The frequently used NAs for the treatment of HBV are Entecavir (ETV), Tenofovir disoproxil fumarate (TDF), and Tenofovir alafenamide fumarate (TAF). ETV, TDF and TAF inhibit HBV polymerate activity, to exert antiviral effects (30, 31). NAs are orally administered, well-tolerated agents that directly inhibit HBV DNA synthesis; however, they do not affect cccDNA (28).

IFNs are endogenous immune molecules with broad-spectrum antiviral effects (32). IFNs mainly include type I IFN (IFN-I), type II IFN (IFN-II), and type III IFN (IFN - III) (33). IFN-I include IFN-a, - β, - ϵ, - k, - w, etc., they are produced by nearly all mammalian cells, whereas the IFN-II family consists of a single member, IFN-γ, which plays a critical role in immune regulation and antiviral defense (34). IFN-II can only be produced by activating T cells or NK cells (34). In humans, the four types of IFN-III proteins include IFN - λ 1 (also known as interleukin -29 (IL-29)), IFN - λ 2 (IL-28A), IFN - λ 3 (IL-28B), and IFN - λ 4 (35).

The production of pathogen-associated molecular patterns (PAMPs) from microorganisms or damage-associated molecular patterns (DAMPs) by host cells are detected by pattern recognition receptors (PRRs), which triggers an antiviral response. Following viral entry into the host cell, viral nucleic acids are detected by sensor proteins, including cyclic GMP-AMP synthetase/stimulator of interferon genes (cGAS/STING), TLRs (3, 7, 8, and 9), and retinoic acid-inducible gene I/melanoma differentiation-associated protein 5 (RIG-I/MDA5), which initiate a downstream antiviral signaling cascade. Among the critical proteins synthesized during this response is IFN (36).

Currently, IFN-I, primarily IFN-α and Peg-IFN-α, are clinically approved for the treatment of CHB. IFN-α has a short serum half-life and needs to be injected subcutaneously many times a week for the treatment of CHB. Peg-IFN-α includes Peg-IFN-α-2a and Peg-IFN-α-2b, they are semi-synthetic long-acting interferons obtained by PEGylation of IFN, a process that significantly extends their serum half-life (37). This article focuses on IFN-α and Peg-IFN-α.

PKR, a serine/threonine kinase activated through dsRNA-dependent autophosphorylation, is a critical antiviral protein induced by IFN-α (73). Activated PKR catalyzes phosphorylation of the translation initiation factor eIF-2α, resulting in inhibition of translation (74). One study indicates that PKR is a key mediator of IFN-α-induced anti-HBV activity, primarily through its role in suppressing viral protein synthesis (75). RIG-I can augment the IFN-α mediated antiviral response against HBV by upregulating the expression of PKR (76).

Mx proteins are IFN-inducible proteins belonging to the dynein superfamily of high-molecular-weight guanine triphosphatases (GTPases), which are implicated in diverse antiviral responses (77, 78). The Mx proteins, first detected in mammals, participates in diverse cellular processes including endocytosis and mitochondria, plastid, and peroxisome dynamics (79). The expression of human Mx1 and Mx2, leads to the formation of antiviral proteins (MxA and MxB), respectively, which are well-known ISG products (80). Two mechanisms by which Mx1 inhibits HBV have been proposed. First, Mx1 blocks the export of viral mRNA (81). Second, Mx1 binds to the HBc protein and immobilizes it near the perinuclear membrane, interrupting capsid formation (82). Wang et al. demonstrated that the MX2 functions as a critical antiviral effector, acting as a host restriction factor in HBV replication by reducing cccDNA and suppressing viral RNA synthesis. Consequently, Mx2 may represent a novel intrinsic HBV inhibitor with potential therapeutic applications (83).

