Hepatitis B virus (HBV) infection remains a global health issue, affecting an estimated 254 million people globally and resulting in nearly 1.1 million deaths each year. The Western Pacific and African regions bear the highest disease burden, highlighting ongoing disparities and the urgent need for enhanced prevention and treatment strategies aligned with WHO sustainability goals (1, 2). It is a member of the Hepadnaviridae family and primarily infects hepatocytes, leading to both acute and chronic liver inflammation. The virus is transmitted through blood, sexual contact, and from mother to child during birth. Understanding the molecular mechanisms behind HBV infection, immune evasion, and pathogenesis is critical for developing effective therapeutic strategies (3).

Hepatitis B virus (HBV) replication follows a complex, multi-step cycle that is central to its persistence and chronicity. Upon entry into hepatocytes through the sodium taurocholate co-transporting polypeptide (NTCP) receptor, the virus releases its relaxed circular DNA (RC DNA), which is subsequently converted into covalently closed circular DNA (cccDNA). This cccDNA functions as a stable, episomal template for the transcription of various viral RNAs, including the pregenomic RNA (pgRNA). The pgRNA is then encapsulated into core particles, where it undergoes reverse transcription to generate progeny rcDNA. These newly formed core particles can either be enveloped for virion secretion or recycled back to the nucleus to amplify the cccDNA pool, thereby facilitating the perpetuation of chronic infection (4). This replication cycle underscores the pivotal role of cccDNA in HBV’s immune evasion strategies, directly linking to the innate immune pathways discussed in subsequent sections.

The innate immune response serves as the host’s first line of defense against viral infections, and its activation depends on the recognition of pathogen-associated molecular patterns (PAMPs) (5, 6). Specialized pattern recognition receptors (PRRs) identify virus-specific molecular structures and trigger cascade reactions, inducing the production of type I and III interferons (IFN-I/III) (7–10). Through autocrine and paracrine mechanisms, interferons stimulate the expression of interferon-stimulated genes (ISGs), which restrict viral replication within host cells and play crucial roles in initiating innate immune responses (11). Therefore, a deeper understanding of the molecular basis by which the host innate immune system recognizes and responds to viral infections is essential for elucidating viral transmission and pathogenesis and developing effective therapeutic interventions (12–14). Studies have shown that PRRs responsible for recognizing viral nucleic acids mainly include Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), and cytosolic DNA sensors (15–17). Activation of these PRRs further induces robust IFN-I/III antiviral responses, promoting the expression of multiple ISGs (e.g., APOBEC3G, IFITM family, and MX1) to suppress viral replication and spread (11, 18).

However, hepatitis viruses have evolved various mechanisms to evade or interfere with the host innate immune surveillance. For instance, HBV covalently closed circular DNA (cccDNA) effectively circumvent innate immune recognition and inhibit interferon signaling pathways (12, 13). Thus, investigating the molecular mechanisms of PRR-mediated viral recognition, signal transduction pathways, and viral immune evasion strategies during hepatitis virus infections is critical for understanding the mechanisms of viral chronicity and guiding the development of novel therapeutic approaches (e.g., TLR agonists or IFN combination therapies) (19, 20).

This review summarizes recent advances in our understanding of how host PRRs recognize HBV and initiate innate immune responses. It delves into the molecular mechanisms and regulatory networks underlying key receptor activation and outlines viral strategies for innate immune evasion. We anticipate that these insights will provide new research perspectives and therapeutic targets for the prevention and treatment of viral hepatitis.

In order to provide a clear overview of the study’s findings, one table (Table 1) and one figure (Figure 1) present a comprehensive summary of the key mechanisms and interactions involved in the immune response to hepatitis B virus, which are discussed throughout the manuscript.

