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Cytokine regulation of high-output nitric oxide (NO) derived from inducible NO synthase (iNOS) is critically involved in inflammation biology and host defense. Herein, we set out to characterize the role of type I interferon (IFN) as potential regulator of hepatic iNOS in vitro and in vivo. In this regard, we identified in murine Hepa1-6 hepatoma cells a potent synergism between pro-inflammatory interleukin-β/tumor necrosis factor-α and immunoregulatory IFNβ as detected by analysis of iNOS expression and nitrite release. Upregulation of iNOS by IFNβ coincided with enhanced binding of signal transducer and activator of transcription-1 to a regulatory region at the murine iNOS promoter known to support target gene expression in response to this signaling pathway. Synergistic iNOS induction under the influence of IFNβ was confirmed in alternate murine Hepa56.1D hepatoma cells and primary hepatocytes. To assess iNOS regulation by type I IFN in vivo, murine acetaminophen (APAP)-induced sterile liver inflammation was investigated. In this model of acute liver injury, excessive necroinflammation drives iNOS expression in diverse liver cell types, among others hepatocytes. Herein, we demonstrate impaired iNOS expression in type I IFN receptor-deficient mice which associated with diminished APAP-induced liver damage. Data presented indicate a vital role of type I IFN within the inflamed liver for fine-tuning pathological processes such as overt iNOS expression.
Interleukin (IL)-22 is a STAT3-activating cytokine displaying characteristic AU-rich elements (ARE) in the 3'-untranslated region (3'-UTR) of its mRNA. This architecture suggests gene regulation by modulation of mRNA stability. Since related cytokines undergo post-transcriptional regulation by ARE-binding tristetraprolin (TTP), the role of this destabilizing protein in IL-22 production was investigated. Herein, we demonstrate that TTP-deficient mice display augmented serum IL-22. Likewise, IL-22 mRNA was enhanced in TTP-deficient splenocytes and isolated primary T cells. A pivotal role for TTP is underscored by an extended IL-22 mRNA half-life detectable in TTP-deficient T cells. Luciferase-reporter assays performed in human Jurkat T cells proved the destabilizing potential of the human IL-22-3'-UTR. Furthermore, overexpression of TTP in HEK293 cells substantially decreased luciferase activity directed by the IL-22-3'-UTR. Transcript destabilization by TTP was nullified upon cellular activation by TPA/A23187, an effect dependent on MEK1/2 activity. Accordingly, IL-22 mRNA half-life as determined in TPA/A23187-stimulated Jurkat T cells decreased under the influence of the MEK1/2 inhibitor U0126. Altogether, data indicate that TTP directly controls IL-22 production, a process counteracted by MEK1/2. The TTP-dependent regulatory pathway described herein likely contributes to the role of IL-22 in inflammation and cancer and may evolve as novel target for pharmacological IL-22 modulation.
Acetaminophen (APAP, N-acetyl-p-aminophenol, or paracetamol) overdosing is a prevalent cause of acute liver injury. While clinical disease is initiated by overt parenchymal hepatocyte necrosis in response to the analgetic, course of intoxication is substantially influenced by associated activation of innate immunity. This process is supposed to be set in motion by release of danger-associated molecular patterns (DAMPs) from dying hepatocytes and is accompanied by an inflammatory cytokine response. Murine models of APAP-induced liver injury emphasize the complex role that DAMPs and cytokines play in promoting either hepatic pathogenesis or resolution and recovery from intoxication. Whereas the function of key inflammatory cytokines is controversially discussed, a subclass of specific cytokines capable of efficiently activating the hepatocyte signal transducer and activator of transcription (STAT)-3 pathway stands out as being consistently protective in murine models of APAP intoxication. Those include foremost interleukin (IL)-6, IL-11, IL-13, and IL-22. Above all, activation of STAT3 under the influence of these cytokines has the capability to drive hepatocyte compensatory proliferation, a key principle of the regenerating liver. Herein, the role of these specific cytokines during experimental APAP-induced liver injury is highlighted and discussed in a broader perspective. In hard-to-treat or at-risk patients, standard therapy may fail and APAP intoxication can proceed toward a fatal condition. Focused administration of recombinant STAT3-activating cytokines may evolve as novel therapeutic approach under those ill-fated conditions.