In humans, the A3 cytidine deaminases subfamily comprises seven principal homologs, designated as A3A through A3H. Among them, A3A, A3C, and A3H possess a single cytosine deaminase (CD) domain. In contrast, A3B, A3D, A3F, and A3G contain two CD domains; however, only the CD2 domain exhibits catalytic activity. The CD1 domain, while not catalytically active, participates in the binding RNA or single-stranded DNA and facilitates the incorporation of APOBEC3 into viral capsids (84). Researchers have shown that the normal human liver expresses the mRNAs of A3B, A3C, A3F, and A3G. In primary human hepatocytes, IFN-α stimulates the expression of these cytidine deaminases, and the full-length protein A3B_L, A3F, and A3G possess anti-HBV activities (85, 86). The A3 cytidine deaminases affect HBV replication through several mechanisms, including inducing G-to-A hypermutations, inhibiting viral gene transcription, and reducing the production of viral particles (87). These G-to-A mutations are commonly observed in HBV isolates and may significantly affect the pathogenesis of HBV (88, 89). IFN-α can interfere with the synthesis of negative-strand DNA viruses by inducing the expression of A3G and binding to viral DNA polymerases (90). A3G inhibits HBV replication by inhibiting viral genome preRNA packaging, rather than by inducing G-a hypermutations (91). The A3B protein blocks the binding of heterogeneous ribonucleoprotein K (hnRNP K) to the HBV enhancer II and HBV S gene transcription, and hnRNP can promote the expression of HBV. In addition, A3B has been found to directly inhibit the HBV S gene promoter activity (92).

GBPs are a family of IFN-induced GTPases and are the most abundant of IFN-γ-induced immune proteins (93–95). GBP1 has been implicated in the generation of innate immunity in the host and exerts antiviral and antibacterial effects. Several studies have shown that GBP1 can inhibit hantavirus (96), swine fever virus (97), hepatitis E virus (98), H5N1 influenza virus (99). Research has shown that co-treatment with Peg-IFN-α-2b and GBP1 overexpression significantly amplifies the antiviral effect of IFN, whereas silencing GBP1 partially reverses this response, underscoring GBP1’s role as a key positive regulator of IFN-α-mediated immunity against HBV. GBP1 inhibits its expression by directly binding to HBs, and the N-terminal GTP domain of GBP1 can suppress HBs. This indicates that GBP1 can inhibit the expression of HBs to block HBV infection (100). Chen et al. performed a comprehensive analysis of the antiviral response and signal activation mediated by IFN-α isoforms, and found that IFN-α14 was the most effective isoform in inhibiting HBV covalently closed circulating DNA transcription and HBV e antigen/HBV surface antigen production, and guanylate binding protein 5 was identified as an HBV restriction factor (101). The effect of GBPs on the anti-hepatitis B virus effect of IFN deserves further exploration.

TRIM proteins belong to the RING finger E3-ubiquitin (RING-E3) ligase and contain over 80 members (102). TRIM family members are characterized by their conserved RBCC domain that comprises the RING (R), one or two B-boxes (B), and the coiled-coil (CC) domains (103). TRIM family members are differently expressed in mouse CD4⁺ T cell subsets, macrophages, and DCs, and are constitutively expressed via IFN-I dependent and non-dependent mechanisms (104). TRIM proteins are commonly used as E3 ubiquitin ligases and are involved in diverse biological processes to modulate the key cellular functions by enhancing protein ubiquitination and degradation. These abundant c-terminal domains allow them to bind to different substrates and exert different regulatory roles, which determines the specificity and functional diversity of TRIM (105). Extensive research has highlighted the role of TRIM proteins in antiviral responses against hepatitis B. In particular, TRIM19, TRIM38, and TRIM25 have been implicated in HBsAg clearance and improved therapeutic outcomes following peg-IFN-α treatment (106, 107). TRIM38 exerts antiviral effects as ISG, inhibiting HBV replication under the stimulation of IFN-α, while up-regulating Mx1, IFIT1 and STAT1 (106). Studies have indicated that TRIM25 interacts with HBx to promote the ubiquitination of the HBx-k90 site, promoting the HBx degradation. On the other hand, TRIM25 may serve as an adapter, enhancing RIG-I recognition of pgRNAs, which further facilitates IFN production. This suggests that TRIM25 can directly and indirectly regulate HBV replication (108). TRIM21 promotes ubiquitin-mediated degradation of hepatocyte nuclear factor 4α proteasome, resulting in decreased HBV transcription levels and inhibition of HBV replication (109). The SNP rs10838543 genotype in TRIM22 influences the response to Peg-IFN-α treatment, increasing the secretion of cytokines interferon lambda 1, C-C chemokine ligand 3 (CCL3) and CCL5 in hepatocytes by modulating the cytokine-cytokine receptor interaction signaling pathway. In addition, it was positively correlated with Peg-IFNα-induced treatment response in HBeAg-positive CHB patients (110). Transient receptor potential vanillin 2 (TRPV2) is a multimodal ion channel involved in a variety of physiological and pathological processes (111). Guo et al. reported that viral infection induced TRIM21 expression via IFN-I (via autocrine signaling) and bystander cells (via paracrine signaling) of infected cells,TRIM21 catalyzes the k48-linked ubiquitination of TRPV2 at Lys295, promoting the proteasome-dependent degradation of TRPV2 and inhibiting viral infection (112). In vitro studies demonstrate that IFN can promote the expression of TRIM26, which inhibits HBx by promoting ubiquitin-mediated HBx degradation. In addition, TRIM26 rs116806878 may serve as a biomarker for assessing the response to Peg-IFN-α in CHB patients (113). TRIM28 can degrade HBx and inhibit HBV replication (114). The TRIM protein family, consisting of numerous members, can promote the host antiviral defenses. Its molecular mechanisms in the context of chronic liver diseases, including hepatitis B, have been extensively reviewed in the literature (115).

