title: Protection of Insects against Viral Infection by Apoptosis-Dependent Phagocytosis.
abstract: We investigated whether phagocytosis participates in the protection of insects from viral infection using the natural host-virus interaction between Drosophila melanogaster and Drosophila C virus (DCV). Drosophila S2 cells were induced to undergo apoptotic cell death upon DCV infection. However, UV-inactivated virus was unable to cause apoptosis, indicating the need for productive infection for apoptosis induction. S2 cells became susceptible to phagocytosis by hemocyte-derived l(2)mbn cells after viral infection, and the presence of phagocytes in S2 cell cultures reduced viral proliferation. Phagocytosis depended, in part, on caspase activity in S2 cells, as well as the engulfment receptors Draper and integrin βν in phagocytes. To validate the in vivo situation, adult flies were abdominally infected with DCV, followed by the analysis of fly death and viral growth. DCV infection killed flies in a dose-responding manner, and the activation of effector caspases was evident, as revealed by the cleavage of a target protein ectopically expressed in flies. Furthermore, hemocytes isolated from infected flies contained DCV-infected cells, and preinjection of latex beads to inhibit the phagocytic activity of hemocytes accelerated fly death after viral infection. Likewise, viral virulence was exaggerated in flies lacking the engulfment receptors, and was accompanied by the augmented proliferation of virus. Finally, phagocytosis of DCV-infected cells in vitro was inhibited by phosphatidylserine-containing liposome, and virus-infected flies died early when a phosphatidylserine-binding protein was ectopically expressed. Collectively, our study demonstrates that the apoptosis-dependent, phosphatidylserine-mediated phagocytosis of virus-infected cells plays an important role in innate immune responses against viral infection in Drosophila.
authors.affiliation: Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan; Faculty of Pharmacy, Hasanuddin University, Makassar, South Sulawesi 90245, Indonesia; and.
authors.forename: Firzan
authors.identifier: http://orcid.org/0000-0003-0989-4023
authors.initials: F
authors.lastname: Nainu
authors.affiliation: School of Pharmacy, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Tanaka
authors.affiliation: Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan; School of Pharmacy, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Akiko
authors.identifier: http://orcid.org/0000-0002-7811-4409
authors.initials: A
authors.lastname: Shiratsuchi
authors.affiliation: Graduate School of Medical Sciences, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan; School of Pharmacy, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan nakanaka@p.kanazawa-u.ac.jp.
authors.forename: Yoshinobu
authors.identifier: http://orcid.org/0000-0002-8767-3587
authors.initials: Y
authors.lastname: Nakanishi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D053470:Caspases, Effector / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000276:immunology* / Q000821:virology; D006434:Hemocytes / Q000502:physiology* / Q000821:virology; D007113:Immunity, Innate; D007304:Insect Viruses / Q000472:pathogenicity / Q000502:physiology* / Q000528:radiation effects; D039641:Integrin beta Chains / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010586:Phagocytes / Q000502:physiology* / Q000821:virology; D010587:Phagocytosis / Q000235:genetics; D010718:Phosphatidylserines / Q000378:metabolism; D014466:Ultraviolet Rays; D014774:Virulence; D014777:Virus Diseases / Q000276:immunology*
chemical_list: D029721:Drosophila Proteins; D039641:Integrin beta Chains; D008565:Membrane Proteins; D010718:Phosphatidylserines; C495322:drpr protein, Drosophila; C084344:integrin beta5; D053470:Caspases, Effector