Atlantic salmon is characterized with high sensitivity to low dissolved oxygen levels. Hypoxia can affect diverse biological processes with consequences that can be manifested immediately or with delay. Effects of hypoxia on the immune system and the resistance to a bacterial pathogen were investigated. Two groups were reared at respectively normal (NO, 100%) and low (LO, 60%) levels of dissolved oxygen over 10 months. Smoltification was initiated by a winter signal for six weeks, followed by constant light for six weeks. Samples were collected at the start and end of light period. Expression of 92 immune and stress genes was analyzed in the gill, head kidney and spleen using a Biomark HD. Most of differentially expressed genes showed higher levels in LO fish compared to NO fish; many immune genes were downregulated during smoltification and these changes were stronger in NO fish. A notable exception were pro-inflammatory genes upregulated in gill of NO fish. Further, salmon was challenged with Moritella viscosa, the causative agent of winter ulcer. Mortality was registered from five days post infection (dpi) to the end of trial at 36 dpi. Survival was consistently higher in NO than LO fish, reaching a maximum difference of 18% at 21-23 dpi that reduced to 10% at the end. Analyses with a genome-wide microarray at 36 dpi showed strong responses to the pathogen in gill and spleen. Notable features were the stimulation of eicosanoid metabolism, suggesting an important role of lipid mediators of inflammation, and the down-regulation of chemokines. Many immune effectors were activated, including multiple lectins and acute phase proteins, enzymes producing free radicals and matrix metalloproteinases. The transcriptomic changes induced with a bacterial challenge were similar in NO and LO. After the challenge, interferons a and g and panel of genes of innate antiviral immunity showed higher expression in LO, especially in the gill. The results from the present study suggest that chronic hypoxia in early life stimulated immune genes and attenuated their down-regulation associated with smoltification. However, these changes did not improve protection against a bacterial pathogen of major concern in salmon aquaculture.

中文翻译：

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大西洋鲑鱼 (Salmo salar L.) 在缺氧条件下的发育诱导免疫基因表达的持续变化并降低对粘氏杆菌的抵抗力

大西洋鲑鱼的特点是对低溶解氧水平高度敏感。缺氧会影响不同的生物过程，其后果可以立即或延迟表现出来。研究了缺氧对免疫系统的影响和对细菌病原体的抵抗力。两组分别在正常 (NO, 100%) 和低 (LO, 60%) 溶解氧水平下饲养 10 个月。六周的冬季信号引发了烟化，然后是六周的持续光照。在光照期开始和结束时收集样品。使用 Biomark HD 分析了 92 种免疫和应激基因在鳃、头肾和脾脏中的表达。与 NO 鱼相比，LO 鱼中的大多数差异表达基因显示出更高的水平；许多免疫基因在幼鱼化过程中被下调，这些变化在 NO 鱼中更强。一个显着的例外是 NO 鱼鳃中促炎基因上调。此外，鲑鱼还受到了冬季溃疡病原菌粘孢子菌的攻击。从感染后五天 (dpi) 到试验结束 36 dpi 记录死亡率。NO 的存活率始终高于 LO 鱼，在 21-23 dpi 时达到 18% 的最大差异，最后减少到 10%。用 36 dpi 的全基因组微阵列分析显示对鳃和脾中的病原体有强烈反应。值得注意的特征是类花生酸代谢的刺激，表明炎症的脂质介质的重要作用和趋化因子的下调。许多免疫效应器被激活，包括多种凝集素和急性期蛋白、产生自由基的酶和基质金属蛋白酶。细菌攻击诱导的转录组变化在 NO 和 LO 中相似。攻击后，干扰素 a 和 g 以及先天抗病毒免疫基因组在 LO 中表现出更高的表达，尤其是在鳃中。本研究的结果表明，生命早期的慢性缺氧会刺激免疫基因并减弱其与幼化相关的下调。然而，这些变化并没有提高对鲑鱼养殖中主要关注的细菌病原体的保护。干扰素 a 和 g 以及先天抗病毒免疫基因组在 LO 中表现出较高的表达，尤其是在鳃中。本研究的结果表明，生命早期的慢性缺氧会刺激免疫基因并减弱其与幼化相关的下调。然而，这些变化并没有提高对鲑鱼养殖中主要关注的细菌病原体的保护。干扰素 a 和 g 以及先天抗病毒免疫基因组在 LO 中表现出较高的表达，尤其是在鳃中。本研究的结果表明，生命早期的慢性缺氧会刺激免疫基因并减弱其与幼化相关的下调。然而，这些变化并没有提高对鲑鱼养殖中主要关注的细菌病原体的保护。