IL-22-dependent attenuation of T cell-dependent (ConA) hepatitis in herpes virus entry mediator deficiency

Th17 cells in the liver: balancing autoimmunity and pathogen defense

In addition to carcinogenesis, T helper 17 (Th17) cells (a subtype of CD4 + T lymphocytes) are involved in the acute, chronic, and cirrhotic phases of liver diseases; however, their role in the development and progression of liver diseases remains unclear. It is difficult to elucidate the role of Th17 cells in liver diseases due to their dichotomous nature, i.e., plasticity in terms of pathogenic or host protective function depending on environmental and time phase factors. Moreover, insufficient depletion of Th17 cells by inhibiting the cytokines and transcription factors involved in their production causes difficulties in analyzing their specific role in vitro and in vivo murine models, partially due to complex interaction. This review summarizes the recent progress in understanding the plasticity and function of hepatic Th17 cells and type 3 cytokines.

Immunopathobiology and therapeutic targets related to cytokines in liver diseases

Chronic liver injury with any etiology can progress to fibrosis and the end-stage diseases cirrhosis and hepatocellular carcinoma. The progression of liver disease is controlled by a variety of factors, including liver injury, inflammatory cells, inflammatory mediators, cytokines, and the gut microbiome. In the current review, we discuss recent data on a large number of cytokines that play important roles in regulating liver injury, inflammation, fibrosis, and regeneration, with a focus on interferons and T helper (Th) 1, Th2, Th9, Th17, interleukin (IL)-1 family, IL-6 family, and IL-20 family cytokines. Hepatocytes can also produce certain cytokines (such as IL-7, IL-11, and IL-33), and the functions of these cytokines in the liver are briefly summarized. Several cytokines have great therapeutic potential, and some are currently being tested as therapeutic targets in clinical trials for the treatment of liver diseases, which are also described.

BTLA-HVEM Checkpoint Axis Regulates Hepatic Homeostasis and Inflammation in a ConA-Induced Hepatitis Model in Zebrafish

The BTLA-HVEM checkpoint axis plays extensive roles in immunomodulation and diseases, including cancer and autoimmune disorders. However, the functions of this checkpoint axis in hepatitis remain limited. In this study, we explored the regulatory role of the Btla-Hvem axis in a ConA-induced hepatitis model in zebrafish. Results showed that Btla and Hvem were differentially expressed on intrahepatic Cd8⁺ T cells and hepatocytes. Knockdown of Btla or Hvem significantly promoted hepatic inflammation. Btla was highly expressed in Cd8⁺ T cells in healthy liver but was downregulated in inflamed liver, as evidenced by a disparate proportion of Cd8⁺Btla⁺ and Cd8⁺Btla^- T cells in individuals without or with ConA stimulation. Cd8⁺Btla⁺ T cells showed minimal cytotoxicity to hepatocytes, whereas Cd8⁺Btla^- T cells were strongly reactive. The depletion of Cd8⁺Btla^- T cells reduced hepatitis, whereas their transfer enhanced hepatic inflammation. These observations indicate that Btla endowed Cd8⁺Btla⁺ T cells with self-tolerance, thereby preventing them from attacking hepatocytes. Btla downregulation deprived this tolerization. Mechanistically, Btla-Hvem interaction contributed to Cd8⁺Btla⁺ T cell tolerization, which was impaired by Hvem knockdown but rescued by soluble Hvem protein administration. Notably, Light was markedly upregulated on Cd8⁺Btla^- T cells, accompanied by the transition of Cd8⁺Btla⁺Light^- to Cd8⁺Btla^-Light⁺ T cells during hepatitis, which could be modulated by Cd4⁺ T cells. Light blockade attenuated hepatitis, thereby suggesting the positive role of Light in hepatic inflammation. These findings provide insights into a previously unrecognized Btla-Hvem-Light regulatory network in hepatic homeostasis and inflammation, thus adding a new potential therapeutic intervention for hepatitis.

CD160 serves as a negative regulator of NKT cells in acute hepatic injury

CD160 and BTLA both bind to herpes virus entry mediator. Although a negative regulatory function of BTLA in natural killer T (NKT) cell activation has been reported, whether CD160 is also involved is unclear. By analyzing CD160^-/- mice and mixed bone marrow chimeras, we show that CD160 is not essential for NKT cell development. However, CD160^-/- mice exhibit severe liver injury after in vivo challenge with α-galactosylceramide (α-GalCer). Moreover, CD160^-/- mice are more susceptible to Concanavalin A challenge, and display elevated serum AST and ALT levels, hyperactivation of NKT cells, and enhanced IFN-γ, TNF, and IL-4 production. Lastly, inhibition of BTLA by anti-BTLA mAb aggravates α-GalCer-induced hepatic injury in CD160^-/- mice, suggesting that both CD160 and BTLA serve as non-overlapping negative regulators of NKT cells. Our data thus implicate CD160 as a co-inhibitory receptor that delivers antigen-dependent signals in NKT cells to dampen cytokine production during early innate immune activation.

Enhanced Regeneration and Hepatoprotective Effects of Interleukin 22 Fusion Protein on a Predamaged Liver Undergoing Partial Hepatectomy

Liver ischemia-reperfusion injury (IRI) and regeneration deficiency are two major challenges for surgery patients with chronic liver disease. As a survival factor for hepatocytes, interleukin 22 (IL-22) plays an important role in hepatoprotection and the promotion of regeneration after hepatectomy. In this study, we aim to investigate the roles of an interleukin 22 fusion protein (IL-22-FP) in mice with a predamaged liver after a two-third partial hepatectomy (PHx). Predamaged livers in mice were induced by concanavalin A (ConA)/carbon tetrachloride (CCl4) following PHx with or without IL-22-FP treatment. A hepatic IRI mouse model was also used to determine the hepatoprotective effects of IL-22-FP. In the ConA/CCl4 model, IL-22-FP treatment alleviated liver injury and accelerated hepatocyte proliferation. Administration of IL-22-FP activated the hepatic signal transducer and activator of transcription 3 (STAT3) and upregulated the expression of many mitogenic proteins. IL-22-FP treatment prior to IRI effectively reduced liver damage through decreased aminotransferase and improved liver histology. In conclusion, IL-22-FP promotes liver regeneration in mice with predamaged livers following PHx and alleviates IRI-induced liver injury. Our study suggests that IL-22-FP may represent a promising therapeutic drug against regeneration deficiency and liver IRI in patients who have undergone PHx.

