Screening the fruitfly immune system

Conventional and non-conventional Drosophila Toll signaling

The discovery of Toll in Drosophila and of the remarkable conservation in pathway composition and organization catalyzed a transformation in our understanding of innate immune recognition and response. At the center of that picture is a cascade of interactions in which specific microbial cues activate Toll receptors, which then transmit signals driving transcription factor nuclear localization and activity. Experiments gave substance to the vision of pattern recognition receptors, linked phenomena in development, gene regulation, and immunity into a coherent whole, and revealed a rich set of variations for identifying non-self and responding effectively. More recently, research in Drosophila has illuminated the positive and negative regulation of Toll activation, the organization of signaling events at and beneath membranes, the sorting of information flow, and the existence of non-conventional signaling via Toll-related receptors. Here, we provide an overview of the Toll pathway of flies and highlight these ongoing realms of research.

Drosophila melanogaster S2 cells: a model system to study Chlamydia interaction with host cells

Chlamydia spp. are major causes of important human diseases, but dissecting the host-pathogen interactions has been hampered by the lack of bacterial genetics and the difficulty in carrying out forward genetic screens in mammalian hosts. RNA interference (RNAi)-based methodologies for gene inactivation can now be easily carried out in genetically tractable model hosts, such as Drosophila melanogaster, and offer a new approach to identifying host genes required for pathogenesis. We tested whether Chlamydia trachomatis infection of D. melanogaster S2 cells recapitulated critical aspects of mammalian cell infections. As in mammalian cells, C. trachomatis entry was greatly reduced by heparin and cytochalasin D. Inclusions were formed in S2 cells, acquired Golgi-derived sphingolipids, and avoided phagolysosomal fusion. Elementary body (EB) to reticulate body (RB) differentiation was observed, however, no RB to EB development or host cell killing was observed. RNAi-mediated inactivation of Rac, a Rho GTPase recently shown to be required for C. trachomatis entry in mammalian cells, inhibits C. trachomatis infection in S2 cells. We conclude that Drosophila S2 cells faithfully mimic early events in Chlamydia host cell interactions and provides a bona fide system to systematically dissect host functions important in the pathogenesis of obligate intracellular pathogens.