Previous Exposure to an RNA Virus Does Not Protect against Subsequent Infection in Drosophila melanogaster

BACKGROUND Immune priming has been shown to occur in a wide array of invertebrate taxa, with individuals exposed to a pathogen showing increased protection upon subsequent exposure. However, the mechanisms underlying immune priming are poorly understood. The antiviral RNAi response in Drosophila melanogaster is an ideal candidate for providing a specific and acquired response to subsequent infection. We exposed D. melanogaster to two challenges of a virus known to produce an antiviral RNAi response, to examine whether any protective effects of prior exposure on survival were observed. RESULTS In this experiment we found no evidence that prior exposure to Drosophila C Virus (DCV) protects flies from a subsequent lethal challenge, with almost identical levels of mortality in flies previously exposed to DCV or a control. CONCLUSIONS Our results confirm the finding that 'acquired' immune responses are not ubiquitous across all invertebrate-pathogen interactions. We discuss why we may have observed no effect in this study, with focus on the mechanistic basis of the RNAi pathway.