Borca M V, Carrillo C, Zsak L, Laegreid W W, Kutish G F, Neilan J G, Burrage T G, Rock D L
Plum Island Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Greenport, New York 11944-0848, USA.
J Virol. 1998 Apr;72(4):2881-9. doi: 10.1128/JVI.72.4.2881-2889.1998.
An African swine fever virus (ASFV) gene with similarity to the T-lymphocyte surface antigen CD2 has been found in the pathogenic African isolate Malawi Lil-20/1 (open reading frame [ORF] 8-DR) and a cell culture-adapted European virus, BA71V (ORF EP402R) and has been shown to be responsible for the hemadsorption phenomenon observed for ASFV-infected cells. The structural and functional similarities of the ASFV gene product to CD2, a cellular protein involved in cell-cell adhesion and T-cell-mediated immune responses, suggested a possible role for this gene in tissue tropism and/or immune evasion in the swine host. In this study, we constructed an ASFV 8-DR gene deletion mutant (delta8-DR) and its revertant (8-DR.R) from the Malawi Lil-20/1 isolate to examine gene function in vivo. In vitro, delta8-DR, 8-DR.R, and the parental virus exhibited indistinguishable growth characteristics on primary porcine macrophage cell cultures. In vivo, 8-DR had no obvious effect on viral virulence in domestic pigs; disease onset, disease course, and mortality were similar for the mutant delta8-DR, its revertant 8-DR.R, and the parental virus. Altered viral infection was, however, observed for pigs infected with delta8-DR. A delay in spread to and/or replication of delta8-DR in the draining lymph node, a delay in generalization of infection, and a 100- to 1,000-fold reduction in virus titers in lymphoid tissue and bone marrow were observed. Onset of viremia for delta8-DR-infected animals was significantly delayed (by 2 to 5 days), and mean viremia titers were reduced approximately 10,000-fold at 5 days postinfection and 30- to 100-fold at later times; moreover, unlike in 8-DR.R-infected animals, the viremia was no longer predominantly erythrocyte associated but rather was equally distributed among erythrocyte, leukocyte, and plasma fractions. Mitogen-dependent lymphocyte proliferation of swine peripheral blood mononuclear cells in vitro was reduced by 90 to 95% following infection with 8-DR.R but remained unaltered following infection with delta8-DR, suggesting that 8-DR has immunosuppressive activity in vitro. Together, these results suggest an immunosuppressive role for 8-DR in the swine host which facilitates early events in viral infection. This may be of most significance for ASFV infection of its highly adapted natural host, the warthog.
在致病性非洲分离株马拉维Lil-20/1（开放阅读框[ORF]8-DR）和一种细胞培养适应的欧洲病毒BA71V（ORF EP402R）中发现了一个与T淋巴细胞表面抗原CD2相似的非洲猪瘟病毒（ASFV）基因，并且已证明该基因与ASFV感染细胞中观察到的血细胞吸附现象有关。ASFV基因产物与CD2（一种参与细胞间粘附和T细胞介导的免疫反应的细胞蛋白）在结构和功能上的相似性表明，该基因可能在猪宿主的组织嗜性和/或免疫逃避中发挥作用。在本研究中，我们从马拉维Lil-20/1分离株构建了一个ASFV 8-DR基因缺失突变体（delta8-DR）及其回复株（8-DR.R），以在体内研究基因功能。在体外，delta8-DR、8-DR.R和亲本病毒在原代猪巨噬细胞培养物上表现出难以区分的生长特性。在体内，8-DR对家猪的病毒毒力没有明显影响；突变体delta8-DR、其回复株8-DR.R和亲本病毒的发病时间、病程和死亡率相似。然而，在用delta8-DR感染的猪中观察到病毒感染发生了改变。观察到delta8-DR在引流淋巴结中的扩散和/或复制延迟，感染的全身性扩散延迟，并且在淋巴组织和骨髓中的病毒滴度降低了100至1000倍。delta8-DR感染动物的病毒血症发作明显延迟（延迟2至5天），在感染后5天平均病毒血症滴度降低约10000倍，在后期降低30至100倍；此外，与8-DR.R感染的动物不同，病毒血症不再主要与红细胞相关，而是在红细胞、白细胞和血浆部分中均匀分布。用8-DR.R感染后，猪外周血单个核细胞在体外依赖丝裂原的淋巴细胞增殖减少了90%至95%，但用delta8-DR感染后仍未改变，这表明8-DR在体外具有免疫抑制活性。总之，这些结果表明8-DR在猪宿主中具有免疫抑制作用，这有助于病毒感染的早期事件。这对于ASFV感染其高度适应的天然宿主疣猪可能具有最重要的意义。