Interleukin (IL)-10 and IL-22 are key members of the IL-10 cytokine family that share characteristic properties such as defined structural features, usage of IL-10R2 as one receptor chain, and activation of signal transducer and activator of transcription (STAT)-3 as dominant signaling mode. IL-10, formerly known as cytokine synthesis inhibitory factor, is key to deactivation of monocytes/macrophages and dendritic cells. Accordingly, pre-clinical studies document its anti-inflammatory capacity. However, the outcome of clinical trials assessing the therapeutic potential of IL-10 in prototypic inflammatory disorders has been disappointing. In contrast to IL-10, IL-22 acts primarily on non-leukocytic cells, in particular epithelial cells of intestine, skin, liver, and lung. STAT3-driven proliferation, anti-apoptosis, and anti-microbial tissue protection is regarded a principal function of IL-22 at host/environment interfaces. In this hypothesis article, hidden/underappreciated pro-inflammatory characteristics of IL-10 and IL-22 are outlined and related to cellular priming by type I interferon. It is tempting to speculate that an inherent inflammatory potential of IL-10 and IL-22 confines their usage in tissue protective therapy and beyond that determines in some patients efficacy of type I interferon treatment.
BACKGROUND: Recent findings support the idea that interleukin (IL)-22 serum levels are related to disease severity in end-stage liver disease. Existing scoring systems--Model for End-Stage Liver Disease (MELD), Survival Outcomes Following Liver Transplantation (SOFT) and Pre-allocation-SOFT (P-SOFT)--are well-established in appraising survival rates with or without liver transplantation. We tested the hypothesis that IL-22 serum levels at transplantation date correlate with survival and potentially have value as a predictive factor for survival.
MATERIAL AND METHODS: MELD, SOFT, and P-SOFT scores were calculated to estimate post-transplantation survival. Serum levels of IL-22, IL-6, IL-10, C-reactive protein (CRP), and procalcitonin (PCT) were collected prior to transplantation in 41 patients. Outcomes were assessed at 3 months, 1 year, and 3 years after transplantation.
RESULTS: IL-22 significantly correlated with MELD, P-SOFT, and SOFT scores (Rs 0.35, 0.63, 0.56 respectively, p<0.05) and with the discrimination in post-transplantation survival. IL-6 showed a heterogeneous pattern (Rs 0.40, 0.63, 0.57, respectively, p<0.05); CRP and PCT did not correlate. We therefore added IL-22 serum values to existing scoring systems in a generalized linear model (GLM), resulting in a significantly improved outcome prediction in 58% of the cases for both the P-SOFT (p<0.01) and SOFT scores (p<0.001).
CONCLUSIONS: Further studies are needed to address the concept that IL-22 serum values at the time of transplantation provide valuable information about survival rates following orthotopic liver transplantation.
Interleukin (IL)-18, formerly known as interferon (IFN)-γ-inducing factor, is a crucial mediator of host defence and inflammation. Control of IL-18 bioactivity by its endogenous antagonist IL-18 binding protein (IL-18BP) is a major objective of immunoregulation. IL-18BP is strongly up-regulated by IFN-γ, thereby establishing a negative feedback mechanism detectable in cell culture and in vivo. Here we sought to investigate in D.L. Dexter (DLD) colon carcinoma cells molecular mechanisms of IL-18BP induction under the influence of IFN-γ. Mutational analysis revealed that a proximal γ-activated sequence (GAS) at the IL-18BP promoter is of pivotal importance for expression by IFN-γ-activated cells. Use of siRNA underscored the essential role of the signal transducer and activator of transcription (STAT)-1 in this process. Indeed, electrophoretic mobility shift assay and chromatin immunoprecipitation analysis proved STAT1 binding to this particular GAS site. Maximal expression of IL-18BP was dependent on de novo protein synthesis but unaffected by silencing of interferon regulatory factor-1. Altogether, data presented herein indicate that direct action of STAT1 on the IL-18BP promoter at the proximal GAS element is key to IL-18BP expression by IFN-γ-stimulated DLD-1 colon carcinoma cells.
IL-22 is an immunoregulatory cytokine displaying pathological functions in models of autoimmunity like experimental psoriasis. Understanding molecular mechanisms driving IL-22, together with knowledge on the capacity of current immunosuppressive drugs to target this process, may open an avenue to novel therapeutic options. Here, we sought to characterize regulation of human IL22 gene expression with focus on the established model of Jurkat T cells. Moreover, effects of the prototypic immunosuppressant cyclosporin A (CsA) were investigated. We report that IL-22 induction by TPA/A23187 (T/A) or αCD3 is inhibited by CsA or related FK506. Similar data were obtained with peripheral blood mononuclear cells or purified CD3(+) T cells. IL22 promoter analysis (-1074 to +156 bp) revealed a role of an NF-AT (-95/-91 nt) and a CREB (-194/-190 nt) binding site for gene induction. Indeed, binding of CREB and NF-ATc2, but not c-Rel, under the influence of T/A to those elements could be proven by ChIP. Because CsA has the capability to impair IκB kinase (IKK) complex activation, the IKKα/β inhibitor IKKVII was evaluated. IKKVII likewise reduced IL-22 induction in Jurkat cells and peripheral blood mononuclear cells. Interestingly, transfection of Jurkat cells with siRNA directed against IKKα impaired IL22 gene expression. Data presented suggest that NF-AT, CREB, and IKKα contribute to rapid IL22 gene induction. In particular the crucial role of NF-AT detected herein may form the basis of direct action of CsA on IL-22 expression by T cells, which may contribute to therapeutic efficacy of the drug in autoimmunity.
