Laval Kathlyn, Favoreel Herman W, Nauwynck Hans J
Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medecine, Ghent University, Salisburylaan 133, B-9820 Merelbeke, Belgium.
J Gen Virol. 2015 Jan;96(Pt 1):118-130. doi: 10.1099/vir.0.067363-0. Epub 2014 Sep 19.
Equine herpesvirus type 1 (EHV-1) replicates in the epithelial cells of the upper respiratory tract and disseminates through the body via a cell-associated viraemia in monocytic cells, despite the presence of neutralizing antibodies. However, the mechanism by which EHV-1 hijacks immune cells and uses them as 'Trojan horses' in order to disseminate inside its host is still unclear. Here, we hypothesize that EHV-1 delays its replication in monocytic cells in order to avoid recognition by the immune system. We compared replication kinetics in vitro of EHV-1 in RK-13, a cell line fully susceptible to EHV-1 infection, and primary horse cells from the myeloid lineage (CD172a(+)). We found that EHV-1 replication was restricted to 4 % of CD172a(+) cells compared with 100 % in RK-13 cells. In susceptible CD172a(+) cells, the expression of immediate-early (IEP) and early (EICP22) proteins was delayed in the cell nuclei by 2-3 h post-infection (p.i.) compared with RK-13, and the formation of replicative compartments by 15 h p.i. Virus production in CD172a(+) cells was significantly lower (from 10(1.7) to 10(3.1) TCID50 per 10(5) inoculated cells) than in RK-13 (from 10(5) to 10(5.7) TCID50 per 10(5) inoculated cells). Less than 0.02 % of inoculated CD172a(+) cells produced and transmitted infectious virus to neighbouring cells. Pre-treatment of CD172a(+) cells with inhibitors of histone deacetylase activity increased and accelerated viral protein expression at very early times of infection and induced productive infection in CD172a(+) cells. Our results demonstrated that the restriction and delay of EHV-1 replication in CD172a(+) cells are part of an immune evasive strategy and involve silencing of EHV-1 gene expression associated with histone deacetylases.
1型马疱疹病毒（EHV-1）在上呼吸道上皮细胞中复制，并通过单核细胞中的细胞相关病毒血症在体内传播，尽管存在中和抗体。然而，EHV-1劫持免疫细胞并将其用作“特洛伊木马”以便在其宿主体内传播的机制仍不清楚。在此，我们假设EHV-1延迟其在单核细胞中的复制以避免被免疫系统识别。我们比较了EHV-1在RK-13（一种对EHV-1感染完全敏感的细胞系）和来自髓系谱系的原代马细胞（CD172a(+)）中的体外复制动力学。我们发现，与RK-13细胞中100%的感染率相比，EHV-1的复制在CD172a(+)细胞中被限制在4%。在易感的CD172a(+)细胞中，与RK-13相比，感染后（p.i.）2-3小时，细胞核中立即早期（IEP）和早期（EICP22）蛋白的表达延迟，并且在感染后15小时复制区室的形成延迟。CD172a(+)细胞中的病毒产生明显低于RK-13（每10(5)个接种细胞中，CD172a(+)细胞为10(1.7)至10(3.1)个半数组织培养感染剂量（TCID50），RK-13为10(5)至10(5.7)个TCID50）。接种的CD172a(+)细胞中不到0.02%产生并将感染性病毒传播给邻近细胞。用组蛋白脱乙酰酶活性抑制剂预处理CDl72a(+)细胞可在感染的极早期增加并加速病毒蛋白表达，并在CDI72a(+)细胞中诱导产生性感染。我们的结果表明，EHV-1在CD172a(+)细胞中的复制受限和延迟是免疫逃避策略的一部分，并且涉及与组蛋白脱乙酰酶相关的EHV-1基因表达的沉默。