Covalently closed circular (cccDNA) is a stable mini-chromosome formed by HBV in the nuclei of infected liver cells, serving as a template for viral RNA transcription and supporting the synthesis of viral proteins and genome replication (60–62). The long-term retention of cccDNA is the fundamental cause of HBV chronicity. It can stably exist in the host cell nucleus for several months (with a half-life of approximately 40 days), maintaining an infected state through intracellular genomic recovery, and a continuous replenishment pool (pool) of secondary infection (63–65). Because cccDNA is located in the cell nucleus and has a stable chromatin structure, existing drugs find it difficult to directly target and eliminate it, which has become the main obstacle to the radical cure of HBV (66, 67). cccDNA is formed by relaxed circular DNA (rcDNA) (68), rcDNA contains an incomplete double-stranded structure, and existing evidence indicates that its broken ends need to be repaired by the host DNA repair system (such as ligase, polymerase, etc.) to form a covalently closed circular structure (60, 69–71). The complete set of host factors has not yet been fully elucidated yet (60). The level of serum HBV DNA not only includes cccDNA and rcDNA but also Double-stranded Linear DNA (dslDNA). It can originate from abnormally processed rcDNA or by-products during the infection process, plays a secondary role in viral infection and pathological mechanisms (72).

cccDNA is located within the nucleus of infected hepatocytes and forms a microsomal structure, which is assembled into chromatin by host histones and non-histones. This structure is similar to that of host DNA, making cccDNA less likely to be recognized by the immune system as a foreign substance (73–75). The nuclear localization of cccDNA makes it a difficult target for antiviral and immune responses (66, 76), thereby avoiding direct detection and clearance by the innate immune system. The actively transcribed cccDNA forms an interaction network with the host genome, further strengthening its “pseudo-host” attribute and preventing it from being cleared (77). Furthermore, the activity of the DNA innate immune sensing pathway in liver cells is low. This inherent poor reactivity makes hepatocytes lack a strong innate immune recognition ability even when facing exogenous DNA such as HBV cccDNA (21, 78).

Cyclic GMP-AMP synthase (cGAS) is a crucial cytosolic DNA sensor that plays a vital role in innate immunity and cellular processes. cGAS detects both foreign and self-DNA, producing cGAMP to activate the STING pathway and trigger immune responses (22–24). As a cytoplasmic DNA sensor, cGAS can recognize naked relaxed circular HBV DNA (rcDNA) in vitro, activating the cGAS-STING pathway to induce innate immune responses (25, 26, 79). When the cGAS pathway is forcibly activated, the intracellular level of cccDNA can be significantly reduced, indicating that cGAS has the potential to inhibit cccDNA (80). However, the immune escape mechanism of HBV hinders this process. Experiments have shown that in cell culture models and humanized mice, HBV infection inhibits the activity and expression level of cGAS, thereby weakening the host’s immune surveillance of the virus (27).

It has been discovered that interferon-inducible protein 16 (IFI16) is a unique intrinsic immune sensor in the nucleus that is capable of recognizing and binding to HBV cccDNA within the liver cell nucleus. Targeting the interferon-stimulated response element (ISRE) in cccDNA promotes epigenetic inhibition (such as promoting inhibitory histone modification). Therefore, inhibiting the transcription of cccDNA and replication of HBV (28, 29). Although IFI16 can recognize cccDNA and initiate inhibition, the persistent presence of cccDNA itself indicates that this recognition mechanism is insufficient to completely eliminate it in the in vivo environment, or that there are pathways to evade the continuous action of this mechanism. This may be related to the expression regulation of IFI16 itself, the protective structure of cccDNA microchromosomes, or the interference of other host/viral factors (66).

A recent study by Ren et al. identified ATP-binding cassette subfamily F member 1 (ABCF1) as a novel host restriction factor that directly binds HBV covalently closed circular DNA (cccDNA). ABCF1 recognizes cccDNA via its KKx4 motif and undergoes PolyQ-mediated phase separation, which both activates type I/III interferon responses and inhibits HBV transcription by preventing RNA polymerase II recruitment. HBV counteracts this defense by HBx-mediated ubiquitination and degradation of SOX4, thereby suppressing ABCF1 transcription (30). These findings reveal a previously unrecognized innate immune mechanism against cccDNA and highlight ABCF1 as a potential therapeutic target for HBV infection. Moreover, Stadler et al. (2021) discovered that the deamination of cccDNA mediated by APOBEC3A, an important DNA cytosine deaminase in the human body, requires the induction of interferon signaling (31, 81). As demonstrated by Julie Lucifora et al. (2014), APOBEC3A, along with APOBEC3B, is essential for the interferon-α or LTβR agonist-induced degradation of HBV cccDNA (82). These molecules target cccDNA in the nucleus, catalyzing cytidine deamination and triggering irreversible degradation of cccDNA without harming the host genome. This process provides a promising basis for new therapies aimed at curing hepatitis B.

