Identification and functional characterization of a second chain of the interleukin-10 receptor complex

Adjunctive treatment of disseminated Mycobacterium avium complex infection with interferon alpha-2b in a patient with complete interferon-gamma receptor R1 deficiency

We report adjunct treatment of (interferon) IFN-alpha2b (Intron-A) in a patient with complete interferon-gamma receptor R1 (IFNGR1) deficiency suffering from disseminated infection with Mycobacterium avium complex (MAC) resistant to multiple anti-mycobacterial agents. A low dose of IFN-alpha2b (3 x 10(6) units/m(2) three times weekly subcutaneously) successfully attenuated progressive hepatosplenomegaly and abdominal/retroperitoneal/pelvic lymphadenopathy, although the patient continued to be mycobacteremic. This is the first report of a complete IFNGR1 deficiency treated with adjuvant IFN-alpha2b for disseminated MAC infection.

The role of p38 mitogen-activated protein kinase in regulating interleukin-10 gene expression in Burkitt's lymphoma cell lines

In malignant B lymphoma cells interleukin-10 (IL-10) expression is frequently upregulated. This effect is thought to support to the malignant transformation of these cells and to be a potential target for pharmacotherapy. To define better the mechanism for upregulation of the IL-10 gene, we tested the association between IL-10 and p38 mitogen-activated protein kinase (MAPK) in several Epstein-Barr virus (EBV) infected and non-infected Burkitt's lymphoma (BL) cell lines. The all BL cell lines expressed IL-10 and IL-10 receptor mRNAs, and produced IL-10. p38 MAPK was constitutively phosphorylated in the cytoplasm of the BL cell lines. We further analyzed molecular effects of p38 MAPK on IL-10 expression in Akata cells. Exogenous IL-10 lead rapidly to phosphorylation of Jak1 and Tyk2 as transducers of signals of IL-10, and promoted growth of Akata cells in a dose-dependent manner. The phosphorylation of cytoplasmic p38 MAPK in Akata cells was reduced by the serine/threonine kinase inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7). A specific inhibitor of p38 MAPK, SB203580, blocked simultaneously STAT3 DNA-binding activity, and IL-10 mRNA expression, IL-10 production, and then the cell growth was inhibited. These results indicate that the p38 MAPK pathway is functionally linked to IL-10 gene expression and supports the view that the constitutive activation of cytoplasmic p38 MAPK in BL cells is a step in the upregulation of IL-10 gene expression and lymphomagenesis.

Orf virus interleukin-10 inhibits cytokine synthesis in activated human THP-1 monocytes, but only partially impairs their proliferation

The sheep parapoxvirus orf virus (ORFV) induces acute, pustular skin lesions in humans. ORFV encodes an orthologue of interleukin-10 (IL-10) that, whilst it closely resembles ovine IL-10 (91 % amino acid identity), shows only 75 % amino acid identity to human IL-10 (hIL-10). The anti-inflammatory potential of ORFV IL-10 in human ORFV infection was investigated by examining its immunosuppressive effects on THP-1 monocytes. ORFV IL-10 and hIL-10 were shown to have equivalent inhibitory effects on the synthesis of proinflammatory cytokines in lipopolysaccharide-activated monocytes, but differed in their abilities to inhibit monocyte proliferation. Structural modelling of ORFV IL-10 revealed differences from hIL-10 in residues predicted to interact with IL-10 co-receptor 2 (IL-10R2), whereas there were very few differences in the residues predicted to interact with IL-10R1. These findings suggest that the partial ability of ORFV IL-10 to inhibit THP-1 monocyte proliferation may be due to the absence of critical residues that mediate the interaction with human IL-10R2.

Inhibition of type I and type III interferons by a secreted glycoprotein from Yaba-like disease virus

Type I (IFN-alpha/beta) and type III (IFN-lambdas) IFNs are important components of the host antiviral response. Although type III IFNs possess intrinsic antiviral activity similar to that of type I IFNs, they signal through a specific unique receptor complex, and their functional importance for antiviral resistance is largely uncharacterized. Here, we report the first virus defense mechanism that directly targets type III IFNs. Y136 from Yaba-like disease virus, a yatapoxvirus, is a secreted glycoprotein related to protein B18 from Vaccinia virus, a known type I IFN-binding protein and a member of the Ig superfamily. Surprisingly, whereas B18 inhibits only type I IFNs, Y136 inhibits both type I and type III IFNs. Y136 inhibits IFN-induced signaling and suppresses IFN-mediated biological activities including up-regulation of MHC class I antigen expression and induction of the antiviral state. These data demonstrate that poxviruses have developed unique strategies to counteract IFN-mediated antiviral protection and highlight the importance of type III IFNs in antiviral defense. These results suggest that type III IFNs may be an effective treatment for some poxviral infections.

