In vivo consequences of liver-specific interleukin-22 expression in mice: Implications for human liver disease progression

Ambiguous roles of innate lymphoid cells in chronic development of liver diseases

Innate lymphoid cells (ILCs) are defined as a distinct arm of innate immunity. According to their profile of secreted cytokines and lineage-specific transcriptional factors, ILCs can be categorized into the following three groups: group 1 ILCs (including natural killer (NK) cells and ILC1s) are dependent on T-bet and can produce interferon-γ; group 2 ILCs (ILC2s) are dependent on GATA3 and can produce type 2 cytokines, including interleukin (IL)-5 and IL-13; and, group 3 ILCs (including lymphoid tissue-like cells and ILC3s) are dependent on RORγt and can produce IL-22 and IL-17. Collaborative with adaptive immunity, ILCs are highly reactive innate effectors that promptly orchestrate immunity, inflammation and tissue repair. Dysregulation of ILCs might result in inflammatory disorders. Evidence regarding the function of intrahepatic ILCs is emerging from longitudinal studies of inflammatory liver diseases wherein they exert both physiological and pathological functions, including immune homeostasis, defenses and surveillance. Their overall effect on the liver depends on the balance of their proinflammatory and antiinflammatory populations, specific microenvironment and stages of immune responses. Here, we review the current data about ILCs in chronic liver disease progression, to reveal their roles in different stages as well as to discuss their therapeutic potency as intervention targets.

The role of IL-22 in the resolution of sterile and nonsterile inflammation

In a broad sense, inflammation can be conveniently characterised by two phases: the first phase, which is a pro-inflammatory, has evolved to clear infection and/or injured tissue; and the second phase concerns regeneration of normal tissue and restitution of normal physiology. Innate immune cell-derived pro-inflammatory cytokines and chemokines activate and recruit nonresident immune cells to the site of infection, thereby amplifying the inflammatory responses to clear infection or injury. This phase is followed by a cytokine milieu that promotes tissue regeneration. There is no absolute temporal distinction between these two phases, and cytokines may have dual pleiotropic effects depending on the timing of release, inflammatory microenvironment or concentrations. IL-22 is a cytokine with reported pro- and anti-inflammatory roles; in this review, we contend that this protein has primarily a function in restitution of normal tissue and physiology.

Diverse effects of interleukin-22 on pancreatic diseases

Interleukin-22 (IL-22) is involved in the development of lymphocytes and serves as a rapid and early source of the effector cytokines that are released in response to pathogen-induced changes in the microenvironment. Recent research has implicated IL-22 as a potential contributing factor to the spectrum of inflammation-related pancreatic diseases, particularly pancreatitis, fibrosis, carcinoma and diabetes. In this review, we summarize the current knowledge on the roles of IL-22 in the various pancreatic pathogenesis, providing insights into the underlying cellular and signaling mechanisms that will help guide future research into promising interventional targets with therapeutic potential.

Role of nonresolving inflammation in hepatocellular carcinoma development and progression

Hepatocellular carcinoma (HCC) has become a leading cause of cancer-related death, making the elucidation of its underlying mechanisms an urgent priority. Inflammation is an adaptive response to infection and tissue injury under strict regulations. When the host regulatory machine runs out of control, nonresolving inflammation occurs. Nonresolving inflammation is a recognized hallmark of cancer that substantially contributes to the development and progression of HCC. The HCC-associated inflammation can be initiated and propagated by extrinsic pathways through activation of pattern-recognition receptors (PRRs) by pathogen-associated molecule patterns (PAMPs) derived from gut microflora or damage-associated molecule patterns (DAMPs) released from dying liver cells. The inflammation can also be orchestrated by the tumor itself through secreting factors that recruit inflammatory cells to the tumor favoring the buildup of a microenvironment. Accumulating datas from human and mouse models showed that inflammation promotes HCC development by promoting proliferative and survival signaling, inducing angiogenesis, evading immune surveillance, supporting cancer stem cells, activating invasion and metastasis as well as inducing genomic instability. Targeting inflammation may represent a promising avenue for the HCC treatment. Some inhibitors targeting inflammatory pathways have been developed and under different stages of clinical trials, and one (sorafenib) have been approved by FDA. However, as most of the data were obtained from animal models, and there is a big difference between human HCC and mouse HCC models, it is challenging on successful translation from bench to bedside.

Hepatic Immune System: Adaptations to Alcohol

Both the innate and adaptive immune systems are critical for the maintenance of healthy liver function. Immune activity maintains the tolerogenic capacity of the liver, modulates hepatocellular response to various stresses, and orchestrates appropriate cellular repair and turnover. However, in response to heavy, chronic alcohol exposure, the finely tuned balance of pro- and anti-inflammatory functions in the liver is disrupted, leading to a state of chronic inflammation in the liver. Over time, this non-resolving inflammatory response contributes to the progression of alcoholic liver disease (ALD). Here we review the contributions of the cellular components of the immune system to the progression of ALD, as well as the pathophysiological roles for soluble and circulating mediators of immunity, including cytokines, chemokines, complement, and extracellular vesicles, in ALD. Finally, we compare the role of the innate immune response in health and disease in the liver to our growing understanding of the role of neuroimmunity in the development and maintenance of a healthy central nervous system, as well as the progression of neuroinflammation.

A catch-22: Interleukin-22 and cancer

Barrier surfaces of multicellular organisms are in constant contact with the environment and infractions to the integrity of epithelial surfaces is likely a frequent event. Interestingly, components of the immune system, that can be activated by environmental compounds such as the microbiota or nutrients, are interspersed among epithelial cells or directly underlie the epithelium. It is now appreciated that immune cells continuously receive and integrate signals from the environment. Curiously, such continuous reception of stimulation does not normally trigger an inflammatory response but mediators produced by immune cells in response to such signals seem to rather promote barrier integrity and repair. The molecular mediators involved in this process are poorly understood. In recent years, the cytokine interleukin-22, produced mainly by group 3 innate lymphoid cells (ILCs), has been studied as a paradigm for how immune cells can control various aspects of epithelial cell function because expression of its receptor is restricted to non-hematopoietic cells. We will summarize here the diverse roles of IL-22 for the malignant transformation of epithelial cells, for tumor growth, wound healing and tissue repair. Furthermore, we will discuss IL-22 as a potential therapeutic target.

Dual roles of IL-22 at ischemia-reperfusion injury and acute rejection stages of rat allograft liver transplantation

Interleukin-22 (IL-22) is a recently identified regulator of inflammation, but little is known about its role in liver transplantation. Therefore, in this study, we explored the roles and the underlying mechanisms of IL-22 in acute allograft rejection by using a rat allogeneic liver transplantation model. Results showed that allograft liver transplantation led to damage of the parent liver and to significantly increased IL-22 expression in the allograft liver and plasma of the recipient rats compared with the rats who received isografts. Moreover, the significantly increased IL-22 expression was accompanied by markedly increased level of phospho-STAT3 in the allogeneic liver tissues after transplantation. Of note, neutralization of the IL-22 protein in recipient rats significantly worsened the function of the allograft liver at 1 day post-transplantation (ischemia-reperfusion injury, IRI) but improved the function at 7 days post-transplantation (acute rejection, AR). At IRI stage, IL-22 protected liver function through the increase of anti-apoptosis and pro-regeneration cytokines. However, IL-22 led to the increase of pro-inflammation factors at AR stage, accompanied by the marked increase of the Th17 and the marked decrease of Treg cells in allograft recipient rats through modulating the expression of chemokines for different cell types, which however were reversed by in vivo IL-22 neutralization. Results indicate the dual roles of IL-22 and suggest the differential potential clinical application of IL-22 at different stage of allograft liver transplantation.

