About 90-98% of ingested alcohol is metabolized in the liver, making it the primary organ responsible for alcohol breakdown and elimination. The remaining 2-10% is excreted unchanged through urine, sweat, and breath (14). Cells outside the liver, such as neurons, astrocytes, gastrointestinal epithelial cells, lung cells, and immune cells, including monocytes and lymphocytes, can metabolize small amounts of alcohol using enzymes like cytochrome P450 (CYP2E1) and catalase. These extrahepatic pathways contribute to less than 10% of overall alcohol metabolism.

Alcohol metabolism primarily involves a two-step enzymatic process catalyzed by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), converting ethanol first into acetaldehyde and then into acetate. Later is further broken down into carbon dioxide and water. The liver plays a central role in clearing acetaldehyde, a highly reactive and carcinogenic intermediate (15). In chronic alcohol use, sustained acetaldehyde accumulation exposes hepatocytes to toxic concentrations. Blood acetaldehyde can transiently reach 10-20 µM in the portal circulation immediately after alcohol intake, while hepatic acetaldehyde concentrations may be 5–10 times higher (16). Exposing hepatocytes to such high levels is sufficient to induce protein adduct formation, oxidative stress, and DNA damage (17, 18).

In addition, chronic alcohol intake shifts metabolism toward CYP2E1 because ADH becomes saturated at higher alcohol levels. This leads to strong induction and stabilization of CYP2E1 in the liver and other tissues. The shift increases alcohol breakdown but also generates large amounts of reactive oxygen species (ROS), contributing to tissue damage during chronic drinking. The process is dynamic and reversible upon alcohol withdrawal. Factors such as alcohol-mediated induction of CYP2E1, ALDH2 deficiency, and impaired liver function can further elevate acetaldehyde levels and reduce its clearance.

Alcohol metabolism disrupts cellular homeostasis through interconnected mechanisms that impact multiple organelles and signaling pathways. Its toxic byproducts, acetaldehyde and malondialdehyde, react with proteins to form malondialdehyde-acetaldehyde (MAA) adducts. This distorts protein structure and impairs endoplasmic reticulum (ER) function. Acetaldehyde further compromises the ER by modifying chaperones and enzymes, interfering with disulfide bond formation and glycosylation, depleting glutathione, disturbing calcium signaling, and causing homocysteine accumulation (19–21). These combined disruptions overwhelm the ER protein-folding capacity, triggering the unfolded protein response (UPR) and promoting inflammation and apoptosis.

Alcohol and endogenous aldehydes also cause DNA double-strand breaks and chromosomal rearrangements in hematopoietic stem cells. These genetic damages compromise stem cell function, promote abnormal mutations, and increase the risk for cancer and blood disorders (18). Mitochondrial metabolism is similarly affected. Alcohol increases the NADH/NAD⁺ ratio, reduces ATP production, and disrupts fatty acid oxidation, leading to steatosis and mitochondrial injury (22, 23). The resulting redox imbalance and loss of antioxidant defenses heighten susceptibility to oxidative stress. Alcohol additionally activates stress pathways such as MAPK, NF-κB, and JNK, further driving inflammation and cell death (24, 25).

By weakening the intestinal barrier, alcohol allows bacterial lipopolysaccharide (LPS) to reach the liver and activate TLR4 signaling in Kupffer cells, amplifying hepatic inflammation (26, 27). In addition, alcohol directly activates Kupffer cells, monocytes, macrophages, and antigen-presenting cells, altering cytokine production and modulating T-cell responses (28–30). These collectively promote the immune dysregulation, persistent inflammation, and tissue injury characteristic of ALD.

In HBV-infected individuals, alcohol further enhances liver damage by promoting viral replication and impairing immune responses, which contributes to increased hepatitis activity. For example, studies from our lab and others show that alcohol increases HBV DNA and viral protein levels, correlating with higher ALT/AST and liver injury (31–33). This has been seen in both immunocompetent and immunocompromised HBV transgenic mouse models. In these models, alcohol-fed mice exhibit multiple-fold increases in HBV surface antigen (HBsAg), serum viral DNA, HBV RNA, and liver viral protein expression. This results in severe hepatic steatosis, liver injury, and eventually progresses to end-stage liver disease (31, 33, 34).