Proteasome-mediated proteolysis of the interleukin-10 receptor is important for signal downregulation

The cytokine interleukin-10 (IL-10) is an important regulator of immune cell function, proliferation, and survival. The IL-10 receptor (IL-10R) consists of two subunits, IL-10R1 and IL-10R2, both belonging to the class II cytokine receptor superfamily. Like other members of the cytokine receptor superfamily, IL-10R stimulation leads to activation of Jak family kinases and Stat transcription factors. To identify additional signal transduction pathways used by the IL-10R, we purified 92-kDa and 100-kDa proteins that coprecipitated with IL-10R1 from IL-10-stimulated cells. Both proteins were found to be related to the 97-kDa subunit of the regulatory component of the 26S proteasome. Subsequent studies confirmed that the IL-10R1 undergoes ligand- dependent internalization and proteasome-mediated degradation. An IL-10R1 cytoplasmic domain mutant deficient for internalization exhibited prolonged signaling through Jak1 and Stat3, reinforcing the importance of receptor internalization for signal termination.

Human interferon lambda-1 (IFN-lambda1/IL-29) modulates the Th1/Th2 response

Interferon lambda-1 (IFN-lambda1/IL-29) is a member of the Type-III interferon family, which contains three ligands: IFN-lambda1, 2 and 3. These three ligands use the same unique heterodimeric receptor composed of CRF2-12 (IFN-lambda-R1/IL-28Ralpha) and CRF2-4 (IL10-R-beta) chains. Like their close relatives, the Type-I interferons, IFN-lambda1, 2 and 3, promote the phosphorylation of STAT1 and STAT2, induce the ISRE3 complex, elevate OAS and MxA expression and exhibit antiviral activity in vitro. Their use of the IL10-R-beta chain and their ability to phosphorylate STAT3, STAT4 and STAT5 suggested that they may also exhibit immunomodulatory activity; their antiviral action led us to hypothesize that this activity might be directed toward the Th1/Th2 system. Here, we have demonstrated that IFN-lambda1 altered the activity of Th cells in three separate experimental systems: (i) mitogen stimulation, (ii) mixed-lymphocyte reaction (MLR) and (iii) stimulation of naive T cells by monocyte-derived dendritic cells (mDC). In Con-A stimulation assays, the inclusion of IFN-lambda1 consistently led to markedly diminished levels of secreted interleukin (IL-13) with occasional coincident, modest elevation of secreted IFN-gamma. IL-13 secretion was 100-fold more sensitive to IFN-lambda1 than was IFN-gamma secretion. These observations were also made in the allogeneic two-way MLR. IFN-lambda1 was able to alter cytokine-mediated Th biasing and when naive T cells were exposed to allogeneic mDC that had been matured in the presence of IFN-lambda1, secreted IL-13 was again markedly and consistently reduced, whereas secreted IFN-gamma was largely unaltered. These functions were independent of IL-10. Our data support a hitherto unsuspected role for IFN-lambda1 in modulating the development of Th1 and Th2 cells, with an apparent emphasis on the diminution of IL-13 secretion.

Human interleukin 24 (MDA-7/IL-24) protein kills breast cancer cells via the IL-20 receptor and is antagonized by IL-10

The melanoma differentiation-associated gene-7 (mda-7/IL-24) is a unique member of the interleukin 10 (IL-10) family of cytokines, with ubiquitous tumor cell pro-apoptotic activity. Recent data have shown that IL-24 is secreted as a glycosylated protein and functions as a pro-Th1 cytokine and as a potent anti-angiogenic molecule. In this study, we analyzed the activity of Ad-mda7 and its protein product, secreted IL-24, against human breast cancer cells. We show that Ad-mda7 transduction of human breast cancer cells results in G(2)/M phase cell cycle arrest and apoptotic cell death, which correlates with secretion of IL-24 protein. Neutralizing antibody against IL-24 significantly inhibited Ad-mda7 cytotoxicity. IL-24 and IL-10 both engage their cognate receptors on breast cancer cells resulting in phosphorylation and activation of STAT3, however, IL-10 receptor binding failed to induce cell killing, indicating that tumor cell killing by IL-24 is independent of STAT3 phosphorylation. Treatment with exogenous IL-24 induced apoptosis in breast cancer cells and this effect was abolished by addition of anti-IL-24 antibody or anti-IL-20R1, indicating that bystander cell killing is mediated via IL-24 binding to the IL-20R1/IL-20R2 heterodimeric receptor complex. Co-administration of the related cytokine IL-10 inhibited killing mediated by IL-24 and concomitantly inhibited IL-24 mediated up-regulation of the tumor suppressor proteins, p53 and p27(Kip1). In summary, we have defined a tumor-selective cytotoxic bystander role for secreted IL-24 protein and identified a novel receptor-mediated death pathway in breast cancer cells, wherein the related cytokines IL-24 and IL-10 exhibit antagonistic activity.