Macrophages are highly plastic leukocytes that differentiate from monocytes following their entry into extravascular tissues. Macrophages can enter various tissues under inflammatory or non-inflammatory conditions and assume different functions and phenotypes according to the cues they receive from the environment. The notion that inflammation in general and macrophage responses in particular affect physiological phenomena that were previously considered to be not immune-related has enhanced and broadened our understanding of macrophage function during inflammation and its resolution....
Interleukin-22 predicts severity and death in advanced liver cirrhosis: a prospective cohort study
(2012)
Background: Interleukin-22 (IL-22), recently identified as a crucial parameter of pathology in experimental liver damage, may determine survival in clinical end-stage liver disease. Systematic analysis of serum IL-22 in relation to morbidity and mortality of patients with advanced liver cirrhosis has not been performed so far.
Methods: This is a prospective cohort study including 120 liver cirrhosis patients and 40 healthy donors to analyze systemic levels of IL-22 in relation to survival and hepatic complications.
Results: A total of 71% of patients displayed liver cirrhosis-related complications at study inclusion. A total of 23% of the patients died during a mean follow-up of 196 +/- 165 days. Systemic IL-22 was detectable in 74% of patients but only in 10% of healthy donors (P <0.001). Elevated levels of IL-22 were associated with ascites (P = 0.006), hepatorenal syndrome (P <0.0001), and spontaneous bacterial peritonitis (P = 0.001). Patients with elevated IL-22 (>18 pg/ml, n = 57) showed significantly reduced survival compared to patients with regular ([less than or equal to]18 pg/ml) levels of IL-22 (321 days versus 526 days, P = 0.003). Other factors associated with overall survival were high CRP ([greater than or equal to]2.9 mg/dl, P = 0.005, hazard ratio (HR) 0.314, confidence interval (CI) (0.141 to 0.702)), elevated serum creatinine (P = 0.05, HR 0.453, CI (0.203 to 1.012)), presence of liver-related complications (P = 0.028, HR 0.258 CI (0.077 to 0.862)), model of end stage liver disease (MELD) score [greater than or equal to]20 (P = 0.017, HR 0.364, CI (0.159 to 0.835)) and age (P = 0.011, HR 1.047, CI (1.011 to 1.085)). Adjusted multivariate Cox proportional-hazards analysis identified elevated systemic IL-22 levels as independent predictors of reduced survival (P = 0.007, HR 0.218, CI (0.072 to 0.662)).
Conclusions: In patients with liver cirrhosis, elevated systemic IL-22 levels are predictive for reduced survival independently from age, liver-related complications, CRP, creatinine and the MELD score. Thus, processes that lead to a rise in systemic interleukin-22 may be relevant for prognosis of advanced liver cirrhosis.
Background: The transcription factor T-bet is pivotal for initiation of Th1-related immunoactivation. Identification of novel genes directly regulated by T-bet is crucial.
Results: Genome-wide analysis and subsequent experiments revealed that T-bet up-regulates IL-36γ/IL-1F9 in myeloid cells.
Conclusion: IL-1-related IL-36γ is a direct T-bet target in myeloid cells.
Significance: Observations suggest that IL-36γ , besides IFNγ, contributes to T-bet functions in immunopathology
By concerted action in dendritic (DC) and T cells, T-box expressed in T cells (T-bet, Tbx21) is pivotal for initiation and perpetuation of Th1 immunity. Identification of novel T-bet-regulated genes is crucial for further understanding the biology of this transcription factor. By combining siRNA technology with genome-wide mRNA expression analysis, we sought to identify new T-bet-regulated genes in predendritic KG1 cells activated by IL-18. One gene robustly dependent on T-bet was IL-36γ, a recently described novel IL-1 family member. Promoter analysis revealed a T-bet binding site that, along with a κB site, enables efficient IL-36γ induction. Using knock-out animals, IL-36γ reliance on T-bet was extended to murine DC. IL-36γ expression by human myeloid cells was confirmed using monocyte-derived DC and M1 macrophages. The latter model was employed to substantiate dependence of IL-36γ on endogenous T-bet in human primary cells. Ectopic expression of T-bet likewise mediated IL-36γ production in HaCaT keratinocytes that otherwise lack this transcription factor. Additional experiments furthermore revealed that mature IL-36γ has the capability to establish an inflammatory gene expression profile in human primary keratinocytes that displays enhanced mRNA levels for TNFα, CCL20, S100A7, inducible NOS, and IL-36γ itself. Data presented herein shed further light on involvement of T-bet in innate immunity and suggest that IL-36γ, besides IFNγ, may contribute to functions of this transcription factor in immunopathology.