A key mechanism underlying this effect is that alcohol enhances HBV replication by stimulating the activity of the viral core and surface promoters. This effect is strongly amplified by CYP2E1-mediated oxidative stress, which increases transcription factor activity on these promoters. Importantly, this oxidative effect can be reversed by antioxidants such as glutathione (35). This underscores oxidative stress as a central driver in alcohol-induced augmentation of HBV replication, alongside alcohol metabolism impacts on immune impairment. In addition, alcohol can alter the lipid composition and function of lipid rafts. These rafts are specialized domains within hepatocyte membranes that are required for HBV entry, assembly, and release. Changes in lipid rafts enhance HBV entry into liver cells and may facilitate virus assembly and release, thereby indirectly increasing viral replication (36).

HBV promotes HCC through multiple mechanisms, including persistent inflammation, viral DNA integration, and epigenetic dysregulation (37). Viral proteins such as HBx and preS/S contribute to oxidative stress and activate oncogenic pathways. Alcohol exacerbates these effects by enhancing viral replication, liver damage, and fibrosis, collectively accelerating hepatocarcinogenesis. A key mechanism underlying this synergy involves alcohol-induced activation of LPLA2 via ATF4-dependent transcription, thereby elevating bis(monoacylglycero)phosphate (BMP) levels in tumors. LPLA2 is a lysosome-associated enzyme central to lipid metabolism. LPLA2 drives HCC cell proliferation by activating the MAPK/ERK signaling cascade, which is further strengthened by BMP synthase CLN5 and BMP supplementation.

Knockdown of LPLA2 or CLN5 markedly reduces alcohol-enhanced tumor growth. Clinically, high LPLA2 expression correlates with poor patient outcomes, underscoring the ATF4/LPLA2/BMP axis as a pivotal driver of alcohol-accelerated HBV-associated HCC (38). HBV proteins, including HBx and HBc, are most affected by alcohol metabolism, mediating many downstream effects linking alcohol use with worsened HBV-related liver disease. HBx aggravates alcohol-induced liver injury by increasing oxidative stress, lipid peroxidation, and harmful lipid changes (39). In HBx-transgenic mice, alcohol causes higher acetaldehyde levels and more severe steatohepatitis by allowing HBx to bind and degrade mitochondrial ALDH2, reducing acetaldehyde clearance. The resulting acetaldehyde buildup drives oxidative stress, toxic lipid production, and cancer risk (40).

Studies in both humans and mice indicate that ALDH2 deficiency leads to greater susceptibility to carcinogen-induced liver tumors. ALDH2 deficiency did not affect liver disease progression but increased HCC risk in cirrhotic HBV patients with AUD (41). Mechanistically, ALDH2-deficient hepatocytes produce large quantities of oxidized mitochondrial DNA, which are packaged into extracellular vesicles and transferred to neighboring cancer cells. Together with acetaldehyde, this activates several oncogenic pathways, including JNK, STAT3, BCL-2, and TAZ. These combined signals promote HCC development and progression (41).

Additionally, reduced ALDH2 expression in liver cancer tissues correlates with increased tumor growth, migration, and poor prognosis, and this deficiency disrupts cellular redox balance and metastatic potential (42–44). HBx also modulates microRNAs (including miR-187-5p and miR-3188), interferes with tumor suppressors, and stimulates stem-like properties via pathways such as Wnt/β-catenin and CXCR4. It enhances hepatocyte proliferation, migration, invasion, cytoskeletal remodeling, and lipid dysregulation, further promoting liver injury and carcinogenesis (45–48). By disrupting cell signaling, inhibiting DNA repair, altering gene expression, and reprogramming metabolism, HBx induces genomic instability, chronic inflammation, stemness, and abnormal lipid metabolism. This accelerates progression to cancer and can be particularly pronounced in CHB infection, where persistent viral protein expression and ongoing liver injury create a pro-oncogenic environment.