Expression of constitutively active STAT3 can replicate the cytokine-suppressive activity of interleukin-10 in human primary macrophages

There is general agreement that signal transducer and activation of transcription 3 (STAT3) is required to mediate the anti-inflammatory activities of interleukin (IL)-10. However, STAT3 is activated by multiple factors that do not share the anti-inflammatory activity of IL-10. The question remains whether STAT3 is sufficient for the anti-inflammatory effects or whether there are other signals required, as had been suggested previously. We set out to map the human IL-10 receptor and to identify the key elements involved in transducing the cytokine-suppressive effects of IL-10. We were able to show an absolute requirement for both of the tyrosine residues found within the YXXQ-STAT3-docking site within the IL-10 receptor 1 and that no other signals appeared to be required. We used a constitutively active STAT3 to determine whether expression of this factor could suppress lipopolysaccharide-induced tumor necrosis factor and IL-6 production. Our data show that STAT3 activity can suppress both IL-6 and tumor necrosis factor production in lipopolysaccharide-stimulated macrophages. However, in synovial fibroblasts, STAT3 did not suppress IL-6 production, suggesting that the cellular environment plays an important role in dictating whether STAT3 drives a pro- or anti-inflammatory response.

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.

Molecular characterization, 3D modelling and expression analysis of sea bass (Dicentrarchus labrax L.) interleukin-10

Interleukin-10 (IL-10) is a pleiotropic cytokine generally known for its relevance in the resolution of inflammation, but that also has immunostimulatory properties. Here is described the isolation and characterization of the sea bass IL-10 (sbIL-10) cDNA and gene. The sbIL-10 gene encodes a 187 amino acid protein and comprises a five exon-four intron structure as other known IL-10 genes. Important structural residues are maintained in the sbIL-10 protein, including the four cysteines responsible for the two intra-chain disulfide bridges reported for human IL-10. The 3D structure of sbIL-10 was predicted. This first homology model of a fish IL-10 reveals a high degree of compatibility between the dimeric quaternary architectures of sbIL-10 and its mammalian counterparts. The phylogenetic analysis clusters sbIL-10 with other IL-10s, apart from IL-10-related molecules. The involvement of IL-10 in sea bass immune responses was demonstrated by investigating the expression profiles of IL-1beta and IL-10 in the head-kidney and spleen following intraperitoneal injection of UV-killed Photobacterium damselae ssp. piscicida. Furthermore, involvement of IL-10 in the resolution of inflammation is for the first time suggested in fish, due to the delayed maximal mRNA levels of sbIL-10 compared to those of the pro-inflammatory IL-1beta.

The roles for cytokines in the generation and maintenance of regulatory T cells

As an essential mechanism for self-tolerance, immune suppression has attracted much attention since the discovery of suppressor T cells, now called regulatory T cells (Tregs), in the 1990s. Different types of Tregs have been described based on distinct expression patterns of surface markers and cytokines. Cytokines are not only essential for function but also important for the generation of Tregs. Interleukin-2 (IL-2), transforming growth factor-beta, IL-10, and other immunoregulatory molecules have been shown to control the generation of Tregs. The presence of other types of cells, in particular antigen-presenting cells (APCs), is critical for the generation of Tregs. Cytokines can serve as either initiators or intermediates for the interactions between APCs and Tregs. This review discusses our current knowledge of how cytokines regulate the generation and maintenance of Tregs.

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.

Conformational changes mediate interleukin-10 receptor 2 (IL-10R2) binding to IL-10 and assembly of the signaling complex

Interleukin-10 receptor 2 (IL-10R2) is a critical component of the IL-10.IL-10R1.IL-10R2 complex which regulates IL-10-mediated immunomodulatory responses. The ternary IL-10 signaling complex is assembled in a sequential order with the IL-10.IL-10R1 interaction occurring first followed by engagement of the IL-10R2 chain. In this study we map the IL-10R2 binding site on IL-10 using surface plasmon resonance and cell-based assays. Critical IL-10R2 binding residues are located in helix A adjacent to the previously identified IL-10R1 recognition surface. Interestingly, IL-10R2 binding residues located in the N-terminal end of helix A exhibit large structural differences between unbound cIL-10 and cIL-10.IL-10R1 crystal structures. This suggests IL-10R1-induced conformational changes regulate IL-10R2 binding and assembly of the ternary IL-10.IL-10R1.IL-10R2 complex. The basic mechanistic features of the assembly process are likely shared by six additional class-2 cytokines (viral IL-10s, IL-22, IL-26, IL-28A, IL28B, and IL-29) to promote IL-10R2 binding to six additional receptor complexes. These studies highlight the importance of structure in regulating low affinity protein-protein interactions and IL-10 signal transduction.

mda-7/IL-24: multifunctional cancer-specific apoptosis-inducing cytokine

"Differentiation therapy" provides a unique and potentially effective, less toxic treatment paradigm for cancer. Moreover, combining "differentiation therapy" with molecular approaches presents an unparalleled opportunity to identify and clone genes mediating cancer growth control, differentiation, senescence, and programmed cell death (apoptosis). Subtraction hybridization applied to human melanoma cells induced to terminally differentiate by treatment with fibroblast interferon (IFN-beta) plus mezerein (MEZ) permitted cloning of melanoma differentiation associated (mda) genes. Founded on its novel properties, one particular mda gene, mda-7, now classified as a member of the interleukin (IL)-10 gene family (IL-24) because of conserved structure, chromosomal location, and cytokine-like properties has become the focus of attention of multiple laboratories. When administered by transfection or adenovirus-transduction into a spectrum of tumor cell types, melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) induces apoptosis, whereas no toxicity is apparent in normal cells. mda-7/IL-24 displays potent "bystander antitumor" activity and also has the capacity to enhance radiation lethality, to induce immune-regulatory activities, and to inhibit tumor angiogenesis. Based on these remarkable attributes and effective antitumor therapy in animal models, this cytokine has taken the important step of entering the clinic. In a Phase I clinical trial, intratumoral injections of adenovirus-administered mda-7/IL-24 (Ad.mda-7) was safe, elicited tumor-regulatory and immune-activating processes, and provided clinically significant activity. This review highlights our current understanding of the diverse activities and properties of this novel cytokine, with potential to become a prominent gene therapy for cancer.