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.

Impact of An Soup of Miao nationality on expression of Occludin in intestinal mucosa and content of IL-22 in hepatic tissue in mice with acute liver failure

AIM

To evaluate the effect of An Soup of Miao nationality on acute hepatic failure by detecting the expression of Occludin in the intestinal mucosa and the content of interleukin-22 (IL-22) in liver tissue.

METHODS

Forty male SD rats were randomly and equally divided into four groups, namely, normal control group, acute liver failure model group, bifid triple viable bacteria group, and An Soup group. The bifid triple viable bacteria group and An Soup group were gavaged with bifid triple viable bacteria and An Soup once a day for 9 d; the normal control group and acute liver failure model group were gavaged with equal volume of normal saline. At the 8^th day, all groups except the normal control group were subcutaneously injected with 300 mg/kg thioacetamide (prepared with TAA and normal saline) once a day for two consecutive days to induce acute hepatic failure. At the 10^th day, the rats were killed, serum samples were taken to detect the levels of alanine aminotransferase and aspartate aminotransferase, and ileal tissue that was 3 cm away from the ileocecal junction and hepatic tissue were taken to detect the expression of Occludin in the intestinal mucosa and the content of IL-22 in hepatic tissue, respectively.

RESULTS

Except for the normal control group, the levels of serum transaminase and content of IL-22 in hepatic tissue increased significantly in the other three groups (P < 0.01). Compared with the model group, the levels of serum transaminase decreased significantly in the bifid triple viable bacteria group and An Soup group (P < 0.05), but the difference between the bifid triple viable bacteria group and An Soup group was not significant (P > 0.05). Compared with the model group, the content of IL-22 in hepatic tissue increased significantly in the bifid triple viable bacteria group and An Soup group (P < 0.05), but there was no significant difference between the bifid triple viable bacteria group and An Soup group (P > 0.05). Except the normal control group, the expression level of Occludin in the intestinal mucosa decreased in other three groups (P < 0.01). Compared with the model group, the expression of Occludin in the intestinal mucosa increased significantly in the bifid triple viable bacteria group and An Soup group (P < 0.05), although the difference between the bifid triple viable bacteria group and An Soup group was not significant (P > 0.05).

CONCLUSION

An Soup has dietary effects on acute hepatic failure by protecting intestinal mucosal barrier and up-regulating IL-22 expression.

Paeoniflorin exerts a nephroprotective effect on concanavalin A-induced damage through inhibition of macrophage infiltration

BACKGROUND

It is well established that macrophage infiltration is involved in concanavalin A (conA)-induced liver injury. However, the role of macrophages in conA-induced renal injury remains unknown. The aims of this study were to investigate macrophage infiltration in conA-induced renal injury and determine whether paeoniflorin (PF) could inhibit macrophage infiltration into the kidney.

METHODS

BALB/C mice were pre-treated with or without PF 2 h (h) before conA injection. At 8 h after con A injection, all the mice were sacrificed; The liver and kidney histology were studied. The renal CD68 expression was detected by immunohistochemical and real-time PCR analysis. The level of expression of C-X-C chemokine receptor type 3 (CXCR3) was analyzed by western blot, immunohistochemical and real-time PCR. The pathophysiological involvement of CXCR3 in macrophage infiltration were investigated using dual-colour immunofluorescence microscopy.

RESULTS

PF administration significantly reduced the elevated serum levels of alanine transaminase (ALT), blood urea nitrogen (BUN), creatinine (Cr) and the severity of liver and renal damage compared with that in the conA-vehicle group. PF administration inhibited the increase in renal IL1β mRNA expression and concentration. Furthermore, immunohistochemical analysis showed that macrophages secreted CXCR3 in the kidneys of the conA-vehicle mice. Immunofluorescence microscopy demonstrated CXCR3 bound tightly to C-X-C motif ligand 11 (CXCL11) in the kidneys of the conA-vehicle mice and showed that PF treatment could suppress CXCR3/CXCL11 over-activation.

CONCLUSIONS

Macrophage infiltration was a notable pathological change in the kidneys of conA-treated mice. PF administration attenuated conA-induced renal damage, at least in part, by inhibiting the over-activated CXCR3/CXCL11 signal axis.

Dihydroquercetin (DHQ) ameliorated concanavalin A-induced mouse experimental fulminant hepatitis and enhanced HO-1 expression through MAPK/Nrf2 antioxidant pathway in RAW cells

Autoimmune hepatitis represents a ubiquitous human health problem and has a poor prognosis. Dihydroquercetin (DHQ), a well-known antioxidant, significantly inhibits fulminant hepatitis through anti-oxidant and anti-inflammation mechanisms. In this study, we show that administration of DHQ ameliorated concanavalin A (ConA)-induced mouse liver injury by increasing the survival rate, reducing the serum ALT and AST level, preventing histopathological injuries and decreasing pro-inflammatory cytokine mRNA expression in hepatic tissue. As macrophages/Kupffer cells in oxidative stress and pro-inflammatory mediators play an important role in the pathogenesis of immune-mediated hepatitis, we further exposed mouse RAW264 macrophage cell lines to ConA in vitro and found that DHQ significantly inhibited mRNA expression and secretion of IFN-γ and TNF-α in cell culture supernatant. In addition, DHQ significantly enhanced heme oxygenase-1 (HO-1) expression in a dose- and time-dependent manner via increased Nrf2 expression in cytoplasm and nuclear translocation. Furthermore, DHQ enhanced phosphorylation of three members of the mitogen-activated protein kinase (MAPK) family, and cell treatment with MEK/ERK (PD98059), p38 (SB203580) and JNK (SP600125) inhibitors reduced DHQ-induced HO-1 expression. These results indicate that DHQ possesses hepatoprotective properties against ConA-induced liver injury, which are attributed to its ability to scavenge oxidative stress and to inhibit the release of inflammatory mediators via upregulation of HO-1 activity through the MAPK/Nrf2 signaling pathway in macrophages/Kupffer cells.

