Liver cirrhosis and immune dysfunction

Abstract

Cirrhosis is end-stage liver disease resulting from various etiologies and is a common cause of death worldwide. The progression from compensated to decompensated cirrhosis to acute-on-chronic liver failure (ACLF) is due to multiple factors, including continuation of alcohol use or continued exposure to other toxins, an imbalance of the gut microbiota (dysbiosis), increased gut permeability and a disrupted immune response. This disrupted immune response is also named cirrhosis-associated immune dysfunction, which is characterized by worsening systemic inflammation with concomitant immune paralysis, as liver disease deteriorates. This review highlights central immunologic events during the exacerbation of cirrhosis and characterizes the different immune cell populations involved therein.

Graphical Abstract

Graphical Abstract.

Introduction

Cirrhosis is currently the eleventh most common cause of death globally, accounting for 2 million deaths per year with an estimated 3.5% of global mortality (1–3). It is the seventh most common cause of disability-associated life-years, or life-years lost due to premature mortality and reduced health (4), in people aged 50–74 years, the twelfth top etiology in the 25–49-year age range, and the sixteenth top cause across all ages (5, 6). Alcohol-associated liver disease (7), chronic viral hepatitis (8) and metabolic-associated fatty liver disease/nonalcoholic fatty liver disease (MAFLD/NAFLD) (9) are the most common causes of cirrhosis worldwide.

Cirrhosis is a progressive and dynamic chronic liver disease; it is the end-stage manifestation of hepatic fibrosis in the setting of chronic liver inflammation, characterized by the formation of regenerative hepatic nodules, separated by fibrotic septa and associated with major distortion in vascular architecture (3, 10). Studies have demonstrated that cirrhosis is no longer considered an irreversible progressive disease, if the cause of the disease is removed (11–13). Cirrhosis is associated with multiple gastrointestinal abnormalities, including impaired bile flow, intestinal dysmotility, altered gastric pH and intestinal innate immune response, and gut microbiome dysbiosis (14–16). Intestinal dysbiosis is defined as a microbial imbalance with its associated deleterious effects on the colonized host (14, 17). However, it is also considered a systemic disease, as it affects most organ systems of the body, including the immune system (18).

In this review, we will describe immunopathologic mechanisms associated with cirrhosis, decompensation of cirrhosis and acute-on-chronic liver failure (ACLF).

Liver decompensation and ACLF

Cirrhosis oftentimes starts with an asymptomatic stage, known as compensated cirrhosis, which can last for multiple years, before it progresses to advanced, decompensated cirrhosis (19). It is estimated that 5–7% of patients with compensated cirrhosis progress to decompensated cirrhosis per year (20). Decompensated cirrhosis is defined as an acute deterioration in liver function in a patient with cirrhosis, including the new onset of portal hypertension, ascites (that is, the accumulation of large amounts of fluid within the peritoneal cavity), variceal hemorrhage, hepatic encephalopathy and jaundice among other symptoms (21, 22).

An acute precipitating event (hepatic or extrahepatic) can occur at any time from compensated to decompensated stages, such as bacterial infection or active alcoholism that may challenge liver homeostasis, producing a life-threatening syndrome called ACLF (23, 24). ACLF is a severe syndrome of acutely decompensated cirrhosis and is characterized by the presence of organ system dysfunction and failures in one or more major organ systems including the liver, kidneys, brain, coagulation, circulation and respiratory system (23, 24). Organ failure is the feature that differentiates ACLF from decompensated cirrhosis without ACLF; the most affected organs are liver and kidney, resulting in high short-term mortality (23, 24). Similar to decompensated cirrhosis, ACLF is characterized by the presence of systemic inflammation, although even more severe, which is associated with higher mortality (25).