Immature monocytes from G-CSF-mobilized peripheral blood stem cell collections carry surface-bound IL-10 and have the potential to modulate alloreactivity

Production of the anti-inflammatory cytokine IL-10 by monocytes has been implicated as a probable negative regulator of graft-versus-host disease (GvHD) in patients undergoing allogeneic stem cell transplants (SCT). Monocytes from G-CSF-mobilized peripheral blood stem cell (gmPBSC) collections have been reported to produce more IL-10 than unmobilized monocytes in response to proinflammatory factors such as LPS. Why this should occur is unclear. In this study, monocyte phenotype and IL-10 localization and release were investigated in PB mononuclear cells (MNC) from 27 healthy donors mobilized for allogeneic SCT and from 13 patients with hematological malignancies mobilized for autologous SCT. All isolates contained elevated total percentages of monocytes in comparison with unmobilized PB, a high proportion of which displayed an immature phenotype. Stimulation of gmPB MNC with an inflammatory stimulus [fixed Staphylococcus aureus cells (SAC)] induced rapid up-regulation of CD14, indicating conversion to mature status. Localization studies indicated that IL-10 was predominantly present, bound on the surface of CD64(+)/CD14(low/neg) immature monocytes. Inflammatory stimuli (LPS, polyinosinic:polycytidylic acid, or SAC) induced release of variable quantities of IL-10 from the cell surface. MNC, separated into surface IL-10-positive or -negative fractions, differed in their ability to stimulate alloreactivity in MLR, and IL-10(+) MNC induced significantly lower levels of proliferation than IL-10(-) MNC. Thus, the subset of immature monocytes carrying surface-bound IL-10 in gmPB has the potential to modulate alloreactivity and GvHD after allogeneic SCT through cell-to-cell contact and released IL-10.

Cytomegalovirus interleukin-10 expression in infected cells does not impair MHC class I restricted peptide presentation on bystanding antigen-presenting cells

Human cytomegalovirus (HCMV) has evolved strategies to counteract its surveillance by the immune system. Mitigation of antiviral immune responses is considered critical for establishment of viral latency and for spread. Recently, a gene encoding an interleukin-10 homologue (cmvIL-10) has been discovered in the HCMV genome. Using recombinant cmvIL-10, several mostly immunosuppressive functions of the molecule have been described. However, the role of cmvIL-10 in the context of viral infection was not addressed. To be able to analyze this issue, we generated cmvIL- 10-negative viral mutants. Using these mutants, we tested whether the expression of cmvIL-10 by infected cells would render bystander antigen-presenting cells less efficient in their capacity to present antigenic peptides in the context of MHC class I. To test this, CTL clones specific for the viral nonapeptides P65(495-503) and IE1(297-305) were used as tools. Culture supernatant from fibroblasts infected with cmv-IL10-negative viruses was supplemented with increasing concentrations of recombinant cmvIL-10. Treatment of human THP-1 cells with these conditioned media did not impair their capacity to present HCMV-derived nonapeptides in the context of MHC-class I, even when high concentrations of cmvIL-10 were used. To investigate whether close cell contact was important, fibroblasts were infected with either wild-type HCMV or cmvIL-10 null mutants and were cocultured with nonpermissive lymphoblastoid cell lines, serving as target cells. No correlation was found between the ability of HCMV strains to express the cmvIL-10 gene and the capacity of neighboring LCL to present peptides in the context of MHC class I. Consequently, we propose that cmvIL- 10 expressed in the context of HCMV infection has no direct impact on MHC class I-restricted antigen presentation of noninfected bystander cells.

Characterization of the mouse IFN-lambda ligand-receptor system: IFN-lambdas exhibit antitumor activity against B16 melanoma