Tissue-Specific Regulation of p38α-Mediated Inflammation in Con A-Induced Acute Liver Damage

Because p38α plays a critical role in inflammation, it has been an attractive target for the development of anti-inflammation therapeutics. However, p38α inhibitors showed side effects, including severe liver toxicity, that often prevailed over the benefits in clinical studies, and the mechanism of toxicity is not clear. In this study, we demonstrate that p38α regulates the inflammatory responses in acute liver inflammation in a tissue-specific manner, and liver toxicity by p38α inhibitors may be a result of the inhibition of protective activity of p38α in the liver. Genetic ablation of p38α in T and NKT cells protected mice from liver injury in Con A-induced liver inflammation, whereas liver-specific deletion of p38α aggravated liver pathology. We found that p38α deficiency in the liver increased the expression of chemokines to recruit more inflammatory cells, indicating that p38α in the liver plays a protective anti-inflammatory role during acute liver inflammation. Therefore, our results suggest that p38α regulates the inflammatory responses in a tissue-specific manner, and that the tissue-specific p38α targeting strategies can be used for the development of an effective anti-inflammation treatment with an improved side-effect profile.

Acute and chronic effects of IL-22 on acetaminophen-induced liver injury

Acetaminophen (APAP)-induced liver injury (AILI) accounts for half of the acute liver failure cases in the United States. A better understanding of the underlying mechanisms of AILI is necessary for the development of novel antidotes. We found that pretreatment with IL-22 protected mice from APAP-mediated hepatotoxicity. The protection was dependent on STAT3, as IL-22 failed to reduce APAP hepatotoxicity in liver-specific STAT3 knockout mice. In contrast to the acute exposure to IL-22, the endogenous chronic overexpression of IL-22 in IL-22 transgenic (TG) mice or IL-22 adenovirus treatment for 6 wk resulted in a markedly increased susceptibility to AILI. Furthermore, the hepatic expression levels of cytochrome 2E1 (Cyp2E1) and Cyp1A2 were much higher in IL-22TG mice. Ablation of Cyp2E1 but not hepatic STAT3 abolished AILI and protein-adduct formation in IL-22TG mice. Finally, hepatic expression of HNF-1α, a transcriptional factor that is known to control Cyp2E1 expression, was elevated in IL-22TG mice compared with wild-type mice. Upregulation of hepatic Cyp2E1 was only observed in mice with constitutive overexpression of IL-22 but not with short-term treatment with one dose of IL-22 or multiple doses of IL-22 for 2 wk. In conclusion, short-term acute IL-22 exposure protects mice against AILI through STAT3 activation; however, chronic constitutive overexpression of IL-22 exacerbates AILI by increasing Cyp2E1 and toxic reactive APAP metabolite production. These findings may not only enhance our understanding of the effects of chronic inflammation on AILI in patients with liver disease, but are also helpful to identify novel therapeutic targets for the treatment of AILI.

Tonsil-derived mesenchymal stem cells alleviate concanavalin A-induced acute liver injury

Acute liver failure, the fatal deterioration of liver function, is the most common indication for emergency liver transplantation, and drug-induced liver injury and viral hepatitis are frequent in young adults. Stem cell therapy has come into the limelight as a potential therapeutic approach for various diseases, including liver failure and cirrhosis. In this study, we investigated therapeutic effects of tonsil-derived mesenchymal stem cells (T-MSCs) in concanavalin A (ConA)- and acetaminophen-induced acute liver injury. ConA-induced hepatitis resembles viral and immune-mediated hepatic injury, and acetaminophen overdose is the most frequent cause of acute liver failure in the United States and Europe. Intravenous administration of T-MSCs significantly reduced ConA-induced hepatic toxicity, but not acetaminophen-induced liver injury, affirming the immunoregulatory capacity of T-MSCs. T-MSCs were successfully recruited to damaged liver and suppressed inflammatory cytokine secretion. T-MSCs expressed high levels of galectin-1 and -3, and galectin-1 knockdown which partially diminished interleukin-2 and tumor necrosis factor α secretion from cultured T-cells. Galectin-1 knockdown in T-MSCs also reversed the protective effect of T-MSCs on ConA-induced hepatitis. These results suggest that galectin-1 plays an important role in immunoregulation of T-MSCs, which contributes to their protective effect in immune-mediated hepatitis. Further, suppression of T-cell activation by frozen and thawed T-MSCs implies great potential of T-MSC banking for clinical utilization in immune-mediated disease.

Update on primary sclerosing cholangitis genetics

PURPOSE OF REVIEW

The pathogenesis of primary sclerosing cholangitis (PSC) involves heritable factors. This review summarizes the recent genetic studies and discusses the implications of identified risk loci.

RECENT FINDINGS

A total of 16 PSC susceptibility loci have been identified in genome-wide association studies and related study designs. At least 33 additional loci are involved in what is increasingly acknowledged to represent a general pool of genetic risk loci for immune-mediated diseases. One important group of genes is part of well characterized immune pathways (e.g. interleukin 2 signaling), whereas for other loci the relationship to PSC pathophysiology is less evident. Importantly, the loci collectively account for only 7.3% of overall PSC liability, thus pointing to a large contribution from environmental factors to PSC development. The individual PSC risk genes cannot be interpreted within a simple cause-effect model used for monogenic traits, but need to be explored for their individual biological correlates, preferably in a disease context. To some extent, as exemplified for the human leukocyte antigen and FUT2 associations, genetic findings may guide the discovery of interacting and co-occuring environmental susceptibility factors.

