Impact of dietary protein content on the immune response of Drosophila melanogaster

The most accepted evolutionary explanation for lifespan extension on dietary restriction (DR) is the disposable soma theory, which explains it as increased investment in somatic maintenance when facing nutrient shortage until the resumption of nutrients. However, immunity, a critical somatic trait, shows ambiguous results in response to DR. Addressing this issue, I did a comprehensive analysis of various parameters contributing to the immune response under the influence of a protein-restricted diet in Drosophila melanogaster. I standardized a system of different dietary regimes, which resolves the animals in terms of holistic immune parameters, like survival to the infection and bacterial clearance rate. Surprisingly, I saw no substantial differences in the induction of the most vital immune regulatory genes at the level of the whole animal. I further targeted the two professional immune cells, i.e., fat body and hemocytes, and did a transcriptomic analysis under an immune-induced state in different dietary conditions. Here I detected that in the fat body, the direct immune response is equally induced in all diets while the indirect response was proportional to the protein quantity of the food. While in hemocytes the whole immune response was directly proportional to the amount of protein in the food. Altogether, I provide a possible mechanism for the differences in the immune outcome of animals on reduced dietary protein. I also provide evidence for resource allocation strategies within the immune system, which change with the intensity of the immune stress and dietary stress