Recently discovered type III IFNs (IFN-lambda) exert their antiviral and immunomodulatory activities through a unique receptor complex composed of IFN-lambdaR1 and interleukin-10 receptor 2. To further study type III IFNs, we cloned and characterized mouse IFN-lambda ligand-receptor system. We showed that, similar to their human orthologues, mIFN-lambda2 and mIFN-lambda3 signal through the IFN-lambda receptor complex, activate IFN stimulated gene factor 3, and are capable of inducing antiviral protection and MHC class I antigen expression in several cell types including B16 melanoma cells. We then used the murine B16 melanoma model to investigate the potential antitumor activities of IFN-lambdas. We developed B16 cells constitutively expressing murine IFN-lambda2 (B16.IFN-lambda2 cells) and evaluated their tumorigenicity in syngeneic C57BL/6 mice. Although constitutive expression of mIFN-lambda2 in melanoma cells did not affect their proliferation in vitro, the growth of B16.IFN-lambda2 cells, when injected s.c. into mice, was either retarded or completely prevented. We found that rejection of the modified tumor cells correlated with their level of IFN-lambda2 expression. We then developed IFN-lambda-resistant B16.IFN-lambda2 cells (B16.IFN-lambda2Res cells) and showed that their tumorigenicity was also highly impaired or completely abolished similar to B16.IFN-lambda2 cells, suggesting that IFN-lambdas engage host mechanisms to inhibit melanoma growth. These in vivo experiments show the antitumor activities of IFN-lambdas and suggest their strong therapeutic potential.

Class II cytokine receptor gene cluster is a major locus for hepatitis B persistence

Persistent hepatitis B virus infection is a major risk factor for hepatocellular carcinoma, the most frequent cancer in some developing countries. Up to 95% of those infected at birth and 15% of those infected after the neonatal period fail to clear hepatitis B virus, together resulting in approximately 350 million persistent carriers worldwide. Via a whole genome scan in Gambian families, we have identified a major susceptibility locus as a cluster of class II cytokine receptor genes on chromosome 21q22. Coding changes in two of these genes, the type I IFN receptor gene, IFN-AR2, and the IL-10RB gene that encodes a receptor chain for IL-10-related cytokines including the IFN-lambdas, are associated with viral clearance (haplotype P value = 0.0003), and in vitro assays support functional roles for these variants in receptor signaling.

Anti-inflammatory effect of interleukin-10 on human neutrophil respiratory burst involves inhibition of GM-CSF-induced p47PHOX phosphorylation through a decrease in ERK1/2 activity

Interleukin-10 (IL-10) exerts its anti-inflammatory properties by down-regulating polymorphonuclear neutrophil (PMN) functions such as reactive oxygen species (ROS) production via NADPH oxidase. The molecular mechanisms underlying this process are unclear. Partial phosphorylation of the NADPH oxidase cytosolic component p47(PHOX) induced by proinflammatory cytokines, such as granulocyte-macrophage colony stimulating factor (GM-CSF) and tumor necrosis factor (TNF)-alpha, is essential for priming ROS production by PMN. The aim of this study was to determine whether IL-10 inhibits GM-CSF- and TNFalpha-induced p47(PHOX) phosphorylation and to investigate the molecular mechanisms involved in this effect. We found that IL-10 selectively inhibited GM-CSF- but not TNFalpha-induced p47PHOX phosphorylation in a concentration-dependent manner. As GM-CSF-induced p47PHOX phosphorylation is mediated by extracellular signal-regulated kinase 1/2 (ERK1/2), we tested the effect of IL-10 on this pathway. We found that IL-10 inhibited GM-CSF-induced ERK1/2 activity in an immunocomplex kinase assay. This inhibitory effect was confirmed by analyzing the phosphorylation status of the endogenous substrate of ERK1/2, p90RSK, in intact PMN. Furthermore, IL-10 decreased ROS production by adherent GM-CSF-treated PMN in keeping with the higher ROS production observed in whole blood from IL-10 knockout mice compared to their wild-type counterparts. Together, these results suggest that IL-10 inhibits GM-CSF-induced priming of ROS production by inhibiting p47PHOX phosphorylation through a decrease in ERK1/2 activity. This IL-10 effect could contribute to the tight regulation of NADPH oxidase activity at the inflammatory site.

Interleukin-10 and chronic liver disease

Interleukin (IL)-10 is an important immunoregulatory cytokine produced by many cell populations. Numerous investigations suggest that IL-10 plays a major role in chronic liver diseases. IL-10 gene polymorphisms are possibly associated with liver disease susceptibility or severity. Recombinant human IL-10 has been produced and is currently tested in clinical trials. These trials may give new insights into the immunobiology of IL-10 and suggest that the IL-10/IL-10 receptor system may become a new therapeutic target.

Interactions among the components of the interleukin-10 receptor complex

We used fluorescence resonance energy transfer previously to show that the interferon-gamma (IFN-gamma) receptor complex is a preformed entity mediated by constitutive interactions between the IFN-gammaR2 and IFN-gammaR1 chains, and that this preassembled entity changes its structure after the treatment of cells with IFN-gamma. We applied this technique to determine the structure of the interleukin-10 (IL-10) receptor complex and whether it undergoes a similar conformational change after treatment of cells with IL-10. We report that, like the IFN-gamma receptor complex, the IL-10 receptor complex is preassembled: constitutive but weaker interactions occur between the IL-10R1 and IL-10R2 chains, and between two IL-10R2 chains. The IL-10 receptor complex undergoes no major conformational changes when cells are treated with cellular or Epstein-Barr viral IL-10. Receptor complex preassembly may be an inherent feature of Class 2 cytokine receptor complexes.

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.

