Functional dissection of an innate immune response by a genome-wide RNAi screen

PLoS Biol. 2004 Aug;2(8):E203. doi: 10.1371/journal.pbio.0020203. Epub 2004 Jun 22.


The innate immune system is ancient and highly conserved. It is the first line of defense and the only recognizable immune system in the vast majority of metazoans. Signaling events that convert pathogen detection into a defense response are central to innate immunity. Drosophila has emerged as an invaluable model organism for studying this regulation. Activation of the NF-kappaB family member Relish by the caspase-8 homolog Dredd is a central, but still poorly understood, signaling module in the response to gram-negative bacteria. To identify the genes contributing to this regulation, we produced double-stranded RNAs corresponding to the conserved genes in the Drosophila genome and used this resource in genome-wide RNA interference screens. We identified numerous inhibitors and activators of immune reporters in a cell culture model. Epistatic interactions and phenotypes defined a hierarchy of gene action and demonstrated that the conserved gene sickie is required for activation of Relish. We also showed that a second gene, defense repressor 1, encodes a product with characteristics of an inhibitor of apoptosis protein that inhibits the Dredd caspase to maintain quiescence of the signaling pathway. Molecular analysis revealed that Defense repressor 1 is upregulated by Dredd in a feedback loop. We propose that interruption of this feedback loop contributes to signal transduction.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Blotting, Western
  • Caspase 8
  • Caspases / metabolism
  • Cell Line
  • Drosophila
  • Drosophila Proteins / metabolism
  • Epistasis, Genetic
  • Gene Expression Regulation
  • Gene Library
  • Genes, Reporter
  • Genome*
  • Image Processing, Computer-Assisted
  • Immunity, Innate
  • Insect Proteins / metabolism
  • Microscopy, Fluorescence
  • Models, Biological
  • Models, Genetic
  • Molecular Sequence Data
  • NF-kappa B / metabolism
  • Phenotype
  • RNA Interference*
  • RNA, Double-Stranded / metabolism
  • Sequence Homology, Amino Acid
  • Signal Transduction
  • Transcription Factors / metabolism
  • Up-Regulation
  • beta-Galactosidase / metabolism


  • Drosophila Proteins
  • Insect Proteins
  • NF-kappa B
  • RNA, Double-Stranded
  • Rel protein, Drosophila
  • Transcription Factors
  • beta-Galactosidase
  • Caspase 8
  • Caspases
  • dredd protein, Drosophila