Abstract
Immune responses in insects are differentially triggered depending on the infection route used by the pathogen. In most studies involving Drosophila melanogaster and viruses, infection is done by injection, while oral infection, which is probably the most common route of viral entry in nature, remains unexplored. Here, we orally infected adults and larvae from wild-type and RNA interference (RNAi) mutant flies with different RNA viruses. We found that, in contrast with what is observed following virus injection, oral infections initiated at larval or adult stages are cleared in adult flies. Virus elimination occurred despite a larger infectious dose than for injected flies and evidence of viral replication. RNAi mutant flies suffered greater mortality relative to wild-type flies following oral infection, but they also eliminated the virus, implying that RNAi is not essential for viral clearance and that other immune mechanisms act during oral infections. We further showed that information of infection by RNA viruses acquired orally leaves a trace under a DNA form, which confers protection against future reinfection by the same virus. Together, this work presents evidence of clearance and immune priming for RNA viruses in insects and challenges the current view of antiviral immunity in insects.
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Data availability
The data that support the findings of this study are available from the corresponding author upon request. In-house codes are also available at any time upon request to the authors. Small RNA libraries are publicly available in the Sequence Read Archive with accession codes PRJNA396531 and PRJNA473322.
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Acknowledgements
We thank members of the Saleh Lab, especially V. Mongelli, and the Mefistófeles Lab for fruitful discussions, and A. Buck, M.-A. Felix and L. Frezal for help with 5′-tripRNA detection. This work was supported by the European Research Council (FP7/2013–2019 ERC CoG 615220) to M.-C.S. and the French Government’s Investissement d’Avenir program, Laboratoire d’Excellence Integrative Biology of Emerging Infectious Diseases (grant ANR-10-LABX-62-IBEID) to M.-C.S. and L.L. J.A.M. was supported by an AXA Research fund. L.L. received support from the City of Paris Emergence(s) program in Biomedical Research, the European Union’s Horizon 2020 research and innovation programme under ZikaPLAN grant agreement No. 734584, and the Agence Nationale de la Recherche (grants ANR-16-CE35-0004 and ANR-17-ERC2-0016-01).
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J.A.M. and M.-C.S. conceived the study, and J.A.M., V.G., L.F. and H.B. performed the investigations. L.F. contributed software, and J.A.M., L.F. and L.L. performed the formal analyses. J.A.M., L.L. and M.-C.S. wrote the paper and acquired funding.
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Mondotte, J.A., Gausson, V., Frangeul, L. et al. Immune priming and clearance of orally acquired RNA viruses in Drosophila. Nat Microbiol 3, 1394–1403 (2018). https://doi.org/10.1038/s41564-018-0265-9
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DOI: https://doi.org/10.1038/s41564-018-0265-9
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