like particles(IBD-VLPs)from crude feedstock.Various characteristics were studied with highperformance size-exclusion chromatography(HP-SEC),sodium dodecyl sulphate–polyacrylamide gel electrophoresis(SDS-PAGE)and transmission electron microscopy(TEM)analyses.Subsequently,the separation of IBD-VLPs using polyethylene glycol(PEG)/sodium citrate-based aqueous two-phase systems(ATPSs)was conducted and optimised.Moreover,a scale-up study of the best ATPS constituted of 15%PEG 6000,11%sodium citrate and 10%crude feedstock was performed to compare the separation performance of IBD-VLPs with and without centrifugation-assisted.The results indicated that the optimised ATPS with centrifugation-assisted for both 5 g and 50 g systems showed good recovery of IBDVLPs of>97%in the interphase between the PEG-rich top and salt-rich bottom phases.These optimised systems also showed high removal efficiencies of impurities of>95%.The results demonstrated that aqueous two-phase extraction could be a promising technology for efficient VLPs separation.

Application of monoclonal antibodies against chicken infectious bursal disease virus(IBDV)

Preliminary study has been made to test wether three strains McAb（1B1,5D6, 6D8）are against the same antigen determinant.Througn ELISA additive and competition expeiments,itproved that these three strains are against different antigen determinant.The result of positiveserum antigen component analysis with 2 strains IBDV McAb showed that sample IBD positiveserum had obvious inhibition against combination of 5D6 McAb with corresponding antigen.Theresults of substitution of corresponding component in ELISA inhibition experiment and compari-son of non-IBD serum （SPF chicken serum,ND,MD,IA positive serum）proved that IBD anti-serum was the only one showing inhibition against 5D6 McAb.Comparison with AGP and electro-microscope observation showed that ELISA inhibition experiment was characterised by high-specificity,rapidity and sensitiveness.799 serum samples were tested with ELISA inhibition anddouble immunodiffusion（AGP） experiments.ELISA had gotten 486 positive,with positive rate of60.83%;and AGP 334。

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.

Genetic Analysis of the VP2 Hypervariable Region of Thirty-six Infectious Bursal Disease Virus Isolates in China during 2009-2012

[Objective] Infectious bursal disease （IBD） is a highly contagious immuno- suppressive disease caused by infectious bursal disease virus （IBDV）. IBDV is ge- netically prone to mutation, which results in challenges to the disease prevention and control. Thus, it is necessary to continuously monitor the prevalence of IBDV. [Method] 36 IBDVs were identified from ten provinces in China from 2009 to 2012. Partial fragments of VP2, including the hypervariable region （HVR）, from new iso- lates were sequenced and analyzed through comparisons with published sequences of IBDV, including 18 strains isolated previously by our lab and 24 reference strains from China and around the world. [Result] Phylogenetic analysis showed a co-exis- tence of IBDV strains belonging to classic, variant, attenuated, and very virulent IB- DV （wlBDV） in China. wlBDVs remain the predominant strains in China and the new subgroup was emerging. Alignment analysis revealed several distinct amino acid mutations that might be involved in virulence or antigenicity variation. [Conclu- sion] The results offered evolutionary clues showing the emerging trend of obvious variations and diversity of IBDV in major poultry-producing regions of China particu- larly in recent years. These findings will contribute to a better understanding of the genetic evolution of IBDV.

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.

An improved scheme for infectious bursal disease virus genotype classification based on both genome-segments A and B

Infectious bursal disease(IBD)is caused by infectious bursal disease virus(IBDV),which has a genome consisting of two segments of double-stranded linear RNA.IBDVs have been traditionally divided into four phenotypes based on their pathogenicity and antigenicity,including classic,variant,very virulent,and attenuated IBDV.With the emergences of divergent molecular characteristics of novel strains produced by continuous mutations and recombination,it is increasingly difficult to define new IBDV strains using the traditional descriptive classification method.The most common classification scheme for IBDV with segmented genome is based solely on segment A,while the significance of segment B has been largely neglected.In this study,an improved scheme for IBDV genotype classification based on the molecular characteristics of both VP2(a viral capsid protein encoded by segment A)and VP1(an RNA-dependent RNA polymerase protein encoded by segment B)was proposed for the first time.In this scheme,IBDV was classified into nine genogroups of A and five genogroups of B,respectively;the genogroup A2 was further divided into four lineages.The commonly used phenotypic classifications of classic,variant,very virulent,and attenuated IBDVs correspond to the A1 B1,A2 B1,A3 B2,and A8 B1 genotypes of the proposed classification scheme.The novel variant IBDVs including the strains identified in this study were classified as belonging to genotype A2 d B1.The flexibility and versatility of this improved classification scheme will allow the unambiguous identification of existing and emerging IBDV strains,which will greatly facilitate molecular epidemiology studies of IBDV.

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.