A Protective Function of IL-22BP in Ischemia Reperfusion and Acetaminophen-Induced Liver Injury

Acute liver injury can be secondary to a variety of causes, including infections, intoxication, and ischemia. All of these insults induce hepatocyte death and subsequent inflammation, which can make acute liver injury a life-threatening event. IL-22 is a dual natured cytokine which has context-dependent protective and pathogenic properties during tissue damage. Accordingly, IL-22 was shown to promote liver regeneration upon acute liver damage. However, other studies suggest pathogenic properties of IL-22 during chronic liver injury. IL-22 binding protein (IL-22BP, IL-22Ra2) is a soluble inhibitor of IL-22 that regulates IL-22 activity. However, the significance of endogenous IL-22BP in acute liver injury is unknown. We hypothesized that IL-22BP may play a role in acute liver injury. To test this hypothesis, we used Il22bp-deficient mice and murine models of acute liver damage induced by ischemia reperfusion and N-acetyl-p-aminophenol (acetaminophen) administration. We found that Il22bp-deficient mice were more susceptible to acute liver damage in both models. We used Il22 × Il22bp double-deficient mice to show that this effect is indeed due to uncontrolled IL-22 activity. We could demonstrate mechanistically increased expression of Cxcl10 by hepatocytes, and consequently increased infiltration of inflammatory CD11b+Ly6C+ monocytes into the liver in Il22bp-deficient mice upon liver damage. Accordingly, neutralization of CXCL10 reversed the increased disease susceptibility of Il22bp-deficient mice. In conclusion, our data indicate that IL-22BP plays a protective role in acute liver damage, via controlling IL-22-induced Cxcl10 expression.

Increased circulating Th22 cells in patients with acute gouty arthritis: A CONSORT-compliant article

BACKGROUND

T-helper 22 (Th22) cells are involved in host immunity against pathogen invasion and have been implicated in the pathogenesis of inflammatory diseases. However, the roles of Th22 cells in acute gouty arthritis remain unclear.

METHODS

A case-control study was employed to illustrate the clinical significance of Th22 cells in acute gouty arthritis. In this study, 27 patients with acute gouty arthritis, 22 patients with intercritical gout (IG), and 20 healthy controls were recruited, and peripheral blood cells and plasma were collected for the detection of Th22, Th17, and Th1 cells, and plasma interleukin (IL)-22.

RESULTS

The relative and absolute numbers of Th22 and Th17 cells were significantly higher in patients with acute gouty arthritis than in patients with IG and healthy controls. Plasma IL-22 levels were consistently higher in patients with acute gouty arthritis than in patients with IG and healthy controls (P < .05). Th22 cell numbers were positively correlated with Th1 (r = 0.648, P < .05) and Th17 (r = 0.379, P < .05) cell numbers in patients with gout. Moreover, Th22 cell numbers and plasma IL-22 levels were positively correlated with C-reactive protein levels (Th22: r = 0.444, P < .05; IL-22: r = 0.282, P < .05).

CONCLUSION

Our results indicate that peripheral blood levels of Th22 cells increase during acute gouty arthritis suggesting a role for these cells in the pathophysiology of the disease.

Role of Interleukin-22 in chronic liver injury

Liver fibrosis is the result of an exacerbated wound-healing response associated with chronic liver injury. Advanced liver fibrosis results in cirrhosis, liver failure, and portal hypertension and frequently requires liver transplantation. The host immune response has an important role driving fibrosis deposition by activating hepatic stellate cells (HSCs). Interleukin-22 (IL-22) is a cytokine that plays a key role in promoting antimicrobial immunity and tissue repair at barrier surfaces. Data from literature suggest that IL-22 has a protective role in the liver by reducing fibrosis in some pathological conditions, however the results are contradictory. This review highlights current knowledge of IL-22' role in chronic liver injury, as well as its therapeutic potential for the treatment of chronic liver injury.

Tethering Interleukin-22 to Apolipoprotein A-I Ameliorates Mice from Acetaminophen-induced Liver Injury

Increasing evidence indicates that interleukin-22 (IL-22) holds tremendous potential as a protective agent in preventing liver injury, but its pleiotropic effects and pathogenic role in carcinogenesis, rheumatoid arthritis and psoriasis restrict its systemic application. Here, we first developed a nanoparticle (liposIA) as a liver-targeted agent through IL-22 tethered to apolipoprotein A-I (ApoA-I) in a gene therapy vector. LiposIA was prepared using thin film dispersion method and the complexes exhibited desirable nanoparticle size, fine polydisperse index, highly efficient transfection, and excellent serum and storage stability. Biodistribution and hepatic STAT3 phosphorylation studies revealed that IL-22 tethered to ApoA-I led to highly efficient liver targeting. More importantly, our studies showed that a single-dose of liposIA was able to protect mice against acetaminophen-induced liver injury and did not initiate inflammatory response or systemic toxicity in vivo. During this process, activated STAT3/Erk and Akt/mTOR signaling transductions were observed, as well as inhibition of reactive oxygen species (ROS) generation, which prevented mitochondrial dysfunction. These studies demonstrated that IL-22 tethered to apolipoprotein A-I could target and ameliorate acetaminophen-induced acute liver injury, which highlighted that a targeted strategy for IL-22 delivery might have broad utility for the protection of hepatocellular damage.

The role of T helper 17 cells in the pathogenesis of hepatitis B virus-related liver cirrhosis (Review)

In chronic hepatitis B virus (HBV)-infected patients, T helper 17 (Th17) cells are significantly elevated. Th17 cells initiate immune-mediated pathogenesis and have a critical role in the process of HBV-related liver cirrhosis (HBV-LC). The mechanisms underlying this process are attributed to Th17-secreted cytokines, which include interleukin (IL)-17, IL-21 and IL-22; however, a systemic analysis regarding these mechanisms has yet to be conducted. Therefore, the present study aimed to investigate the role of Th17 cells in the pathogenesis of HBV-LC. All randomized clinical trials, case series, case reports and meta-analyses that contained the aforementioned keywords were included in the review process. In addition, unpublished information from the Food and Drug Administration was included. The findings indicated that Th17-secreted cytokines, including IL-17, IL-21 and IL-22, function by activating or silencing hepatic stellate cells, modulating proinflammatory and pro- or antifibrogenic effectors, regulating extracellular matrix formation, upregulating chemokine expression, and inducing hepatocellular damage or hepatoprotection during the HBV-LC process. In addition, Th17 cells and Th17-secreted cytokines may be considered a potential tool in the diagnosis or treatment of HBV-LC. The present review summarized the role of Th17 cells in the pathogenesis of HBV-LC in order to deepen the clinical understanding of the role of Th17 cells and also to support the development of effective therapies for patients with HBV-LC.

