The fruit fly Drosophila relies on innate immune mechanisms to defend against diverse pathogens,including bacteria,fungi,and viruses.Among these innate immune mechanisms,the RNAi pathway is a major antiviral defense in Drosophila and other insects,while the Toll pathway is the major immune response against Gram-positive (Gram+) bacteria,fungi and certain RNA viruses.Interestingly,although mammalian Toll-like receptors (TLRs) have been extensively studied for the mechanisms of their antiviral functions,the mechanism by which viral infection is able to induce the Drosophila Toll immune pathway still remains elusive.In antiviral RNAi,Drosophila Dicer-2 is an essential component that functions as the pattern recognition receptor (PRR) to detect viral double-stranded RNA (dsRNA),followed by processing it into virus-derived siRNAs.Here we show that Dicer-2 is also required for the Toll immune signaling,and the requirement of Dicer-2 was observed both in cells and in adult flies.