Human interleukin-10-related T cell-derived inducible factor: molecular cloning and functional characterization as an hepatocyte-stimulating factor

Structure of IL-22 bound to its high-affinity IL-22R1 chain

IL-22 is an IL-10 family cytokine that initiates innate immune responses against bacterial pathogens and contributes to immune disease. IL-22 biological activity is initiated by binding to a cell-surface complex composed of IL-22R1 and IL-10R2 receptor chains and further regulated by interactions with a soluble binding protein, IL-22BP, which shares sequence similarity with an extracellular region of IL-22R1 (sIL-22R1). IL-22R1 also pairs with the IL-20R2 chain to induce IL-20 and IL-24 signaling. To define the molecular basis of these diverse interactions, we have determined the structure of the IL-22/sIL-22R1 complex. The structure, combined with homology modeling and surface plasmon resonance studies, defines the molecular basis for the distinct affinities and specificities of IL-22 and IL-10 receptor chains that regulate cellular targeting and signal transduction to elicit effective immune responses.

Crystal structure of the IL-22/IL-22R1 complex and its implications for the IL-22 signaling mechanism

Interleukin-22 (IL-22) is a member of the interleukin-10 cytokine family, which is involved in anti-microbial defenses, tissue damage protection and repair, and acute phase responses. Its signaling mechanism involves the sequential binding of IL-22 to interleukin-22 receptor 1 (IL-22R1), and of this dimer to interleukin-10 receptor 2 (IL-10R2) extracellular domain. We report a 1.9A crystal structure of the IL-22/IL-22R1 complex, revealing crucial interacting residues at the IL-22/IL-22R1 interface. Functional importance of key residues was confirmed by site-directed mutagenesis and functional studies. Based on the X-ray structure of the binary complex, we discuss a molecular basis of the IL-22/IL-22R1 recognition by IL-10R2.

IL-23 and Th17 cytokines in intestinal homeostasis

The discovery of the Th1/Th2 paradigm of CD4(+) T-cell subsets redefined our understanding of immunity by highlighting the essential roles of cytokine networks in the induction and regulation of immune responses. Most recently, the identification of an additional subset, known as Th17 cells, has further illustrated the complexity and diversity of effector CD4(+) T cells. Th17 responses have been closely associated with the cytokine interleukin (IL)-23 and, although originally pinpointed as having a deleterious role in autoimmune tissue pathology, the IL-23/Th17 axis has also been associated with protective immunity at mucosal surfaces. Recent progress has highlighted the heterogeneous nature of Th17 responses, has demonstrated diverse cellular sources for Th17-associated cytokines, and has begun to dissect the individual roles of these cytokines in different disease processes. Here, we will review the evidence linking the IL-23/Th17 axis to chronic intestinal inflammation and also will discuss its beneficial roles in intestinal protection and homeostasis.

Induction and effector functions of T(H)17 cells

T helper (T(H)) cells constitute an important arm of the adaptive immune system because they coordinate defence against specific pathogens, and their unique cytokines and effector functions mediate different types of tissue inflammation. The recently discovered T(H)17 cells, the third subset of effector T helper cells, have been the subject of intense research aimed at understanding their role in immunity and disease. Here we review emerging data suggesting that T(H)17 cells have an important role in host defence against specific pathogens and are potent inducers of autoimmunity and tissue inflammation. In addition, the differentiation factors responsible for their generation have revealed an interesting reciprocal relationship with regulatory T (T(reg)) cells, which prevent tissue inflammation and mediate self-tolerance.

Interleukin-22 deficiency accelerates the rejection of full major histocompatibility complex-disparate heart allografts

Interleukin-22 (IL-22) was recently described as an effector cytokine produced by TH17 CD4(+) T lymphocytes that, cooperatively with IL-17, mediates IL-23-driven inflammation. Because there was experimental evidence for the role of IL-17 in acute rejection of vascularized allografts, we undertook the present study to assess the function of IL-22 in the process. There was an early transient expression of IL-22 in C57BL/6 mouse cardiac allografts (2-4 days posttransplantation) transplanted to BALB/c recipients. The main source of IL-22 among infiltrating leukocytes was cells expressing the macrophage/monocyte markers Mac3 and CD11b. T cells and granulocytes present in the rejected graft did not express IL-22. Surprisingly, the absence of IL-22 accelerated the rejection of fully histoincompatible hearts. Histology of rejected organs revealed the presence of intensive intragraft thrombosis and disseminated hemorrhagic necrosis. Taken together, these results demonstrated that IL-22 was not an effector lymphokine in cardiac allograft rejection, but early intragraft expression of the cytokine protected it from rejection.

Maturing dendritic cells are an important source of IL-29 and IL-20 that may cooperatively increase the innate immunity of keratinocytes

IL-19, IL-20, IL-22, IL-24, IL-26, IL-28, and IL-29 are new members of the IL-10 interferon family. Monocytes are well-known sources of IL-19, IL-20, and IL-24. We demonstrated here that monocytes also expressed IL-29, and monocyte differentiation into macrophages (Mphi) or dendritic cells (DCs) strongly changed their production capacity of these cytokines. Maturation of DCs with bacterial stimuli induced high expression of IL-28/IL-29 and IL-20. Simulated T cell interaction and inflammatory cytokines induced IL-29 and IL-20 in maturing DCs, respectively. Compared with monocytes, DCs expressed only minimal IL-19 levels and no IL-24. The differentiation of monocytes into Mphi reduced their IL-19 and terminated their IL-20, IL-24, and IL-29 production capacity. Like monocytes, neither Mphi nor DCs expressed IL-22 or IL-26. The importance of maturing DCs as a source of IL-28/IL-29 was supported by the much higher mRNA levels of these mediators in maturing DCs compared with those in CMV-infected fibroblasts, and the presence of IL-28 in lymph nodes but not in liver of lipopolysaccharide-injected mice. IL-19, IL-20, IL-22, IL-24, and IL-26 do not seem to affect Mphi or DCs as deduced from the lack of corresponding receptor chains. The significance of IL-20 and IL-28/IL-29 coexpression in maturing DCs may lie in the broadly amplified innate immunity in neighboring tissue cells like keratinocytes. In fact, IL-20 induced the expression of antimicrobial proteins, whereas IL-28/IL-29 enhanced the expression of toll-like receptors (TLRs) and the response to TLR ligands. However, the strongest response to TLR2 and TLR3 activation showed keratinocytes in the simultaneous presence of IL-20 and IL-29.

The aryl hydrocarbon receptor links TH17-cell-mediated autoimmunity to environmental toxins

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor best known for mediating the toxicity of dioxin. Environmental factors are believed to contribute to the increased prevalence of autoimmune diseases, many of which are due to the activity of T(H)17 T cells, a new helper T-cell subset characterized by the production of the cytokine IL-17. Here we show that in the CD4+ T-cell lineage of mice AHR expression is restricted to the T(H)17 cell subset and its ligation results in the production of the T(H)17 cytokine interleukin (IL)-22. AHR is also expressed in human T(H)17 cells. Activation of AHR by a high-affinity ligand during T(H)17 cell development markedly increases the proportion of T(H)17 T cells and their production of cytokines. CD4+ T cells from AHR-deficient mice can develop T(H)17 cell responses, but when confronted with AHR ligand fail to produce IL-22 and do not show enhanced T(H)17 cell development. AHR activation during induction of experimental autoimmune encephalomyelitis causes accelerated onset and increased pathology in wild-type mice, but not AHR-deficient mice. AHR ligands may therefore represent co-factors in the development of autoimmune diseases.