SUMMARY

Multiple PSC susceptibility loci are now available for exploration in experimental model systems and patient-centered research.

Interleukin-22: A Bridge Between Epithelial Innate Host Defense and Immune Cells

Interleukin-22 (IL-22), an IL-10 family cytokine, is produced by various leukocytes. The receptor of IL-22, however, is preferentially detected on peripheral tissue epithelial cells. IL-22 functions as a unique messenger from immune system to tissue epithelial cells and to regulate homeostasis of epithelia. IL-22 is able to directly enhance antimicrobial defense mechanisms in epithelial cells and to facilitate epithelial barrier repair and wound healing process. It, therefore, possesses an irreplaceable role in host defense against certain pathogens that specifically invade epithelial cells. In addition, IL-22 can help to preserve the integrity and homeostasis of various epithelial organs during infection or inflammation. The importance of its tissue-protective function is manifested in many inflammatory situations such as inflammatory bowel diseases (IBD) and hepatitis. On the other hand, as a cytokine, IL-22 is capable of induction of proinflammatory responses, especially in synergy with other cytokines. Consequently, IL-22 contributes to pathogenesis of certain inflammatory diseases for example psoriasis.

Interleukin-22 as a molecular adjuvant facilitates IL-17-producing CD8+ T cell responses against a HBV DNA vaccine in mice

Interleukin-22 (IL-22) is mainly produced by activated Th1 cells, Th17 cells and NK cells and promotes anti-microbial defense, pro-inflammatory and tissue remodeling responses. However, its potential use as a vaccine adjuvant has not been tested. In this study, we tested if a DNA construct expressing IL-22 (pVAX-IL-22) could be used as a molecular adjuvant to enhance host immune responses induced by HBV DNA vaccination (pcD-S2). After immunizing mice with pcD-S2 combined with pVAX-IL-22, we didn't find enhancement of HBsAg-specific antibody responses in comparison to mice immunized with pcD-S2 alone. However, there was an enhancement of the level of IL-17 expression in antigen specific CD8(+) cytotoxic T lymphocytes (Tc17). By using CD8 T-cell knockout (KO) and IL-17 KO mice, Tc17 cells were found to be a dominant population driving cytotoxicity. Importantly, there was a correlation between pVAX-IL-22 enhancement of T lymphocytes and a reduction of HBsAg-positive hepatocytes in HBsAg transgenic mice. These results demonstrate that IL-22 might be used as an effective adjuvant to enhance cellular immune responses during HBsAg DNA vaccination since it can induce Tc17 cells to break tolerance in HBsAg transgenic mice.

Protective effects of necrostatin-1 against concanavalin A-induced acute hepatic injury in mice

Objective. Necrostatin-1 (Nec-1) inhibits receptor-interacting protein 1 (RIP1) kinase and programmed necrosis. This study was designed to examine the protective effects and mechanisms of Nec-1 in concanavalin A- (ConA-) induced hepatitis in mice. Methods. C57BL/6 mice were exposed to ConA via tail vein injection and injected intraperitoneally with Nec-1 or vehicle. Levels of serum liver enzymes and histopathology were determined. Levels of inflammatory cytokines with ConA-induced hepatitis were determined with real-time polymerase chain reaction (real-time PCR). The expression of TNF-α, RIP1, and LC3 was detected with immunohistochemical staining. The expression of TNF-α, IFN-γ, IL2, IL6, caspase 3, RIP1, beclin-1, and LC3 protein was assessed by immunofluorescence and western blotting. Autophagosomes were observed with transmission electron microscopy (TEM). Results. Amelioration in liver functions and histopathological changes and the suppression of inflammatory cytokine production were observed in Nec-1-injected mice. Western blotting analysis showed that the expression of TNF-α, IFN-γ, IL2, IL6, and RIP1 was significantly reduced in the Nec-1-injected mice, which was confirmed by immunofluorescence and immunohistochemistry. Autophagosome formation was significantly reduced by Nec-1 treatment, as the expression of beclin-1 and LC3, determined with immunofluorescence and western blotting. Conclusion. These results demonstrate that Nec-1 prevents ConA-induced liver injury via RIP1-related and autophagy-related pathways.

HVEM: An unusual TNF receptor family member important for mucosal innate immune responses to microbes

The herpes virus entry mediator (HVEM or CD270) is a member of the tumor necrosis factor receptor superfamily (TNFRSF), and therefore it is also known as TNFRSF14. We have recently provided evidence showing a novel signaling pathway downstream of HVEM leading to signal transducer and activator of transcription 3 (STAT3) activation in epithelial cells. As STAT3 regulates the expression of genes important for host defense in epithelial cells, as well as the differentiation of retinoid-related orphan receptor (ROR)γt+ Th17 and innate lymphoid cells (ILC), our finding that HVEM activates STAT3 has revealed fresh insights into the potential regulatory function of HVEM in different cellular contexts. Therefore, although further investigations will be required, HVEM is emerging as a major player in mucosal host defense, capable of regulating several cellular responses.

IL-22, not simply a Th17 cytokine

Interleukin-22 (IL-22) has important functions in host defense at mucosal surfaces as well as in tissue repair. It is unique as a cytokine that is produced by immune cells, including T-helper (Th) cell subsets and innate lymphocytes, but acts only on non-hematopoietic stromal cells, in particular epithelial cells, keratinocytes, and hepatocytes. Although IL-22 is beneficial to the host in many infectious and inflammatory disorders, depending on the target tissue it can be pathogenic due to its inherent pro-inflammatory properties, which are further enhanced when IL-22 is released together with other pro-inflammatory cytokines, in particular IL-17. To avoid pathology, IL-22 and IL-17 production have to be controlled tightly and independently. While common factors such as signal transducer and activator of transcription 3 (STAT3) and retinoid orphan receptor γt (RORγt) drive the expression of both cytokines, other factors, such as c-Maf act specifically on IL-22 and enable the separate expression of either cytokine. Here, we discuss the production of IL-22 from various T-cell populations as well as protective versus pathogenic roles of IL-22. Finally, we focus on recent advances in our understanding of the molecular regulation of IL-22 in T cells.

