Immune activation increases susceptibility to oxidative tissue damage in Zebra Finches

1. The innate immune response involves the production of highly reactive molecules (reactive oxygen and nitrogen species, ROS and RNS). These toxic compounds can effectively destroy invading pathogens but can also, non-specifically, target host cells. Tissue damage caused by ROS and RNS can be substantial if the inflammatory response is overactive, potentially inducing a so-called immunopathology. 2. In this study, we induced an inflammatory response in Zebra Finches by the way of a LPS injection (lipopolysaccharide of the cell wall of Escherichia coli), using as a control a group of birds injected with saline (phosphate-buffered saline). Body mass was measured both before and 24 h after the procedure. We also took a blood sample 24 h after injection, to measure the resistance of red blood cells to a standardized free radical attack. The experiment was repeated twice with different individuals to ascertain the repeatability of the results. 3. We found that birds injected with LPS lost significantly more body mass during the 24 It that followed, compared with control individuals. Similarly, LPS individuals were more susceptible to oxidative tissue damage, as their red blood cells had a weaker resistance to a free-radical attack than the red blood cells of control birds. 4. This result shows that the inflammatory response with the associated production of cytotoxic compounds can produce side-effects that may potentially result in increased damage to host tissues, therefore representing an immunopathology cost.