A tightly regulated IL-22 response maintains immune functions and homeostasis in systemic viral infection

Interleukin-22 (IL-22) plays an important role in host immunity and tissue homeostasis in infectious and inflammatory diseases. However, the function and regulation of IL-22 in viral infection remain largely unknown. Here, we report that viral infection triggered early IL-22 production from the liver and lymphoid organs. γδ T cells are the main immune cells to produce IL-22 in the liver, a process mediated by the IL-23/phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. In the presence of IL-23, IL-22 production is independent of aryl hydrocarbon receptor (AhR) signaling. In acute and persistent viral infections, IL-22 deficiency resulted in thymic and splenic hypertrophy, while excessive IL-22 induced atrophy in these lymphoid organs. Moreover, IL-22 deficiency enhanced T cell responses to promote viral clearance, but increased IL-22 in vivo decreased T cell numbers and functions in the liver and lymphoid tissues. Together, our findings reveal a significant effect of the IL-23/PI3K/mTORC1 axis on regulating IL-22 production and also identify a novel role of IL-22 in controlling antiviral T cell responses in the non-lymphoid and lymphoid organs during acute and persistent viral infections.

Targeting inflammation for the treatment of alcoholic liver disease

Alcoholic liver disease (ALD) is a leading cause of chronic liver disease with a wide spectrum of manifestations including simple steatosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Liver injury in ALD is caused by chronic inflammation, which has been actively investigated as a therapeutic target for the treatment of ALD for over the last four decades. In this review, we summarize a wide variety of inflammatory mediators that have been shown to contribute to the pathogenesis of ALD, and discuss the therapeutic potential of these mediators for the treatment of ALD.

Biological effects of bone marrow mesenchymal stem cells on hepatitis B virus in vitro

The aim of the present study was to explore the effects of co‑culturing bone marrow‑derived mesenchymal stem cells (BM-MSCs) cultured with hepatitis B virus (HBV)‑infected lymphocytes in vitro. BM‑MSCs and lymphocytes from Brown Norway rats were obtained from the bone marrow and spleen, respectively. Rats were divided into the following five experimental groups: Group 1, splenic lymphocytes (SLCs); group 2, HepG2.2.15 cells; group 3, BM‑MSCs + HepG2.2.15 cells; group 4, SLCs + HepG2.2.15 cells; and group 5, SLCs + BM‑MSCs + HepG2.2.15 cells. The viability of lymphocytes and HepG2.2.15 cells was assessed using the MTT assay at 24, 48 and 72 h, respectively. Levels of supernatant HBV DNA and intracellular HBV covalently closed circular DNA (cccDNA) were measured using quantitative polymerase chain reaction. Supernatant cytokine levels were measured by enzyme‑linked immunosorbent assay (ELISA). T cell subsets were quantified by flow cytometry using fluorescence‑labeled antibodies. In addition, the HBV genome sequence was analyzed by direct gene sequencing. Levels of HBV DNA and cccDNA in group 5 were lower when compared with those in group 3 or group 4, with a significant difference observed at 48 h. The secretion of interferon‑γ was negatively correlated with the level of HBV DNA, whereas secretion of interleukin (IL)‑10 and IL‑22 were positively correlated with the level of HBV DNA. Flow cytometry demonstrated that the percentage of CD3+CD8+ T cells was positively correlated with the levels of HBV DNA, and the CD3+CD4+/CD3+CD8+ ratio was negatively correlated with the level of HBV DNA. Almost no mutations in the HBV DNA sequence were detected in HepG2.2.15 cells co‑cultured with BM‑MSCs, SLCs, or in the two types of cells combined. BM‑MSCs inhibited the expression of HBV DNA and enhanced the clearance of HBV, which may have been mediated by the regulation of the Tc1/Tc2 cell balance and the mode of cytokine secretion to modulate cytokine expression.

Update on the Mechanisms of Liver Regeneration

Liver possesses many critical functions such as synthesis, detoxification, and metabolism. It continually receives nutrient-rich blood from gut, which incidentally is also toxin-rich. That may be why liver is uniquely bestowed with a capacity to regenerate. A commonly studied procedure to understand the cellular and molecular basis of liver regeneration is that of surgical resection. Removal of two-thirds of the liver in rodents or patients instigates alterations in hepatic homeostasis, which are sensed by the deficient organ to drive the restoration process. Although the exact mechanisms that initiate regeneration are unknown, alterations in hemodynamics and metabolism have been suspected as important effectors. Key signaling pathways are activated that drive cell proliferation in various hepatic cell types through autocrine and paracrine mechanisms. Once the prehepatectomy mass is regained, the process of regeneration is adequately terminated. This review highlights recent discoveries in the cellular and molecular basis of liver regeneration.

Retinoic Acid Regulates Immune Responses by Promoting IL-22 and Modulating S100 Proteins in Viral Hepatitis

Although large amounts of vitamin A and its metabolite all-trans retinoic acid (RA) are stored in the liver, how RA regulates liver immune responses during viral infection remains unclear. In this study, we demonstrated that IL-22, mainly produced by hepatic γδ T cells, attenuated liver injury in adenovirus-infected mice. RA can promote γδ T cells to produce mTORC1-dependent IL-22 in the liver, but inhibits IFN-γ and IL-17. RA also affected the aptitude of T cell responses by modulating dendritic cell (DC) migration and costimulatory molecule expression. These results suggested that RA plays an immunomodulatory role in viral infection. Proteomics data revealed that RA downregulated S100 family protein expression in DCs, as well as NF-κB/ERK pathway activation in these cells. Furthermore, adoptive transfer of S100A4-repressed, virus-pulsed DCs into the hind foot of naive mice failed to prime T cell responses in draining lymph nodes. Our study has demonstrated a crucial role for RA in promoting IL-22 production and tempering DC function through downregulating S100 family proteins during viral hepatitis.

Hypoxic modulation of hepatocyte responses to the cytokine interleukin-22

The cytokine interleukin-22 (IL-22) is a potent regulator of tissue responses during inflammation. Depending on the context of inflammation, IL-22 can have protective or inflammatory effects on epithelial cells. This dual nature of IL-22 leads us to hypothesize that its activity must be exquisitely regulated to prevent host tissue damage. Environmental factors may act as a cellular cue as to how cells respond to IL-22. Inflammatory environments are characterized by low oxygen and thus we examined whether cells respond differently to IL-22 hypoxia compared with normoxia. In this study, we show that hepatocyte responses to IL-22 stimulation are reduced in hypoxic environments. IL-22 stimulation of hepatocytes incubated in low oxygen led to reduced levels of activated signal transducer and activator of transcription 3 and further downstream effects such as reduced induction of the anti-microbial protein, lipocalin-2. This modulation appears to be independent of the hypoxia-inducible factor-1α signaling pathway. Thus, hypoxia that accompanies chronic inflammation may be a mechanism to regulate the bioactivity of the dual-natured IL-22 cytokine.