The circulation of unique reassortment strains of infectious bursal disease virus in Pakistan

Infectious bursal disease(IBD),caused by IBD virus(IBDV),is one of the most devastating and immunosuppressive diseases of the poultry and has been a constraint on the sustainable poultry production around the globe including Pakistan.While the disease is threatening the poulty industry,the nature of predominant strains of IBDV in Pakistan remained l-defined.In this study,an epidemiology survey was conducted in the main chicken-farming regions of Pakistan.The batch of Pakistan IBDVs genes simultaneously covering both VP1 and VP2 were amplified,sequenced,and analyzed.The unique segment-reassortant IBDVs(vv-A/Uniq-B),carrying segmentA from vvIBDV and segment B from one unique ancestor,were identifed as one important type of circulating strains in Pakistan.The data also discovered the characteristic molecular features of Pakistan IBDVs,which will contribute to scientific vaccine selection and effective prevention of the disease.

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.

Evaluation of the Protection against Infectious Bursal Disease (IBD) Challenge in Progeny Born to Parents Having Received a Vaccination Program Using a Herpesvirus of Turkey-Infectious Bursal Disease (HVT-IBD) Vector Vaccine

Broiler breeder vaccination against IBD is usually based on the injection of at least one inactivated vaccine in oil adjuvant, typically included in a combined vaccine. Priming using one or several IBD vaccine (s) has been the most common way to immunize the breeders so far. In summary, protection against vvIBD challenge in chicks of one commercial genetic line vaccinated in ovo with the HVT-IBD vector vaccine was demonstrated. The parents’ IBD vaccination program, using the HVT-IBD vector vaccine alone, the HVT-IBD vector vaccine plus IBD inactivated vaccine, and inactivated IBD vaccine alone, did not impair their progeny’s in ovo HVT-IBD vector vaccine take and subsequent protection against vvIBD virus challenge. An advantage in terms of immunization of the progeny against vvIBD was shown in the chicks born to breeders vaccinated with the HVT-IBD vaccine as a primer, as compared to breeders vaccinated with the inactivated vaccine alone. High level of IBD maternally-derived antibodies transmitted to the progeny by their parents induces together with an early onset of immunity by in ovo injection of a HVT-IBD vector vaccine clinical protection, as monitored on bursas, after vvIBD virus challenge.

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.

Effect of Chicken Akirin2 Gene on Immune Response Induced by VP2 DNA Vaccine of Infectious Bursal Dis-ease Virus

[ Abstracts ] In order to investigate the effect of chicken Akirin2 gene on the immune response induced by VP2 DNA vaccine of infectious bursal disease virus （IBDV）. [ Methods] The 14-day-old SPF chickens were immunized with recombinant plasmids expressing VP2 protein and Akirin2 protein, and strength- ened immunization was conducted at the 14＇~ day after the first immunization. Finally, test chickens were challenged with IBDVBC6-85 virulent strain. [ Resultss ] Test results showed that Akirin2 gene could enhance the specific immune response induced by VP2 DNA vaccine, improve the proliferation of peripheral blood lym- phocytes and ＇affect the expressing of cytokines TNF-a, IFN-Y, IL-1β, IL-2, IL-4, IL 6, IL-9, IL-10, IL-17 and IL-18. Effects of recombinant plasmids co-ex- pressing Akirin2 protein and VP2 protein on cytokine expression showed some differences with the recombinant plasmids expressing Akirir/2 protein or VP2 protein along. [ Conclusions] Chicken Akirin2 gene could significantly enhance the humoral immune response and cellular immune response induced by VP2 DNA vaccine of IBDV.

我国部分地区A2dB1型传染性法氏囊病病毒新型变异株的鉴定及序列分析

为持续了解传染性法氏囊病病毒新型变异株(Novel variant infectious bursal disease virus,nVarIBDV)在我国流行情况,研究收集2021—2022年6个主要养禽地区疑似传染性法氏囊病(Infectious bursal disease,IBD)鸡病料,采用RT-PCR进行检测,并对11株IBDV代表毒株的基因组双节段代表区段VP2-HVR和VP1-B-marker进行基因测序及序列分析。结果显示:所检测病料的IBDV阳性率为20.65%(19/92),其中11株IBDV代表毒株均为A2dB1型nVarIBDV。研究表明,nVarIBDV在我国主要养禽地区仍持续流行,而且出现了值得注意的新的突变位点,有必要进行持续的IBDV流行病学监测。