Cirrhosis-associated immune dysfunction syndrome

Cirrhosis and ACLF are associated with moderate and severe systemic inflammation, respectively, with increased inflammatory cytokines, oxidative stress, and markers of activated neutrophils and macrophages in the blood and in the liver (19, 23, 26, 27). Translocation of bacterial products from the gut into the bloodstream secondary to intestinal dysbiosis, increased intestinal permeability and impaired gut immunity promotes systemic inflammation (14–16, 26, 28). Inflammatory markers can have predictive implications in this setting; the magnitude of the white blood count predicts the development of ACLF, ACLF progression and related mortality (23, 27, 29); the neutrophil to lymphocyte ratio predicts short-term mortality (30); and procalcitonin (31–34) and C-reactive protein (CRP) (23, 31, 32, 34–36) predict infection and short-term mortality in decompensated cirrhotic patients. Although systemic inflammation occurs in liver cirrhosis, an “immune paralysis” or immune deficiency is often observed, a clinical state that has been called cirrhosis-associated immune dysfunction syndrome (18, 37). The intensity of cirrhosis-associated immune dysfunction correlates with the severity of liver insufficiency, bacterial translocation and organ failure (37).

When cirrhosis progresses from compensated to decompensated stages to ACLF, systemic inflammation and cirrhosis-associated immune dysfunction with immune deficiency worsen (Fig. 1): while inflammatory cytokines, such as tumor necrosis factor (TNF), interleukin 6 (IL6), IL8, macrophage chemotactic protein 1 [MCP1, also known as C–C motif chemokine ligand 2 (CCL2)], macrophage inflammatory protein 1 beta (MIP1B, also known as CCL4), interferon gamma-inducible protein 10 [IP-10, also known as C–X–C motif chemokine ligand 10 (CXCL10)] and granulocyte colony-stimulating factor (GCSF) (25, 38–40), successively increase during that sequence; a few anti-inflammatory cytokines, including IL10 and the IL1-receptor antagonist (IL1RN), also increase (25, 39). Immune deficiency is characterized by decreased neutrophilic phagocytosis and increased respiratory burst in decompensated cirrhosis (41–44) and ACLF (45, 46). Phagocytosis (47) and superoxide production by monocytes (48) are decreased in cirrhosis and deteriorate with severity of cirrhosis. Monocytic human leukocyte antigen-DR (HLA-DR) expression and ex vivo TNF production are increased in decompensated cirrhosis (49), whereas both are reduced in ACLF (39, 50, 51).

Fig. 1.

Progression of cirrhosis-associated immune dysfunction during deterioration of cirrhosis. Cirrhosis-associated immune dysfunction worsens with more-severe systemic inflammation and immune deficiency, while cirrhosis progresses from compensated to decompensated stages to ACLF. Worsening of cirrhosis-associated immune dysfunction is expressed by increasing acute-phase proteins, such as CRP; increasing inflammatory cytokines, i.e. TNF, IL6, IL8, MCP1 (CCL2), MIP1B (CCL4), IP-10 (CXCL10) and GCSF; increasing anti-inflammatory cytokines, including IL10 and IL1RN; decreased phagocytosis and increased oxidative burst by neutrophils; decreased phagocytosis and superoxide production by monocytes, and increased monocytic HLA-DR expression and ex vivo TNF production in decompensated cirrhosis, which are decreased in ACLF. Created with a license from Biorender.com.

Infections in cirrhosis including spontaneous bacterial peritonitis

Ascites (derived from askos, Greek, meaning “bag” or “sack” (52)), is the most common complication of decompensated cirrhosis with more than 50% of patients developing ascites within 10 years of diagnosis (53, 54). It is associated with a poor 5-year survival of 56.5% (55), which is oftentimes due to an infectious etiology, including spontaneous bacterial peritonitis (55), urinary tract infection, pneumonia (56) or fungal infections (57). Cirrhosis-associated immune dysfunction allows life-threatening infections in this clinical context (37). Spontaneous bacterial peritonitis is the most frequent infection in cirrhotic patients with ascites, traditionally diagnosed by diagnostic paracentesis, identifying an ascitic fluid polymorphonuclear cell count ≥ 250 cells per mm³ (58, 59), and it is associated with a high 1-year mortality rate of over 80% (59). Interestingly, a polymorphonuclear cell count ≥ 125 cells per mm³ has been found to have a similar 1-year mortality rate with only 25% of the patients surviving (59). Urinary tract infection is the second most common bacterial infection in cirrhosis after spontaneous bacterial peritonitis (56).