Free fatty acids sensitize hepatocytes to bile acid-induced apoptosis

Delivery of free fatty acids to the liver in nonalcoholic fatty liver disease (NAFLD) may render hepatocytes more vulnerable to glycochenodeoxycholic acid (GCDCA)-induced apoptosis. Fat overloading was induced in HepG2-Ntcp cells and primary rat hepatocytes by incubation with palmitic or oleic acid. Apoptosis was quantified by measuring caspase 3/7 activity and transcription of interleukin (IL) 8 and IL-22 by quantitative real-time PCR. Oleic acid (500 microM) alone did not induce apoptosis, while palmitic acid (500 microM) increased apoptosis 5-fold. GCDCA did not induce significant apoptosis at low micromolar concentrations (5-30 microM) in non-steatotic cells. However, at the same concentrations, GCDCA increased apoptosis 3-fold in oleic acid-pretreated HepG2-Ntcp cells and 3.5-fold in primary rat hepatocytes. Pretreatment with oleic acid increased GCDCA-induced gene transcription of the proinflammatory cytokines IL-8 and IL-22 5-fold and 19-fold, respectively. Thus, low levels of cholestasis normally not considered harmful could advance liver injury in patients with NAFLD.

The biological functions of T helper 17 cell effector cytokines in inflammation

T helper 17 (Th17) cells belong to a recently identified T helper subset, in addition to the traditional Th1 and Th2 subsets. These cells are characterized as preferential producers of interleukin-17A (IL-17A), IL-17F, IL-21, and IL-22. Th17 cells and their effector cytokines mediate host defensive mechanisms to various infections, especially extracellular bacteria infections, and are involved in the pathogenesis of many autoimmune diseases. The receptors for IL-17 and IL-22 are broadly expressed on various epithelial tissues. The effector cytokines of Th17 cells, therefore, mediate the crucial crosstalk between immune system and tissues, and play indispensable roles in tissue immunity.

Crystallization and preliminary X-ray diffraction analysis of human IL-22 bound to the extracellular IL-22R1 chain

Interleukin-22 (IL-22) is a potent mediator of cellular inflammatory responses. Crystals of IL-22 bound to the extracellular high-affinity cell-surface receptor sIL-22R1 have been grown from polyethylene glycol solutions. Crystals suitable for X-ray diffraction analysis were only obtained with mutants of IL-22 and sIL-22R1 that removed the N-linked glycosylation sites found in the wild-type amino-acid sequences. The crystals belonged to space group P2(1), with unit-cell parameters a = 50.43, b = 76.33, c = 114.92 A, beta = 92.45 degrees , and diffracted X-rays to 3.2 A resolution. The crystallographic asymmetric unit contained two IL-22-sIL-22R1 complexes, corresponding to a solvent content of approximately 52%.

Substitution of pseudokinase domain residue Val-617 by large non-polar amino acids causes activation of JAK2

Explaining the uniqueness of the acquired somatic JAK2 V617F mutation, which is present in more than 95% of polycythemia vera patients, has been a challenge. The V617F mutation in the pseudokinase domain of JAK2 renders the unmutated kinase domain constitutively active. We have performed random mutagenesis at position 617 of JAK2 and tested each of the 20 possible amino acids for ability to induce constitutive signaling in Ba/F3 cells expressing the erythropoietin receptor. Four JAK2 mutants, V617W, V617M, V617I, and V617L, were able to induce cytokine independence and constitutive downstream signaling. Only V617W induced a level of constitutive activation comparable with V617F. Also, only V617W stabilized tyrosine-phosphorylated suppressor of cytokine signaling 3 (SOCS3), a mechanism by which JAK2 V617F overcomes inhibition by SOCS3. The V617W mutant induced a myeloproliferative disease in mice, mainly characterized by erythrocytosis and megakaryocytic proliferation. Although JAK2 V617W would predictably be pathogenic in humans, the substitution of the Val codon, GTC, by TTG, the codon for Trp, would require three base pair changes, and thus it is unlikely to occur. We discuss how the predicted conformations of the activated JAK2 mutants can lead to better screening assays for novel small molecule inhibitors.

A role for T cell-derived interleukin 22 in psoriatic skin inflammation

Interleukin (IL)-22 is a T cell-derived cytokine that has been reported recently to induce cutaneous inflammation in an experimental murine model of psoriasis, and to induce in vitro an inflammatory-like phenotype. In the present study, we assessed the presence of IL-22 and the IL-22 receptor 1 (IL-22R1) in skin lesions, skin-derived T cells, as well as IL-22 levels in sera from patients with psoriasis. IL-22R1 and IL-10R2 transcripts are expressed at a similar level in psoriatic and healthy skin. In contrast, IL-22 mRNA expression was up-regulated in psoriatic skin lesions compared to normal skin, whereas IL-22 mRNA levels in peripheral blood mononuclear cells from psoriatic patients and normal subjects were similar. Circulating IL-22 levels were significantly higher in psoriatic patients than in normal subjects. T cells isolated from psoriatic skin produced higher levels of IL-22 in comparison to peripheral T cells isolated from the same patients. IL-10 was expressed at similar levels in skin biopsies and peripheral blood mononuclear cells of psoriatic patients and normal subjects. Finally, we show here that supernatants of lesional psoriatic skin-infiltrating T cells induce an inflammatory response by normal human epidermal keratinocytes, resembling that observed in psoriatic lesions. Taken together, the results reported in this study indicate that IL-22 is a cytokine produced by skin-infiltrating lymphocytes that is potentially involved in initiation and/or maintenance of the pathogenesis of psoriasis.

Interleukin-22 but not interleukin-17 provides protection to hepatocytes during acute liver inflammation

The cytokine interleukin-22 (IL-22) is primarily expressed by T helper 17 (Th17) CD4(+) T cells and is highly upregulated during chronic inflammatory diseases. IL-22 receptor expression is absent on immune cells, but is instead restricted to the tissues, providing signaling directionality from the immune system to the tissues. However, the role of IL-22 in inflammatory responses has been confounded by data suggesting both pro- and anti-inflammatory functions. Herein, we provide evidence that during inflammation, IL-22 played a protective role in preventing tissue injury. Hepatocytes from mice deficient in IL-22 were highly sensitive to the detrimental immune response associated with hepatitis. Additionally, IL-22-expressing Th17 cells provided protection during hepatitis in IL-22-deficient mice. On the other hand, interleukin-17 (IL-17), which is coexpressed with IL-22 and can induce similar cellular responses, had no observable role in liver inflammation. Our data suggest that IL-22 serves as a protective molecule to counteract the destructive nature of the immune response to limit tissue damage.

The expression of interleukin-22 and S100A7, A8, A9 mRNA in patients with psoriasis vulgaris

In order to study the expression of interleukin-22 (IL-22) and S100A7, A8, A9 mRNA in the skin lesions of patients with psoriasis vulgaris and their relationship, the biopsies were taken from skin lesions in 35 patients with psoriasis vulgaris and the skin of 16 normal controls, and the expression levels of IL-22 and S100A7, A8 and A9 mRNA were detected by semi-quantitative RT-PCR. The results showed that (1) IL-22 and S100A8, A9 mRNA were positively expressed in the psoriatic skin lesions but negatively expressed in the normal controls; The expression level of S100A7 was (1.133+/-0.040) in the psoriatic skin lesions, significantly higher than that in the normal controls (0.744+/-0.037, P<0.01). (2) There were significantly positive correlations between the expression of IL-22/S100A7 mRNA, IL-22/S100A8 mRNA, IL-22/S100A9 mRNA in the psoriasis vulgaris (r(1)=0.543, r (2)=0.774, r(3)=0.621, P<0.01). It was concluded that IL-22 and S100A7, A8, A9 might play important roles in the occurrence and progression of psoriasis.

