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...