In conclusion, HBV cccDNA largely escapes detection by key DNA sensors, with pathways such as cGAS–STING being functionally suppressed during infection. Sensors, such as IFI16 and ABCF1, can recognize cccDNA, but their antiviral effects are insufficient for clearance, as HBV actively limits their activity. Clearance mechanisms requiring strong interferon signaling, such as APOBEC3A-mediated deamination, are further hindered by the weak initial recognition of cccDNA, enabling viral persistence.

The key proteins encoded by hepatitis B virus (HBV)—including the core protein (HBc/Cp), the surface antigen proteins (HBsAg), the transcriptional regulator X protein (HBx) and the e antigen (HBeAg). These proteins can modulate innate immune sensing receptors as well as interferon signaling pathways, thereby enabling HBV to evade immune clearance and establish persistent infection.

In light of the mechanisms underlying HBV’s evasion of innate immunity, targeting Pattern Recognition Receptor (PRR) pathways has emerged as a promising strategy for modulating antiviral responses in HBV infection. Several TLR agonists are currently being investigated in preclinical or early clinical stages for their potential therapeutic benefits.

GS-9620 (Vesatolimod), an orally administered TLR7 agonist, has been developed to restore antiviral immunity in CHB by activating host innate immune responses. Although GS-9620 does not directly target hepatocytes, it predominantly acts on peripheral blood mononuclear cells (PBMCs), particularly plasmacytoid dendritic cells (pDCs), leading to the induction of endogenous interferon type I (IFN-I) and interferon-stimulated genes (ISGs). This activation suppresses HBV RNA, DNA, and viral antigen expression through non-cytolytic mechanisms, without directly affecting cccDNA (149). In vivo studies show a dose-dependent effect, with increased innate immune activation creating a more favorable antiviral environment (150). Despite its promising safety profile and tolerability in CHB patients, clinical trials have not demonstrated significant reductions in HBsAg or serological conversion, suggesting that GS-9620 may be more effective as part of combination therapies rather than as a standalone curative treatment (151, 152). Further clinical trials, such as those investigating RO7020531, have highlighted the limitations of TLR7-mediated innate immune activation in humans. Although RO7020531 can induce interferon-related signaling in vivo, the activation plateaus within clinically tolerable doses, limiting its antiviral efficacy (19).

In contrast, JNJ-64794964 exemplifies the potential of TLR7 agonists to achieve a stronger antiviral effect. In murine models, robust activation of TLR7 leads to non-cytolytic suppression of HBV DNA and HBsAg to undetectable levels, with sustained viral control even after treatment cessation (153). However, these results depend on the intensity of immune activation and the experimental conditions, suggesting the need for careful consideration of their clinical relevance. Additionally, AIC649 represents a broader immunomodulatory strategy, targeting both TLR9-dependent and -independent pathways. Although monotherapy with AIC649 shows modest antiviral activity, its combination with nucleoside analogs enhances immune responses and extends viral suppression (154).

Together, these studies highlight the potential of PRR agonists to activate the innate immune system and suppress HBV replication. However, the magnitude and durability of these effects vary across agents and clinical settings, emphasizing the importance of evaluating PRR agonists primarily as components of combination therapy.

The innate immune system provides the first line of defense against pathogenic infection, either through its direct antiviral effects or by indirectly initiating primary adaptive immune responses. In recent years, our understanding of the molecular mechanisms and pathways driving innate immune activation during HBV infection has advanced considerably. At the same time, we have also discovered more ways in which HBV evades the surveillance of the innate immune system. A thorough study of the relationship between the two can enable us to re-examine the current clinical treatment plans, identifying their shortcomings and prospects. In this review, we have thoroughly discussed the interaction relationships between innate immunity and the three components (DNA, RNA, and proteins) of HBV and have also listed some of the latest research findings in related fields.

