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.
Subject(s)
Drosophila Proteins/physiology , Drosophila/microbiology , Genes, Insect , Insect Proteins/physiology , Membrane Proteins/physiology , Phagocytosis , Receptors, Cell Surface/physiology , Amino Acid Motifs , Amino Acid Sequence , Animals , Bacterial Infections/prevention & control , Drosophila/cytology , Drosophila/embryology , Drosophila/genetics , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Embryo, Nonmammalian , Escherichia coli/pathogenicity , Flow Cytometry , Frameshift Mutation , Histidine/chemistry , In Situ Hybridization , Insect Proteins/chemistry , Insect Proteins/genetics , Insect Proteins/metabolism , Macrophages/metabolism , Membrane Proteins/chemistry , Membrane Proteins/genetics , Membrane Proteins/metabolism , Molecular Sequence Data , Open Reading Frames , RNA Interference , RNA, Messenger/metabolism , Receptors, Cell Surface/genetics , Receptors, Cell Surface/metabolism , Sequence Homology, Amino Acid , Serratia marcescens/pathogenicityABSTRACT
Phagocytosis is a complex and apparently evolutionarily conserved process that plays a central role in the immune response to infection. By ultrastructural and functional criteria, Drosophila hemocyte (macrophage) phagocytosis resembles mammalian phagocytosis. Using a non-saturated forward genetic screen for larval hemocyte phagocytosis mutants, D-SCAR and profilin were identified as important regulators of phagocytosis in Drosophila. In both hemocytes ex vivo and the macrophage-like S2 cell line, lack of D-SCAR significantly decreased phagocytosis of Escherichia coli and Staphylococcus aureus. In contrast, profilin mutant hemocytes exhibited increased phagocytic activity. Analysis of double mutants suggests that D-SCAR and profilin interact during phagocytosis. Finally, RNA interference studies in S2 cells indicated that the D-SCAR homolog D-WASp also participates in phagocytosis. This study demonstrates that Drosophila provides a viable model system in which to dissect the complex interactions that regulate phagocytosis.