抗传染性法氏囊病毒VP2蛋白单克隆抗体的制备及鉴定

传染性法氏囊病(infectious bursal disease,IBD)是由传染性法氏囊病毒(Infectious bursal bursal virus,IBDV)引起的一种高度传染性疾病,以雏鸡法氏囊萎缩、腿肌出血等为特征性病变,给世界家禽产业造成重大经济损失。目前,由新型变异株引起的IBD在我国呈现流行趋势。为建立基于IBDV VP2蛋白的免疫学诊断技术,本研究以新型变异毒株IBDV-LY21/2为模板,扩增其VP2基因,随后构建重组原核表达质粒pCold-Ⅰ-IBDV-VP2并转化BL21(DE3)大肠杆菌进行诱导表达,通过考马斯亮蓝染色和Western blot检测重组蛋白His-VP2的表达情况,并对其进行纯化和浓度测定。将His-VP2免疫BALB/c小鼠后,采用iELISA检测血清抗体效价,最后制备单克隆抗体并对其鉴定。结果显示,获得的重组蛋白His-VP2分子量约为50 kDa,浓度为8 mg/mL;通过两次亚克隆获得3株杂交瘤细胞株1G10F12、3E3E9、4D12G12,且重链均为IgG1型,轻链均为κ型;其中1G10F12、3E3E9可与重组蛋白Myc-VP2产生Western blot和IFA反应,而4D12G12只能与其产生IFA反应。本研究为IBD诊断方法的建立奠定了基础,同时为深入研究VP2蛋白的功能提供生物学工具。

枯草芽孢杆菌fmbJ产生的新型抗微生物物质体外抗NDV和IBDV的活性分析

测定了枯草芽孢杆菌fmbJ株产生的新型抗微生物物质的体外抗新城疫病毒(Newcastle disease virus,NDV)lasota株、传染性法式囊病病毒(Infectious Bursal Disease Virus,IBDV)哈尔滨(H)株作用。结果表明该新型抗微生物物质对鸡胚成纤维(Chicken Embryo Fibroblasts,CEF)细胞的TD50和TD0分别为128.95mg/L、25.79mg/L;对NDVlasota株、IBDV H株所致细胞病变效应有明显的抑制作用,可使细胞存活率显著升高;该抗微生物物质具有抗NDVlasota株、IBDV H株作用;并具有预防其感染及抑制其复制的作用。其抗病毒作用效果和病毒唑相当,由于其对CEF细胞的毒性较弱,可作为一种抗病毒药物进行开发研究。

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).

超强毒IBDV细胞克隆化毒回归鸡后的致病性与VP_2基因高变区的分子变化

为了研究超强毒鸡传染性法氏囊病病毒(vvIBDV)的致病性及其VP2基因高变区的分子变化,以vvIBDVGX8/99株囊毒为研究对象,将该毒在SPF鸡胚连传10代后,再在鸡胚成纤维细胞(CEF)上连续盲传。该病毒在CEF上传至22代时开始引发CEF细胞病变,随之在96孔细胞培养板上用无限稀释法连续克隆2次后获得了4个病毒克隆,再将该4个病毒克隆分别连续回传3～5周龄SPF鸡10代。分别比较4个克隆毒及其回传SPF鸡后不同传代毒,对4～6周龄SPF鸡的致病性及VP2高变区氨基酸分子的变化,结果表明,4个克隆化毒的细胞培养毒对SPF鸡只有0～6 7%的致死率,不同克隆毒的SPF鸡传代毒对SPF鸡的致病性却都逐渐增强,但程度差异很大,其中克隆#5在回鸡1、5和10代后的致死率从0分别增加到10%、20%和27%;克隆#4从6 7%增加至13%、17%和23%;但克隆#1和#3的致病性变化相对较小。相对于原始囊毒及鸡胚毒,4个克隆化毒在测序的VP2高变区的约145个氨基酸中,有10个位点发生了相同的变异,变得与适应细胞的疫苗毒D78株基本一致,在回鸡传代导致对鸡毒力增强的过程中,这10个位点中大多数氨基酸不再变化,只有第253位和256位氨基酸从囊毒的Q和I变为细胞适应毒的H和V后,有些病毒克隆回鸡至第10代时又变为原囊毒的Q和I。

人工感染IBDV鸡法氏囊的电镜研究

通过透射电镜系统观察了人工感染传染性法氏囊病病毒（ＩＢＤＶ）后鸡法氏囊各类细胞的病理变化。感染后１２～２４ｈ，病毒粒子主要见于髓质淋巴细胞中，细胞中可见到大量纤维样病毒发生基质及无囊膜包围的大型病毒晶格，细胞核染色质浓缩，核中出现纤维样结构。感染后３６ｈ，淋巴细胞开始大量裂解死亡。无囊膜包围的病毒晶格也出现于髓质网状细胞中，被感染的网状细胞并不裂解，而表现出细胞凋亡的特征：染色质固缩呈颗粒块状，胞质浓缩，最终被巨噬细胞吞噬。病毒粒子同样大量出现于巨噬细胞、网状上皮细胞、粒细胞和扁平上皮细胞的吞噬囊泡中，但未出现病毒复制的特征。我们的结果显示法氏囊髓质部的未成熟淋巴细胞是ＩＢＤＶ的最适靶细胞，ＩＢＤＶ感染可引起法氏囊淋巴细胞的大量坏死，同时诱导髓质部网状细胞凋亡。