An important event in disease progression in cirrhosis is bacterial translocation, which is defined as the migration of viable bacteria or bacterial products from the intestinal lumen to mesenteric lymph nodes or other extraintestinal organs and sites (60, 61). Factors leading to increased bacterial translocation in cirrhotic patients are intestinal bacterial overgrowth, deficiencies in host immune defenses and increased permeability or damage to the intestinal mucosal barrier (61, 62). Additionally, gene polymorphisms in toll-like receptor 2 (TLR2) and nucleotide oligomerization domain 2 (NOD2) have been linked to bacterial translocation and spontaneous bacterial peritonitis (63–65). Further, the microbiome is profoundly distorted in cirrhosis, which is partly secondary to altered motility of the small bowel (66, 67), changed bile acid metabolism (68, 69), reduced bile flow (14, 70) and widespread proton-pump inhibitor usage (14, 71). Patients with liver disease and in particular cirrhosis also experience fungal dysbiosis with increased fungal products in the systemic circulation (72–75). Use of antibiotics and proton-pump inhibitors is a risk factor for fungal dysbiosis in cirrhosis (76). One of the fungal infections in patients with cirrhosis is spontaneous fungal peritonitis (57), which has a 1-month mortality rate in the range 50–73% (77–79). Microbiome-based interventions to improve dysbiosis and disease burden have been recently reviewed in various liver diseases including cirrhosis (80).

Intestinal and hepatic firewalls

The mesenteric lymph nodes contribute to the intestinal firewall as the first line of defense against invading gut microbes; the liver is a vascular firewall and second firewall that captures microbes translocated from the gut into portal circulation (81). In particular, resident liver macrophages, or Kupffer cells, phagocytose and clear translocated microbes in the liver independently from the spleen (81).

In cirrhosis, intestinal permeability and bacterial translocation are increased (82–84), which results in activation of intestinal immune cells and intestinal inflammation (85–87). Intestinal inflammation can further contribute to intestinal permeability and bacterial translocation (88). With increasing bacterial translocation, the first intestinal firewall becomes overwhelmed and is not able to clear microbes. Bacteria and bacterial products such as lipopolysaccharides (LPS) or other microbial products enter the portal vein blood, and the second firewall in the liver becomes more important for clearance (81). In health, low amounts of LPS reach the liver enabling a tolerogenic environment (89). In (liver) disease, Kupffer cells effectively kill translocated bacteria and bacterial products, assisted by LPS-binding protein and TLR4 (the cellular LPS receptor) enhancing the uptake by Kupffer cells (90–92). However, if bacterial translocation worsens and persists, overwhelming both firewalls, liver inflammation induced by Kupffer cells and other immune cells develops, associated with hepatocyte death, and induction and progression of hepatic fibrosis by hepatic stellate cells (14, 15).

The features and mechanisms of various hepatic and systemic immune deficiencies commonly seen in cirrhosis and ACLF are summarized below (Table 1).

Table 1.