Interleukin-22 inhibits bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is a progressive and fatal fibrotic disease of the lungs with unclear etiology. Recent insight has suggested that early injury/inflammation of alveolar epithelial cells could lead to dysregulation of tissue repair driven by multiple cytokines. Although dysregulation of interleukin- (IL-) 22 is involved in various pulmonary pathophysiological processes, the role of IL-22 in fibrotic lung diseases is still unclear and needs to be further addressed. Here we investigated the effect of IL-22 on alveolar epithelial cells in the bleomycin- (BLM-) induced pulmonary fibrosis. BLM-treated mice showed significantly decreased level of IL-22 in the lung. IL-22 produced γδ T cells were also decreased significantly both in the tissues of lungs and spleens. Administration of recombinant human IL-22 to alveolar epithelial cell line A549 cells ameliorated epithelial to mesenchymal transition (EMT) and partially reversed the impaired cell viability induced by BLM. Furthermore, blockage of IL-22 deteriorated pulmonary fibrosis, with elevated EMT marker ( α -smooth muscle actin ( α -SMA)) and overactivated Smad2. Our results indicate that IL-22 may play a protective role in the development of BLM-induced pulmonary fibrosis and may suggest IL-22 as a novel immunotherapy tool in treating pulmonary fibrosis.

In vitro antigen-specific induction of IL-22 in human subjects that resolved HCV infection

AIMS: To determine if in vitro production of IL-22 and IL-17 correlated with resolution of HCV infection. MATERIALS #ENTITYSTARTX00026; METHODS: Human peripheral blood cells isolated from a well-defined cohort of resolved and chronic HCV-infected subjects were used to measure HCV-, influenza- and mitogen-activated T-cell proliferation. In addition, IL-22 and IL-17 production was measured via ELISAs and flow cytometry. RESULTS: Resolved HCV subjects had a significantly higher T-cell proliferative response to recombinant NS3 protein compared with chronic HCV subjects. Resolved subjects had a dose-dependent IL-22 response to recombinant NS3 compared with chronic HCV subjects. CONCLUSION: IL-22 production is associated with antigen-specific induction of CD4 (+) T cells in individuals that resolved HCV infection, suggesting a potential role for IL-22 in HCV clearance.

IL-22 Protects Against Liver Pathology and Lethality of an Experimental Blood-Stage Malaria Infection

The host response following malaria infection depends on a fine balance between levels of pro-inflammatory and anti-inflammatory mediators resulting in the resolution of the infection or immune-mediated pathology. Whilst other components of the innate immune system contribute to the pro-inflammatory milieu, T cells play a major role. For blood-stage malaria, CD4(+) and γδ T cells are major producers of the IFN-γ that controls parasitemia, however, a role for TH17 cells secreting IL-17A and other cytokines, including IL-17F and IL-22 has not yet been investigated in malaria. TH17 cells have been shown to play a role in some protozoan infections, but they also are a source of pro-inflammatory cytokines known to be involved in protection or pathogenicity of infections. In the present study, we have investigated whether IL-17A and IL-22 are induced during a Plasmodium chabaudi infection in mice, and whether these cytokines contribute to either protection or to pathology induced during the infection. Although small numbers of IL-17- and IL-22-producing CD4 T cells are induced in the spleens of infected mice, a more pronounced induction is observed in the liver, where increases in mRNA for IL-17A and, to a lesser extent, IL-22 were observed and CD8(+) T cells, rather than CD4 T cells, are a major source of these cytokines in this organ. Although the lack of IL-17 did not affect the outcome of infection or pathology, lack of IL-22 resulted in 50% mortality within 12 days after infection with significantly greater weight loss at the peak of infection and significant increase in alanine transaminase in the plasma in the acute infection. As parasitemias and temperature were similar in IL-22 KO and wild-type control mice, our observations support the idea that IL-22 but not IL-17 provides protection from the potentially lethal effects of liver damage during a primary P. chabaudi infection.

Interleukin-22 is produced by invariant natural killer T lymphocytes during influenza A virus infection: potential role in protection against lung epithelial damages

Invariant natural killer T (iNKT) cells are non-conventional lipid-reactive αβ T lymphocytes that play a key role in host responses during viral infections, in particular through the swift production of cytokines. Their beneficial role during experimental influenza A virus (IAV) infection has recently been proposed, although the mechanisms involved remain elusive. Here we show that during in vivo IAV infection, mouse pulmonary iNKT cells produce IFN-γ and IL-22, a Th17-related cytokine critical in mucosal immunity. Although permissive to viral replication, IL-22 production by iNKT cells is not due to IAV infection per se of these cells but is indirectly mediated by IAV-infected dendritic cells (DCs). We show that activation of the viral RNA sensors TLR7 and RIG-I in DCs is important for triggering IL-22 secretion by iNKT cells, whereas the NOD-like receptors NOD2 and NLRP3 are dispensable. Invariant NKT cells respond to IL-1β and IL-23 provided by infected DCs independently of the CD1d molecule to release IL-22. In vitro, IL-22 protects IAV-infected airway epithelial cells against mortality but has no role on viral replication. Finally, during early IAV infection, IL-22 plays a positive role in the control of lung epithelial damages. Overall, IAV infection of DCs activates iNKT cells, providing a rapid source of IL-22 that might be beneficial to preserve the lung epithelium integrity.