Preassembly and ligand-induced restructuring of the chains of the IFN-gamma receptor complex: the roles of Jak kinases, Stat1 and the receptor chains

We previously demonstrated using noninvasive technologies that the interferon-gamma (IFN-gamma) receptor complex is preassembled (1). In this report we determined how the receptor complex is preassembled and how the ligand-mediated conformational changes occur. The interaction of Stat1 with IFN-gammaR1 results in a conformational change localized to IFN-gammaR1. Jak1 but not Jak2 is required for the two chains of the IFN-gamma receptor complex (IFN-gammaR1 and IFN-gammaR2) to interact; however, the presence of both Jak1 and Jak2 is required to see any ligand-dependant conformational change. Two IFN-gammaR2 chains interact through species-specific determinants in their extracellular domains. Finally, these determinants also participate in the interaction of IFN-gammaR2 with IFN-gammaR1. These results agree with a detailed model of the IFN-gamma receptor that requires the receptor chains to be pre-associated constitutively for the receptor to be active.

Modulation of the activation of Stat1 by the interferon-gamma receptor complex

The activation of Stat1 by the interferon-gamma (IFN-gamma) receptor complex is responsible for the transcription of a significant portion of IFN-gamma induced genes. Many of these genes are responsible for the induction of an apoptotic state in response to IFN-gamma. In the absence of Stat1 activation, IFN-gamma instead induces a proliferative response. Modifying Stat1 activation by IFN-gamma may have pharmacological benefits. We report that the rate of activation of Stat1 can be altered in HeLa cells by overexpressing either the IFN-gammaR1 chain or the IFN-gammaR2 chain. These alterations occur in hematopoietic cell lines: Raji cells and monocytic cell lines, which have average and above-average IFN-gammaR2 surface expression, activate Stat1 similarly to HeLa cells and HeLa cells overexpressing IFNgammaR2, respectively. The rapid Stat1 activation seen in HeLa cells can be inhibited by overexpressing a chimeric IFN-gammaR2 chain that does not bind Jak2 or (when high concentrations of IFN-gamma are used) by overexpressing IFN-gammaR1. These data are consistent with a model in which the recruitment of additional Jak2 activity to a signaling complex accelerates the rate of Stat1 activation. We conclude that the rate of activation of Stat1 in cells by IFN-gamma can be modified by regulating either receptor chain and speculate that pharmacological agents which modify receptor chain expression may alter IFN-gamma receptor signal transduction.

Potent antitumor activity of oncolytic adenovirus expressing mda-7/IL-24 for colorectal cancer

It has been demonstrated that interleukin 24 (IL-24, also called melanoma differentiation associated gene 7) exerts antitumor activity. In this study, we investigated whether oncolytic adenovirus-mediated gene transfer of IL-24 could induce strong antitumor activity. A tumor-selective replicating adenovirus expressing IL-24 (ZD55-IL-24) was constructed by insertion of an IL-24 expression cassette into the ZD55 vector, which is based on deletion of the adenoviral E1B 55-kDa gene. ZD55-IL-24 could express substantially more IL-24 than Ad-IL-24 because of replication of the vector. It has been shown that ZD55-IL-24 exerted a strong cytopathic effect and significant apoptosis in tumor cells with p53 dysfunction. Moreover, no cytotoxic and apoptotic effects could be seen in normal cells infected with ZD55-IL-24. Expression of IL-24 did not interfere with viral replication induced by oncolytic adenovirus. Activation of caspase 3 and caspase 9, and induction of bax gene expression, were involved in tumor cell apoptosis induced by ZD55-IL-24. Treatment of established tumors with ZD55-IL-24 showed much stronger antitumor activity than that induced by ONYX-015 or Ad-IL- 24. These data indicated that oncolytic adenovirus expressing IL-24 could exert potential antitumor activity and offer a novel approach to cancer therapy.

Maternal tolerance to H-Y is independent of IL-10

It has been suggested that the maternal immune system favors noncytotoxic, "TH-2" immune responses in order to tolerate the developing fetus. In some strains of mice, pregnant females will reject a male skin graft, even as they tolerate their male fetuses. This rejection is based on responsiveness to the male antigen H-Y. In this study we test whether functional maternal tolerance of male fetuses is critically dependent on the TH-2 cytokine Interleukin 10 (IL-10). Normal and IL-10-deficient (10-KO) females were sensitized against H-Y by intraperitoneal injection of male spleen cells before mating with 10-KO males. Litters born to 10-KO females were of comparable size to those born to normal females of the same genetic background. The proportion of males per litter was not adversely affected by IL-10 deficiency. Taken together, our work and others suggest that IL-10 may not be critically important for maternal tolerance of the fetus and extends the evidence against the idea that successful mouse pregnancy depends on TH-2 deviation of the maternal immune system.

