Eater, a Transmembrane Protein Mediating Phagocytosis of Bacterial Pathogens in Drosophila

Abstract

Phagocytosis is a complex, evolutionarily conserved process that plays a central role in host defense against infection. We have identified a predicted transmembrane protein, Eater, which is involved in phagocytosis in Drosophila. Transcriptional silencing of the eater gene in a macrophage cell line led to a significant reduction in the binding and internalization of bacteria. Moreover, the N terminus of the Eater protein mediated direct microbial binding which could be inhibited with scavenger receptor ligands, acetylated, and oxidized low-density lipoprotein. In vivo, eater expression was restricted to blood cells. Flies lacking the eater gene displayed normal responses in NF-kappaB-like Toll and IMD signaling pathways but showed impaired phagocytosis and decreased survival after bacterial infection. Our results suggest that Eater is a major phagocytic receptor for a broad range of bacterial pathogens in Drosophila and provide a powerful model to address the role of phagocytosis in vivo.

Methods to study Drosophila immunity

“…Enterococcus faecalis and Staphylococcus aureus have been used to probe the Toll pathway in survival experiments, and occasionally Aerococcus viridans has been used to stimulate a Toll-dependent immune response. S. aureus is especially interesting to probe the role of phagocytosis and melanization [22,23,131]. Among DAP-type Gram-positive bacteria, Listeria monocytogenes, Listeria innocua, Bacillus megaterium and Bacillus subtilis are currently being used (for example [24]).…”

“…The phagocytosis assay described below has been optimised in our lab from a combination of similar methods [23,103,104]. In this protocol, larval hemocytes are collected and mixed with fluorescent heat-killed bacteria, incubated and then run on a flow cytometer to measure the fraction of cells phagocytosing and the intensity of phagocytic uptake.…”

Bacterial strategies to overcome insect defences

“…Different types of free and sessile blood cells, named haemocytes, are activated in response to infection, but our understanding of the mechanisms and consequences of this activation is still fragmentary. Mobile plasmatocytes in the haemocoel are responsible for phagocytosis, which is important to fight bacterial invasion 97 .…”

Senescence of the cellular immune response in Drosophila melanogaster

“…Drosophila haemocytes either circulate freely throughout the haemolymph or are sessile [11]. Phagocytosis is initiated by binding of pathogen recognition receptors such as Eater [14] and PGRP-LC [15], and may be mediated by opsonin molecules that target microbes for engulfment [10]. Once haemocytes encounter a microbe the cytoskeleton is remodelled to enable endocytosis, before it is destroyed by lysosomal enzymes and reactive oxygen species [12].…”