Immunoregulatory Role of NK Cells in Tissue Inflammation and Regeneration

NK cells represent an important first line of defense against viral infection and cancer and are also involved in tissue homeostasis. Studies of NK cell activation in the last decade have revealed that they are able to respond to the inflammatory stimuli evoked by tissue damage and contribute to both progression and resolution of diseases. Exacerbation of the inflammatory response through interactions between immune effector cells facilitates the progression of non-alcoholic fatty liver disease (NAFLD) into steatosis, cirrhosis, and hepatocellular carcinoma (HCC). When hepatic damage is incurred, macrophage activation is crucial for initiating cross talk with neighboring cells present in the liver, including hepatocytes and NK cells, and the importance of this interaction in shaping the immune response in liver disease is increasingly recognized. Inflicted structural damage can be in part regenerated via the process of self-limiting fibrosis, though persistent hepatic damage will lead to chronic fibrosis and loss of tissue organization and function. The cytotoxic activity of NK cells plays an important role in inducing hepatic stellate cell apoptosis and thus curtailing the progression of fibrosis. Alternatively, in some diseases, such as HCC, NK cells may become dysregulated, promoting an immunosuppressive state where tumors are able to escape immune surveillance. This review describes the current understanding of the contributions of NK cells to tissue inflammation and metabolic liver diseases and the ongoing effort to develop therapeutics that target the immunoregulatory function of NK cells.

Serum levels of interleukin-22, cardiometabolic risk factors and incident type 2 diabetes: KORA F4/FF4 study

AIMS

Interleukin-22 (IL-22) has beneficial effects on body weight, insulin resistance and inflammation in different mouse models, but its relevance for the development of type 2 diabetes in humans is unknown. We aimed to identify correlates of serum IL-22 levels and to test the hypothesis that higher IL-22 levels are associated with lower diabetes incidence.

METHODS

Cross-sectional associations between serum IL-22, cardiometabolic risk factors and glucose tolerance status were investigated in 1107 persons of the population-based KORA F4 study. The prospective association between serum IL-22 and incident type 2 diabetes was assessed in 504 initially non-diabetic study participants in both the KORA F4 study and its 7-year follow-up examination KORA FF4, 76 of whom developed diabetes.

RESULTS

Male sex, current smoking, lower HDL cholesterol, lower estimated glomerular filtration rate and higher serum interleukin-1 receptor antagonist were associated with higher IL-22 levels after adjustment for confounders (all P < 0.05). Serum IL-22 showed no associations with glucose tolerance status, prediabetes or type 2 diabetes. Baseline serum IL-22 levels (median, 25th/75th percentiles) for incident type 2 diabetes cases and non-cases were 6.28 (1.95; 12.35) and 6.45 (1.95; 11.80) pg/ml, respectively (age and sex-adjusted P = 0.744). The age and sex-adjusted OR (95% CI) per doubling of IL-22 for incident type 2 diabetes of 1.02 (0.85; 1.23) was almost unchanged after consideration of further confounders.

CONCLUSIONS

High serum levels of IL-22 were positively rather than inversely associated with several cardiometabolic risk factors. However, these associations did not translate into an increased risk for type 2 diabetes. Thus, our data argue against the utility of IL-22 as biomarker for prevalent or incident type 2 diabetes in humans, but identify potential determinants of IL-22 levels which merits further research in the context of cardiovascular diseases.

Immune cells in liver regeneration

After partial hepatectomy, hepatocytes proliferate to restore mass and function of the liver. Macrophages, natural killer (NK) cells, natural killer T (NKT) cells, dendritic cells (DC), eosinophils, gamma delta T (γδT) cells, and conventional T cells, as well as other subsets of the immune cells residing in the liver control liver regeneration, either through direct interactions with hepatocytes or indirectly by releasing inflammatory cytokines. Here, we review recent progress regarding the immune cells in the liver and their functions during liver regeneration.

How Does Interleukin-22 Mediate Liver Regeneration and Prevent Injury and Fibrosis?

Interleukin-22 (IL-22) is a pluripotent T cell-derived cytokine which is a member of IL-10 cytokine family. It is the only interleukin produced by immune cells but does not target immune system components. IL-22 is mainly produced by dendritic cells (DCs) and TH17, TH22, NK, and NKT cells and targets a number of body tissues including liver, pancreas, and other epithelial tissues. It provokes a series of downstream signaling pathways upon binding with IL-22R complex which protects liver damage through STAT3 activation. IL-22BP is an inhibitor of IL-22 which has 20-1000x more affinity to bind with IL-22 compared to IL-22R1 that inhibits IL-22 activity. Its level was found to be positively correlated with the severity of liver damage and fibrosis. So, the present review is an effort to reveal the exact mechanism lying in the hepatoprotective activity of IL-22 and some of its future therapeutic implications.

Cytokine-Mediated Immunopathogenesis of Hepatitis B Virus Infections

Hepatitis B virus (HBV) infection is a worldwide health problem, with approximately one third of populations have been infected, among which 3-5% of adults and more than 90% of children developed to chronic HBV infection. Host immune factors play essential roles in the outcome of HBV infection. Thus, ineffective immune response against HBV may result in persistent virus replications and liver necroinflammations, then lead to chronic HBV infection, liver cirrhosis, and even hepatocellular carcinoma. Cytokine balance was shown to be an important immune characteristic in the development and progression of hepatitis B, as well as in an effective antiviral immunity. Large numbers of cytokines are not only involved in the initiation and regulation of immune responses but also contributing directly or indirectly to the inhibition of virus replication. Besides, cytokines initiate downstream signaling pathway activities by binding to specific receptors expressed on the target cells and play important roles in the responses against viral infections and, therefore, might affect susceptibility to HBV and/or the natural course of the infection. Since cytokines are the primary causes of inflammation and mediates liver injury after HBV infection, we have discussed recent advances on the roles of various cytokines [including T helper type 1 cells (Th1), Th2, Th17, regulatory T cells (Treg)-related cytokines] in different phases of HBV infection and cytokine-related mechanisms for impaired viral control and liver damage during HBV infection. We then focus on experimental therapeutic applications of cytokines to gain a better understanding of this newly emerging aspect of disease pathogenesis.

P2X1-regulated IL-22 secretion by innate lymphoid cells is required for efficient liver regeneration

Paracrine signalling mediated by cytokine secretion is essential for liver regeneration after hepatic resection, yet the mechanisms of cellular crosstalk between immune and parenchymal cells are still elusive. Interleukin-22 (IL-22) is released by immune cells and mediates strong hepatoprotective functions. However, it remains unclear whether IL-22 is critical for the crosstalk between liver lymphocytes and parenchymal cells during liver regeneration after partial hepatectomy (PH). Here, we found that plasma levels of IL-22 and its upstream cytokine, IL-23, are highly elevated in patients after major liver resection. In a mouse model of PH, deletion of IL-22 was associated with significantly delayed hepatocellular proliferation and an increase of hepatocellular injury and endoplasmic reticulum stress. Using Rag1(-/-) and Rag2(-/-) γc(-/) (-) mice, we show that the main producers of IL-22 post-PH are conventional natural killer cells and innate lymphoid cells type 1. Extracellular adenosine triphosphate (ATP), a potent danger molecule, is elevated in patients immediately after major liver resection. Antagonism of the P2-type nucleotide receptors, P2X1 and P2Y6, significantly decreased IL-22 secretion ex vivo. In vivo, specific inhibition of P2X1 was associated with decreased IL-22 secretion, elevated liver injury, and impaired liver regeneration.

CONCLUSION

This study shows that innate immune cell-derived IL-22 is required for efficient liver regeneration and that secretion of IL-22 in the regenerating liver is modulated by the ATP receptor, P2X1. (Hepatology 2016;63:2004-2017).