Influence of IL-10RA and IL-22 polymorphisms on outcome of hepatitis C virus infection

BACKGROUND

Two receptor chains, IL-10RA and IL-10RB, are known to mediate the functions of interleukin-10 (IL-10), which has been shown to be involved in the progression of persistent hepatitis C virus (HCV) infection. Little information is available on the role of host genetic variation in IL-10 receptor genes and outcome of HCV infection. IL-22, an IL-10 homologue, shares the IL-10RB receptor chain with IL-10 and has antiviral properties. We investigated the possible role of polymorphisms in the IL-10RA and IL-22 genes in hepatitis C disease pathogenesis.

METHODS

This study population consisted of 631 HCV patients, recruited from several hepatology clinics across Europe. We genotyped four single-nucleotide polymorphisms (SNPs) in the IL-10RA and six SNPs in the IL-22 gene by ligation detection reaction or restriction fragment length polymorphism. Outcome of HCV infection was assessed according to viral clearance, treatment response, severity of fibrosis and overall inflammation.

CONCLUSIONS

Variation in IL-10RA appeared to be correlated with response to treatment and inflammation. Two SNPs in IL-22 affected treatment response and viral clearance respectively. We furthermore report on allele and haplotype frequencies and linkage disequilibrium for IL-10RA and IL-22. Our results indicate that genetic variation in these genes may play a modulatory role in the outcome of hepatitis C infection.

The interleukin-22/STAT3 pathway potentiates expression of inducible nitric-oxide synthase in human colon carcinoma cells

Inducible nitric-oxide synthase (iNOS) has been identified as a marker and mediator of disease in human colonic inflammation and carcinogenesis. Accordingly, identification of mediators that trigger iNOS in colon carcinoma/epithelial cells is an important topic of current research. Here we demonstrate that interleukin (IL)-22, a newly described member of the IL-10 cytokine family, potently synergizes with interferon (IFN)-gamma for iNOS expression in human DLD-1 colon carcinoma cells. Detection of both IL-22 receptor chains and STAT3 phosphorylation proved robust IL-22 responsiveness of these cells. Short interfering RNA technology identified STAT3 as being crucial for up-regulation of iNOS. Compared with IFNgamma, STAT1 phosphorylation by IL-22 was insufficient. IL-22 did not stabilize IL-1beta/tumor necrosis factor-alpha/IFNgamma-induced iNOS mRNA. IL-22 also failed to amplify expression of the prototypic IFNgamma-inducible parameters IL-18-binding protein and CXCL-10, indicating that IL-22 is not a general amplifier of IFNgamma functions. This assumption is furthermore supported by the observation that IL-22 was unable to enhance cellular activation of the pro-inflammatory transcription factor nuclear factor-kappaB. In contrast, IL-22 increased iNOS promoter activation as detected by using DLD-1 cells stably transfected with a corresponding 16-kb promoter construct (pNOS2(16)-Luc). IL-22 likewise enhanced iNOS in Caco-2 colon carcinoma cells. With IL-22 we introduce a novel potent determinant of iNOS expression in human colon carcinoma/epithelial cells. Considering the eminent functions of STAT3 and iNOS in inflammation and carcinogenesis, IL-22 may represent a novel target for immunotherapeutic intervention.

IL-22 induces lipopolysaccharide-binding protein in hepatocytes: a potential systemic role of IL-22 in Crohn's disease

Crohn's disease (CD) is a common, chronic, inflammatory bowel disease characterized by intestinal infiltration of activated immune cells and distortion of the intestinal architecture. In this study, we demonstrate that IL-22, a cytokine that is mainly produced by activated Th1 and Th17 cells, was present in high quantities in the blood of CD patients in contrast to IFN-gamma and IL-17. In a mouse colitis model, IL-22 mRNA expression was elevated predominantly in the inflamed intestine but also in the mesenteric lymph nodes. IL-22BP, the soluble receptor for IL-22, demonstrated an affinity to IL-22 that was at least 4-fold higher than its membrane-bound receptor, and its strong constitutive expression in the intestine and lymph nodes was decreased in the inflamed intestine. To investigate the possible role of systemic IL-22 in CD, we then administered IL-22 to healthy mice and found an up-regulation of LPS-binding protein (LBP) blood levels reaching concentrations known to neutralize LPS. This systemic up-regulation was associated with increased hepatic but not renal or pulmonary LBP mRNA levels. IL-22 also enhanced the secretion of LBP in human primary hepatocytes and HepG2 hepatoma cells in vitro. This increase was mainly transcriptionally regulated and synergistic with that of other LBP inducers. Finally, elevated LBP levels were detected in CD patients and the mouse colitis model. These data suggest that systemic IL-22 may contribute to the prevention of systemic inflammation provoked by LPS present in the blood of CD patients through its induction of hepatic LBP.

Inhibition of interleukin-22 attenuates bacterial load and organ failure during acute polymicrobial sepsis

Interleukin-22 (IL-22) is a recently discovered proinflammatory cytokine, structurally related to IL-10. Since IL-22 is induced by lipopolysaccharide in vivo, we studied the role of IL-22 in a model of polymicrobial peritonitis. Quantitative real-time reverse transcription-PCR analysis showed marked induction of IL-22 and IL-22 receptor in spleen and kidney during the course of sepsis. The biological activity of IL-22 is modulated by IL-22-binding protein (IL-22BP), which is considered a natural antagonist of IL-22. To further analyze the role of IL-22 during septic peritonitis, mice were treated with recombinant IL-22BP generated as Fcgamma2a fusion protein. IL-22BP-Fc completely blocked IL-22-induced STAT3 activation in hepatocytes in vitro. Treatment of mice with IL-22BP-Fc 4 h before sepsis induction led to enhanced accumulation of neutrophils and mononuclear phagocytes and a reduced bacterial load at the site of infection. In addition, IL-22 blockade led to an enhanced bacterial clearance in liver and kidney and reduced kidney injury. These results imply an important proinflammatory role of IL-22 during septic peritonitis, contributing to bacterial spread and organ failure. IL-22 therefore appears to play an important role in the regulation of inflammatory processes in vivo.

The murine liver is a potential target organ for IL-19, IL-20 and IL-24: Type I Interferons and LPS regulate the expression of IL-20R2

BACKGROUND/AIMS

The biological functions of the recently discovered IL-10-related cytokines IL-19, IL-20, IL-22, IL-24 and their receptors IL-20R1, IL-20R2 and IL-22R are not clear. Therefore, the expression of these cytokines and their receptors in the hepatic acute phase response to LPS was analysed. Type I interferons have important immunomodulatory functions in bacterial infections. We investigated if they influence release and organ-specific expression of TNF, IL-6 and IL-10 and the responsiveness of liver to IL-10 related cytokines during the reaction to LPS in vivo.

METHODS

B6 and congenic IFNAR-/- mice were intraperitoneally injected with 5mg/kg LPS. Systemic release of cytokines was quantified by ELISA. Organ-specific expression of cytokines and their receptors was evaluated by (semi quantitative or quantitative) RT-PCR.