ISG20 is an IFN-induced antiviral exoribonuclease (116). Basal level expression of ISG20 was detected in hepatocytes and was highly up-regulated following IFN treatment, while ISG20 knockdown promoted HBV replication and weakened the IFN-mediated antiviral effects. ISG20 selectively binds to a unique stem-loop structure called ϵ (ϵ) in all HBV RNA species and degrades viral RNA to inhibit HBV replication. The C-terminal exonuclease III domain of ISG20 was found to be mediate the HBV-RNA ϵ interactions (117). Elsewhere, the ISG20 expression was implicated in the development of responses to IFN-α therapy in patients with CHB. ISG20 levels in liver tissue of nonresponders were reduced prior to IFN α therapy, and ISG20 levels were highly up-regulated after the treatment in responders (118). An in vitro study demonstrated that ISG20 exerted anti-HBV activity by acting as a putative repressor that binds to the HBV-enhancing II/Cp region (119).

The host proteins induced by IFN antiviral therapy are diverse. IFIT3 enhances the IFN-α effector signaling pathway by promoting STAT2 phosphorylation, and overexpression of IFIT3 enhances the expression of IFN-α -triggered ISGs, including MxA, OAS1, and PKR, significantly. Decreased the secretion of HBsAg and HBeAg and the replication of HBV (120). In addition, RNA helicase DEAD-Box Helicase 5 (DDX5) has been identified as a critical regulator of STAT1 translation, with its knockdown significantly impairing the antiviral efficacy of IFN-α in inhibiting HBV replication. These findings suggest that DDX5 is a pivotal regulator in innate immunity and serves as an important factor in enhancing the therapeutic effects of adjuvant IFN-α treatment (121). Furthermore, IFI6 was found to inhibit the HBV replication in cell and mouse model by downregulating the expression of the gene of HBV enhancer II and core promoter (EnhII/Cp) (122). Other host factors, including TNF-α, mammalian p38 MAPK, IFITMs, USP18, SOCS proteins, were reviewed elsewhere (72).

Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease that affects approximately 32.4% of the global population and leads to liver fibrosis and end-stage liver complications (123). NAFLD and metabolic syndrome are mutually causal. Abnormal lipid metabolism plays an important role in NAFLD. In order to standardize the diagnosis and treatment of NAFLD, in 2020, the International Expert Group on Fatty Liver recommended that NAFLD be renamed metabolic dysfunction-associated fatty liver disease (MAFLD) (124).Hepatic steatosis can progress to metabolic dysfunction-associated steatohepatitis (MASH), elevating the risk of cirrhosis and HCC. Within 10 years, 10-29% of MASH patients develop cirrhosis, of which 4-27% progress to HCC (125). The number of patients with hepatitis B and MAFLD has been increasing yearly, and the impact of fatty liver on the progression of hepatitis B and antiviral efficacy has received widespread investigation. Liu et al. studied the effect and mechanism of hepatocyte steatosis on HBV replication and secretion, and the results showed that hepatocyte steatosis inhibited HBsAg and HBV DNA secretion by inducing hepatocyte internal reticulum stress (126). Liver biopsy findings indicate that MASH negatively impacts ISG expression and macrophage gene signatures in the liver, potentially disrupting antiviral immune pathways, enhancing viral replication, and amplifying inflammatory responses, thereby increasing the risk of advanced fibrosis in patients with CHB (127). Findings from a prior study showed that concurrent hepatic steatosis enhanced the HBsAg response in CHB patients without overt liver failure receiving antiviral therapy, particularly in HBeAg-negative patients. Factors such as young age, those treated with NAs in combination with Peg-IFN-α, lower initial HBsAg levels, and the presence of hepatic steatosis predict the success of treatment (128). Wu et al. demonstrated that elevated lipid levels may improve HBsAg clearance in patients with CHB. IFN-α can increase triglyceride levels and induce hepatic steatosis by upregulating the expression level of acyl-CoA synthetase long chain family member 1, which indirectly promotes HBsAg clearance in patients with CHB (129). In a prospective study, patients with inactive HBsAg<200 IU/ml HBsAg were divided into treatment and control groups, and patients in the treatment group were administered with Peg-IFN for 96 weeks, and those in the control group did not receive any antiviral therapy and were observed for 96 weeks. The results showed that the cumulative clearance rates of HBsAg in patients with mild, moderate and severe steatosis at week 96 were 71.42%, 74.07% and 47.05%, respectively. The inactive HBsAg carriers with moderate steatosis exhibited the highest sensitivity to Peg-IFN, and the HBsAg clearance rate in the moderate steatosis group was significantly higher than that in the non-steatosis group (130). However, another study suggested that hepatic steatosis did not affect the virologic response, but did affect the biochemical response in patients with CHB after 48 weeks of Peg-IFN-α treatment (131). Data has shown that hepatic steatosis contributes to Peg-IFN-α therapy failure in patients with CHB (132). However, other scholars have found that mild hepatic steatosis does not influence of efficiency of 48 weeks of Peg-IFNα-2a therapy in CHB patients (133). Abnormal lipid metabolism and its associated liver disease combined with CHB are very common in clinical practice, and the traditional view is that hepatic steatosis aggravates the progression of CHB. Through this literature review, we have found different conclusions, so whether lipid metabolism and its related liver diseases occur differently under specific conditions still need further clinical observation, which should attract our attention and may become a hot spot for future research.

Bile acids (BAs) are amphiphilic molecules generated from cholesterol metabolism, and are produced in the liver and secreted into the duodenum. Studies have reported that BAs promote the digestion and absorption of lipids, regulate the metabolism of cholesterol, and enhancing bile secretion (134). Abnormal accumulation of BAs, especially taurocholic acid (TCA), stimulates the HBV replication by impairing the effector function of CD8⁺ T and NK cells in CHB patients. Notably, TCA-mediated activation of hepatic stellate cells has been demonstrated to be positively associated with cirrhosis progression. Aberrant accumulation of BAs, particularly TCA, drives macrophage polarization and creates an immuno-suppressive tumor microenvironment that promotes initial tumor expansion and tumor growth in HCC (135). Zhen et al. found that serum BAs, especially TCA, were significantly elevated in HBeAg-positive CHB patients compared with those in healthy individuals and patients in other phases of chronic HBV infection. Moreover, serum BAs, particularly TCA, can block the response to Peg-IFN-α treatment in HBeAg-positive CHB patients. Mechanistic investigations have shown that in the HBeAg-positive CHB patients, BAs reduced the number and proportion of CD3⁺CD8⁺ T cells and NK cells, and impaired effector function (136). Others have uncovered that BAs promote the transcription and expression of HBV genes in hepatocyte lines, and BAs stimulate the HBV gene expression to abolish the antiviral effects of IFN-α (137). However, evidence shows that BAs synthesis is enhanced in different cells, including immune and parenchymal cells, following viral infection, suggesting that BAs participate in the initiation of cellular antiviral responses (138). Liang et al. showed that the farnesoid X receptor (FXR)–interferon regulatory factor 3 (IRF3) interaction impairs the transcriptional activity of IRF3 and damages the activation of interferon signaling and the antiviral response of cells. FXR inhibitors have been shown to enhance IFN expression and promote cellular antiviral responses (139). Notably, BAs function as endogenous agonists of mitochondrial protein 2 (MFN2), and physiologically relevant levels of BAs may strengthen the innate immune response by facilitating MFN2-mediated pathogen detection. However, if the host fails to clear the invading pathogens, resulting in liver damage and cholestasis, elevated BA levels may shift toward amplifying excessive inflammatory responses. Although this may initially serve as an adaptive defense mechanism, it can ultimately exert detrimental effects on the host (140).

