Data from: Oxidant trade-offs in immunity: an experimental test in a lizard

Immune system functioning and maintenance entails costs which may limit investment into other processes such as reproduction. Yet, the proximate mechanisms and ‘currencies’ mediating the costs of immune responses remain elusive. In vertebrates, up-regulation of the innate immune system is associated with rapid phagocytic production of pro-oxidant molecules (so-called ‘oxidative burst’ responses). Oxidative burst responses are intended to eliminate pathogens but may also constitute an immunopathological risk as they may induce oxidative damage to self cells. To minimize the risk of infection and, at the same time, damage to self, oxidative burst activity must be carefully balanced. The current levels of pro- and antioxidants (i.e. the individual oxidative state) is likely to be a critical factor affecting this balance, but this has not yet been evaluated. Here, we perform an experiment on wild-caught painted dragon lizards (Ctenophorus pictus) to examine how the strength of immune-stimulated oxidative burst responses of phagocytes in whole blood relates to individual oxidative status under control conditions and during an in vivo immune challenge with Escherichia coli lipopolysaccharide (LPS). Under control conditions, oxidative burst responses were not predicted by the oxidative status of the lizards. LPS-injected individuals showed a strong increase in pro-oxidant levels and a strong decrease in antioxidant levels compared to control individuals demonstrating a shift in the pro-/antioxidant balance. Oxidative burst responses in LPS-injected lizards were positively related to post-challenge extracellular pro-oxidants (reflecting the level of cell activation) and negatively related to pre-challenge levels of mitochondrial superoxide (suggesting an immunoregulatory effect of this pro-oxidant). LPS-challenged males had higher oxidative burst responses than females, and in females oxidative burst responses seemed to depend more strongly on antioxidant status than in males. Our results confirm the idea that oxidative state may constrain the activity of the innate immune system. These constraints may have important consequences for the way selection acts on pro-oxidant generating processes.

免疫系统的运作与维持需要消耗资源，这可能会限制生物对繁殖等其他生命过程的资源投入。然而，介导免疫反应成本的近因机制与"成本通货"（currencies）仍不甚明晰。在脊椎动物中，先天免疫系统的上调会伴随吞噬细胞快速产生促氧化分子，即所谓的"呼吸爆发（oxidative burst）"反应。呼吸爆发反应本用于清除病原体，但同时也可能引发免疫病理风险——因为它们可能会对自身细胞造成氧化损伤。为了在最小化感染风险的同时避免自身受损，呼吸爆发的活性必须受到严格调控。当前促氧化剂与抗氧化剂的水平（即个体的氧化状态）可能是影响这一调控平衡的关键因素，但这一点尚未得到实证验证。

本研究针对野外捕获的彩龙蜥蜴（Ctenophorus pictus）开展实验，旨在探究在对照条件与体内注射大肠杆菌脂多糖（LPS）的免疫激发状态下，全血中吞噬细胞经免疫刺激后产生的呼吸爆发反应强度与个体氧化状态的关联。

实验结果显示：在对照条件下，蜥蜴的氧化状态无法预测其呼吸爆发反应强度。与对照组个体相比，注射LPS的个体其促氧化剂水平显著升高，抗氧化剂水平显著下降，表明促/抗氧化平衡发生了明显偏移。注射LPS的蜥蜴的呼吸爆发反应与激发后胞外促氧化剂水平呈正相关（反映细胞激活程度），而与激发前线粒体超氧化物水平呈负相关（提示该促氧化剂具有免疫调节作用）。经LPS激发的雄性个体的呼吸爆发反应强度高于雌性个体，且雌性的呼吸爆发反应相较于雄性，更依赖于抗氧化状态。

本研究结果证实了"氧化状态可能制约先天免疫系统活性"这一假说。这种制约作用可能会对自然选择作用于促氧化生成过程的方式产生重要影响。