In the DNA components of HBV, we focused on cccDNA and discussed in detail the survival strategies of HBV’s cccDNA and how it evaded the key DNA sensor, cGAS. Moreover, although studies have shown that sensors such as IFI16 and ABCF1 can recognize cccDNA, their antiviral effects are insufficient to completely eliminate the virus alone, because HBV actively limits their activity. Similarly, the deamination mediated by APOBEC3A requires sufficient interferon-induced signals to be effective. The immune escape environment created by cccDNA weakens and hinders the initial recognition of these receptors, leading to viral persistence. Currently, the mainstream treatment for viral DNA in clinical practice mainly relies on nucleoside analogs (NAs) to inhibit the synthesis and replication of viral DNA, targeting the viral reverse transcriptase and thereby inhibiting HBV DNA replication, but it rarely achieves a functional cure because cccDNA is difficult to be eliminated (155, 156). Recent advances highlight the potential of capsid assembly modulators (CAMs) as innovative antiviral strategies against HBV. GST-HG141, a novel CAM, functions by disrupting viral nucleocapsid formation and thereby impeding HBV DNA synthesis and pregenomic RNA (pgRNA) encapsidation. In a very recent (Aug 2025) Phase II randomized, placebo-controlled trial, GST-HG141 demonstrated significant antiviral efficacy in chronic hepatitis B patients with low-level viremia despite long-term nucleostide analog therapy. Treatment led to marked reductions in both HBV DNA and pgRNA, with favorable safety and tolerability profiles (157). These promising results suggest that GST-HG141 may represent a breakthrough therapeutic option and provide a new direction for targeting HBV at the DNA level.

Among the RNA components of HBV, we have listed some TLR receptors and elaborated on their possible innate immune roles in HBV infection through some basic experiments. Although there is still a lack of sufficient understanding of the interaction between TLR receptors and HBV, the conclusions drawn from some TLR receptor agonist trials are still valuable for clarifying the mechanism and for clinical drug development (158). We have focused on the interaction between the most crucial pgRNA in HBV RNA and the RIG-I receptor. RIG-I recognizes the 5’-triphosphate end of pgRNA and initiates downstream reactions. HBV, through means such as ADAR1 and TIAR, modifies pgRNA or directly reduces the activity of RIG-I to achieve the purpose of evading immunity. We have also introduced the new hotspot in HBV research: svRNA. With the advancement of technology, the research on svRNA may promote the understanding of the HBV pathogenesis and provide a new perspective for identifying potential biomarkers and therapeutic targets. In terms of the treatment methods targeting HBV RNA, the RNA-targeted therapies that have become a hot topic in recent years include anti-sense oligonucleotides (ASO) and RNA interference (RNAi), which can target the viral pregenomic RNA to reduce the expression and replication of viral proteins. These therapies use small interfering RNA (siRNA) to silence the HBV genes, thereby lowering the levels of DNA, RNA and proteins (159–162). At present, RNA-targeted therapies are still in the experimental stage. Their clinical efficacy is stronger as a monitoring tool than as a standalone therapy (163, 164). In-depth investigations of HBV RNA and its associated receptors will enhance the theoretical foundation of RNA-targeted therapeutic strategies and may facilitate future breakthroughs.

In the protein components of HBV, we have listed four main protein components in HBV infection and explained how they achieve their persistent infection by influencing the innate immunity. Targeting HBV key protein–host interaction interfaces and reinforcing host-intrinsic antiviral defenses hold significant promise for achieving a functional cure. Future research should focus on the optimization and clinical translation of HBx–DDB1 inhibitors and HBsAg–TAK1/TAB2 dissociation compounds, as well as explore the feasibility of enhancing host E3 ligases, such as TRIM25. Advancing these strategies may ultimately provide novel solutions to eradicate HBV infection and prevent virus-associated hepatocellular carcinoma.

Looking forward, although emerging therapies targeting HBV DNA, RNA, and proteins are promising, single-agent strategies remain insufficient to achieve a functional cure (148, 149). Combination therapies are likely to provide the breakthrough: integrating nucleostide analogs with novel agents such as capsid assembly modulators, RNA-targeted therapies, and immune modulators (e.g., HBx–DDB1 inhibitors or TLR agonists) could suppress viral replication, counter immune evasion, and restore host antiviral responses at multiple levels (165, 166). Future research should focus on optimizing multi-target regimens and identifying the most effective timing for combination interventions, ultimately paving the way toward a functional cure for HBV.