Molecular Mechanisms Governing IL-24 Gene Expression

Interleukin-24 (IL-24) belongs to the IL-10 family of cytokines and is well known for its tumor suppressor activity. This cytokine is released by both immune and nonimmune cells and acts on non-hematopoietic tissues such as skin, lung and reproductive tissues. Apart from its ubiquitous tumor suppressor function, IL-24 is also known to be involved in the immunopathology of autoimmune diseases like psoriasis and rheumatoid arthritis. Although the cellular sources and functions of IL-24 are being increasingly investigated, the molecular mechanisms of IL-24 gene expression at the levels of signal transduction, epigenetics and transcription factor binding are still unclear. Understanding the specific molecular events that regulate the production of IL-24 will help to answer the remaining questions that are important for the design of new strategies of immune intervention involving IL-24. Herein, we briefly review the signaling pathways and transcription factors that facilitate, induce, or repress production of this cytokine along with the cellular sources and functions of IL-24.

IL-22 attenuates IL-25 production by lung epithelial cells and inhibits antigen-induced eosinophilic airway inflammation

BACKGROUND

IL-22 functions as both a proinflammatory cytokine and an anti-inflammatory cytokine in various inflammations, depending on the cellular and cytokine milieu. However, the roles of IL-22 in the regulation of allergic airway inflammation are still largely unknown.

OBJECTIVE

We sought to determine whether IL-22 is involved in the regulation of allergic airway inflammation.

METHODS

We examined IL-22 production and its cellular source at the site of antigen-induced airway inflammation in mice. We also examined the effect of IL-22 neutralization, as well as IL-22 administration, on antigen-induced airway inflammation. We finally examined the effect of IL-22 on IL-25 production from a lung epithelial cell line (MLE-15 cells).

RESULTS

Antigen inhalation induced IL-22 production in the airways of sensitized mice. CD4(+) T cells, but not other lymphocytes or innate cells, infiltrating in the airways produced IL-22, and one third of IL-22-producing CD4(+) T cells also produced IL-17A. The neutralization of IL-22 by anti-IL-22 antibody enhanced antigen-induced IL-13 production, eosinophil recruitment, and goblet cell hyperplasia in the airways. On the other hand, intranasal administration of recombinant IL-22 attenuated antigen-induced eosinophil recruitment into the airways. Moreover, anti-IL-22 antibody enhanced antigen-induced IL-25 production in the airways, and anti-IL-25 antibody reversed the enhancing effect of anti-IL-22 antibody on antigen-induced eosinophil recruitment into the airways. Finally, IL-22 inhibited IL-13-mediated enhancement of IL-25 expression in IL-1β- or LPS-stimulated MLE-15 cells.

CONCLUSION

IL-22 attenuates antigen-induced airway inflammation, possibly by inhibiting IL-25 production by lung epithelial cells.

Regulation of the development of acute hepatitis by IL-23 through IL-22 and IL-17 production

IL-23 plays a critical role in the expansion of highly proinflammatory Th17 cells secreting IL-17 and IL-22. Recently, we demonstrated that Notch signaling drives IL-22 secretion through the aryl hydrocarbon receptor (AHR) and plays a protective role in Con A-induced hepatitis. In this study, we investigated the role of IL-23 in hepatitis using IL-23p19- and IL-17-deficient mice. In WT mice, the injection of Con A induced the upregulation of various cytokines, which included IL-23, IL-22, IL-17, IFN-γ and TNF-α. In IL-23p19-deficient mice, exacerbated hepatitis was observed and serum IL-22 and IL-17 levels were greatly reduced, whereas in IL-17-deficient mice, ameliorated hepatitis was observed. The injection of exogenous IL-22 protected p19-deficient mice from hepatitis, whereas the injection of exogenous IL-23 significantly increased the serum levels of not only IL-22 but also IL-17, and less effectively protected against hepatitis in IL-17-dependent and -independent manners. Finally, it was revealed that STAT3, STAT4 and Notch contributed to the production of both the cytokines, and that the AHR was important only for IL-22 production in response to Con A and IL-23 in liver mononuclear cells. These results suggest that IL-23 plays a protective role in hepatitis through IL-22 production and also a pathological role via IL-17-dependent and -independent mechanisms.

Aryl hydrocarbon receptor-induced signals up-regulate IL-22 production and inhibit inflammation in the gastrointestinal tract

BACKGROUND & AIMS

The pathogenesis of inflammatory bowel disease (IBD) is believed to involve an altered balance between effector and regulatory T cells. Aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor that mediates the toxicity of dioxins, controls T-cell responses. We investigated the role of AhR in inflammation and pathogenesis of IBD in humans and mouse models.

METHODS

AhR expression was evaluated in intestinal tissue samples from patients with IBD and controls by real-time polymerase chain reaction (PCR) and flow cytometry. Intestinal lamina propria mononuclear cells (LPMCs) were activated in the presence or absence of the AhR agonist 6-formylindolo(3, 2-b)carbazole (Ficz). Colitis was induced in mice using trinitrobenzene sulfonic acid (TNBS), dextran sulfate sodium (DSS), or T-cell transfer. Mice were given injections of Ficz or the AhR antagonist 2-metyl-2H-pyrazole-3-carboxylic acid; some mice first received injections of a blocking antibody against interleukin (IL)-22. Cytokines were quantified by real-time PCR and flow cytometry.

RESULTS

Intestine tissue from patients with IBD expressed significantly less AhR than controls. In LPMCs from patients with IBD, incubation with Ficz reduced levels of interferon gamma (IFN)-γ and up-regulated IL-22. Mice injected with Ficz were protected against TNBS-, DSS-, and T-cell transfer-induced colitis; they had marked down-regulation of inflammatory cytokines and induction of IL-22. Mice given AhR antagonist produced more inflammatory cytokines and less IL-22 and developed a severe colitis. Neutralization of endogenous IL-22 disrupted the protective effect of Ficz on TNBS-induced colitis.

