Establishing a foundation for investigating the role of nutrition on immunity in wildlife

This review examines existing research on relationships between two established disciplines, nutrition and immunology, with a specific focus on the complement system in vertebrate organisms and how its functioning is affected by nutritional status. The available studies assessed the effects of certain vitamins, lipids, carbohydrates, proteins, and overall body condition, measured as body mass index (BMI), on the three complement activation pathways (classical, lectin, and alternative) and their components (C1q, C1s, C3, C4, C5, C6, C8, C9, and C3 proactivator) in blood plasma. Across studies, an increased abundance and/or activity of complement components in plasma was observed in rodents and humans after intake of vitamin A, vitamin C, lipids, and proteins. Higher relative activity was also observed in bats with high body mass index (BMI), a measure of general body condition. Overall, results indicate that nutritional status has a pronounced effect on the complement system in species studied. However, only few studies have investigated effects of nutrition on complement in non-model organisms, such as wildlife, indicating major gaps in knowledge related to taxa that more likely experience nutrient limitations, e.g. through seasonal variation in resources, droughts, etc. as compared with model organisms used under laboratory settings. Understanding potential relationships between nutrition and immunity in a broader suite of species is crucial, nonetheless, due to the number of emerging wildlife diseases that are spreading at an alarming rate. Therefore, I critiqued the available evidence to help predict how wildlife hosts will resist or tolerate diseases, such as white-nose syndrome, sylvatic plague, and avian influenza, based on the nutritional status of an individual host. I also considered methodological approaches and assessed their potential for use in wildlife. The studies in this review used different methods to measure complement protein activity, such as hemolytic and functional assays. Future studies can also take advantage of newer high-throughput methods, such as proteomics combined with functional assays. This can lead to a more comprehensive understanding of the efficacy of complement proteins to neutralize invading pathogens under different host nutritional states. My investigation into relationships between nutrition and complement will also inform similar investigations to uncover effects of nutrition on other aspects of immunity, such as antimicrobial peptides. Overall, my assessment concludes that complement is a good candidate for investigating the role of nutrition on immunity in wildlife because it is sensitive to changes in some nutritional components, particularly vitamins, lipids, and proteins.