Role of Thioester-containing proteins in the immune response of Drosophila against entomopathogenic nematodes and their mutualistic bacteria. Upasana Shokal, Ioannis Eletherianos. Department of Biological Sciences, George Washington University, Washington, DC.

   Drosophila melanogaster is an outstanding model to understand the intricacies of signaling during host-pathogen interactions and innate immune defense mechanisms. The fly employs different immune responses according to the type of pathogen it encounters. While most Drosophila studies have so far concentrated on immune responses to bacteria, fungi and viruses, little is known about how eukaryotic parasites such as insect pathogenic nematodes interact with the fly immune system. Recent studies on the entomopathogenic nematode Heterorhabditis bacteriophora and its mutualistic bacteria Photorhabdus luminescens have started to investigate the fly response to nematodes carrying the bacteria (axenic worms), nematode lacking the bacteria (symbiotic worms) and the bacteria alone. The advantage of using this model is that the immune response of the fly can be studied against each partner of the mutualistic interaction that allows comparative studies between antibacterial and anti-nematode defenses. Thioester-containing proteins (TEPs) are conserved throughout the animal kingdom. In mammals they are involved in complement system activation or exhibit a protease inhibitor activity whereas in insects they act as opsonins, binding to parasites and promoting their phagocytosis or encapsulation. Recent studies in Drosophila have shown that TEPs are not involved in the immune defense against certain bacterial and fungal pathogens. Here we present data on the potential role of TEPs in the immune response of Drosophila against infection by Heterorhabditis nematodes and their Photorhabdus bacteria (separately or together). Such studies will provide additional information on the functional significance of Drosophila immune factors in anti-nematode reactions, which is of potential importance in both medicine and agriculture.