CONCLUSIONS

AhR is down-regulated in intestinal tissue of patients with IBD; AhR signaling, via IL-22, inhibits inflammation and colitis in the gastrointestinal tract of mice. AhR-related compounds might be developed to treat patients with IBDs.

Regulation and functions of the IL-10 family of cytokines in inflammation and disease

The IL-10 family of cytokines consists of nine members: IL-10, IL-19, IL-20, IL-22, IL-24, IL-26, and the more distantly related IL-28A, IL-28B, and IL-29. Evolutionarily, IL-10 family cytokines emerged before the adaptive immune response. These cytokines elicit diverse host defense mechanisms, especially from epithelial cells, during various infections. IL-10 family cytokines are essential for maintaining the integrity and homeostasis of tissue epithelial layers. Members of this family can promote innate immune responses from tissue epithelia to limit the damage caused by viral and bacterial infections. These cytokines can also facilitate the tissue-healing process in injuries caused by infection or inflammation. Finally, IL-10 itself can repress proinflammatory responses and limit unnecessary tissue disruptions caused by inflammation. Thus, IL-10 family cytokines have indispensable functions in many infectious and inflammatory diseases.

Border patrol: regulation of immunity, inflammation and tissue homeostasis at barrier surfaces by IL-22

The maintenance of barrier function at exposed surfaces of the mammalian body is essential for limiting exposure to environmental stimuli, preventing systemic dissemination of commensal and pathogenic microbes and retaining normal homeostasis of the entire body. Indeed, dysregulated barrier function is associated with many infectious and inflammatory diseases, including psoriasis, influenza, inflammatory bowel disease and human immunodeficiency virus, which collectively afflict millions of people worldwide. Studies have shown that interleukin 22 (IL-22) is expressed at barrier surfaces and that its expression is dysregulated in certain human diseases, which suggests a critical role in the maintenance of normal barrier homeostasis. Consistent with that, studies of mouse model systems have identified a critical role for signaling by IL-22 through its receptor (IL-22R) in the promotion of antimicrobial immunity, inflammation and tissue repair at barrier surfaces. In this review we will discuss how the expression of IL-22 and IL-22R is regulated, the functions of the IL-22-IL-22R pathway in regulating immunity, inflammation and tissue homeostasis, and the therapeutic potential of targeting this pathway in human disease.

Role of adhesion molecules and inflammation in Venezuelan equine encephalitis virus infected mouse brain

Background

Neuroinvasion of Venezuelan equine encephalitis virus (VEEV) and subsequent initiation of inflammation in the brain plays a crucial role in the outcome of VEEV infection in mice. Adhesion molecules expressed on microvascular endothelial cells in the brain have been implicated in the modulation of the blood brain barrier (BBB) and inflammation in brain but their role in VEEV pathogenesis is not very well understood. In this study, we evaluated the expression of extracellular matrix and adhesion molecules genes in the brain of VEEV infected mice.

Findings

Several cell to cell adhesion molecules and extracellular matrix protein genes such as ICAM-1, VCAM-1, CD44, Cadherins, integrins, MMPs and Timp1 were differentially regulated post-VEEV infection. ICAM-1 knock-out (IKO) mice infected with VEEV had markedly reduced inflammation in the brain and demonstrated a delay in the onset of clinical symptoms of disease. A differential regulation of inflammatory genes was observed in the IKO mice brain compared to their WT counterparts.

Conclusions

These results improve our present understanding of VEEV induced inflammation in mouse brain.

Signal transducer and activator of transcription 3 in liver diseases: a novel therapeutic target

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is activated by many cytokines and growth factors and plays a key role in cell survival, proliferation, and differentiation. STAT3 activation is detected virtually in all rodent models of liver injury and in human liver diseases. In this review, we highlight recent advances of STAT3 signaling in liver injury, steatosis, inflammation, regeneration, fibrosis, and hepatocarcinogenesis. The cytokines and small molecules that activate STAT3 in hepatocytes may have therapeutic benefits to treat acute liver injury, fatty liver disease, and alcoholic hepatitis, while blockage of STAT3 may have a therapeutic potential to prevent and treat liver cancer.

Role of myeloid-derived suppressor cells in amelioration of experimental autoimmune hepatitis following activation of TRPV1 receptors by cannabidiol

Background

Myeloid-derived suppressor cells (MDSCs) are getting increased attention as one of the main regulatory cells of the immune system. They are induced at sites of inflammation and can potently suppress T cell functions. In the current study, we demonstrate how activation of TRPV1 vanilloid receptors can trigger MDSCs, which in turn, can inhibit inflammation and hepatitis.

Methodology/Principal Findings

Polyclonal activation of T cells, following injection of concanavalin A (ConA), in C57BL/6 mice caused acute hepatitis, characterized by significant increase in aspartate transaminase (AST), induction of inflammatory cytokines, and infiltration of mononuclear cells in the liver, leading to severe liver injury. Administration of cannabidiol (CBD), a natural non-psychoactive cannabinoid, after ConA challenge, inhibited hepatitis in a dose-dependent manner, along with all of the associated inflammation markers. Phenotypic analysis of liver infiltrating cells showed that CBD-mediated suppression of hepatitis was associated with increased induction of arginase-expressing CD11b⁺Gr-1⁺ MDSCs. Purified CBD-induced MDSCs could effectively suppress T cell proliferation in vitro in arginase-dependent manner. Furthermore, adoptive transfer of purified MDSCs into naïve mice conferred significant protection from ConA-induced hepatitis. CBD failed to induce MDSCs and suppress hepatitis in the livers of vanilloid receptor-deficient mice (TRPV1^−/−) thereby suggesting that CBD primarily acted via this receptor to induce MDSCs and suppress hepatitis. While MDSCs induced by CBD in liver consisted of granulocytic and monocytic subsets at a ratio of ∼2∶1, the monocytic MDSCs were more immunosuppressive compared to granulocytic MDSCs. The ability of CBD to induce MDSCs and suppress hepatitis was also demonstrable in Staphylococcal enterotoxin B-induced liver injury.