Mechanisms of immune deficiency in cirrhosis

Location		Mechanism		Results	Contributing Factors
Hepatic	Defective anti-infective protein production	↓ Pattern recognition receptors ↓ Complements and complement receptors	→	↓ Recognition ↓ Opsonization ↓ Clearing of pathogens and pathobionts	Genetics (such as polymorphisms)
		Immune cells
Systemic	Defective systemic immune cells	Neutrophils ↓ Cell count ↓ Phagocytosis ↑ Oxidative burst ↓ Chemotaxis	→	Ineffective killing of pathogens and pathobionts	Genetics, environmental factors (e.g. alcohol use)
		Monocytes ↑ Cell count ↓ Phagocytosis ↓ Superoxide production ↓ Chemotaxis	→	Ineffective killing of pathogens and pathobionts	Genetics, environmental factors (e.g. viruses, alcohol use)
		Natural killer cells ↓ Cell count ↓ Lysis	→	Ineffective killing of pathogens and pathobionts	Genetics, environmental factors (e.g. diet, smoking, alcohol use)
		B cells ↓ Cell count ↓ Immunoglobulin production	→	↓ Opsonization ↓ Killing ↓ Vaccine responsiveness	Genetics, environmental factors (e.g. alcohol use)
		T cells ↓ Cell count ↑ Apoptosis ↓ Proliferation	→	Ineffective killing of pathogens and pathobionts	Genetics, environmental factors (e.g. alcohol use)
Gut-associated lymphoid tissue	Defective intestinal immune cells	T cells, monocytes, dendritic cells ↑ Continuous activity ↑ Cytokine production ↑ Phagocytosis	→	↑ Gut inflammation ↑ Gut permeability ↑ Systemic inflammation	Genetics

Deficient hepatic immunity

Reduction of complement receptor of immunoglobulin on Kupffer cells

Complement receptor of immunoglobulin [CRIg, also known as V-set immunoglobulin-domain-containing 4 (VSIG4)] is expressed on Kupffer cells and binds directly to Gram-positive bacteria or binds to complement C3b to mediate phagocytosis (93–96). Patients with alcohol-associated liver disease or hepatitis have decreased expression of CRIg in their livers, and CRIg-deficient mice were found to have more-severe ethanol-induced liver disease compared with wild-type littermate mice (93). Further, CRIg-deficient mice were less efficient at clearing the Gram-positive bacterium Enterococcus faecalis in the liver after it translocated from the gut (93). Administration of the soluble immunoglobulin-like domain of CRIg (CRIg-Ig) ameliorates ethanol-induced liver disease in mice (93). In another study, CRIg/VSIG4 has been studied in spontaneous bacterial peritonitis: Peritoneal macrophage activation by infection with live bacteria in vitro resulted in a loss of surface VSIG4 and the release of soluble VSIG4 (97). A higher concentration of ascitic soluble VSIG4 has been found to indicate a higher 90-day mortality in spontaneous bacterial peritonitis (97). These findings indicate the important role of CRIg/VSIG4 in clearing translocated bacteria from the liver and preventing liver disease or spontaneous bacterial peritonitis, a mechanism that is deficient in patients with decompensated cirrhosis and alcohol-associated hepatitis. Furthermore, the overall reticuloendothelial system phagocytic activity, estimated by the plasma elimination rate constant of ^99mtechnetium-sulfur colloid, is a significant prognostic factor for patients with decompensated cirrhosis, with a decreased phagocytic activity being associated with more bacterial infections and worse survival (98).

Diminished production of other anti-infective proteins

Cirrhosis dampens the synthesis of other proteins involved in immunity, including the serum and ascitic levels of the complement components C3 and C4 and the total hemolytic component (CH₁₀₀), resulting in decreased opsonic activity and higher likelihood of spontaneous bacterial peritonitis and mortality (99–105). In contrast, alcoholic hepatitis patients have upregulated hepatic C1q and C5 mRNA expression (106). Polymorphisms of pattern-recognition receptors can play a major role as well in liver disease: the risk of severe infections and mortality after liver transplantation depend on polymorphisms and the resulting level of mannose-binding lectin, a recognition molecule of the lectin pathway of complement and a key component of innate immunity (107–111).

Deficient systemic immunity

Deficiency in neutrophils

Portal hypertension-induced splenic sequestration of blood cells, including immune cells (112), results in a numeric deficiency of neutrophils in cirrhosis. Neutrophils are functionally deficient with reduced phagocytosis and a defective oxidative burst with altered superoxide anion production and myeloperoxidase activity (41–46). Decreased chemotaxis reduces neutrophil function as well (42). Alcohol itself reduces neutrophil function further (113). Moreover, neutrophilic phagocytosis depends on genetics, as shown in chronic granulomatous disease (CGD), which can be due to various gene mutations, classically X-linked but also autosomal (114). Other conditions secondary to gene mutations can also display decreased neutrophil chemotaxis and superoxide anion production [e.g. Rac Family Small GTPase 2 (Rac2) mutation] (115).