Interleukin-10 promoter gene polymorphisms have no clear influence on interleukin-10 protein secretion in AIDS-associated B-cell lines

Interleukin-10 (IL-10) is a pleiotropic cytokine involved in several immune responses and expressed by a variety of cell types. IL-10 interacts with at least two subunits of the IL-10 receptors (IL-10R1 and IL-10R2), which are members of the interferon receptor family, and play important roles in ligand binding and signaling. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) methods, the mRNA expression and secretion patterns of IL-10 were studied. IL-10R1 and IL-10R2 mRNA expression patterns were also studied in the tumor-derived human B-cell lines. IL-10 protein is expressed and predominantly secreted by AIDS-associated B-cell lines (AABCL). However, IL-10R1 and IL-10R2 are constitutively and ubiquitously expressed in all the B-cell lines included in our study. These results suggest that B-cell IL-10 functions as an autocrine growth factor, in AABCL. Furthermore, we report that higher secretion of IL-10 observed in AABCL could be due to the specific GCC haplotype of IL-10 promoter polymorphisms, although no specific correlation was observed between IL-10 promoter polymorphisms and IL-10 protein secretion as analyzed by PCR-sequence specific primers methodology and ELISA, respectively.

Genetic variation in the IL-10 pathway modulates severity of acute graft-versus-host disease following hematopoietic cell transplantation: synergism between IL-10 genotype of patient and IL-10 receptor beta genotype of donor

We have previously shown that the interleukin 10 (IL-10)/-592*A allele of the recipient is associated with less severe acute graft-versus-host disease (GVHD) and a lower risk of nonrelapse mortality after hematopoietic cell transplantation (HCT) from an HLA-identical sibling. In the present study, we examined variation in the IL-10 receptor beta gene as a further test of the hypothesis that the IL-10 pathway regulates the risk of acute GVHD. A single nucleotide polymorphism (A/G) at cDNA position 238 of the IL-10 receptor beta gene (IL10RB/c238) was genotyped in 953 HC transplant recipients and their HLA-identical sibling donors. IL-10/-592 and IL10RB/c238 genotypes were tested for association with GVHD by multivariable analysis. The IL-10/-592*A allele of the recipient and IL10RB/c238*G allele of the donor were significantly associated with a lower risk of grades III-IV acute GVHD (trend P < .001 and P = .02, respectively). The donor IL10RB/c238*G allele provided protection among patients with the IL-10/-592 A/C or A/A genotypes but not among patients with the high-risk IL-10/-592 C/C genotype. These data suggest an interaction of the patient IL-10/-592 and donor IL10RB/c238 genotypes on risk of GVHD, further supporting the hypothesis that the IL-10 pathway plays an important role in controlling the severity of acute GVHD.

Bi-allelic presence of the interleukin-10 receptor 1 G330R allele is associated with cirrhosis in chronic HCV-1 infection

Immune response to viral infection is an important determinant of liver injury in chronic hepatitis C (CHC). Experimental and clinical data suggest a protective role of interleukin-10 (IL-10) in hepatic fibrogenesis. The significance of two SNPs of the interleukin-10 receptor 1 (IL-10R1), S138G (SNP3) and G330R (SNP4) was investigated on (i) susceptibility to CHC, (ii) progression of hepatic fibrosis and (iii) response to interferon/ribavirin therapy. DNA and liver biopsies were obtained from 212 patients with HCV (hepatitis C virus)-genotype-1 infection. The allele frequencies were 0.17 for SNP3 and 0.33 for SNP4, both of which were indifferent from healthy controls (0.17 and 0.32, respectively). Stage 1 liver fibrosis was found in 22 cases (10.4%), stage 2 in 108 (50.9%), stage 3 in 27 (12.8%), and stage 4 (cirrhosis) in 55 (25.9%). An association was found between the SNP4 allele and the presence of cirrhosis (P=0.01). Homozygous SNP4 individual variants segregated within the cirrhosis group (P=0.03). We found neither an association with SNP3 nor with the necroinflammatory disease activity (as measured by ALT levels) nor with the response to antiviral therapy. Our work implies that IL-10R1 SNP4 is a recessively inherited risk factor for hepatic cirrhosis in HCV genotype-1 infection.

A model of the ternary complex of interleukin-10 with its soluble receptors

BACKGROUND

Interleukin-10 (IL-10) is a cytokine whose main biological function is to suppress the immune response by induction of a signal(s) leading to inhibition of synthesis of a number of cytokines and their cellular receptors. Signal transduction is initiated upon formation of a ternary complex of IL-10 with two of its receptor chains, IL-10R1 and IL-10R2, expressed on the cell membrane. The affinity of IL-10R1 toward IL-10 is very high, which allowed determination of the crystal structure of IL-10 complexed with the extracellular/soluble domain of IL-10R1, while the affinity of IL-10R2 toward either IL-10 or IL-10/sIL-10R1 complex is quite low. This so far has prevented any attempts to obtain structural information about the ternary complex of IL-10 with its receptor chains.

RESULTS

Structures of the second soluble receptor chain of interleukin-10 (sIL-10R2) and the ternary complex of IL-10/sIL-10R1/sIL-10R2 have been generated by homology modeling, which allowed us to identify residues involved in ligand-receptor and receptor-receptor interactions.