Conclusions/Significance

This study demonstrates for the first time that MDSCs play a critical role in attenuating acute inflammation in the liver, and that agents such as CBD, which trigger MDSCs through activation of TRPV1 vanilloid receptors may constitute a novel therapeutic modality to treat inflammatory diseases.

Activation of farnesoid X receptor attenuates liver injury in systemic lupus erythematosus

To investigate the expression and effect of farnesoid X receptor (FXR) on systemic lupus erythematosus (SLE) liver dysfunction and indicate its hepatoprotective role and the immunomodulatory property. mRNA and protein levels of FXR were determined on the liver specimens of SLE patients with liver injury as well as MRL/lpr rodent models. The FXR agonist chenodeoxycholic acid (CDCA) was administrated to MRL/lpr mice and the control BALB/C with concanavalin A (ConA)-induced liver injury. Blood samples were taken 0, 4, 8, 12, 16, and 24 h after ConA injection for the detection of serum ALT, AST, IFN-γ, TNF-α, and IL-6. FXR was down-regulated at both mRNA and protein levels in the liver specimens of SLE patients with liver injury as well as MRL/lpr mice. MRL/lpr was more susceptible to ConA than BALB/C indicated by significantly higher levels of aminotransferase and inflammatory cytokines. Activation of FXR by CDCA significantly reduced aminotransferase and inflammatory cytokines IFN-γ, TNF-α, and IL-6 caused by ConA injection in MRL/lpr mice. FXR was down-regulated in SLE patients as well as MRL/lpr lupus models with liver dysfunction. FXR activation ameliorated liver injury and suppressed inflammatory cytokines, thereby showing its protective function in SLE. Our findings raised the promising potential target for the treatment of SLE liver injury.

IL-20: biological functions mediated through two types of receptor complexes

IL-20 was discovered 10 years ago as a new member of the IL-10 family of cytokines. IL-20 shares the highest amino-acid sequence identity with IL-10, IL-24 and IL-19. IL-20 is secreted by immune cells and activated epithelial cells like keratinocytes. A high expression of the corresponding IL-20 receptor chains is detected on epithelial cells. In terms of function, IL-20 might therefore mediate a crosstalk between epithelial cells and tissue-infiltrating immune cells under inflammatory conditions. Transgenic and knockout mouse models for some cytokines and receptors of the IL-10-type cytokines have provided new insights into the biology of this family. This review will focus on the biological functions of IL-20 and its receptors within the IL-10 cytokine network.

Interleukin-22: a cytokine produced by T, NK and NKT cell subsets, with importance in the innate immune defense and tissue protection

Interleukin (IL)-22 is a member of the IL-10 cytokine family that is produced by special immune cell populations, including Th22, Th1, and Th17 cells, classical and non-classical (NK-22) NK cells, NKT cells, and lymphoid tissue inducer cells. This cytokine does not influence cells of the hematopoietic lineage. Instead, its target cells are certain tissue cells from the skin, liver and kidney, and from organs of the respiratory and gastrointestinal systems. The main biological role of IL-22 includes the increase of innate immunity, protection from damage, and enhancement of regeneration. IL-22 can play either a protective or a pathogenic role in chronic inflammatory diseases depending on the nature of the affected tissue and the local cytokine milieu. This review highlights the primary effects of IL-22 on its target cells, its role in the defense against infections, in tumorigenesis, in inflammatory diseases and allergy as well as the potential of the therapeutic modulation of IL-22 action.

Th17 cells and their associated cytokines in liver diseases

T helper 17 (Th17) cells are a newly identified subset of T helper cells that play important roles in host defense against extracellular bacteria as well as in the pathogenesis of autoimmune disease. The functions of Th17 cells are mediated via the production of several cytokines including interleukin (IL)-17 and IL-22. Recent studies show that the frequency of IL-17(+) cells is significantly elevated in a variety of chronic liver diseases including alcoholic liver disease, viral hepatitis and hepatocellular carcinoma. IL-17 receptor is expressed virtually on all types of liver cells, while IL-22 receptor expression is restricted to epithelial cells including hepatocytes in the liver. IL-17 seems to play an important role in inducing liver inflammation via stimulating multiple types of liver nonparenchymal cells to produce proinflammatory cytokines and chemokines, while IL-22 appears to be an important factor in promoting hepatocyte survival and proliferation.

The bile acid sensor farnesoid X receptor is a modulator of liver immunity in a rodent model of acute hepatitis

Immune-mediated liver diseases including autoimmune and viral hepatitis are a major health problem worldwide. In this study, we report that activation of the farnesoid X receptor (FXR), a member of the ligand-activated nuclear receptor superfamily and bile sensor highly expressed in the liver, attenuates liver injury in a model of autoimmune hepatitis induced by Con A. We found that FXR gene ablation results in a time-dependent increase of liver expression (up to 20-fold in a 9-mo-old mouse) of osteopontin, a NKT cell-derived extracellular matrix protein and immunoregulatory cytokine. In comparison to wild-type, FXR(-/-) mice are more susceptible to Con A-induced hepatitis and react to Con A administration by an unregulated production of osteopontin. Administering wild-type mice with a synthetic FXR agonist attenuated Con A-induced liver damage and liver expression of the osteopontin gene. By in vitro studies, we found that FXR is expressed by primarily isolated NKT cells and its ablation favors ostepontin production in response to Con A. Chromatin immunoprecipitation assay and coimmunoprecipitation experiments demonstrate that the short heterodimer partner (SHP), a nuclear receptor and FXR target, was expressed by NKT cell hybridomas and increased in response to FXR activation. FXR activates SHP that interacts with and inhibits c-Jun binding to the osteopontin promoter. These data indicate that in NKT cells, FXR activation causes a SHP-mediated inhibition of osteopontin production. These data support the notion that the bile acid sensor FXR regulates the activation of liver NKT cells.