Deficiency in monocytes

Monocytes are more numerous in cirrhosis because of an expansion of inflammatory CD14⁺CD16⁺ monocytes (116, 117). However, phagocytosis, superoxide production and chemotaxis are also defective in monocytes in cirrhosis, similar to neutrophils (47, 48, 104, 118–120). The function of monocyte Fc-gamma receptors is impaired in patients with cirrhosis, which likely contributes to a higher risk of bacterial infections in these patients (47). Contributing to this deficiency, ethanol decreases Fc-gamma receptor-dependent rosette formation by monocytes and their phagocytic capacity (121). HLA-DR expression and ex vivo TNF synthesis by monocytes are heightened in decompensated cirrhosis (49) but decreased in ACLF (39, 50, 51). Similarly, patients with immune-active chronic hepatitis B exhibit an expansion of inflammatory CD14⁺CD16⁺ monocytes that express higher levels of HLA-DR (122), which could enhance the findings above in the appropriate setting. The inflammatory cytokine CCL2 (MCP1) is a potent chemoattractant for monocytes and its serum level increases with severity of cirrhosis (25, 40). Of note, the AA genotype of CCL2 is a risk factor for development of spontaneous bacterial peritonitis (123).

Deficiency in natural killer cells

Natural killer cells show defective response to cytokines and decreased cytolytic activity in cirrhosis (124–126). Acute alcohol ingestion suppresses natural killer cell activity (127) and chronic alcohol use increases their activity, whereas patients with alcohol-related cirrhosis again show reduced natural killer cell activity (125). Another study demonstrated other environmental factors influence natural killer cell activity, including cigarette smoking, intake of green vegetables, meat, dairy products and soybeans (128). Natural killer cells exhibit antifibrotic properties by killing hepatic stellate cells involving various mechanisms, including TNF-related apoptosis-inducing ligand (TRAIL), Fas ligand and the natural killer cell receptors NKG2D and NKp46. This antifibrotic activity is inversely correlated with fibrosis stage (129–131). Mutations related to NKG2D and NKp46 were shown to modulate natural killer cell activity (132, 133).

Deficiency in B lymphocytes

The B cell population is markedly reduced in cirrhosis (134–137). This includes an important subset, CD27⁺ memory B cells, which also shows impaired inflammatory function and ability to synthesize immunoglobulins, resulting in low vaccine responsiveness and higher susceptibility to bacterial infections (137). Alcohol might contribute to the B cell phenotype as well at least partially, since patients with alcohol use disorder exhibit similar findings with reduced B cell counts (138, 139) with abnormal maturation, diminished antigen-specific antibody responses (140) but overall increased total IgA, IgG, and IgM (139, 141). Various gene mutations can arrest B cell maturation resulting in agammaglobulinemia including mutations in Bruton’s tyrosine kinase (Btk) (142), severely affecting the function of B cells.

Deficiency in T lymphocytes

T cell lymphopenia, including CD4⁺ and CD8⁺ T cells, is frequently observed in cirrhosis (49, 143–145). Both activated CD4⁺ and CD8⁺ T cells exhibit higher expression of apoptosis markers (146). Circulating T cells also show reduced proliferative function (147, 148). Similarly, ethanol decreases cell counts and increases apoptosis of thymocytes (149) and T cells (150, 151). Single nucleotide polymorphisms (SNPs) of multiple genes, including CD28, CD86, and cytotoxic T lymphocyte associated protein 4 (CTLA4) can modulate T cell activation (152).

