The effect of maternal immunization on female oxidative status, yolk antioxidants and offspring survival in a songbird

A meta-analysis of impacts of immune response and infection on oxidative status in vertebrates

Inferring from patterns observed in biomedical research, ecoimmunological theory predicts that oxidative stress is a ubiquitous physiological cost that contributes to generating variation in immune function between individuals or species. This prediction is, however, often challenged by empirical studies testing the relationship between immune response or infection and oxidative status markers. This points out the importance of combining ecological immunology and oxidative stress ecology to further our understanding of the proximate causes and fitness consequences of individual variation in health, and adaptability to natural and anthropogenic environmental changes. I reviewed evidence and performed phylogenetic meta-analyses of changes in oxidative status markers owing to either injection of an antigen or infection in captive and free-living vertebrates (141 studies, 1262 effect sizes, 97 species). The dataset was dominated by studies on fish, birds and mammals, which provided 95.8% of effect sizes. Both antigen injection and parasite exposure were associated with changes of oxidative status. There were significant effects of taxonomic class and experimental environment (captivity vs. wild). In contrast with my predictions, age category (young vs. adult), study design (correlational vs. experimental) and proxies of pace of life (clutch size, litter size, and body mass; for birds and mammals only) were negligible in this dataset. Several methodological aspects (type of immunostimulant, laboratory assay, tissue analysed) showed significant effects on both strength and direction of effect. My results suggest that alterations of oxidative status are a widespread consequence of immune function across vertebrates. However, this work also identified heterogeneity in strength and direction of effect sizes, which suggests that immune function does not necessarily result in oxidative stress. Finally, this work identifies methodological caveats that might be relevant for the interpretation and comparability of results and for the application in conservation programs.

Immune challenge-induced oxidative damage may be mitigated by biliverdin

An effective immune response results in the elimination of pathogens, but this immunological benefit may be accompanied by increased levels of oxidative damage. However, organisms have evolved mechanisms to mitigate the extent of such oxidative damage, including the production and mobilization of antioxidants. One potential mechanism of mitigating immune challenge-induced changes in oxidative physiology is increasing biliverdin production. Biliverdin is chemically an antioxidant, but within-tissue correlations between biliverdin concentration and oxidative damage have never been directly examined. To test how biliverdin tissue concentrations are associated with physiological responses to an immune challenge, we exposed northern bobwhite quail (Colinus virginianus) to one of four treatments: injection of a non-pathogenic antigen - either lipopolysaccharide or phytohemagglutinin, control injection of phosphate-buffered saline or a sham procedure with no injection. Twenty-four hours later, we quantified oxidative damage and triglyceride concentration in the plasma, and biliverdin concentration in the plasma, liver and spleen. We found that both types of immune challenge increased oxidative damage relative to both non-injected and vehicle-injected controls, but treatment had no effects on any other metric. However, across all birds, oxidative damage and biliverdin concentration in the plasma were negatively correlated, which is consistent with a localized antioxidant function of biliverdin. Additionally, we uncovered multiple links between biliverdin concentration, change in mass during the immune challenges and triglyceride levels, suggesting that pathways associated with biliverdin production may also be associated with aspects of nutrient mobilization. Future experiments that manipulate biliverdin levels or oxidative damage directly could establish a systemic antioxidant function or elucidate important physiological impacts on body mass maintenance and triglyceride storage, mobilization or transport.