鸡传染性法氏囊病超强毒Gx株感染性分子克隆的构建

本研究以鸡传染性法氏囊病超强毒Gx株(野毒株)基因组为模板,用蛋白酶K法提取病毒基因组核酸dsRNA,在cDNA克隆的5'端上游引入了T7启动子序列,采用Long-accurateRT-PCR(LA-PCR)一步法扩增并克隆了病毒基因组A节段与B节段全长cDNA。序列测定结果表明,基因组A节段全长共3267个核苷酸,包括5'及3'端的非编码区和两个部分重叠的开放阅读框,基因组B节段全长共2843个核苷酸,包括5'及3'端的非编码区和一个开放阅读框。将IBDV-Gx株的A节段全长基因组及B节段全长基因组分别克隆入pMD18-T载体,构建成pMD-A、pMD-B两个带有T7启动子的重组质粒。两个重组质粒线性化后,进行体外转录,然后共电转染于鸡胚成纤维细胞37℃培养72h并传代。收获的细胞传代培养物分别用RT-PCR、间接免疫荧光、蚀斑试验等方法进行鉴定,结果用RT-PCR扩增出了VP3及VP5基因片段,间接免疫荧光检测到了特异性的荧光抗体,蚀斑试验结果表明蚀斑形成单位为3×103PFU/mL。     

鸡传染性法氏囊病病毒超强毒株VP2基因突变对细胞嗜性改变的研究

为研究鸡传染性法氏囊病病毒超强毒株(vvIBDV)细胞嗜性改变的分子基础,本研究通过定点突变、重叠延伸PCR(SOE-PCR)等技术,以vvIBDV HLJ-0504株为骨架构建了两组感染性克隆,并借助已建立的反向遗传操作技术进行病毒拯救。IFA检测、电镜观察及RT-PCR鉴定均显示:Q253H/A284T双点突变的pCAGGHLJ0504A889/980HRT和pCAGGHLJ0504BHRT共转染DF1细胞成功拯救出重组病毒(rHLJ0504HT),而未进行双点突变的pCAGGHLJ0504AHRT和pCAGGHLJ0504BHRT共转染组未获得重组病毒。上述结果表明,双点突变Q253H/A284T能使vvIBDV HLJ-0504适应非允许细胞CEF,但未进行Q253H/A284T双点突变的vvIBDV HLJ-0504不能感染非允许细胞CEF,因此,该研究表明VP2的Q253H/A284T两个氨基酸突变是vvIBDV细胞嗜性改变的分子基础。     

Genetic characterization of very virulent infectious bursal disease viruses from Latin America

Very virulent infectious bursal disease viruses (vvIBDVs) were detected in phenol inactivated bursal samples obtained from Brazil, the Dominican Republic, and Venezuela. After nucleotide sequence analysis of the hypervariable region of VP2 gene, the vvIBDVs from Brazil and Venezuela exhibited all of the 14 nucleotide changes that are conserved in the European UK-661 and most other vvIBDV strains. However, the vvIBDV from the Dominican Republic presented 11 nucleotide changes that are conserved in vvIBDV strains. After phylogenetic analysis, the Latin American strains were found to be related to other vvIBDV strains from Europe, Asia, and Africa. However, Brazilian and Dominican vvIBDVs clustered in two separate subgroups, while the vvIBDVs from Venezuela were closely related to other strains from other parts of the world. By deduced amino acid sequence, the three conserved amino acid residues in vvIBDV strains (222 Ala, 256 Ile, and 294 Ile) were confirmed in the Latin American viruses, and one amino acid change (300 Ala) was unique to all vvIBDVs from the Dominican Republic. The occurrence of this change in the Dominican vvIBDVs may have an impact in their antigenic makeup. Results of this study indicate that the vvIBDVs detected in Latin America are genetically similar to IBDV strains from other parts of the world. However, vvIBDVs from Venezuela were more similar to the vvIBDV strains from Europe and Asia. Of all the samples analyzed, vvIBDVs from Brazil and the Dominican Republic exhibited more genetic changes. These changes may have emerged as a result of the different management practices and environmental conditions present in each particular geographic area.     

Very virulent infectious bursal disease virus in southeastern Europe

Clinical outbreaks of severe acute infectious burial disease (IBD) were recorded since the mid- and late 1990s in several countries in the southeastern part of Europe. Epidemiologic data showed that both infectious bursal disease virus (IBDV)-vaccinated and IBDV-nonvaccinated chickens were affected with acute IBD and mortality up to 50% independent of the IBDV vaccination status of the appropriate parent flocks. For investigation of the causative agent of acute IBD, the variable region of VP2 was amplified, cloned, and sequenced. Nucleotide sequence analysis of polymerase chain reaction fragments showed several silent nucleotide exchanges in comparison with the sequence of the very virulent (vv) IBDV strain UK661. Also, restriction enzyme cleavage sites proposed specific for vvIBDV were present in all investigated strains. On the basis of clinical signs in affected flocks, recorded epidemiologic data, and sequence analysis, it is very likely the IBD-causing strains were of the vv phenotype.     