Deficient gut-associated lymphoid tissue immunity

The gut-associated lymphoid tissue forms the barrier for defense against pathogens from the gut (61). It comprises multi-follicular Peyer’s patches, the vermiform appendix and the numerous isolated lymphoid follicles (153). In cirrhosis, the gut-associated lymphoid tissue is highly active secondary to sustained bacterial translocation from the gut related to increased gut permeability (85). This increased activity is evident from increased numbers of activated T cells, monocytes and dendritic cells in the lamina propria and in mesenteric lymph nodes (85–87). This results in increased cytokine expression and phagocytosis locally (85–87). Interestingly, non-absorbable antibiotics have been shown to reduce this inflammation, which also indicates the role of intestinal dysbiosis in that pathologic process (85–87). Alcohol can also decrease the total number of lymphocytes, B cells, T cells, and macrophages in the intestinal lamina propria and mesenteric lymph nodes (154–156). Intestinal inflammation promotes the worsening systemic inflammation during the progression of cirrhosis (49, 86). Moreover, there is evidence that intestinal inflammation alters intestinal tight-junction protein expression and barrier function in compensated and decompensated cirrhosis (82–84). Gut dysbiosis and bacterial translocation are also facilitated by depressed expression of antimicrobial peptides, including regenerating islet-derived 3 beta (Reg3b) and gamma (Reg3g) (157–159).

Potential targets for cirrhosis-associated immune dysfunction and clinical trials

Treatment of cirrhosis-associated immune dysfunction has to be nuanced, since blunt suppression of systemic inflammation alone might put patients with cirrhosis-associated immune dysfunction at higher risk of bacterial infections, which is a frequent contributor to mortality in patients with compensated and decompensated cirrhosis, and ACLF (160). It is hence important to attempt modulating cirrhosis-associated immune dysfunction in more subtle ways (Fig. 2).

Fig. 2.

Targets to ameliorate cirrhosis and cirrhosis-associated immune dysfunction. Dysbiosis and bacterial translocation, aberrant circulating blood factors and immune cell abnormalities contribute to the pathogenesis and deterioration of cirrhosis and cirrhosis-associated immune dysfunction. Dysbiosis, intestinal inflammation and bacterial translocation can be reduced by antibiotics (e.g. norfloxacin) and fecal microbiota transplant. Yaq-001, a novel carbon absorbent that can absorb LPS and inflammatory cytokines, and TAK-242, an inhibitor of the important LPS receptor TLR4, are currently being evaluated in clinical studies for their use in cirrhosis and ACLF. Elevated circulating factors in the blood, including LPS and other microbial products, prostaglandins, reactive oxygen species (ROS), cytokines and catecholamines, worsen systemic inflammation and cirrhosis. Administration of albumin ameliorates inflammation and cirrhosis by binding these mediators. Liver dialysis devices and plasma exchange strategies remove noxious agents. Cyclooxygenase inhibitors reduce prostaglandin levels and beta-blockers attenuate the effects of catecholamines, improving systemic inflammation and the liver phenotype. Hematopoietic and mesenchymal stem cells as well as a variety of immune cells are markedly decreased and the immune cells do not function properly, worsening systemic inflammation. Administration of GCSF has shown promise in some studies, however it did not show a benefit in others. Infusions with stem cells and progenitor cells have shown beneficial immunomodulatory effects and improved outcome in cirrhosis and ACLF. Thrombopoietin receptor agonists are currently being investigated in clinical studies to improve thrombocytopenia in patients with ACLF. Created with a license from Biorender.com.