The liver receives intestinal content via the portal system, biliary tract, and systemic circulation. The symbiotic relationship between GM and liver is regulated and stabilized by a complex network of interactions, which include metabolic, immunological, and neuroendocrine dialogues between them (141). GM can directly interact with viral particles and affect their infectivity (142). Furthermore, gut microbiota can initiate and activate host antiviral immunity (143). A review by Wirusanti et al. summarized the underlying mechanisms of GM-IFN -virus interactions: 1. GM can promote steady-state IFN-I expression from macrophages and plasmacytoid dendritic cells (pDCs) and homeostatic IFN-III expression from intestinal epithelial cells. 2. Gut microbiota-derived PRRs ligands stimulate the expression levels of IFN. The components of the symbiotic GM generate molecular patterns that can bind to PRRs, and this pattern recognition activates downstream signaling pathways and IFN-I production. 3. Gut microbiota-derived metabolites activate IFN expression (144). In vitro studies have shown that exposure of peripheral blood mononuclear cells to fecal-derived bacterial extracts in patients with hepatitis B without cirrhosis promoted the expansion of T helper 17 cells, while exposure to BE in patients with cirrhosis decreased the number of TH1 cells, suggesting that peripheral immunity may be an integral part of the mechanisms by which the overall bacterial product exerts a profibrotic effect and influences the prognosis of chronic hepatitis B virus infection-associated liver diseases patients (145). Another animal study found that the immune tolerance pathway of HBV was activated in young mice at 6 weeks of age before the establishment of gut bacteria. Moreover, the maturation of gut microbiota in adult mice stimulated hepatic immunity via the TLR4-dependent pathway, leading to rapid clearance of HBV (146).

MiRNAs are small, non-coding RNA involved in the regulation of gene expression by binding to the complementary sequences of the 3’-untranslated region of the target mRNA. This interaction promotes mRNA degradation or translational inhibition, mediated by RNA-induced silencing complex. MiRNAs are involved in various biological processes such as cell development, differentiation, proliferation, apoptosis, and metabolism, and play a role in the pathogenesis of inflammation, fibrosis, and carcinogenesis in liver diseases (147, 148). The mechanisms of miRNAs regulate IFN-I signaling transduction include influencing cell surface IFNAR expression, the activity of STATs, and ISGs expression (41). It has been shown that there is a correlation between serum miRNA levels and IFN treatment response in patients with CHB. Nagura et al. confirmed that serum miR-192-5p levels were associated with IFN treatment response in CHB patients, and multivariate analysis showed that lower miR-192-5p levels at baseline were independent predictors of virologic response (149). Elsewhere, it was found that peripheral circulating exosomes-miRNAs influenced sensitivity to IFN therapy in patients with CHB (150). Moreover, there is evidence that exosomes with low concentrations of miR27b-3p in the serum of Peg-IFN-α treatment responders activate interferon regulator 3/7 in the macrophage IFN-α synthesis pathway (IRF3/7). However, over-expression of miR27b-3p in HepAD38 cells inhibits IFN-α synthesis in macrophages, decreasing the capacity to eliminate HBV, while this inhibition can be alleviated by the use of inhibitors released by exosomes (151). miR-548c-3p also targets TRIM22 to attenuate the therapeutic effect of Peg-IFN-α in HBeAg-positive patients with CHB (152). Pretreated plasma miR-301a-3p and miR-145-5p levels were higher in CHB patients who achieved a collective response or HBsAg loss after Peg-IFN/NA treatment compared with non-responding patients (153). Zhao et al. showed that miR-3613-3p impairs the IFN-induced immune response by targeting cytidine monophosphate kinase 1 in CHB (154). Elevated serum miR-6126 levels during Peg-IFN therapy were associated with a 1-log reduction in HBsAg 48 weeks post-treatment. In vitro studies further demonstrated that miR-6126 suppresses HBsAg production and HBV replication (155).

