Exploring the mechanism behind Wolbachia-mediated antiviral immunity in Drosophila melanogaster

Abstract

The intracellular bacterium Wolbachia pipientis is widely spread amongst insect populations, like Drosophila. Recently, Wolbachia infection was found to reduce virus-induced mortality and lower the viral load in dually infected Drosophila melanogaster. Unravelling the mechanism behind this Wolbachia-induced survival might further elucidate the high prevalence of Wolbachia amongst insect species; but above all it might give new insights in antiviral immunity of insects that spread vector-borne diseases and it might help to better understand antiviral immunity in general. Even thought Wolbachia infection does not induce a clear phenotype in D. melanogaster, it does result in profound changes in transcription, for example of signaling molecules in the Toll, Imd, and JNK pathways. In addition, heat shock proteins, autophagy, and other processes – possibly induced by secreted Ankyrin-repeat-containing proteins of Wolbachia – might be active during Wolbachia infection. Wolbachia was shown to protect against positive sense (+) single-stranded RNA viruses from different families that replicate in association with cellular membranes. These viruses normally promote antiviral RNA interference, Imd and Jak/STAT signaling, autophagy, phagocytosis, and/or apoptosis in Drosophila. Remarkably, Wolbachia does not protect against infection with a double-stranded DNA virus. Unfortunately, little is known about the reactions induced upon double-stranded DNA-virus infection. All together, Wolbachia might protect Drosophila by priming the antiviral immune response, for example by activating Imd and Toll signaling. Importantly, all examined RNA viruses show overlapping cell tropism with Wolbachia, thus Wolbachia might also directly affect viral replication. For example, Wolbachia could slow down viral replication by competing for cellular nutrients, affect vesicle transport, or secrete proteins detrimental to the viruses. Additional research will unravel the mechanism behind the Wolbachia-induced antiviral immunity in Drosophila and the occurrence of this phenomenon amongst other species.