Comparative Analysis of Liver Injury-Associated Cytokines in Acute Hepatitis A and B

PURPOSE

Acute hepatitis A (AHA) and acute hepatitis B (AHB) are caused by an acute infection of the hepatitis A virus and the hepatitis B virus, respectively. In both AHA and AHB, liver injury is known to be mediated by immune cells and cytokines. In this study, we measured serum levels of various cytokines and T-cell cytotoxic proteins in patients with AHA or AHB to identify liver injury-associated cytokines.

MATERIALS AND METHODS

Forty-six patients with AHA, 16 patients with AHB, and 14 healthy adults were enrolled in the study. Serum levels of 17 cytokines and T-cell cytotoxic proteins were measured by enzyme-linked immunosorbent assays or cytometric bead arrays and analyzed for correlation with serum alanine aminotransferase (ALT) levels.

RESULTS

Interleukin (IL)-18, IL-8, CXCL9, and CXCL10 were significantly elevated in both AHA and AHB. IL-6, IL-22, granzyme B, and soluble Fas ligand (sFasL) were elevated in AHA but not in AHB. In both AHA and AHB, the serum level of CXCL10 significantly correlated with the peak ALT level. Additionally, the serum level of granzyme B in AHA and the serum level of sFasL in AHB correlated with the peak ALT level.

CONCLUSION

We identified cytokines and T-cell cytotoxic proteins associated with liver injury in AHA and AHB. These findings deepen the existing understanding of immunological mechanisms responsible for liver injury in acute viral hepatitis.

Biological and pathological activities of interleukin-22

Interleukin (IL)-22, a member of the IL-10 family, is a cytokine secreted by several types of immune cells including IL-22(+)CD4(+) T cells (Th22) and IL-22 expressing innate leukocytes (ILC22). Recent studies have demonstrated that IL-22 is a key component in mucosal barrier defense, tissue repair, epithelial cell survival, and proliferation. Furthermore, accumulating evidence has defined both protective and pathogenic properties of IL-22 in a number of conditions including autoimmune disease, infection, and malignancy. In this review, we summarize the expression and signaling pathway and functional characteristics of the IL-22 and IL-22 receptor axis in physiological and pathological scenarios and discuss the potential to target IL-22 signaling to treat human diseases.

Pathological Roles of Interleukin-22 in the Development of Recurrent Hepatitis C after Liver Transplantation

OBJECTIVE

The aim of this study was to longitudinally evaluate and analyze the role of interleukin-22-producing CD4 positive cells (IL-22) in the pathogenesis of Hepatitis C Virus recurrence after Orthotopic Liver Transplantation (HCV-OLT).

METHODS

15 HCV-OLT, 15 age- and gender- matched non-HCV post-OLT (OLT) and 15 hepatitis C virus infected (HCV) patients were enrolled into our study from the liver transplantation and research center at Beijing 302 Hospital. We determined the frequencies of IL-22 using flow cytometry and expression of IL-22 mRNA using PCR in peripheral blood and liver tissue. We also divided HCV-OLT patients into rapid fibrosis progression (RFP) and slow fibrosis progression (SFP), examined IL-22 cells and analyzed the correlations between IL-22 frequencies and liver injury, fibrosis and clinical parameters. Moreover, we investigated the role of IL-22 in Human Hepatic Stellate Cells (HSCs).

RESULTS

The levels of serum IL-22, frequencies of IL-22 producing cells in peripheral blood mononuclear cells, and expression of IL-22 mRNA and protein in the liver in the HCV-OLT group were significantly higher than that in the HCV and OLT groups. Furthermore, eight (53.3%) patients developed RFP after two years; another three patients were diagnosed liver cirrhosis. The frequencies of IL-22 were much higher in RFP compared with SFP, while no significant difference existed between OLT and SFP. Intrahepatic IL-22 positive cells were located in fibrotic areas and significantly correlated with α-smooth muscle actin (α-SMA) and fibrosis staging scores, not with grading scores and HCRVNA. In vitro, IL-22 administration prevented HSCs apoptosis, promoted HSCs proliferation and activation, up-regulated the expression of HSC-sourced growth factors including α-SMA, TGF-β and TIMP-1, and increased the production of liver fibrosis markers including laminin, hyaluronic acid and collagen type IV.

CONCLUSION

Peripheral and intrahepatic IL-22 is up-regulated and plays a pathological role in exacerbating liver fibrosis by activating HSCs in HCV-OLT patients, which may predict RFP and serve as an attractive target for anti-fibrotic therapy.

Hepatoprotective Effects of Chinese Medicinal Herbs: A Focus on Anti-Inflammatory and Anti-Oxidative Activities

The liver is intimately connected to inflammation, which is the innate defense system of the body for removing harmful stimuli and participates in the hepatic wound-healing response. Sustained inflammation and the corresponding regenerative wound-healing response can induce the development of fibrosis, cirrhosis and eventually hepatocellular carcinoma. Oxidative stress is associated with the activation of inflammatory pathways, while chronic inflammation is found associated with some human cancers. Inflammation and cancer may be connected by the effect of the inflammation-fibrosis-cancer (IFC) axis. Chinese medicinal herbs display abilities in protecting the liver compared to conventional therapies, as many herbal medicines have been shown as effective anti-inflammatory and anti-oxidative agents. We review the relationship between oxidative stress and inflammation, the development of hepatic diseases, and the hepatoprotective effects of Chinese medicinal herbs via anti-inflammatory and anti-oxidative mechanisms. Moreover, several Chinese medicinal herbs and composite formulae, which have been commonly used for preventing and treating hepatic diseases, including Andrographis Herba, Glycyrrhizae Radix et Rhizoma, Ginseng Radix et Rhizoma, Lycii Fructus, Coptidis Rhizoma, curcumin, xiao-cha-hu-tang and shi-quan-da-bu-tang, were selected for reviewing their hepatoprotective effects with focus on their anti-oxidative and ant-inflammatory activities. This review aims to provide new insight into how Chinese medicinal herbs work in therapeutic strategies for liver diseases.

NKp46(+) natural killer cells attenuate metabolism-induced hepatic fibrosis by regulating macrophage activation in mice

Nonalcoholic steatohepatitis (NASH) affects 3%-5% of the U.S. population, having severe clinical complications to the development of fibrosis and end-stage liver diseases, such as cirrhosis and hepatocellular carcinoma. A critical cause of NASH is chronic systemic inflammation promoted by innate immune cells, such as liver macrophages (Mϕ) and natural killer (NK) cells. However, little is known about how the crosstalk between Mϕ and NK cells contributes to regulate NASH progression to fibrosis. In this report, we demonstrate that NKp46(+) cells play an important role in preventing NASH progression to fibrosis by regulating M1/M2 polarization of liver Mϕ. Using a murine model of NASH, we demonstrate that DX5(+)NKp46(+) NK cells are increased during disease and play a role in polarizing Mϕ toward M1-like phenotypes. This NK's immunoregulatory function depends on the production of interferon-gamma (IFN-γ), but not by granzyme-mediated cytolytic activity. Notably, depletion of NKp46(+) cells promotes the development of fibrosis with increased expression of profibrogenic genes as well as skewed M2 Mϕ phenotypes in hepatic tissues.

CONCLUSIONS

NK cell-derived IFN-γ may be essential for maintaining a balanced inflammatory environment that promotes tissue integrity and limiting NASH progression to fibrosis.