Microbiome and bacterial translocation

The microbiome and bacterial translocation play a central role in the pathogenesis of cirrhosis-associated immune dysfunction, and intestinal dysbiosis with its associated intestinal inflammation can be ameliorated with non-absorbable antibiotics (85–87). Clinical trials demonstrated the beneficial use of antibiotics in preventing decompensation of cirrhosis. Prophylactic norfloxacin significantly decreases bacterial infections in cirrhotics with ascites (161), 6-months mortality in patients with advanced cirrhosis (162), as well as recurrence of spontaneous bacterial peritonitis in patients with cirrhosis (163). On the other hand, long-term norfloxacin prophylaxis was independently associated with the development of multidrug-resistant bacterial infections in cirrhotics (164), which is an important cause of mortality in patients with cirrhosis and ACLF (165). Other antibiotics are currently being studied in this setting, including co-trimoxazole as primary prophylaxis for spontaneous bacterial peritonitis to improve overall survival in cirrhotics in a phase 3 clinical trial (NCT04395365) and the combination of rifaximin and simvastatin in patients with decompensated cirrhosis to prevent ACLF development and reduce complications and mortality in a phase 3 clinical trial (NCT03780673). Modulation of the intestinal microbiome via fecal microbiota transplantation is beneficial: significantly more patients with severe alcoholic hepatitis were alive at 3 months after receiving a fecal microbiota transplant daily for 7 days compared with patients who received steroids, pentoxifylline or nutrition only (166). The benefit of the fecal microbiota transplant was still present at 3 years compared with standard of care (P = 0.05) with significantly fewer episodes of ascites and infections (167). A similar study is currently ongoing comparing fecal microbiota transplant plus plasma exchange plus tenofovir vs tenofovir only in hepatitis B virus-related ACLF (NCT04431375). Yaq-001 is a novel synthetic carbon that can absorb bacterial products such as LPS and inflammatory cytokines, and is currently being evaluated in a phase 2 clinical trial in cirrhotics with ascites (NCT03202498). TAK-242 is an inhibitor of TLR4, an important cellular LPS receptor on Kupffer cells and other myeloid cells (90), and is currently being assessed in patients with ACLF with regard to its impact on ACLF severity, mortality, and safety (NCT04620148).

Circulating blood factors

Besides LPS, various other blood factors are known to be increased in (advanced) cirrhotics including prostaglandins (168), inflammatory markers, and catecholamines (169), which might exacerbate immune dysfunction. Multiple studies showed that albumin treatment improved mortality in cirrhotic patients with spontaneous bacterial peritonitis (170) and cirrhotic patients with ascites (171), likely due to its capacity to bind LPS and other bacterial products (lipoteichoic acid and peptidoglycan), reactive oxygen species, nitric oxide and other nitrogen reactive species, and prostaglandins (26, 168). Albumin administration is currently being evaluated in a clinical trial for volume resuscitation in cirrhosis with sepsis-induced hypotension (NCT05059795). A liver dialysis device termed DIALIVE removes albumin-toxin complexes, repletes albumin levels, and removes LPS from the circulation, and has been found to reduce mortality secondary to acetaminophen-induced acute liver failure by 67% (172). Its safety and performance in ACLF are currently being investigated in a clinical trial (NCT03065699). A phase 3 trial is enrolling patients with cirrhosis and ACLF to compare plasma exchange with albumin infusion vs standard of care for short-term survival (NCT03702920). Various other liver dialysis/plasma exchange systems are currently studied in clinical trials (NCT04597164, NCT04195282). Cyclooxygenase-derived eicosanoid prostaglandin E2 drives immunosuppression in patients with acute decompensation of cirrhosis, and treatment with cyclooxygenase inhibitors or albumin restored immune competence and survival following infection with group B Streptococcus in mouse models of cirrhosis (168). Further, a cyclooxygenase-2 inhibitor was found to reduce liver stiffness in pediatric chronic liver disease patients following Kasai portoenterostomy for biliary atresia (173), but no studies involving adult patients with cirrhosis or ACLF evaluating cyclooxygenase inhibitors have been carried out to date. Blood noradrenaline and adrenaline levels are significantly elevated in cirrhotics compared with controls (169). Moreover, noradrenaline levels are higher in ACLF than in acute decompensation and they are higher in acute decompensation than in stable cirrhosis (27). Its levels correlate with inflammatory markers and are highly predictive of 3-month mortality with an area under the receiver operating characteristic curve (AUROC) of 0.91 (27). Interestingly, a retrospective study involving 349 patients showed that use of nonselective beta-blockers decreases systemic inflammation and mortality in ACLF (174). These findings were confirmed in a recent prospective study that showed beta-blockers significantly improve 28-day mortality with lower incidence of acute kidney failure and spontaneous bacterial peritonitis in ACLF, although there was no difference of these measures at 90 days between treatment and placebo groups (175). A similar study about beta-blockers in patients with cirrhosis and uncomplicated ascites is currently ongoing (NCT05057572).

