Dietary impacts on immune competence

Hydrusko, Andrew
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University of Delaware
Diet has a significant impact on the functioning of the immune system, but there is a lack of understanding specifically on how it affects the differing humoral and cellular components of the innate and acquired immune system. We used House Sparrows (Passer domesticus) as a model to look at the impact of dietary composition on these components. Thirty six wild birds of both sexes were collected and maintained on either a high or optimal fat diets. We tested two hypotheses for the impact of diet on gender, one proposing that immunocompetence is energy limited and one proposing that immunocompetence is nutrient limited. To assess the components of the immune system we used several different assays. Bacterial killing assays were used to gauge the humoral constituent of innate immunity while the hemolysishemagglutination (HH) assay was used to measure humoral innate immunity. Acquired immunity was tested with sheep red blood cell (SRBC) assays. Phytohemagglutination Assays (PHA) were used to gauge overall immune response. Diet affected PHA response differently in the two sexes with males responding more to calories and females to nutrients. Bacterial killing ability was not affected by diet but was tied to bird gender, with females exhibiting greater bactericidal ability than males. Females also exhibited stronger primary immune responses than males in the SRBC assays, with correlated secondary and primary immune responses. There was no interaction between any of the immune tests. This reinforces the resilience of the house sparrow to changing dietary conditions while calling attention to a definite separation of the components of the immune system. Further work involving greater dietary challenges will be needed to understand the impacts on these individual systems.