Toll pathway is important for an antiviral response in Drosophila

• Published in: Proceedings of the National Academy of Sciences - PNAS 2005-05, Vol.102 (20), p.7257-7262
• Main Authors: Zambon, R.A, Nandakumar, M, Vakharia, V.N, Wu, L.P
• Format: Article
• Language: English
• Subjects: Animals; Anoxia; Antimicrobial Cationic Peptides - metabolism; antimicrobial peptides; Antivirals; Biological Sciences; disease resistance; DNA Primers; Drosophila; Drosophila - genetics; Drosophila - immunology; Drosophila - virology; Drosophila melanogaster; Drosophila X virus; Escherichia coli; Genetic screening; Hemocytes; hypoxia; immune response; Immune system; immunity; Immunity, Innate - immunology; In Situ Nick-End Labeling; infection; Infections; Innate immunity; insect diseases; Insect Viruses - immunology; Insect Viruses - physiology; Insects; Membrane Glycoproteins - immunology; Membrane Glycoproteins - metabolism; Models, Biological; Oxygen - immunology; Receptors, Cell Surface - immunology; Receptors, Cell Surface - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Signal transduction; Signal Transduction - immunology; Toll-Like Receptors; Tolls; Viral infections; Virus Replication - immunology; Viruses
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0409181102

The innate immune response of Drosophila melanogaster is governed by a complex set of signaling pathways that trigger antimicrobial peptide (AMP) production, phagocytosis, melanization, and encapsulation. Although immune responses against both bacteria and fungi have been demonstrated in Drosophila, identification of an antiviral response has yet to be found. To investigate what responses Drosophila mounts against a viral infection, we have developed an in vivo Drosophila X virus (DXV)-based screening system that identifies altered sensitivity to viral infection by using DXV's anoxia-induced death pathology. Using this system to screen flies with mutations in genes with known or suggested immune activity, we identified the Toll pathway as a vital part of the Drosophila antiviral response. Inactivation of this pathway instigated a rapid onset of anoxia induced death in infected flies and increases in viral titers compared to those in WT flies. Although constitutive activation of the pathway resulted in similar rapid onset of anoxia sensitivity, it also resulted in decreased viral titer. Additionally, AMP genes were induced in response to viral infection similar to levels observed during Escherichia coli infection. However, enhanced expression of single AMPs did not alter resistance to viral infection or viral titer levels, suggesting that the main antiviral response is cellular rather than humoral. Our results show that the Toll pathway is required for efficient inhibition of DXV replication in Drosophila. Additionally, our results demonstrate the validity of using a genetic approach to identify genes and pathways used in viral innate immune responses in Drosophila.