Mechanisms of interleukin-22's beneficial effects in acute pancreatitis

Acute pancreatitis (AP) is a disorder characterized by parenchymal injury of the pancreas controlled by immune cell-mediated inflammation. AP remains a significant challenge in the clinic due to a lack of specific and effective treatment. Knowledge of the complex mechanisms that regulate the inflammatory response in AP is needed for the development of new approaches to treatment, since immune cell-derived inflammatory cytokines have been recognized to play critical roles in the pathogenesis of the disease. Recent studies have shown that interleukin (IL)-22, a cytokine secreted by leukocytes, when applied in the severe animal models of AP, protects against the inflammation-mediated acinar injury. In contrast, in a mild AP model, endogenous IL-22 has been found to be a predominantly anti-inflammatory mediator that inhibits inflammatory cell infiltration via the induction of Reg3 proteins in acinar cells, but does not protect against acinar injury in the early stage of AP. However, constitutively over-expressed IL-22 can prevent the initial acinar injury caused by excessive autophagy through the induction of the anti-autophagic proteins Bcl-2 and Bcl-XL. Thus IL-22 plays different roles in AP depending on the severity of the AP model. This review focuses on these recently reported findings for the purpose of better understanding IL-22's regulatory roles in AP which could help to develop a novel therapeutic strategy.

IL-22-Expressing Murine Lymphocytes Display Plasticity and Pathogenicity in Reporter Mice

IL-22 has multiple activities ranging from tissue repair to inflammation. To characterize the pathogenicity and plasticity of cells that produce IL-22, a novel reporter mouse strain was generated. Homeostatic IL-22 reporter expression was observed in intestinal lymphoid cells identified as CD4 T cells and ILC3 cells. In a model of inflammatory bowel disease, CD4 T cells strongly expressed the IL-22 reporter in mesenteric lymph node. To examine plasticity of IL-22(+) T cells, they were purified after generation in vitro or in vivo from inflamed colon, and then cultured under Th1, Th2, or Th17 conditions. In vitro-generated IL-22(+) CD4 T cells showed relatively durable IL-22 expression under Th1 or Th2 conditions, whereas in vivo-generated cells rapidly lost IL-22 expression under these conditions. In vitro-generated cells could not be diverted to express Th1 or Th2 cytokines despite the expression of "master regulators." In vivo-generated cells could be diverted, at very low frequency, to express Th1 or Th2 cytokines. Both in vitro- and in vivo-generated cells could be induced in vitro to express high levels of IL-17A and IL-17F, assigning them to a "Th17 biased" class. However, IL-27 potently downregulated IL-22 expression. To examine IL-22(+) T cell pathogenicity, in vitro-generated cells were transferred into Rag1(-/-) mice, retaining the modest reporter expression and inducing moderate colitis. In contrast, IL-22 expressers from colitic mice, transferred into secondary hosts, lost reporter expression, acquired high T-bet and modest IFNγ and IL-17 expression, and induced severe colitis. These findings are consistent with a model of strong polarization under optimal in vitro conditions, but a plastic state of T cells in vivo.

Though Active on RINm5F Insulinoma Cells and Cultured Pancreatic Islets, Recombinant IL-22 Fails to Modulate Cytotoxicity and Disease in a Protocol of Streptozotocin-Induced Experimental Diabetes

Interleukin (IL)-22 is a cytokine displaying tissue protective and pro-regenerative functions in various preclinical disease models. Anti-bacterial, pro-proliferative, and anti-apoptotic properties mediated by activation of the transcription factor signal transducer and activator of transcription (STAT)-3 are key to biological functions of this IL-10 family member. Herein, we introduce RINm5F insulinoma cells as rat β-cell line that, under the influence of IL-22, displays activation of STAT3 with induction of its downstream gene targets Socs3, Bcl3, and Reg3b. In addition, IL-22 also activates STAT1 in this cell type. To refine those observations, IL-22 biological activity was evaluated using ex vivo cultivated murine pancreatic islets. In accord with data on RINm5F cells, islet exposure to IL-22 activated STAT3 and upregulation of STAT3-inducible Socs3, Bcl3, and Steap4 was evident under those conditions. As these observations supported the hypothesis that IL-22 may exert protective functions in toxic β-cell injury, application of IL-22 was investigated in murine multiple-low-dose streptozotocin (STZ)-induced diabetes. For that purpose, recombinant IL-22 was administered thrice either immediately before and at disease onset (at d4, d6, d8) or closely thereafter (at d8, d10, d12). These two IL-22-treatment periods coincide with two early peaks of β-cell injury detectable in this model. Notably, none of the two IL-22-treatment strategies affected diabetes incidence or blood glucose levels in STZ-treated mice. Moreover, pathological changes in islet morphology analyzed 28 days after disease induction were not ameliorated by IL-22 administration. Taken together, despite being active on rat RINm5F insulinoma cells and murine pancreatic islets, recombinant IL-22 fails to protect pancreatic β-cells in the tested protocols from toxic effects of STZ and thus is unable to ameliorate disease in the widely used model of STZ-induced diabetes.

Therapeutic Role of Interleukin 22 in Experimental Intra-abdominal Klebsiella pneumoniae Infection in Mice

Interleukin 22 (IL-22) is an IL-10-related cytokine produced by T helper 17 (Th17) cells and other immune cells that signals via IL-22 receptor alpha 1 (IL-22Ra1), which is expressed on epithelial tissues, as well as hepatocytes. IL-22 has been shown to have hepatoprotective effects that are mediated by signal transducer and activator of transcription 3 (STAT3) signaling. However, it is unclear whether IL-22 can directly regulate antimicrobial programs in the liver. To test this hypothesis, hepatocyte-specific IL-22Ra1 knockout (Il22Ra1(Hep-/-)) and Stat3 knockout (Stat3(Hep-/-)) mice were generated and subjected to intra-abdominal infection with Klebsiella pneumoniae, which results in liver injury and necrosis. We found that overexpression of IL-22 or therapeutic administration of recombinant IL-22 (rIL-22), given 2 h postinfection, significantly reduced the bacterial burden in both the liver and spleen. The antimicrobial activity of rIL-22 required hepatic Il22Ra1 and Stat3. Serum from rIL-22-treated mice showed potent bacteriostatic activity against K. pneumoniae, which was dependent on lipocalin 2 (LCN2). However, in vivo, rIL-22-induced antimicrobial activity was only partially reduced in LCN2-deficient mice. We found that rIL-22 also induced serum amyloid A2 (SAA2) and that SAA2 had anti-K. pneumoniae bactericidal activity in vitro. These results demonstrate that IL-22, through IL-22Ra1 and STAT3 singling, can induce intrinsic antimicrobial activity in the liver, which is due in part to LCN2 and SAA2. Therefore, IL-22 may be a useful adjunct in treating hepatic and intra-abdominal infections.

Innate lymphoid cells involve in tumorigenesis

Innate lymphoid cells (ILCs) promptly initiate cytokine responses to pathogen exposure in the mucosa and mucosal-associated lymphoid tissues. ILCs were recently categorized as being of the lymphoid lineage and have been classified into three groups. ILCs play important roles in immunity against pathogens, and an anti-tumor immune-related function was recently demonstrated. In this review we discuss whether and how ILCs involve in the tumorigenesis, providing new insights into the mechanisms underlying the particular functions of ILCs as well as the potential targets for tumor intervention.

