Effects of Endotoxin and Psychological Stress on Redox Physiology, Immunity and Feather Corticosterone in Greenfinches

Assessment of costs accompanying activation of immune system and related neuroendocrine pathways is essential for understanding the selective forces operating on these systems. Here we attempted to detect such costs in terms of disruption to redox balance and interference between different immune system components in captive wild-caught greenfinches (Carduelis chloris). Study birds were subjected to an endotoxin-induced inflammatory challenge and temporary exposure to a psychological stressor (an image of a predator) in a 2*2 factorial experiment. Injection of bacterial endotoxin resulted in up-regulation of two markers of antioxidant protection – erythrocyte glutathione, and plasma oxygen radical absorbance (OXY). These findings suggest that inflammatory responses alter redox homeostasis. However, no effect on markers of oxidative damage to proteins or DNA in erythrocytes could be detected. We found no evidence that the endotoxin injection interfered with antibody production against Brucella abortus antigen or the intensity of chronic coccidiosis. The hypothesis of within-immune system trade-offs as a cost of immunity was thus not supported in our model system. We showed for the first time that administration of endotoxin can reduce the level of corticosterone deposited into feathers. This finding suggests a down-regulation of the corticosterone secretion cascade due to an endotoxin-induced immune response, a phenomenon that has not been reported previously. Exposure to the predator image did not affect any of the measured physiological parameters.

评估免疫系统（immune system）激活及其相关神经内分泌通路（neuroendocrine pathways）所伴随的成本，是阐明作用于这些系统的选择压力的关键前提。本研究以人工饲养的野生捕获红额金翅雀（Carduelis chloris）为研究对象，尝试通过氧化还原平衡紊乱及免疫系统不同组分间的相互干扰这两个指标，检测此类免疫成本。研究采用2×2析因实验设计，受试鸟类分别接受内毒素（endotoxin）诱导的炎症刺激与临时暴露于天敌图像这一心理应激源（psychological stressor）。细菌内毒素注射可上调两种抗氧化保护标志物——红细胞谷胱甘肽（erythrocyte glutathione）与血浆氧自由基吸收能力（OXY）。上述结果提示，炎症反应会改变机体的氧化还原稳态（redox homeostasis）。但本研究未检测到内毒素刺激对红细胞内蛋白质与DNA的氧化损伤标志物存在显著影响。此外，我们未发现内毒素注射会干扰抗布鲁氏菌（Brucella abortus）抗原的抗体生成，亦未对慢性球虫病（chronic coccidiosis）的感染强度产生作用。因此，“免疫系统内部资源权衡作为免疫成本”这一假说，在本研究的模型系统中未得到支持。本研究首次证实，内毒素给药可降低羽毛中沉积的皮质酮（corticosterone）水平。该结果提示，内毒素诱导的免疫反应会下调皮质酮分泌级联反应（corticosterone secretion cascade），这一现象此前未见文献报道。暴露于天敌图像未对所有检测的生理参数产生显著影响。