Potential conflict of interest: Nothing to report. Addressing the important question of hepatitis B virus (HBV) sensing by the hepatocyte innate immune system, a study published in Immunity by Sato et al. identifies retinoic acid‐inducible gene 1 (RIG‐I) as a sensor of HBV pregenomic RNA (pgRNA) and shows that RIG‐I can exert direct antiviral activity.1 Taking advantage of a recently developed cell‐culture model consisting of HepG2 cells overexpressing the viral receptor, NTCP, as well as human hepatocytes, the researchers provide evidence that HBV infection results in production of type III (but not type I) interferons (IFNs), as well as IFN‐stimulated genes (ISGs). From these data, the researchers conclude that the HBV genome or genomic products are actively sensed by the HBV‐containing cell. To pinpoint the pattern recognition receptor (PRR) responsible for this sensing, the researchers silenced the expression of key nucleic acid sensors, including RIG‐I, cGAS, and IFI16. Interestingly, only the silencing of RIG‐I expression reversed IFN expression after HBV genome transfection into hepatoma cells, suggesting a role for RIG‐I in HBV sensing. Moreover, the silencing of both RIG‐I and mitochondrial antiviral signaling (MAVS) expression inhibited induction of IFN expression in HBV‐infected primary human hepatocytes (PHHs). Using nucleic acid extracts from HBV‐transfected Huh7 cells treated with DNase or RNase, the researchers provide evidence that only HBV‐derived RNA is able to trigger IFN expression. Mapping the genetic element mediating induction of IFN type III, the researchers show that the 5’ epsilon (ε) structure of the HBV pgRNA, which mediates encapsidation of the pgRNA into viral capsids, triggers RIG‐I‐mediated type III IFN expression. Using synthetic εRNA and RNA pull‐down assays, the researchers further demonstrate that RIG‐I can directly interact with the ε region of HBV pgRNA (Fig. 1A) that serves as the binding site of the viral polymerase P protein and initiation of reverse transcription. Finally, the researchers provide evidence that RIG‐I can also act as a direct antiviral agent and that this activity appears to be mediated by interfering with the interaction of the viral P protein with HBV pgRNA (Fig. 1B). Taken together, these results suggest that RIG‐I is a sensor of HBV‐inducing antiviral IFN type III immune responses in infected hepatocytes and might also exhibit direct antiviral activity (Fig. 1).Figure 1: Model of HBV‐RIG‐I interactions according to Sato et al. During HBV infection, viral genomic relaxed circular (rc)DNA is imported into the nucleus. rcDNA is then converted into a covalently closed circular (ccc)DNA that serves as a template for the transcription of viral RNA, including pgRNA. (A) HBV sensing by RIG‐I. Sato et al. report that after its export into the cytoplasm, the 5’‐ε region of HBV pgRNA is recognized by RIG‐I. Sensing of RIG‐I induces activation of type III IFN expression. (B) The direct antiviral effect of RIG‐I reported by Sato et al. involves binding of RIG‐I to HBV pgRNA, which inhibits the interaction between viral polymerase (P) and HBV pgRNA, resulting in impairment of reverse transcription.Detection of virus‐derived genetic material by PRRs is one of the first steps initiating antiviral innate immune responses.2 PRRs include Toll‐like receptors (TLRs) and cytoplasmic RIG‐I‐like receptors (RLRs), such as the RNA sensor, RIG‐I.2 RIG‐I mediates detection of cytosolic RNA and subsequent signaling by the MAVS adaptor. The best‐characterized RIG‐I ligand is uncapped 5’‐triphosphate RNA (5’‐pppRNA), which can also be generated by RNA polymerase III after binding to AT‐rich double‐starnded DNA (dsDNA).2 Consequently, RIG‐I is considered to be both a RNA and DNA sensor. PRR sensing leads to activation of type I and III IFN gene expression, triggering a strong, broad, and fast response against viral infections by inducing the expression of ISGs.3 In the liver, HBV—a member of the Hepadnaviridae family—is a leading cause of chronic viral hepatitis and liver cancer worldwide.4 Though adaptive immune responses have been elucidated in great detail, the mechanisms of viral sensing and evasion from innate immune responses are still poorly understood.4 The unique replication strategy of the virus producing its DNA genome through reverse transcription of the pregenomic RNA encapsidated into the viral core particle most likely contributes to limited or absent sensing. Indeed, viral RNAs are capped and polyadenylated, presenting similarities with host messenger RNA. Despite major advancements in the discovery of novel sensing pathways, the sensing of HBV nucleic acids remains elusive.5 This report, which uncovers RIG‐I as an HBV sensor, differs from results of previous studies in the chimpanzee model, where HBV has been shown to evade the induction of early antiviral genes in response to infection.6 Similarly, previous studies in cell‐culture models have suggested that HBV escapes host sensing by shielding the genome in the viral capsid in the cytoplasm (reviewed in a previous work5). On the other hand, more‐recent studies indicate that HBV proteins, such as the polymerase and the HBx protein, can interact with MAVS and DEAD box protein 3, X‐chromosomal and impair their functional activity (reviewed in a previous work4). Interestingly, RIG‐I and MAVS have been shown to play important roles both in sensing of and/or evasion by other hepatotropic viruses. For example, hepatitis C virus (HCV), an RNA virus belonging to the Flaviridae family, is actively recognized by RIG‐I through the HCV dsRNA replicative intermediate in the cytoplasm of hepatocytes (reviewed in a previous work5). HCV is also known to evade IFN responses by several mechanisms, including the cleavage of MAVS by nonstructural (NS)3‐NS4A proteases (reviewed in a previous work5). Hepatitis A virus (HAV), another positive single‐stranded RNA virus targeting the liver, activates the PRR pathway through the RLR helicase, melanoma differentiation‐associated protein 5, in the cytoplasm (reviewed in a previous work5). Viral infection results in MAVS cleavage, thereby evading innate immune responses (reviewed in a previous work5). Collectively, these data suggest that the RIG‐I and RLR pathways are implicated in the sensing of several hepatotropic viruses. Collectively, the observation that RIG‐I may play a role as sensor for HBV RNA stimulates new research to revisit HBV sensing. Further studies in HBV infectious cell‐culture or animal model systems will shed light on the physiological contribution of the described mechanisms to the control of HBV infection. Furthermore, to understand the impact and clinical relevance of this finding, further investigation of innate immune responses during acute and chronic HBV infection in liver biopsies would certainly improve our understanding of the role of innate host responses to HBV infection. Indeed, the impact of this approach has been elegantly demonstrated by recent studies in HCV‐infected patients that advanced our understanding of innate immune responses and IFN‐based therapies.7 Moreover, determining the role of RIG‐I sensing for defined HBV variants associated with different outcomes of disease may also help to understand the contribution of this mechanism for HBV pathogenesis. In this context, it is of interest to note that an HBV variant with enhanced encapsidation of pgRNA and replication has been associated with an outbreak of fulminant hepatitis B.8 Revisiting the role of RIG‐I and other pathways of HBV sensing in patients could also open new perspectives for curing HBV. Thus far, immune‐mediated antiviral strategies are the only approach to achieve durable control and clearance of HBV infection, in at least some patients.4 Thus, the pharmacological exploitation of innate immune response pathways may contribute to the development of urgently needed novel curative strategies. Author names in bold designate shared co‐first authorship