Clinical Implications of Hepatocyte Growth Factor, Interleukin-20, and Interleukin-22 in Serum and Bronchoalveolar Fluid of Patients with Non-Small Cell Lung Cancer

Hepatocyte growth factor (HGF) is involved in tumorigenesis, interleukin-20 (IL-20) is an inhibitor of angiogenesis, and interleukin-22 (IL-22) stimulates tumor growth. The aim of this study was to determine the level of HGF, IL-20, and IL-22 in both serum and bronchoalveolar lavage fluid (BALF) of non-small cell lung cancer (NSCLC) patients before onset of chemotherapy, the nature of the interrelationships between these markers, and their prognostic significance regarding post-chemotherapy survival time. We studied 46 NSCLC patients and 15 healthy subjects as a control group. We found significantly higher serum levels of HGF and IL-22 in the NSCLC patients than those in controls [pg/ml: HGF - 1911 (693-6510) vs. 1333 (838-3667), p = 0.0004; IL-22 - 10.66 (1.44-70.34) vs. 4.69 (0.35-12.29), p = 0.0007]. In contrast, concentrations of HGF and IL-22 in BALF were lower in NSCLC patients than those in controls [pg/ml: HGF - 72 (6-561) vs. 488 (14-2003), p = 0.0002; IL-22 - 2.28 (0.70-6.52) vs. 3.72 (2.76-5.64), p = 0.002]. In the NSCLC patients, there was a negative correlation between the serum level of IL-20 and time to tumor progression (r = -0.405, p = 0.04) and between the serum level of HGF and survival time (r = -0.41, p = 0.005). In addition, a higher serum level of HGF and a higher BALF level of IL-22 in patients were linked with a shorter overall survival. We conclude that HGF, IL-20, and IL-22 in the serum and BALF of NSCLC patients before chemotherapy may be a prognostic of cancer progression.

AAV-IL-22 modifies liver chemokine activity and ameliorates portal inflammation in murine autoimmune cholangitis

There remain significant obstacles in developing biologics to treat primary biliary cholangitis (PBC). Although a number of agents have been studied both in murine models and human patients, the results have been relatively disappointing. IL-22 is a member of the IL-10 family and has multiple theoretical reasons for predicting successful usage in PBC. We have taken advantage of an IL-22 expressing adeno-associated virus (AAV-IL-22) to address the potential role of IL-22 in not only protecting mice from autoimmune cholangitis, but also in treating animals with established portal inflammation. Using our established mouse model of 2-OA-OVA immunization, including α-galactosylceramide (α-GalCer) stimulation, we treated mice both before and after the onset of clinical disease with AAV-IL-22. Firstly, AAV-IL-22 treatment given prior to 2-OA-OVA and α-GalCer exposure, i.e. before the onset of disease, significantly reduces the portal inflammatory response, production of Th1 cytokines and appearance of liver fibrosis. It also reduced the liver lymphotropic chemokines CCL5, CCL19, CXCL9, and CXCL10. Secondly, and more importantly, therapeutic use of AAV-IL-22, administered after the onset of disease, achieved a greater hurdle and significantly improved portal pathology. Further the improvements in inflammation were negatively correlated with levels of CCL5 and CXCL10 and positively correlated with levels of IL-22. In conclusion, we submit that the clinical use of IL-22 has a potential role in modulating the inflammatory portal process in patients with PBC.

IL-22: a promising candidate to inhibit viral-induced liver disease progression and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a growing concern all over the world. With the number of patients rising exponentially with each passing day, HCC is a problem that needs immediate attention. Currently, available treatment strategies focus on controlling the damage after the development of HCC. The options available from chemo- and radio-embolization to surgical resection and transplantation are not efficacious as required due to the complex nature of the disease. Liver regeneration and tissue healing are the subject of great interest today. Interleukin-22 (IL-22) is a cytokine with the ability to regenerate and therefore reverse the injuries caused by a wide range of agents. IL-22 acts via STAT molecule and controls the activity of a wide variety of cell survival and proliferation genes. Experimental data has given a positive insight into the role of IL-22 in inhibition of viral and alcohol-induced hepatocellular carcinoma. A further insight into the nature of IL-22 and the factors that can be manipulated in controlling the activity of IL-22 can help to counter the menace caused by the devastating effects of HCC.

Hepatocytes: a key cell type for innate immunity

Hepatocytes, the major parenchymal cells in the liver, play pivotal roles in metabolism, detoxification, and protein synthesis. Hepatocytes also activate innate immunity against invading microorganisms by secreting innate immunity proteins. These proteins include bactericidal proteins that directly kill bacteria, opsonins that assist in the phagocytosis of foreign bacteria, iron-sequestering proteins that block iron uptake by bacteria, several soluble factors that regulate lipopolysaccharide signaling, and the coagulation factor fibrinogen that activates innate immunity. In this review, we summarize the wide variety of innate immunity proteins produced by hepatocytes and discuss liver-enriched transcription factors (e.g. hepatocyte nuclear factors and CCAAT/enhancer-binding proteins), pro-inflammatory mediators (e.g. interleukin (IL)-6, IL-22, IL-1β and tumor necrosis factor-α), and downstream signaling pathways (e.g. signal transducer and activator of transcription factor 3 and nuclear factor-κB) that regulate the expression of these innate immunity proteins. We also briefly discuss the dysregulation of these innate immunity proteins in chronic liver disease, which may contribute to an increased susceptibility to bacterial infection in patients with cirrhosis.

Characteristics of innate lymphoid cells (ILCs) and their role in immunological disorders (an update)

Innate lymphoid cells (ILCs) are a novel family of hematopoietic effectors and regulators of innate immunity. Although these cells are morphologically similar to B cells and T cells, however they do not express antigen receptors. ILCs seems to have emerging roles in innate immune responses against infectious or non-infectious microorganisms, protection of the epithelial barrier, lymphoid organogenesis and inflammation, tissue remodeling and regulating homeostasis of tissue stromal cells. In addition, it has recently been reported that ILCs have a crucial role in several disorders such as allergy and autoimmunity. Based on their phenotype and functions, ILCs are classified into three major groups called ILCs1, ILCs2, and ILCs3. Here we reviewed the most recent data concerning diverse ILC phenotypes, subclasses, functions in immune responses as well as in immune mediated disorders.

Combination therapy: New hope for alcoholic hepatitis?

Alcoholic hepatitis (AH) is a severe form of alcoholic liver disease with high mortality. The pathogenesis of AH is not fully understood, but it is generally believed that inflammation is a key factor leading to liver failure in AH. Steroids, which have broad immunosuppressive effects, have been used for the treatment of AH over the last forty years. Steroids elicit modest improvement in short-term survival rate in patients with severe AH, but also cause severe side effects. Several specific inflammatory targets (e.g., IL-1, LPS, and gut microbiota) are currently under investigation for the treatment of AH with the goal to obviate or reduce steroid administration. In addition to inflammation, impaired liver regeneration is another major cause of liver failure in AH, which deteriorates further after steroid treatment because inflammation plays a key role in promoting liver repair. Interleukin-22 (IL-22) is a promising drug for the treatment of AH because of its hepatoprotective and anti-fibrotic functions and relatively few known side effects. In addition, IL-22 treatment also ameliorates bacterial infection and kidney injury, two major complications associated with severe AH. IL-22 is currently under investigation in preclinical and clinical studies and may hold great promise for AH by providing more beneficial effects and fewer side effects than current therapies.