Blood cells

The bone marrow of patients with more advanced cirrhosis (Model of End-Stage Liver Disease, or MELD scores > 15) is markedly abnormal with significantly decreased CD34⁺ hematopoietic stem cells and mesenchymal stem cells and increased inflammatory markers such as IL1b and TNF compared with cirrhotics with a MELD score ≤ 15 (176). Administration of GCSF has improved mobilization of CD34⁺ cells, survival, liver stiffness/MELD scores, and infections/sepsis in clinical trials with patients with decompensated cirrhosis (177) and ACLF (178). However, a recent multicenter trial did not show a benefit of GCSF treatment for 90-day transplant-free survival and 360-day transplant-free and overall survival nor was there a difference regarding infection rate when compared with placebo (179). Stem cell infusions have shown promise in ACLF: umbilical cord-derived mesenchymal stem cell infusions every 4 weeks for three times increased survival at 72 weeks and decreased MELD scores, alanine aminotransferase, and total bilirubin levels at 48 weeks in hepatitis B virus-associated ACLF compared with patients who received saline infusions (180). In a similar study, weekly infusions of allogeneic bone marrow-derived mesenchymal stem cells for 4 weeks resulted in significantly lower mortality, MELD scores, and severe infections in hepatitis B virus-associated ACLF compared with standard of care (181). Human allogeneic liver-derived progenitor cells (HALPC) are derived from the parenchymal fraction of healthy human liver tissue and have a liver-specific homing capacity after peripheral intravenous infusion (182). They possess immunomodulatory and antifibrotic properties and were found safe in a recent pilot study in acute decompensation of cirrhosis and ACLF (182, 183). They are currently being evaluated in a phase 2b clinical trial in ACLF patients (NCT04229901). To address the thrombocytopenia frequently observed in advanced liver disease, avatrombopag, a thrombopoietin receptor agonist, is currently being investigated in a phase 4 clinical trial in patients with hepatitis B virus-related ACLF receiving double plasma molecular adsorption system and low volume plasma exchange (NCT05382013).

Conclusions

Multiple factors contribute to the progression of liver disease to compensated, decompensated cirrhosis, and ACLF. A hallmark of this progression is cirrhosis-associated immune dysfunction, characterized by worsening systemic inflammation and immune paralysis, which enables life-threatening infections. Future interventions to thwart this progression should be trialed at different levels, including the gut microbiome, the intestinal barrier, as well as intestinal, hepatic and systemic immune cells among others.

Funding

This work was supported in part by National Institutes of Health (NIH) grant K12 HD85036, University of California San Diego Altman Clinical and Translational Research Institute (ACTRI)/NIH grant KL2TR001444, Pinnacle Research Award in Liver Diseases Grant #PNC22-159963 from the American Association for the Study of Liver Diseases Foundation (to P.H.), NIH grants R01 AA24726, R01 AA020703, U01 AA026939, by Award Number BX004594 from the Biomedical Laboratory Research & Development Service of the VA Office of Research and Development, and a Biocodex Microbiota Foundation Grant (to B.S.) and services provided by NIH research center grants P30 DK120515 and P50 AA011999.

Author contributions

E.H. and P.H. were responsible for writing the manuscript, B.S. edited the manuscript.

Conflicts of interest statement:

B.S. has been consulting for Ambys Medicines, Ferring Research Institute, Gelesis, HOST Therabiomics, Intercept Pharmaceuticals, Mabwell Therapeutics, Patara Pharmaceuticals and Takeda. B.S.’s institution UC San Diego has received grant support from Artizan Biosciences, Axial Biotherapeutics, BiomX, CymaBay Therapeutics, NGM Biopharmaceuticals, Prodigy Biotech and Synlogic Operating Company. B.S. is founder of Nterica Bio.