The double-edged sword of immune defence and damage control: do food availability and immune challenge alter the balance?

1.Animal immune systems must adaptively balance aggressive immune resistance (ability to destroy pathogens) with infection tolerance (ability to withstand the negative effects of infection; e.g., immunopathology or damage due to pathogen metabolism). 2.Insects offer unique insight into this balancing act because phenoloxidase (PO)-mediated melanisation is a key feature of immune resistance, but PO activation obligates the production of non-specific reactive species that can cause self-damage. The antioxidant glutathione (GSH) can provide protection against such reactive molecules, but high levels of GSH can impair melanisation. In support of the hypothesis that GSH can protect insects (e.g., crickets) from self-damage during an immune response, we found that bacterially infected crickets showed a significant positive relationship between GSH haemolymph concentration and fecundity after controlling for bacterial growth rate. That is, GSH may be a mechanism of infection tolerance because...1. 动物免疫系统必须在攻击性免疫抗性（即清除病原体的能力）与感染耐受（即抵御感染带来的负面影响的能力，例如免疫病理损伤或病原体代谢引发的损伤）之间进行适应性平衡。 2. 昆虫为研究这一平衡机制提供了独特视角：酚氧化酶（phenoloxidase, PO）介导的黑化反应是免疫抗性的核心特征，但PO的激活会促使机体产生可引发自身损伤的非特异性活性物质。抗氧化剂谷胱甘肽（glutathione, GSH）可对这类活性物质起到防护作用，但过高浓度的GSH会抑制黑化反应。为验证GSH可在免疫应答过程中保护昆虫（如蟋蟀）免受自身损伤这一假说，我们开展了相关实验：在控制细菌生长速率的前提下，感染细菌的蟋蟀其血淋巴中GSH浓度与繁殖力之间呈现显著正相关关系。换言之，GSH或可作为感染耐受的一种调控机制，原因在于……