l-Arginine enhances immunity to parasitoids in Drosophila melanogaster and increases NO production in lamellocytes

Drosophila melanogaster was used as a model system to explore the link between nutrition and immunity, and to investigate the role of nitric oxide (NO) in enhancing immunity following dietary enhancement with l-arginine. First, we show that adding l-arginine to the food medium increases the ability of D. melanogaster larvae to encapsulate the eggs of the parasitoid Asobara tabida. Secondly, we show that the increase in immunity is specific to l-arginine, and not to an enhanced calorific content, and that immunity decreases when larvae are fed food with added l-NAME, an inhibitor of nitric oxide synthase. Finally, we show that parasitised larvae fed l-arginine have increased haemocyte numbers, and that the lamellocytes (haemocytes which play a key role in encapsulation) show evidence of an increased production of NO. These results suggest that NO plays a key role in immunity and that the effect of NO is mostly targeted via the lamellocytes.