GtxA, a leukotoxic RTX-toxin, has been proposed a main virulence factor of Gallibacterium anatis. To evaluate the impact of GtxA during infection, we experimentally infected laying hens with a G. anatis wild-type (WT) strain and its isogenic gtxA deletion mutant (ΔgtxA), respectively, and monitored the birds during a 6 day period. Birds inoculated with ΔgtxA had significantly reduced gross lesions and microscopic changes compared to the birds inoculated with the WT strain. To assess the host response further, we quantified the expression of pro-inflammatory cytokines and apoptosis genes by RT-qPCR. In the ovarian tissue, the expression levels of IL-4 and TNF-α were significantly lower in the ΔgtxA group compared to the WT group, while IL-6 and IL-10 levels appeared similar in the two groups. In the spleen tissue of ΔgtxA infected chickens, IL-4 expression was also lower compared to the WT infected chickens. The results indicated that GtxA plays a key role in an acute cytokine-mediated Th2-like response against G. anatis infection in the ovary tissue. The pro-inflammatory response in the ovary tissue of birds inoculated with ΔgtxA mutant was thus significantly lower than the wild-type response. This was, at least partly, supported by the apoptosis gene expression levels, which were significantly higher in the ΔgtxA mutant compared to the wild-type infected chickens. In conclusion, GtxA clearly plays an important role in the pathogenesis of G. anatis infections in laying hens. Further investigations into the specific factors regulating the host response is however needed to provide a more complete understanding of the bacteria-host interaction.

中文翻译：

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GtxA 是一种毒力因子，可在蛋鸡感染 Gallibacterium anatis 期间促进 Th2 样反应。

GtxA 是一种白细胞毒性 RTX 毒素，已被认为是 Gallibacterium anatis 的主要毒力因子。为了评估 GtxA 在感染过程中的影响，我们分别用 G. anatis 野生型 (WT) 菌株及其同基因 gtxA 缺失突变体 (ΔgtxA) 对蛋鸡进行了实验性感染，并在 6 天内监测了这些鸡。与接种 WT 菌株的鸟类相比，接种 ΔgtxA 的鸟类具有显着减少的肉眼病变和微观变化。为了进一步评估宿主反应，我们通过 RT-qPCR 量化了促炎细胞因子和凋亡基因的表达。在卵巢组织中，与WT组相比，ΔgtxA组IL-4和TNF-α的表达水平显着降低，而IL-6和IL-10水平在两组中相似。在 ΔgtxA 感染鸡的脾脏组织中，与WT感染的鸡相比，IL-4表达也较低。结果表明，GtxA 在针对 G. anatis 卵巢组织感染的急性细胞因子介导的 Th2 样反应中起关键作用。因此，接种 ΔgtxA 突变体的鸟类卵巢组织中的促炎反应显着低于野生型反应。这至少在一定程度上得到了细胞凋亡基因表达水平的支持，与野生型感染鸡相比，ΔgtxA 突变体的细胞凋亡基因表达水平显着更高。总之，GtxA 显然在蛋鸡 G. anatis 感染的发病机制中起着重要作用。然而，需要进一步研究调节宿主反应的特定因素，以更全面地了解细菌-宿主相互作用。