Recent studies have begun to uncover the role of SNPs in host genes in influencing individual differences in HBV infection susceptibility and IFN response (156). There is a research indicating that the G alleles of Rs2278420 and Rs6509607 are associated with the mRNA levels of zinc finger protein 350 (ZNF350), which may increase the probability of Peg-IFN-α response in HBeAg-positive CHB patients by regulating the JAK-STAT signaling pathway. Low levels of ZNF350 mRNA are associated with complete response, with higher levels of ZNF350 mRNA in patients with suboptimal response. However, it has not yet been fully explained how SNPs regulate the IFN-α signaling pathway (156). Guan et al. found a new SNP (rs7519753) by genome-wide association study (GWAS), the rs7519753 C allele was significantly associated with serum HBsAg loss after Peg-IFN-α treatment in CHB patients, and TP53BP2 expression is higher in liver tissues of individuals carrying this allele. TP53BP2 is a nearby gene located 18 kb downstream of SNP rs7519753, which can promote JAK/STAT signaling by down-regulating SOCS2, thereby enhancing the response of liver cells to IFN - α in vitro and in vivo (157). In a study examining the effects of NAFLD-associated SNPs in patients with HBV infection, only patatin-like phospholipase domain-containing protein 3 (PNPLA3) SNP was significantly associated with hepatic steatosis. In Peg-IFN therapy, PNPLA3 SNP and TLL1 SNP influenced the therapeutic efficacy, and patients without minor alleles of these SNPs showed good results with high virologic response and significantly reduced HBsAg titers (158). In conclusion, future studies about host SNPs will help to identify the advantageous personnel who use Peg-IFN-α/IFN-α to treat CHB, improve the efficiency of treatment, and avoid economic losses caused by ineffective treatment.

Furthermore, the expression levels of molecules, including cytokines, chemokines, IFITs, and IFITMs, can be used to assess the efficacy of IFN in the treatment of CHB. In a study conducted by Wang et al., IFN-related gene chips were utilized to analyze patients with CHB undergoing IFN therapy. The findings indicate that high baseline expression levels of CXCL10, IFIT1, and IFITM1 may serve as predictive biomarkers for a favorable response to IFN therapy. High expression of interleukin-13 receptor α 1 subunit gene, IL15, IFI35 and IFI44 molecules, and decreased expression of IFN-associated growth regulator 2, IL11 receptor α subunit, interleukin 4 receptor, IFN regulator 3, IRF4, Pyrin and HIS domain family member 1 and ADAR molecules may indicate poor IFN response in patients (159).

IL-17A pretreatment decreased the levels of ISGF3 complex and antiviral-related ISGs (ISG15, ISG20 and Mx1) in resonse to IFN-α stimulation, increased the expression of suppressor of cytokine signaling (SOCS) 1, SOCS3 and USP18 (160). Peg-IFN-α therapy upregulate the expression levels of IFN-γ, IL-12p70, IL-7, IL-8, IL-16, IL-4, an IL-13 among responders prior to the observable decline in HBsAg. Furthermore, the levels of several chemokines, including CCL11 (Eotaxin), CCL24 (Eotaxin-2), CCL26 (Eotaxin-3), CCL4 (MIP-1β), CXCL1 (GRO-α), CXCL9 (MIG), CXCL11 (I-TAC), CXCL12 (SDF-1α), and CXCL13 (BLC), were also found to be elevated in these responders (161). Further investigations are warranted to clarify the roles of these cytokines and chemokines in the treatment of CHB with IFN.