IBDV B87株不同鸡胚代次毒力和细胞嗜性差异的比较研究

The study on virulence and cell tropism difference of IBDV B87 passage strains in chicken embryo

关键词:  传染性法氏囊病毒  VP2基因  毒力差异  细胞嗜性

Key words:  IBDV  VP2 gene  virulent difference  cell tropism

摘要:

对IBDV疫苗株 B87的鸡胚传代毒E2和E6的VP2片段进行测序和分析，发现两个代次毒株VP2序列存在7个氨基酸的差异，即S76G, L217S, Q253H, D279N, A284T, I294L, S330R。将E2和E6接种CEF细胞，E2不能在CEF上增殖，而接种E6的CEF细胞可以产生明显的CPE，说明两个毒株对CEF的嗜性不同。分别将E2和E6接种3周龄SPF鸡，进行对鸡的毒力比较，接种后第7 天开始，E2出现囊体比下降，BB指数明显低于E6毒株，相应的法氏囊切片经HE染色后，接种E2的法氏囊滤泡萎缩严重，结构松散，E6只有部分滤泡出现萎缩，滤泡间隔基本正常，说明E2，E6对SPF鸡法氏囊毒力存在明显差异。根据两个毒株的VP2序列差异以及相关研究，推测Q253H/D279N/A284T三个位点突变可能是IBDV毒力和细胞嗜性差异的分子基础，但另外4个位点也可能对IBDV毒力差异产生影响。

Abstract:

E2 and E6 were passage strains of moderate virulent vaccine strain B87 in chicken embryo, VP2 were sequenced and analyzed, and there are 7 amino acid mutations in VP2 between E2 and E6, S76G, L217S, Q253H, D279N, A284T, I294L, S330R. CEF were infected with E2 and E6, E2 could not adapt to CEF, but E6 could induce CPE. 3-weeks SPF chickens were inoculated to compare the safety difference of the two strains, then bursas of Fabricius from each group were removed and evaluated for histo-pathologic lesions at 3d, 7d, 14d and 21d, separately, and the bursa to body weight ratio and bursa: body-weight index(BB Index) were also determined. Chicken experiments reveal that the bursa to body weight ratio of SPF chickens infected with E2 began to decrease from 7 days post inoculation, and the BB Index of E2 was also much lower than that of E6. Formalin-fixed bursas were sectioned and stained with haematoxylin/eosin, bursas of chicks inoculated with E2 show atrophy and loss of the follicular architecture at 7 days post infection, while bursas of that inoculated with E6 had a small part of follicles atrophy, with normal follicular connective tissues. This study suggests that mutations of Q253H/D279N/A284T may be the molecular basis of virulence and cell tropism, but the other 4 mutations may also influence the virulence of IBDV.