Direct evidence of reassortment and mutant spectrum analysis of a very virulent infectious bursal disease virus

The complete genomic sequence of very virulent infectious bursal disease virus (vvIBDV) Gx strain was determined, including the sequences of segment A, encoding the precursor polyprotein, and segment B, encoding the viral RNA polymerase (VP1) and 5'- and 3'-untranslating regions. Alignment of segment A of Gx with the sequences of 12 other vvIBDV strains showed 97.5% to 99.0% amino acid identity, whereas alignment of segment B of Gx with nine other vvIBDV strains revealed high sequence divergence, ranging from 10.3% to 11%. Phylogenetic analysis of segments A and B showed that they were in different branches, indicating that the reassortment occurred in this strain and that segment A and segment B derived from different pathotype strains. The mutant spectrum analysis of quasispecies virus demonstrated that the mean minimum mutation frequency in VP1 was 8.78-fold higher than in the polyprotein. The most frequent mutations were in the first 1986 nucleotides (nonsynonymous mutations) and the last 660 nucleotides (synonymous mutations), indicating that the 219 amino acid residues in the C-terminal of the VP1 form a functional region.     

Detection of cell membrane proteins that interact with virulent infectious bursal disease virus

To detect the molecules that interact with infectious bursal disease virus (IBDV), the chicken B lymphoblastoid cell line, LSCC-BK3, which is permissive for virulent IBDV infection was investigated. The sodium dodecyl sulfate-solubilized plasma membrane fraction from the cells was subjected to a virus overlay protein binding assay. The IBDV specifically bound to proteins in LSCC-BK3 plasma membranes with molecular weights of 70, 82 and 110 kDa. This is the first report to demonstrate cellular molecules that interact with virulent IBDV.     

Mast cell mediated inflammatory response in chickens after infection with very virulent infectious bursal disease virus

The potential role of the mast cells in the invasion of very virulent infectious bursal disease virus (vvIBDV) is unknown. We evaluated mast cell activity and tryptase production after vvIBDV infection in special pathogen-free (SPF) chickens using cytochemistry and immunohistochemistry analyses. The results were as follows: (1) severe histologic lesions were observed in the thymus, spleen, cloacal bursa, liver, kidney and other tissues. vvIBDV viral antigens were detected and presented extensively in the parenchymatous organs, in particular, the cloacal bursa, liver, kidney, thymus, spleen and pancreas. (2) In the vvIBDV-infected group, the mast cell population increased markedly in the liver, kidney, thymus, glandular stomach, spleen and cloacal bursa on days 1, 2 and 3 after vvIBDV infection (p<0.05). However, very few mast cells were observed in those same tissues in the controls, especially in the bursa of Fabricius. (3) Tryptase, a marker for activated mast cells, has a positive correlation with mast cell distribution. The mast cells identified in the tissues were likely to be activated since they were associated with cell degranulation and the presence of tryptase. Furthermore, the co-localization of mast cells, and presence of vvIBDV antigens suggests that the mast cells were activated by vvIBDV infection. Our results also suggest that tryptase may contribute to the inflammation of acute IBD induced by vvIBDV infection. Our research contributes to the further understanding of inflammatory response mechanisms and the contribution of mast cell activity to this process.     

鸡传染性法氏囊病病毒超强株VP2基因重组新城疫病毒胚胎免疫安全性及效力试验

为研制能够同时预防传染性法氏囊病(IBD)和新城疫(ND)的疫苗,本研究选用表达IBD病毒(IBDV)超强毒株(vvIBDV)VP2基因的重组ND病毒(NDV)LaSota疫苗株(rL-VP2),测定其半数鸡胚感染量、平均鸡胚致死时间、脑内接种指数和静脉内致病指数等指标,按不同剂量接种18胚龄SPF鸡胚,分别于出雏后第9d、第14d和第21d采血,用微量凝集法和ELISA方法测定血清中抗NDV抗体和抗IBDV抗体水平,并于出雏后28d用NDV强毒(F48E9株)和vvIBDVGx株攻毒,评估重组疫苗的胚胎免疫效果。结果显示:按104EID50/枚剂量进行免疫不会影响SPF鸡胚出雏率和出雏后21d存活率,并且该免疫组雏鸡能够对NDV强毒和vvIBDV攻毒提供安全的免疫保护。     

一株传染性法氏囊病病毒强毒株的分离与鉴定

鸡传染性法氏囊病是由传染性法氏囊病病毒引起的一种急性传染病。本研究从江苏某疑似发生传染性法氏囊病的鸡场采集病料,通过观察临床症状、病理变化、RT-PCR检测、基因测序、SPF鸡胚接种、琼脂扩散试验和雏鸡攻毒等试验,证实了该鸡群发生了传染性法氏囊病,且分离到一株传染性法氏囊病病毒(JSXY株),该病毒有较强的致病力,VP4基因比较分析发现其与变异株亲缘关系最近,序列同源性为95%。本研究为江苏地区传染性法氏囊病的防治提供了有益的参考。     

传染性法氏囊病病毒超强毒株HLJ-0504全基因组克隆及其新特征分析

为了解传染性法氏囊病病毒(IBDV)HLJ-0504株的分子生物学特征,本研究利用融合PCR技术获得HLJ-0504株全基因组序列。核苷酸和推导氨基酸序列遗传演化分析发现,HLJ-0504A节段位于IBDV超强毒的分枝上,而B节段则介于超强毒株和减毒株之间,形成一个独立分枝,属于一株新的自然重组病毒。VP2抗原性预测分析表明,HLJ-0504株VP2第Ⅰ亲水区中的氨基酸发生突变(D212N),该突变可能导致了HLJ-0504株抗原性发生漂变。本实验结果为深入研究IBDV的分子特征奠定了基础。