RESULTS

The cytokines IL-19, IL-22 and the IL-20R2 receptor subunit are up-regulated by LPS in the liver of normal mice. IFNalpha/beta enhance the secretion and expression of IL-6 and IL-10 during the response to LPS, but also the up-regulation of IL-20R2 expression.

CONCLUSIONS

We show that the liver is a potential target for IL-19, IL-20 and IL-24. During an LPS response, IFNalpha/beta influence cytokine secretion and expression and possibly the response to IL-19 and IL-24.

IL-22 participates in an innate anti-HIV-1 host-resistance network through acute-phase protein induction

Certain individuals are resistant to HIV-1 infection, despite repeated exposure to the virus. Although protection against HIV-1 infection in a small proportion of Caucasian individuals is associated with mutant alleles of the CCR5 HIV-1 coreceptor, the molecular mechanism underlying resistance in repeatedly HIV-1-exposed, uninfected individuals (EU) is unclear. In this study, we performed complementary transcriptome and proteome analyses on peripheral blood T cells, and plasma or serum from EU, their HIV-1-infected sexual partners, and healthy controls, all expressing wild-type CCR5. We report that activated T cells from EU overproduce several proteins involved in the innate immunity response, principally those including high levels of peroxiredoxin II, a NK-enhancing factor possessing strong anti-HIV activity, and IL-22, a cytokine involved in the production of acute-phase proteins such as the acute-phase serum amyloid A (A-SAA). Cell supernatants and serum levels of these proteins were up-regulated in EU. Moreover, a specific biomarker for EU detected in plasma was identified as an 8.6-kDa A-SAA cleavage product. Incubation of in vitro-generated myeloid immature dendritic cells with A-SAA resulted in CCR5 phosphorylation, down-regulation of CCR5 expression, and strongly decreased susceptibility of these cells to in vitro infection with a primary HIV-1 isolate. Taken together, these results suggest new correlates of EU protection and identify a cascade involving IL-22 and the acute phase protein pathway that is associated with innate host resistance to HIV infection.

Triggers of IgE class switching and allergy development

The prevalence of immunoglobulin E (IgE)-mediated allergic diseases has been increasing for the last four decades. In this review determinants for an increased IgE synthesis are discussed on both an epidemiological and on an immunological level with special emphasis on the differentiation of the B cell to an IgE-producing plasma cell. Factors that favor an IgE immune response are low antigen doses and immunization via mucous membranes, but it is highly likely that other environmental factors besides exposure to the allergenic sources play a role. Important factors in the formation of the Thelper type 2 (Th2) T cell subset are the actions of thymic stromal lymphopoietin (TSLP) on dendritic cells and the OX40 ligand on CD4+ T cells. In order for a B lymphocyte to switch to IgE production it needs two signals provided by a Th2 cell in the form of the cytokines interleukin (IL-) 4/IL-13 and ligation of the CD40. In spite of a half-life of only a few days, there is evidence that the IgE response may last for years even without allergen stimulation. This is likely to be caused by long-lived IgE-producing plasma cells, and such cells may be difficult to target therapeutically thus emphasizing the need for more knowledge on preventable causes of IgE- and allergy development.

Structural studies of the interleukin-19 subfamily of cytokines

The interleukin-19 (IL-19) subfamily of cytokines is part of a larger family of homologs of IL-10 that includes two groups of proteins: five viral cytokines, and eight cellular cytokines, having quite different biological activities. Among proteins of the latter group, IL-19, IL-20, IL-22, and IL-24 were suggested to form a structurally unique IL-19 subfamily characterized by their structural features and aggregation state as monomers. IFN-lambda1, IFN-lambda2, and IFN-lambda3 are likely to belong to this subfamily, and it is still not clear whether IL-26 belongs to it or not. In spite of their differences in biological function, all cellular homologs of IL-10 used for signaling a set of five overlapping membrane-bound receptors: three long receptor chains (IL-20R1, IL-22R1, and IFN-lambdaR) and two short receptor chains (IL-20R2 and IL-10R2). Signal transduction is initiated when a cytokine binds two receptor chains, one long and one short, forming a ternary complex. Crystal structures of IL-19 and IL-22 showed that these cytokines consist of seven amphipathic helices of different length organized in helical bundle, covering an extensive hydrophobic core. Based on the similarity of the structures with the structure of a single domain of IL-10, and with the crystal structure of a binary IL-10/IL-10R1 complex, putative receptor binding sites on the surface of IL-19 and IL-22 were identified. This chapter summarizes the available structural data on the IL-19 subfamily of cytokines and their putative ligand/receptor complexes.

IL-22-mediated tumor growth reduction correlates with inhibition of ERK1/2 and AKT phosphorylation and induction of cell cycle arrest in the G2-M phase

IL-22 is a recently discovered cytokine of the IL-10 family that binds to a class II cytokine receptor composed of IL-22R1 and IL-10R2(c) and influences a variety of immune reactions. As IL-22 has also been shown to modulate cell cycle and proliferation mediators such as ERK1/2 and JNK, we studied the role of IL-22 in proliferation, apoptosis, and cell cycle regulation in EMT6 murine breast cancer cells in vitro and in vivo. In this study, we report that murine breast cancer cells express functional IL-22R as indicated by RT-PCR studies, immunoblotting, and STAT3 activation assays. Importantly, IL-22 exposure of EMT6 cells resulted in decreased levels of phosphorylated ERK1/2 and AKT protein kinases, indicating an inhibitory effect of IL-22 on signaling pathways promoting cell proliferation. Furthermore, IL-22 induced a cell cycle arrest of EMT6 cells in the G(2)-M phase. IL-22 reduced EMT6 cell numbers and the proliferation rate by approximately 50% as measured by [(3)H]thymidine incorporation. IL-22 treatment of EMT6 tumor-bearing mice lead to a decreased tumor size and a reduced tumor cell proliferation in vivo, as determined by 3'-deoxy-3'-fluorothymidine-positron emission tomography scans. Interestingly, IL-22 did not induce apoptosis, as determined in annexin V binding assay and caspase-3 activation assay and had no effect on angiogenesis in vivo. In conclusion, our results indicate that IL-22 reduced tumor growth by inhibiting signaling pathways such as ERK1/2 and AKT phosphorylation that promote tumor cell proliferation in EMT6 cells. Therefore, IL-22 may play a role in the control of tumor growth and tumor progression.

Interleukin-22: a novel T- and NK-cell derived cytokine that regulates the biology of tissue cells

Interleukin (IL)-22, discovered in 2000, is a member of the IL-10 family of cytokines. The major sources of IL-22 are activated T1- and NK-cells. IL-22 acts via a heterodimeric receptor complex consisting of IL-22R1 and IL-10R2. Neither resting nor activated immune cells express IL-22R1 or respond to IL-22. In contrast, tissue cells at outer body barriers, i.e. of the skin, kidney, and the digestive and respiratory systems are targets of this cytokine. IL-22 functions by promoting the anti-microbial defense, protecting against damage, and re-organizing non-immune tissues. Furthermore, IL-22 induces acute phase reactants. These findings indicate that IL-22 represents a novel type of immune mediator that, although produced by immune cells, regulates tissue protection and homeostasis.