Protective effect of Th22 cells and intrahepatic IL-22 in drug induced hepatocellular injury

BACKGROUND & AIMS

Th22 cells regulate host immunity against pathogenic invasion, including protecting host against chronic hepatitis B; however, the relationship between drug induced liver injury (DILI) and Th22/Th17 cells is still unclear. We investigated the role of Th22 cells in DILI development.

METHODS

The frequencies of peripheral Th22/Th17/Th1 cells and intrahepatic IL-22/IL-17 production from DILI, non-DILI liver diseases, and healthy controls were examined. Plasma IL-22/IL-17 and the related cytokines were determined in DILI patients at week 0 (defined as the occurrence of liver injury within 7days), 4 and 24. Multivariable stepwise logistic regression was applied to explore the associations between various factors and recovery of DILI.

RESULTS

The frequencies of Th22/Th17 cells were significantly higher in DILI onset patients than HC. Significant increase of Th22 cells and the related cytokines levels was observed in DILI with hepatocellular injury type. There was a positive correlation between intrahepatic IL-22 level and liver regeneration. Plasma IL-22 level was higher in DILI patients with improved liver function than unimproved function. Multivariable analysis showed that the odds ratio (OR) of plasma IL-22 at 4weeks was 1.054 [95% confidence interval (CI), 1.012, 1.124].

CONCLUSIONS

Increased peripheral and intrahepatic IL-22-secreting cells are detected in DILI. Th22 and its related cytokines might be hepato-protective, which might provide new perspective for understanding the immunopathogenesis of DILI. Plasma IL-22 might be a reliable indicator to evaluate the prognosis of DILI and provide a novel therapeutic target for DILI treatment.

Metformin decreases IL-22 secretion to suppress tumor growth in an orthotopic mouse model of hepatocellular carcinoma

Epidemiological, preclinical and cellular studies in the last 5 years have shown that metformin exerts anti-tumoral properties, but its mode of action in cancer remains unclear. Here, we investigated the effects of metformin on a mouse hepatocellular carcinoma (HCC) model and tumor-associated T cell immune responses. Oral metformin administration led to a significant reduction of tumor growth, which was accompanied by decreased interleukin-22 (IL-22). Meanwhile, IL-22-induced STAT3 phosphorylation and upregulation of downstream genes Bcl-2 and cyclin D1 were inhibited by metformin. At the cellular level, metformin attenuated Th1- and Th17-derived IL-22 production. Furthermore, metformin inhibited de novo generation of Th1 and Th17 cells from naive CD4(+) cells. These observations were further supported by the fact that metformin treatment inhibited CD3/CD28-induced IFN-γ and IL-17A expression along with the transcription factors that drive their expression (T-bet [Th1] and ROR-γt [Th17], respectively). The effects of metformin on T cell differentiation were mediated by downregulated STAT3 and STAT4 phosphorylation via the AMP-activated kinase-mammalian target of rapamycin complex 1 pathway. Notably, metformin led to a reduction in glucose transporter Glut1 expression, resulting in less glucose uptake, which is critical to regulate CD4(+) T cell fate. Taken together, these findings provide evidence for the growth-inhibitory and immune-modulatory effects of metformin in HCC and thus, broaden our understanding about the action of metformin in liver cancer treatment.

Biologically active, high levels of interleukin-22 inhibit hepatic gluconeogenesis but do not affect obesity and its metabolic consequences

Background

Interleukin-22 (IL-22), a cytokine with important functions in anti-microbial defense and tissue repair, has been recently suggested to have beneficial effects in obesity and metabolic syndrome in some but not in other studies. Here, we re-examined the effects of IL-22 on obesity, insulin resistance, and hepatic glucose metabolism.

Results

Genetic deletion of IL-22 did not affect high-fat-diet (HFD)-induced obesity and insulin resistance. IL-22 transgenic mice with relatively high levels of circulating IL-22 (~600 pg/ml) were completely resistant to Concanavalin A-induced liver injury but developed the same degree of high fat diet (HFD)-induced obesity, insulin resistance, and fatty liver as the wild-type littermate controls. Similarly, chronic treatment with recombinant mouse IL-22 (rmIL-22) protein did not affect HFD-induced obesity and the associated metabolic syndrome. In vivo treatment with a single dose of rmIL-22 downregulated the hepatic expression of gluconeogenic genes and subsequently inhibited hepatic gluconeogenesis and reduced blood glucose levels both in HFD-fed and streptozotocin (STZ)-treated mice without affecting insulin production. In vitro exposure of mouse primary hepatocytes to IL-22 suppressed glucose production and the expression of gluconeogenic genes. These inhibitory effects were partially reversed by blocking STAT3 or the AMPK signaling pathway.

Conclusion

Biologically active, high levels of IL-22 do not affect obesity and the associated metabolic syndrome. Acute treatment with IL-22 inhibits hepatic gluconeogenesis, which is mediated via the activation of STAT3 and AMPK in hepatocytes.

Interleukin-22 in kidney injury and regeneration

Interleukins have become well-known regulators of innate and adaptive immunity-related tissue inflammation. Recently, IL-22 has gained a lot of interest for its unique functions in maintaining and regaining epithelial integrity. IL-22 is exclusively secreted by different immune cell subsets, while IL-22 receptors are mainly expressed by epithelial cells. As the kidney is largely an epithelial organ, the functional role of IL-22 in the kidney deserves to be explored in detail. Here, we briefly summarize the key features of IL-22 biology and review the available data on its expression and functional roles in kidney injury and kidney regeneration. Furthermore, we provide suggestions on how to explore this evolving field in the future.

Up-regulation of interleukin-22 mediates liver fibrosis via activating hepatic stellate cells in patients with hepatitis C

Interleukin-22 (IL-22) is known to play a critical role in liver immunity. However, the role of IL-22 in HCV-associated liver fibrosis is poorly understood. In this study, patients with HCV infection disclosed significant increases in peripheral numbers of IL-22-producing cells as well as in IL-22 plasma levels. In the liver, the increased intrahepatic IL-22(+) cells were positively correlated with fibrotic staging scores and clinical progression from CHC to cirrhosis. Moreover, the majority of IL-22(+) cells were located in fibrotic areas in the liver of patients with cirrhosis and co-localized with α-smooth muscle actin (α-SMA) positive hepatic stellate cells (HSCs). In vitro, administration of IL-22 was accompanied with inhibited LX-2 cell apoptosis, promoted LX-2 cell proliferation, increased expression of α-SMA, and up-regulated collagen production by LX-2 cells. Collectively, our data provide evidence that IL-22 may contribute to the fibrogenesis of HCV-associated liver fibrosis by activating HSCs.

Role of interleukin-22 in liver diseases

Interleukin (IL)-22, which is discovered by the Dumoutier team during the stimulation of murine BW5147 T lymphoma cells with IL-9, is a member of the IL-10 cytokine family because of the similarity of structure and encoding genes. IL-22 is involved in many inflammatory diseases and autoimmune diseases, such as psoriasis, ulcerative colitis, and systemic lupus erythematosus. Recently it has been found that IL-22 can protect against liver injury and promote hepatocytes proliferation. This paper will make a brief introduction of the role of IL-22 in liver diseases.