Background

There is evidence that chicken IL4 (chIL4) functions similarly to its mammalian analogue by enhancing type 2 T helper (Th2) humoral immunity and promoting protection against parasitic infections; however, no studies have been performed to assess the effect of chIL4 on the pathogenesis of Newcastle disease (ND). To assess the role of chIL4 in velogenic NDV pathogenesis we created a vNDV infectious clone expressing chIL4. We hypothesized that co-expression of chIL4 during virus replication would result in decreased inflammation caused by the Th1 response and thereby increasing survival to challenge with vNDV.

Methods

To evaluate the effect of chIL4 during early infection with velogenic Newcastle disease virus (NDV) in chickens, recombinant NDV clones expressing either chIL4 (rZJ1-IL4) or a control expressing green fluorescent protein (rZJ1-GFP) were created by inserting an expression cassette in an intergenic region of the NDV genome. The pathogenesis of rZJ1-IL4 was assessed in 4-week-old specific pathogen free chickens. The extent of virus replication was evaluated by titration in mucosal secretions and immunohistochemistry in multiple tissues. Expression of chIL4 was confirmed in tissues using immunohistochemistry.

Results

Infection of birds with the rZJ1-IL4 resulted in successful viral replication in vivo and in vitro and generation of the chIL4 in tissues. All birds were clinically normal 2 DPI, with one bird in each group showing conjunctival swelling and enlarged spleens grossly. At 5 DPI, moderate or severe depression was observed in birds infected with rZJ1-GFP or rZJ1-IL4, respectively. Neurological signs and thymic atrophy were observed in one bird infected with rZJ1-IL4. Grossly, conjunctival swelling, mottled spleen and proventricular hemorrhages were observed at 5 DPI in one bird from each group. At 5 DPI, severe necrosis in the spleen, bursa and cecal tonsils were observed in birds infected with rZJ1-GFP, along with minimal evidence of chIL4 expression. In contrast, splenic atrophy, and moderate necrosis in the bursa and cecal tonsils were observed in birds infected with rZJ1-IL4. In addition, chIL4 signal was found in all tissues of rZJ1-IL4 birds at 5DPI.

Conclusions

The production of chIL4 by a recombinant NDV strain resulted in the activation of the positive feedback loop associated with IL4 production. Insertion of chIL4 into NDV may decrease necrosis to lymphoid organs while increasing the severity of lymphoid atrophy and prolonged disease. However, with a low number of birds it is difficult to determine whether these results are significant to disease outcome.

中文翻译：

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感染表达鸡 IL4 的重组毒力 NDV 克隆的鸡的评价

背景

有证据表明，鸡 IL4 (chIL4) 的功能与其哺乳动物类似物相似，可增强 2 型 T 辅助 (Th2) 体液免疫并促进对寄生虫感染的保护；然而，尚未进行任何研究来评估 chIL4 对新城疫 (ND) 发病机制的影响。为了评估 chIL4 在 velogenic NDV 发病机制中的作用，我们创建了一个表达 chIL4 的 vNDV 感染性克隆。我们假设在病毒复制过程中 chIL4 的共表达会导致由 Th1 反应引起的炎症减少，从而增加用 vNDV 攻击的存活率。

方法

为了评估 chIL4 在鸡早期感染新城疫病毒 (NDV) 期间的影响，通过插入表达盒创建表达 chIL4 (rZJ1-IL4) 或表达绿色荧光蛋白 (rZJ1-GFP) 的对照的重组 NDV 克隆在 NDV 基因组的基因间区域。rZJ1-IL4 的发病机制在 4 周龄的无特定病原体鸡中进行了评估。病毒复制的程度通过黏膜分泌物的滴定和多个组织的免疫组织化学来评估。使用免疫组织化学证实了 chIL4 在组织中的表达。

结果

用 rZJ1-IL4 感染鸟类导致病毒在体内和体外复制成功和组织中 chIL4 的产生。所有鸡在 2 DPI 时临床上均正常，每组中的一只鸡表现出明显的结膜肿胀和脾脏肿大。在 5 DPI，分别在感染 rZJ1-GFP 或 rZJ1-IL4 的鸟类中观察到中度或重度抑郁。在一只感染了 rZJ1-IL4 的鸟中观察到神经学体征和胸腺萎缩。大体上，每组中的一只鸟在 5 DPI 时观察到结膜肿胀、斑驳的脾脏和前室出血。在第 5 天，在感染 rZJ1-GFP 的鸟类中观察到脾脏、法氏囊和盲肠扁桃体严重坏死，同时 chIL4 表达的证据很少。相比之下，在感染 rZJ1-IL4 的鸟类中观察到脾脏萎缩和法氏囊和盲肠扁桃体中度坏死。此外，

结论

重组 NDV 毒株产生 chIL4 导致与 IL4 产生相关的正反馈回路的激活。将 chIL4 插入 NDV 可能会减少淋巴器官的坏死，同时增加淋巴萎缩和疾病延长的严重程度。然而，由于家禽数量较少，很难确定这些结果是否对疾病结果有显着影响。