IL-20: biological functions and clinical implications

IL-20 belongs to the IL-10 family and plays a role in skin inflammation and the development of hematopoietic cells. Little is known about its other biological functions and clinical implications, however. Updated information about IL-20, such as its identification, expression, receptors, signaling, biological activities, and potential clinical implications, is illustrated in this review based on our research and on data available in the literature. Our studies of IL-20 show that it is a pleiotropic cytokine with potent inflammatory, angiogenic, and chemoattractive characteristics. Inflammation and angiogenesis are essential for the pathogenesis of rheumatoid arthritis and atherosclerosis. Based on in vitro data and clinical samples, we demonstrated that IL-20 is involved in the diseases of rheumatoid arthritis and atherosclerosis. In addition, we found in our studies that IL-20 signaled through different molecules in several cells. The present review presents the clinical implications of IL-20 in rheumatoid arthritis and atherosclerosis. It may provide new therapeutic options in the future.

IL-22 regulates the expression of genes responsible for antimicrobial defense, cellular differentiation, and mobility in keratinocytes: a potential role in psoriasis

IL-22 is an IFN-IL-10 cytokine family member, which is produced by activated Th1 and NK cells and acts primarily on epithelial cells. Here we demonstrate that IL-22, in contrast to its relative IFN-gamma, regulates the expression of only a few genes in keratinocytes. This is due to varied signal transduction. Gene expressions regulated by IL-22 should enhance antimicrobial defense [psoriasin (S100A7), calgranulin A (S100A8), calgranulin B (S100A9)], inhibit cellular differentiation (e.g., profilaggrin, keratins 1 and 10, kallikrein 7), and increase cellular mobility [e.g., matrix metalloproteinease 1 (MMP1, collagenase 1), MMP3 (stromelysin 1), desmocollin 1]. In contrast, IFN-gamma favored the expression of MHC pathway molecules, adhesion molecules, cytokines, chemokines, and their receptors. The IL-22 effects were transcriptional and either independent of protein synthesis and secretion, or mediated by a secreted protein. Inflammatory conditions, but not keratinocyte differentiation, amplified the IL-22 effects. IL-22 application in mice enhanced cutaneous S100A9 and MMP1 expression. High IL-22 levels in psoriatic skin were associated with strongly up-regulated cutaneous S100A7, S100A8, S100A9, and MMP1 expression. Psoriatic patients showed strongly elevated IL-22 plasma levels, which correlated with the disease severity. Expression of IL-22 and IL-22-regulated genes was reduced by anti-psoriatic therapy. In summary, despite similarities, IFN-gamma primarily amplifies inflammation, while IL-22 may be important in the innate immunity and reorganization of epithelia.

IL-22 is increased in active Crohn's disease and promotes proinflammatory gene expression and intestinal epithelial cell migration

IL-22 is produced by activated T cells and signals through a receptor complex consisting of IL-22R1 and IL-10R2. The aim of this study was to analyze IL-22 receptor expression, signal transduction, and specific biological functions of this cytokine system in intestinal epithelial cells (IEC). Expression studies were performed by RT-PCR. Signal transduction was analyzed by Western blot experiments, cell proliferation by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay and Fas-induced apoptosis by flow cytometry. IEC migration was studied in wounding assays. The IEC lines Caco-2, DLD-1, SW480, HCT116, and HT-29 express both IL-22 receptor subunits IL-22R1 and IL-10R2. Stimulation with TNF-alpha, IL-1beta, and LPS significantly upregulated IL-22R1 without affecting IL-10R2 mRNA expression. IL-22 binding to its receptor complex activates STAT1/3, Akt, ERK1/2, and SAPK/JNK MAP kinases. IL-22 significantly increased cell proliferation (P = 0.002) and phosphatidylinsitol 3-kinase-dependent IEC cell migration (P < 0.00001) as well as mRNA expression of TNF-alpha, IL-8, and human beta-defensin-2. IL-22 had no effect on Fas-induced apoptosis. IL-22 mRNA expression was increased in inflamed colonic lesions of patients with Crohn's disease and correlated highly with the IL-8 expression in these lesions (r = 0.840). Moreover, IL-22 expression was increased in murine dextran sulfate sodium-induced colitis. IEC express functional receptors for IL-22, which increases the expression of proinflammatory cytokines and promotes the innate immune response by increased defensin expression. Moreover, our data indicate intestinal barrier functions for this cytokine-promoting IEC migration, which suggests an important function in intestinal inflammation and wound healing. IL-22 is increased in active Crohn's disease and promotes proinflammatory gene expression and IEC migration.

Regulation of T cells and cytokines by the interleukin-10 (IL-10)-family cytokines IL-19, IL-20, IL-22, IL-24 and IL-26

The family of IL-10-related cytokines includes several human members, IL-19, IL-20, IL-22, IL-24 and IL-26, and a series of herpesviral and poxviral paralogs. Some of these cytokines share common receptor subunits. In this study, we investigated the effects of these cytokines on naive T cell differentiation, antigen-specific T cell suppression, survival ad expression of surface markers in comparison to IL-10 and cytomegalovirus (CMV)-IL-10. Human CD45RA(+) T cells were stimulated in the presence of IL-10-family cytokines in sequential 12-day cycles. After three to four cycles of stimulation, IL-10 and CMV-IL-10 led to increased IFN-gamma and IL-10 but decreased IL-4 and IL-13. Interestingly, long-term exposure of T cells to IL-19, IL-20 and IL-22 down-regulated IFN-gamma but up-regulated IL-4 and IL-13 in T cells and supported the polarization of naive T cells to Th2-like cells. In contrast, neutralization of endogenous IL-22 activity by IL-22-binding protein decreased IL-4, IL-13 and IFN-gamma synthesis. The antigen-specific suppressor activity of IL-10 and CMV-IL-10 was not observed for any of the other IL-10-family cytokines. These data demonstrate that IL-19, IL-20 and IL-22 may participate in T cell-mediated diseases by distinct regulation of T cell cytokine profiles.

Interleukin-22 and its crystal structure

Interleukin-22 (IL-22) is a cytokine that regulates the production of acute phase proteins of the immunological response. On binding to its cognate receptor (IL-22R1), which is associated to the interleukin-10 receptor 2 (IL-10R2), IL-22 promotes activation of signal transducer and activator of transcription (STAT) pathway and several other cellular responses. A soluble receptor termed interleukin-22 binding protein (IL-22BP) is also able to bind to IL-22 as a natural protein antagonist, and probably provides systemic regulation of IL-22 activity. This inflammatory response system is analyzed here in terms of its molecular physiology and structural assembly. Three-dimensional (3D) model of IL-22 and structural basis of its interactions with the cognate receptors are discussed.

JAK1 and Tyk2 Activation by the Homologous Polycythemia Vera JAK2 V617F Mutation

The majority of polycythemia vera (PV) patients harbor a unique somatic mutation (V617F) in the pseudokinase domain of JAK2, which leads to constitutive signaling. Here we show that the homologous mutations in JAK1 (V658F) and in Tyk2 (V678F) lead to constitutive activation of these kinases. Their expression induces autonomous growth of cytokine-dependent cells and constitutive activation of STAT5, STAT3, mitogen-activated protein kinase, and Akt signaling in Ba/F3 cells. The mutant JAKs exhibit constitutive signaling also when expressed in fibrosarcoma cells deficient in JAK proteins. Expression of the JAK2 V617F mutant renders Ba/F3 cells hypersensitive to insulin-like growth factor 1 (IGF1), which is a hallmark of PV erythroid progenitors. Upon selection of Ba/F3 cells for autonomous growth induced by the JAK2 V617F mutant, cells respond to IGF1 by activating STAT5, STAT3, Erk1/2, and Akt on top of the constitutive activation characteristic of autonomous cells. The synergic effect on proliferation and STAT activation appears specific to the JAK2 V617F mutant. Our results show that the homologous V617F mutation induces activation of JAK1 and Tyk2, suggesting a common mechanism of activation for the JAK1, JAK2, and Tyk2 mutants. JAK3 is not activated by the homologous mutation M592F, despite the presence of the conserved GVC preceding sequence. We suggest that mutations in the JAK1 and Tyk2 genes may be identified as initial molecular defects in human cancers and autoimmune diseases.