Accumulation of high levels of HBsAg adds another layer of oncogenic stress by inducing ER stress. This initially activates autophagy but eventually impairs its degradation phase. ER stress-related transcription factors ATF4 and ATF6 suppress LAMP2, essential for autophagosome-lysosome fusion, leading to impaired autophagic flux and cellular waste buildup. This sustains hepatocyte proliferation and advances HCC development (49). Furthermore, the HBV PreS1 protein promotes HCC by stimulating the emergence and self-renewal of liver cancer stem cells. It enhances cancer stem cell marker expression, promoting tumor growth and supporting a highly proliferative, drug-resistant cell population that drives cancer progression and recurrence (50).

Collectively, these findings highlight the synergistic harmful impact of alcohol and HBV on liver disease progression, consistent with epidemiological data showing higher HBV marker levels and worse liver outcomes, including cirrhosis and HCC, in alcoholic individuals with HBV infection.

Alcohol and acetaldehyde impair HBV antigen presentation by disrupting multiple steps of the MHC-I pathway in hepatocytes. Acetaldehyde reduces the surface display of HBV peptide-MHC-I complexes by suppressing proteasome activity, downregulating immunoproteasome subunits (LMP2, LMP7), and impairing peptide-loading components such as TAP1 and tapasin, while also inhibiting IFN-γ signaling (51–53). In parallel, chronic ethanol exposure in mice impairs dendritic cell presentation of exogenous antigens through MHC II and alters costimulatory profiles, leading to diminished antigen−specific T−cell activation despite largely preserved MHC I cross−presentation (54). Additionally, acetaldehyde-induced ER stress and Golgi fragmentation interfere with the trafficking of these complexes to the cell surface, further limiting recognition by CTLs (55, 56).

Efficient MHC I antigen display depends on intact anterograde ER-to-Golgi-to-plasma membrane transport of peptide-loaded complexes (57). In alcohol-exposed hepatocytes, acetaldehyde-driven ER stress and Golgi fragmentation impair this secretory pathway, leading to intracellular retention of MHC I complexes within the ER, ER-Golgi intermediate compartment (ERGIC), or fragmented Golgi (55, 58–60). This trafficking blockade directly reduces surface presentation of HBV peptide-MHC I complexes, as demonstrated in HBV models in which acetaldehyde selectively suppresses MHC I surface expression through organelle dysfunction. Alcohol metabolism also diminishes proteasomal and aminopeptidase activity, reducing peptide generation required for MHC-I loading (61). Collectively, these mechanisms compromise antigen processing, presentation, and immune recognition of HBV-infected hepatocytes, promoting viral persistence and immune evasion.

Alcohol impairs immune recognition of HBV-infected hepatocytes by reducing their ability to present CTL epitopes. Clinical studies in HBV-positive patients with alcohol use show distinct immune alterations depending on disease stage. In compensated cirrhosis, T cells display both activation and exhaustion markers, accompanied by reduced cytokine production. In decompensated cirrhosis, CD8⁺ T cell numbers are decreased, CD4/CD8 ratios are altered, and T cell proliferation increases, but activation and exhaustion markers are lost. These changes occur within a highly inflammatory environment. Similar immune defects are observed in alcohol-related cirrhosis, including depletion and functional impairment of MAIT (mucosal-associated invariant T) cells and elevated soluble immune checkpoint molecules, such as sTIM-3 (62). Together, these alterations contribute to weakened antiviral immunity and create a permissive environment for viral persistence.

In our study, we utilized fumarylacetoacetate hydrolase (Fah)-/-, Rag2-/-, common cytokine receptor gamma chain knock-out (FRG-KO) humanized mice engrafted with HLA-A2-positive hepatocytes. Alcohol feeding resulted in decreased presentation of the HBV core 18–27 epitope bound to HLA-A2 on infected hepatocytes. This reduction stemmed from alcohol-induced suppression of proteasome activity and ER stress, which collectively impaired HBV peptide processing and inhibited trafficking of HBV-MHC-I complexes to the cell surface. The resulting attenuation of MHC class I-restricted antigen presentation weakened CTL-mediated cytotoxicity against infected hepatocytes, facilitating viral persistence and progression to end-stage liver disease (63).

