Inflammatory challenge increases measures of oxidative stress in a free-ranging, long-lived mammal

Summary Oxidative stress - the imbalance between reactive oxygen species (ROS) and neutralising antioxidants - has been under debate as the main cause of ageing in aerobial organisms. The level of ROS should increase during infections as part of the activation of an immune response, leading to oxidative damage on proteins, lipids and DNA. Yet, it is unknown how long-lived organisms, especially mammals, cope with oxidative stress. Bats are known to carry a variety of zoonotic pathogens and at the same time are despite their high mass-specific basal metabolic rate unusually long-lived, which may be partly caused by low oxidative damage of organs. Here, we ask if an immune challenge causes oxidative stress in free-ranging bats, measuring two oxidative stress markers. We injected 20 short-tailed fruit bats (Carollia perspicillata) with bacterial derived lipopolysaccharides (LPS) and 20 individuals with phosphate-buffered saline solution (PBS) as a control. Individuals injected with LPS showed an immune reaction by increased white blood cell count after 24h, whereas there was no significant change in leukocyte counts in control animals. The biological antioxidant potential (BAP) remained the same in both groups, but reactive oxygen metabolites (ROM) increased after treatment with LPS, indicating a significant increase in oxidative stress in animals when mounting an immune reaction toward the inflammatory challenge. Control individuals did not show a change in oxidative stress markers. We conclude that in a long-lived mammal, even high concentrations of antioxidants do not immediately neutralise free radicals produced during a cellular immune response. Thus, fighting an infection may lead to oxidative stress in bats.