Interleukin-22, a member of the IL-10 subfamily, induces inflammatory responses in colonic subepithelial myofibroblasts

BACKGROUND & AIMS

Interleukin (IL)-22, a member of the IL-10 subfamily, is a recently identified T-cell-derived cytokine. We investigated IL-22 expression in the inflamed mucosa of patients with inflammatory bowel disease (IBD) and analyzed its biologic activities in human colonic subepithelial myofibroblasts (SEMFs).

METHODS

Mucosal IL-22 expression was evaluated by immunohistochemical procedures. The effects of IL-22 on colonic SEMFs were investigated by cDNA microarrays, Northern blots, enzyme-linked immunosorbent assay, and electrophoretic gel mobility shift assays (EMSAs).

RESULTS

IL-22 was not detectable in normal colonic mucosa. In IBD mucosa, IL-22 expression was detectable in CD4-positive T cells. IL-22-positive cells were increased in ulcerative colitis and even more so in Crohn's disease. IL-22 receptor expression colocalized with a marker of SEMFs. IL-22 did not modulate SEMF proliferation and collagen synthesis. cDNA microarray analyses demonstrated that, in colonic SEMFs, IL-22 increased the messenger RNA (mRNA) expression of inflammatory cytokines (IL-6, IL-8, IL-11, and leukemia inhibitory factor [LIF]), chemokines, and matrix metalloproteinases. IL-22 induced an activation of nuclear factor (NF)-kappaB and activating protein (AP)-1 within 1 hour, and a blockade of NF-kappaB and AP-1 activation markedly reduced IL-22 induction of IL-6, IL-8, IL-11, and LIF mRNA. MAP-kinase inhibitors (PD98059, U0216, and SB202190) significantly reduced IL-22 induction of cytokine secretion. The combination of either IL-17 plus IL-22 or IL-19 plus IL-22 additively up-regulated cytokine secretion.

CONCLUSIONS

IL-22 derived from activated T cells acts on SEMFs to elicit expression of proinflammatory cytokines and matrix-degrading molecules indicating proinflammatory/remodeling roles in IBD.

Janus Kinases Affect Thrombopoietin Receptor Cell Surface Localization and Stability

The thrombopoietin receptor (TpoR) regulates hematopoietic stem cell renewal, megakaryocyte differentiation, and platelet formation. TpoR signals by activating Janus kinases JAK2 and Tyk2. Here we show that, in addition to signaling downstream from the activated TpoR, JAK2 and Tyk2 strongly promote cell surface localization and enhance total protein levels of the TpoR. This effect is caused by stabilization of the mature endoglycosidase H-resistant form of the receptor. Confocal microscopy indicates that TpoR colocalizes partially with recycling transferrin in Ba/F3 cells. The interaction with JAK2 or Tyk2 appears to protect the receptor from proteasome degradation. Sequences encompassing Box1 and Box2 regions of the receptor cytosolic domain and an intact JAK2 or Tyk2 FERM domain are required for these effects. We discuss the relevance of our results to the reported defects of TpoR processing in myeloproliferative diseases and to the mechanisms of Tpo signaling and clearance via the TpoR.

Expression patterns of IL-10 ligand and receptor gene families provide leads for biological characterization

The expression patterns of the IL-10 ligand and receptor genes were examined in normal and transformed cell lines of human hematopoietic and non-hematopoietic origin. IL-10 family ligands, IL-10, IL-19, IL-20, IL-22, IL-24 and IL-26 were predominantly expressed by hematopoietic cells. IL-10, IL-24 and IL-26 were produced by both monocytes and T cells, IL-19 and IL-20 were produced by monocytes whereas IL-22 was produced mainly by activated T cells. The receptors of the IL-10 family, IL-10R1, IL-10R2, IL-20R1, IL-20R2, IL-22R1 and IL-22 BP were also expressed in a distinct pattern when probed on these cell lines. The expression of IL-10R2 was ubiquitous whereas IL-10R1 was predominantly expressed on hematopoietic cells, including, T cells, B cells, NK cells, monocytes and dendritic cells. IL-20R1, IL-20R2 and IL-22R1 were absent or expressed at extremely low levels on cells of the hematopoietic lineage. These receptors were mainly found on epithelial and stromal cells fibroblasts of various tissues. Interestingly, IL-22BP was quite specifically expressed by dendritic cells. These data point to a function of the novel IL-10 family members in communication and interaction between cells of the hematopoietic and non-hematopoietic lineages, a role quite distinct from the immunomodulating effects of IL-10 itself.

Full house: 12 receptors for 27 cytokines

With the sequencing of the human genome nearing completion, it appears that all members of the class II cytokine receptor family (CRF2) have been identified and partially characterized. The entire family is composed of exactly one dozen members. Eleven of them combine as various heterodimers to transduce signals across the cellular membrane for 27 cytokines divided into four structurally related groups: 6 cytokines of the IL-10 family, 17 type I IFNs, 1 type II IFN and 3 IFN-lambdas. The last CRF2 member is the soluble receptor which can neutralize the action of one of the cytokines of the IL-10 family, IL-22. Although the extracellular domains of all CRF2 proteins reveal primary and structural homology, their intracellular domains are very dissimilar. Nevertheless, signaling events induced through various combinations of CRF2 subunits partially overlap, leading to the induction of overlapping but cytokine-specific biological activities.

Evolution of the Class 2 cytokines and receptors, and discovery of new friends and relatives

The sequencing of a wide variety of genomes and their transcripts has allowed researchers to determine how proteins or protein families evolved and how strongly during evolution a protein has been conserved. In this report, we analyze the evolution of the Class 2 ligands and their cognate receptors by analyzing Class 2 ligand and receptor chain gene sequences from a variety of DNA sequence databases. Both the Class 2 cytokines and receptor chains appear to have developed during the evolution of the chordate phyla: distant homologues of type I interferon (IFN) receptors are the only Class 2 cytokine receptors identified in the Ciona genomes, while a wide variety of Class 2 ligands and receptor chains are encoded in the currently available genomes of bony vertebrates (teleost fish, amphibians, reptiles, birds, mammals). Phylogenetic trees of ligands and ligand-binding receptor chains demonstrate that proteins involved in conferring antiviral activity diverged before those involved in adaptive immunity. Genes encoding IFNs and IFN receptors duplicated multiple times during chordate evolution, suggesting that duplication of genes encoding IFN activity conveyed an evolutionary advantage. Altogether, these data support a model whereby the original Class 2 cytokines and receptors evolved and duplicated during the evolution of the chordate innate immune response system; new receptor and ligand duplications evolved into signaling molecules to fulfill communication requirements of a highly specialized and differentiated vertebrate immune system. In addition, the genomic analysis led to the discovery of some new members of this family.

Expression of interleukin-22 in rheumatoid arthritis: potential role as a proinflammatory cytokine

OBJECTIVE

Interleukin-22 (IL-22) is a novel cytokine of the IL-10 family. Although its pathophysiologic function is largely unknown, induction of acute-phase responses by IL-22 has suggested proinflammatory properties. In this study, we sought to examine whether IL-22 plays a role in the pathogenesis of rheumatoid arthritis (RA).