Chronic alcohol exposure also disrupts hepatic lipid metabolism during HBV infection. This occurs through activation of the HBx/SWELL1/arachidonic acid signaling axis, with HBx and SWELL1 upstream and arachidonic acid as a downstream effector. Activation of this pathway disturbs lipid synthesis and breakdown, causing abnormal lipid accumulation and metabolic dysfunction in hepatocytes (64). HBx further contributes to hepatocarcinogenesis by modulating genes involved in arachidonic acid metabolism (65). Additionally, alcohol and HBV co-exposure enhances regulatory T-cell (Treg) activation in HBV-transgenic mice, leading to immunosuppression that further limits the clearance of infected hepatocytes (64).

CHB is also characterized by T-cell exhaustion, which is worsened by alcohol and includes up-regulation of PD-1, CTLA-4, and TIM-3 (66), impaired mitochondrial function in T cells (23, 67), and impaired antigen-presenting function of dendritic and Kupffer cells (68–70). This promotes the persistence of HBV-infection, development of end-stage liver diseases, including HCC. Even moderate drinking increases the risk of HCC progression.

Paradoxically, controlled low-dose alcohol exposure enhances dendritic cell (DC) maturation and exosome-driven T-cell activation in CHB, countering typical immunosuppression. In vitro alcohol treatment of DCs from HBV patients and transgenic mice upregulates costimulatory molecules (CD80/CD86), MHC, and T-cell priming cytokines, restoring functional DC responses. Moreover, exosomes from these alcohol-conditioned DCs boost HBV-specific CD8⁺ and CD4⁺ T-cell proliferation and effector function in vivo, challenging the notion of alcohol as solely detrimental by revealing context- and dose-dependent immunostimulatory effects (71).

Collectively, these findings indicate that chronic or high-dose alcohol consumption profoundly impairs antigen presentation, CTL function, and immune-metabolic homeostasis in the liver, thereby promoting viral persistence, immune evasion, and metabolic stress. These combined effects create a permissive environment for progressive liver disease and increase the risk of HBV-associated HCC.

Alcohol reduces both the number and function of intrahepatic B cells, thereby decreasing antibody production against HBV antigens. This impairment of B-cell-mediated immunity delays viral clearance and promotes CHB infection. Mechanistically, alcohol increases Fas expression on intrahepatic B220⁺ and CD138⁺ B cells and stimulates production of immunosuppressive cytokines, including TGF-β and IL-10, by CD19⁺ B cells. Alcohol also decreases intrahepatic T peripheral helper (Tph) cells and T follicular helper (Tfh) cells, lowers IL-21 production by Tfh-like and CD8⁺PD-1⁺ cells, and reduces splenic germinal center B cell areas. Since Tph and Tfh cells support B cell differentiation and antibody production, their reduction impairs humoral immune responses, further hindering HBV clearance (72).

NK cells are key innate immune effectors in HBV infection, where they control viral replication through cytolysis, degranulation, and secretion of antiviral cytokines such as IFN-γ and TNF-α (73, 74). These early NK-driven responses help limit HBV spread but can also cause liver injury by killing infected hepatocytes through Fas/FasL and TRAIL pathways (74). In CHB infection, NK cells exhibit a dual role: they continue to suppress viral replication through non-cytolytic mechanisms, yet their heightened cytotoxicity contributes to inflammation, fibrosis, and progressive liver damage (75, 76).

Alcohol exposure further disrupts NK cell function in HBV-infected livers. Alcohol reduces NK antiviral activity, alters activating receptor expression, and creates an immunosuppressive cytokine environment that weakens early HBV clearance (77, 78). At the same time, alcohol can drive inappropriate NK activation that worsens liver injury. In HBV-carrier mouse models, alcohol-exposed NK cells suppress CD8⁺ T-cell antiviral responses, promoting T-cell dysfunction and delayed viral control. NK-cell depletion restores this CD8⁺ T-cell activity (79). Alcohol amplifies NK-cell immune dysregulation by weakening their antiviral activity while enhancing their tissue-damaging responses. This dual effect accelerates HBV persistence and worsens liver disease progression.