METHODS

Expression of IL-22 and IL-22 receptor 1 (IL-22R1) was examined by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunohistochemical analysis. The effects of recombinant IL-22 (rIL-22) on cultured synovial fibroblasts derived from RA patients (RASF), with regard to the proliferation of synovial fibroblasts and production of monocyte chemoattractant protein 1 (MCP-1), were examined by alamer blue assay and enzyme-linked immunosorbent assay, respectively.

RESULTS

IL-22 messenger RNA was detected by RT-PCR in RA synovial tissues and mononuclear cells isolated from RA synovial fluid samples. High levels of IL-22 were expressed both in the lining and the sublining layers of RA synovial tissues. Staining for vimentin and CD68, as markers of synovial fibroblasts and macrophages, respectively, showed that the majority of IL-22-positive cells were synovial fibroblasts and macrophages. IL-22R1 was also expressed in both the lining and the sublining layers of RA synovial tissues. The majority of cells expressing IL-22R1 were positive for vimentin, but not for CD68. Expression of IL-22 and IL-22R1 in RASF was confirmed by RT-PCR and Western blot analysis. In vitro, rIL-22 significantly increased proliferation of RASF and production of MCP-1 by RASF above the value of medium controls. Moreover, MAPK activation was induced in RASF in response to IL-22 stimulation.

CONCLUSION

These data suggest that IL-22, produced by synovial fibroblasts and macrophages, promotes inflammatory responses in RA synovial tissues by inducing the proliferation and chemokine production of synovial fibroblasts.

A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera

Myeloproliferative disorders are clonal haematopoietic stem cell malignancies characterized by independency or hypersensitivity of haematopoietic progenitors to numerous cytokines. The molecular basis of most myeloproliferative disorders is unknown. On the basis of the model of chronic myeloid leukaemia, it is expected that a constitutive tyrosine kinase activity could be at the origin of these diseases. Polycythaemia vera is an acquired myeloproliferative disorder, characterized by the presence of polycythaemia diversely associated with thrombocytosis, leukocytosis and splenomegaly. Polycythaemia vera progenitors are hypersensitive to erythropoietin and other cytokines. Here, we describe a clonal and recurrent mutation in the JH2 pseudo-kinase domain of the Janus kinase 2 (JAK2) gene in most (> 80%) polycythaemia vera patients. The mutation, a valine-to-phenylalanine substitution at amino acid position 617, leads to constitutive tyrosine phosphorylation activity that promotes cytokine hypersensitivity and induces erythrocytosis in a mouse model. As this mutation is also found in other myeloproliferative disorders, this unique mutation will permit a new molecular classification of these disorders and novel therapeutical approaches.

IL-22 inhibits epidermal differentiation and induces proinflammatory gene expression and migration of human keratinocytes

IL-22 belongs to a family of cytokines structurally related to IL-10, including IL-19, IL-20, IL-24, and IL-26. In contrast to IL-10, IL-22 has proinflammatory activities. IL-22 signals through a class II cytokine receptor composed of an IL-22-binding chain, IL-22RA1, and the IL-10RB subunit, which is shared with the IL-10R. In the present study, we show that short-term cultured human epidermal keratinocytes express a functional IL-22R but no IL-10R. Accordingly, IL-22 but not IL-10 induces STAT3 activation in keratinocytes. Using a cDNA array screening approach, real-time RT-PCR, and Western blot analysis, we demonstrate that IL-22 up-regulates, in a dose-dependent manner, the expression of S100A7, S100A8, S100A9, a group of proinflammatory molecules belonging to the S100 family of calcium-binding proteins, as well as the matrix metalloproteinase 3, the platelet-derived growth factor A, and the CXCL5 chemokine. In addition, IL-22 induces keratinocyte migration in an in vitro injury model and down-regulates the expression of at least seven genes associated with keratinocyte differentiation. Finally, we show that IL-22 strongly induces hyperplasia of reconstituted human epidermis. Taken together, these results suggest that IL-22 plays an important role in skin inflammatory processes and wound healing.

Interleukin-24 and its receptors

Interleukin 24 (IL-24) is a new member of the IL-10 family of cytokines and it signals through two heterodimeric receptors: IL-20R1/IL-20R2 and IL-22R1/IL-20R2. Upon binding to its receptors, IL-24 induces rapid activation of Stat-1 and Stat-3 transcription factors, which appear to play a role in cell survival and proliferation. Under physiological conditions, the major sources of IL-24 are the activated monocytes and T helper 2 cells, whereas the major IL-24 target tissues, based on the receptor expression pattern, are non-haematopoietic in origin, and include skin, lung and reproductive tissues. Structurally and functionally, IL-24 is highly conserved across species. This review highlights our current knowledge of IL-24 as a cytokine, with much less emphasis placed on the non-receptor-mediated functions (a subject of several reviews) focused on in much of the earlier literature on IL-24. The potential roles of IL-24 as part of a complex cytokine network in wound healing, psoriasis and cancer are discussed.

Interleukin-21 enhances T-helper cell type I signaling and interferon-gamma production in Crohn's disease

BACKGROUND & AIMS

T-helper (Th)1 cells play a central role in the pathogenesis of tissue damage in Crohn's disease (CD). Interleukin (IL)-12/STAT4 signaling promotes Th1 cell commitment in CD, but other cytokines are needed to maintain activated Th1 cells in the mucosa. In this study, we examined the expression and role of IL-21, a T-cell-derived cytokine of the IL-2 family; in tissues and cells isolated from patients with inflammatory bowel disease.

METHODS

IL-21 was examined by Western blotting in whole mucosa and lamina propria mononuclear cells (LPMCs) from patients with CD, ulcerative colitis (UC), and controls. We also examined the effects of exogenous IL-12 on IL-21 production, as well as the effects of blocking IL-21 with an IL-21-receptor Ig fusion protein. Interferon (IFN)-gamma was measured in the culture supernatants by enzyme-linked immunosorbent assay, and phosphorylated STAT4 and T-bet were examined by Western blotting.

RESULTS

IL-21 was detected in all samples, but its expression was higher at the site of disease in CD in comparison with UC and controls. Enhanced IL-21 was seen in both ileal and colonic CD and in fibrostenosing and nonfibrostenosing disease. IL-12 enhanced IL-21 in normal lamina propria lymphocytes through an IFN-gamma-independent mechanism, and blocking IL-12 in CD LPMCs decreased anti-CD3-stimulated IL-21 expression. Neutralization of IL-21 in CD LPMC cultures decreased phosphorylated STAT4 and T-bet expression, thereby inhibiting IFN-gamma production.

CONCLUSIONS

Our data suggest that IL-21 contributes to the ongoing Th1 mucosal response in CD.

Is there an interaction between interleukin-10 and interleukin-22?

Interleukin(IL)-10 and IL-22 are structurally related cytokines. Their heterodimeric receptors consist of the cytokine-specific chains IL-10R1 and IL-22R1, respectively, and the common chain IL-10R2. This study focused on the question of whether IL-10 modulates IL-22 effects and vice versa. This question is important because IL-10 and IL-22 exert anti- and proinflammatory effects, respectively, and, as we show here, are simultaneously present in both systemic and local inflammation. The revealed lacking concomitance of IL-10R1 and IL-22R1 on identical cells excluded any possible interaction between IL-10 and IL-22 apart from the competition for IL-10R2. To study this competition, monocytes and hepatocytes were chosen. The dependence of the cytokine action on IL-10R2 was verified. Interestingly, no influence of IL-22 on IL-10 effects was observed. The same was true when IL-22 was used in complex with IL-22-binding protein. Similarly, no influence of IL-10 was found on IL-22 action. This missing competition seemed to be due to a lack of binding between IL-10R2 and the native cytokines in the absence of their corresponding R1 chain. However, IL-10R2 interacted with defined IL-10- and IL-22-derived peptides supporting the hypothesis that cytokine binding to its corresponding R1 chain creates a binding site on this cytokine for IL-10R2.

Cloning of murine IL-22 receptor alpha 2 and comparison with its human counterpart

We have identified the mouse and rat homologs of human interleukin-22 receptor alpha 2 (IL-22R alpha 2) and compared the localization, structure, and expression of the encoding murine and human genes. The mouse IL-22R alpha 2-encoding gene is located on chromosome 10A3 between, like in human, the genes for interferon-gamma R1 and IL-20R1. It spans a region of approximately 10 kb therefore being three times shorter than the human gene. Although the overall gene structure in both species is similar, the mouse gene lacks a counterpart to the third coding exon of the human gene known to be alternatively spliced. Like in human, mouse and rat IL-22R alpha 2 exist only as soluble receptors as deduced from the lack of transmembrane and intracellular domains encoding sequences. Quantitative expression analyses showed, analogically to the human system, a limited tissue distribution of mouse IL-22R alpha 2 mRNA. Differential modulation of IL-22R alpha 2 mRNA expression was observed upon systemic inflammation in mice in spleen, thymus, and lymph node.

Expression of interleukin-22 in murine carcinoma cells did not influence tumour growth in vivo but did improve survival of the inoculated hosts

Interleukin (IL)-22, a novel cytokine belonging to the IL-10 family, is secreted from activated T and natural killer cells and is possibly involved in inflammatory responses. We examined whether expression of the IL-22 gene in murine colon carcinoma Colon 26 cells (Colon 26/IL-22) could produce any antitumour effects in the inoculated mice. Although growth of Colon 26/IL-22 tumours in syngeneic mice was not different from that of parent tumours, survival of the mice that were subcutaneously or intraperitoneally inoculated with Colon 26/IL-22 tumours was significantly prolonged compared with the mice inoculated with parent tumours. Metastasis was not influenced by IL-22 expressed in tumours. Expression of the IL-22 receptor-specific gene, IL-22R, was not induced in spleen cells stimulated with concanavalin A, anti-CD3 or anti-CD40 antibody, despite constitutive expression of the IL-10R2 gene, which encodes another component of the heterodimeric IL-22 receptor complex. IL-22 thereby does not directly act on immunocompetent cells, and IL-22 expressed in tumours can favour apothanasia of inoculated hosts.

Interleukin-10 suppression of myeloid cell activation--a continuing puzzle

Efforts to identify the signal transduction pathways used by interleukin-10 (IL-10) have resulted in limited success. The anti-inflammatory effects elicited by IL-10, and the mechanisms by which these are mediated, are still relatively unknown. Understanding the signalling mechanisms behind the suppression of cytokine expression by IL-10 could be of potential therapeutic interest. Although the consensus is that the Janus kinase, Jak1, as well as the signal transducer and activator of transcription STAT3 are central, much controversy exists about the participation and roles of many other signalling pathways targeted by IL-10. The mechanisms of cytokine suppression proposed by various groups have included transcriptional, post-transcriptional and post-translational regulation of IL-10 target genes; nevertheless no unifying model has emerged thus far. Here we would like to highlight novel findings and discuss their implications in the context of current understanding of IL-10 signalling.

Cloning and characterization of chicken IL-10 and its role in the immune response to Eimeria maxima

We isolated the full-length chicken IL-10 (chIL-10) cDNA from an expressed sequence tag library derived from RNA from cecal tonsils of Eimeria tenella-infected chickens. It encodes a 178-aa polypeptide, with a predicted 162-aa mature peptide. Chicken IL-10 has 45 and 42% aa identity with human and murine IL-10, respectively. The structures of the chIL-10 gene and its promoter were determined by direct sequencing of a bacterial artificial chromosome containing chIL-10. The chIL-10 gene structure is similar to (five exons, four introns), but more compact than, that of its mammalian orthologues. The promoter is more similar to that of Fugu IL-10 than human IL-10. Chicken IL-10 mRNA expression was identified mainly in the bursa of Fabricius and cecal tonsils, with low levels of expression also seen in thymus, liver, and lung. Expression was also detected in PHA-activated thymocytes and LPS-stimulated monocyte-derived macrophages, with high expression in an LPS-stimulated macrophage cell line. Recombinant chIL-10 was produced and bioactivity demonstrated through IL-10-induced inhibition of IFN-gamma synthesis by mitogen-activated lymphocytes. We measured the expression of mRNA for chIL-10 and other signature cytokines in gut and spleen of resistant (line C.B12) and susceptible (line 15I) chickens during the course of an E. maxima infection. Susceptible chickens showed higher levels of chIL-10 mRNA expression in the spleen, both constitutively and after infection, and in the small intestine after infection than did resistant chickens. These data indicate a potential role for chIL-10 in changing the Th bias during infection with an intracellular protozoan, thereby contributing to susceptibility of line 15I chickens.

The IL-10R2 binding hot spot on IL-22 is located on the N-terminal helix and is dependent on N-linked glycosylation

IL-22 is a class 2 alpha-helical cytokine involved in the generation of inflammatory responses. These activities require IL-22 to engage the cell surface receptors IL-22R1 and the low-affinity signaling molecule IL-10R2. IL-10R2 also interacts with five other class 2 cytokines: IL-10, IL-26, and the interferon-like cytokines IL-28A, IL-28B, and IL-29. Here, we define the IL-10R2 binding site on IL-22 using surface plasmon resonance (SPR) and site-directed mutagenesis. Surprisingly, the binding hot spot on IL-22 includes asparagine 54 (N54), which is post-translationally modified by N-linked glycosylation. Further characterization of the glycosylation reveals that only a single fucosylated N-acetyl glucosamine on N54 is required for maximal IL-10R2 binding. Biological responses of IL-22 mutants measured in cell-based luciferase assays correlate with the in vitro SPR studies. Together, these data suggest that IL-22 activity may be modulated via changes in the glycosylation state of the ligand during inflammation.

Interleukin-10 and related cytokines and receptors

The Class 2 alpha-helical cytokines consist of interleukin-10 (IL-10), IL-19, IL-20, IL-22, IL-24 (Mda-7), and IL-26, interferons (IFN-alpha, -beta, -epsilon, -kappa, -omega, -delta, -tau, and -gamma) and interferon-like molecules (limitin, IL-28A, IL-28B, and IL-29). The interaction of these cytokines with their specific receptor molecules initiates a broad and varied array of signals that induce cellular antiviral states, modulate inflammatory responses, inhibit or stimulate cell growth, produce or inhibit apoptosis, and affect many immune mechanisms. The information derived from crystal structures and molecular evolution has led to progress in the analysis of the molecular mechanisms initiating their biological activities. These cytokines have significant roles in a variety of pathophysiological processes as well as in regulation of the immune system. Further investigation of these critical intercellular signaling molecules will provide important information to enable these proteins to be used more extensively in therapy for a variety of diseases.