Macrophages sense HBV infection mainly through pattern recognition receptors (PRRs) such as TLR4, TLR2, and other DNA sensors like cGAS-STING that detect viral components, HBV DNA, HBsAg, and core proteins (80). The recognition of HBV by these receptors activates downstream signaling pathways, including the NF-κB and JAK-STAT pathways. NF-κB promotes the transcription of pro-inflammatory cytokines (IL-1β, TNF-α). At the same time, the JAK-STAT pathway, triggered by interferons, induces interferon-stimulated genes (ISGs) with antiviral effects. These processes allow macrophages to initiate innate immune responses against HBV (80, 81). In our study, IFN-α-activated macrophages suppressed HBV replication in hepatocytes by decreasing HBV RNA, DNA, and cccDNA levels via induction of ISGs such as APOBEC3G, ISG15, and OAS1. Alcohol disrupts this protective communication between macrophages and hepatocytes, inhibiting ISG induction and increasing HBV replication, which weakens innate antiviral immunity (33).

Recent single-cell RNA sequencing (scRNA-seq) studies have further clarified macrophage heterogeneity and functional states in the context of HBV infection and alcohol exposure. Comparative single-cell analyses of liver immune cells from patients with alcoholic liver cirrhosis (ALC) and HBV-related cirrhosis (HBV-LC) reveal etiology-specific macrophage and broader immune programs. In ALC, intrahepatic monocytes/macrophages are markedly expanded while adaptive immune cells, particularly B and plasma cells, are reduced and metabolically altered, consistent with alcohol-driven myeloid dominance and impaired humoral immunity. In HBV-LC, macrophages are relatively less expanded and appear functionally distinct, with immune profiles more compatible with chronic virus-driven activation rather than the pronounced innate skewing observed in ALC (82). Despite their central role in immune sensing, cytokine production, and hepatocyte communication, few studies have directly examined the combined effects of alcohol, hepatic macrophages, and HBV, limiting mechanistic understanding of how alcohol accelerates viral persistence and disease progression.

More broadly, chronic alcohol exposure reshapes hepatic macrophage populations by promoting the recruitment of bone marrow-derived monocytes, resulting in a mix of resident Kupffer cells and infiltrating macrophages. These macrophages can adopt pro-inflammatory M1-like states that worsen liver injury or shift toward M2-like repair phenotypes (83–85). Alcohol-induced gut permeability further raises LPS levels and activates macrophages through TLR4. This activation leads to the production of inflammatory cytokines such as TNF-α and IL-1β, which contribute to liver inflammation and fibrosis (86). Hepatocyte-macrophage crosstalk also amplifies alcohol-related inflammation. Alcohol stimulates macrophage activation via caspase-dependent release of CD40L-containing extracellular vesicles (EVs) from hepatocytes, which promotes inflammation and contributes to ALD (87).

Additionally, macrophage-derived MLKL supports phagocytosis, aiding bacterial clearance and controlling liver inflammation. In ALD, loss or dysfunction of MLKL in macrophages impairs this protective function, leading to heightened inflammation, tissue damage, and worsened outcomes (88). Chemical models of HCC have demonstrated a direct link between alcohol consumption, macrophage activation, and increased HCC risk. For example, chronic alcohol feeding in diethylnitrosamine (DEN)-induced HCC mice leads to reduced antitumor CD8+ T cells and an increase in tumor-associated macrophages (TAMs), which tend to polarize toward the M2 phenotype after alcohol exposure (89).

This M2 polarization is associated with increased fibrosis and epithelial-mesenchymal transition (EMT), creating a pro-tumor microenvironment that promotes tumor growth. Moreover, alcohol consumption induces macrophages to produce IL-6 via a PRMT1-dependent mechanism, which activates STAT3 signaling in hepatocytes and drives tumor progression. PRMT1, a key enzyme mediating arginine methylation, influences macrophage polarization toward the M2 anti-inflammatory phenotype that supports liver tumor promotion (90). Together, these findings highlight how alcohol modulates macrophage functions at multiple levels to exacerbate liver disease and HCC development.

While direct evidence linking alcohol, macrophage dysfunction, and HBV-driven HCC remains limited, alcohol-induced macrophage activation and altered cytokine production likely exacerbate HBV persistence and liver injury. Evidence from alcohol-related and chemical HCC models suggests that alcohol may polarize macrophages toward a pro-tumorigenic M2-like phenotype. This suppresses antiviral immunity and promotes a liver microenvironment that enhances HBV persistence and hepatocarcinogenesis, accelerating both liver disease and tumor progression. Figure 1 summarizes the effects of alcohol on HBV-mediated liver damage and HCC.