CONCLUSION

The previously experimentally determined structure of the intermediate/binary complex IL-10/sIL-10R1 is the same in the ternary complex. There are two binding sites for the second receptor chain on the surface of the IL-10/sIL-10R1 complex, involving both IL-10 and sIL-10R1. Most of the interactions are hydrophilic in nature, although each interface includes two internal hydrophobic clusters. The distance between C-termini of the receptor chains is 25 A, which is common for known structures of ternary complexes of other cytokines. The structure is likely to represent the biologically active signaling complex of IL-10 with its receptor on the surface of the cell membrane.

Same structure, different function crystal structure of the Epstein-Barr virus IL-10 bound to the soluble IL-10R1 chain

Human IL-10 (hIL-10) is a cytokine that modulates diverse immune responses. The Epstein-Barr virus (EBV) genome contains an IL-10 homolog (vIL-10) that shares high sequence and structural similarity with hIL-10. Although vIL-10 suppresses inflammatory responses like hIL-10, it cannot activate many other immunostimulatory functions performed by the cellular cytokine. These functional differences have been correlated with the approximately 1000-fold lower affinity of vIL-10, compared to hIL-10, for the IL-10R1 receptor chain. To define the structural basis for these observations, crystal structures of vIL-10 and a vIL-10 point mutant were determined bound to the soluble IL-10R1 receptor fragment (sIL-10R1) at 2.8 and 2.7 A resolution, respectively. The structures reveal that subtle changes in the conformation and dynamics of the vIL-10 AB and CD loops and an orientation change of vIL-10 on sIL-10R1 are the main factors responsible for vIL-10's reduced affinity for sIL-10R1 and its distinct biological profile.

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.

Human interleukin-19 and its receptor: a potential role in the induction of Th2 responses

Interleukin-19 (IL-19) is a newly discovered member of the IL-10 family of ligands whose function is presently undefined. We recently described its cloning and initial characterization and in so doing, noted that the induction of IL-19 by LPS in human monocytes was down-regulated by interferon-gamma (IFN-gamma) and up-regulated by IL-4. This preliminary observation led us to speculate that IL-19 may play a role in the Th1/Th2 system and we examined this hypothesis further. Our results suggested that IL-19 is able to influence the maturation of human T-cells. CD4+ T-cells resulting from SEB stimulation in the presence of IL-19 contained a higher proportion of IL-4 producing cells than those developing in the absence of IL-19. This observation was complimented by the observation that fewer IFN-gamma cells accrued in the presence of IL-19, thereby suggesting that IL-19 altered the balance of Th1/Th2 cells in favour of Th2. Furthermore, in whole PBMC cultures, IL-19 up-regulated IL-4 and down-regulated IFNgamma in a dose-dependent manner. These results are presented here in review format, in the context of an overall discussion of IL-19 and its receptor.

Interferons, interferon-like cytokines, and their receptors

Recombinant interferon-alpha (IFN-alpha) was approved by regulatory agencies in many countries in 1986. As the first biotherapeutic approved, IFN-alpha paved the way for the development of many other cytokines and growth factors. Nevertheless, understanding the functions of the multitude of human IFNs and IFN-like cytokines has just touched the surface. This review summarizes the history of the purification of human IFNs and the key aspects of our current state of knowledge of human IFN genes, proteins, and receptors. All the known IFNs and IFN-like cytokines are described [IFN-alpha, IFN-beta, IFN-epsilon, IFN-kappa, IFN-omega, IFN-delta, IFN-tau, IFN-gamma, limitin, interleukin-28A (IL-28A), IL-28B, and IL-29] as well as their receptors and signal transduction pathways. The biological activities and clinical applications of the proteins are discussed. An extensive section on the evolution of these molecules provides some new insights into the development of these proteins as major elements of innate immunity. The overall structure of the IFNs is put into perspective in relation to their receptors and functions.

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.

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.

Dietary n-3 polyunsaturated fatty acids suppress splenic CD4(+) T cell function in interleukin (IL)-10(-/-) mice

Our laboratory has demonstrated that down-regulation of proliferation and cytokine synthesis by CD4(+) T cells in mice fed diets rich in n-3 polyunsaturated fatty acids (PUFA) is highly dependent on the involvement of the co-stimulatory molecule, CD28. It has been reported that the inhibitory cytokine interleukin (IL)-10 acts directly on T cells which up-regulate IL-10 receptor (IL-10R) expression following stimulation via CD28 by efficiently blocking proliferation and cytokine production. Thus, it was hypothesized that dietary n-3 PUFA would suppress T cell function through the effects of IL-10. The proliferation of purified splenic CD4(+) T cells activated in vitro with anti-CD3 and anti-CD28 (alphaCD3/CD28) from conventional mice (C57BL/6) fed either a control corn oil (CO)-enriched diet devoid of n-3 PUFA, docosahexaenoic acid (DHA; 22 : 6) or eicosapentaenoic acid (EPA; 20 : 5) for 14 days was suppressed by dietary DHA and EPA. Surprisingly, a similar trend was seen in IL-10 gene knock-out (IL-10(-/-)) mice fed dietary n-3 PUFA. IL-10R cell surface expression was also significantly down-regulated on CD4(+) T cells from both the C57BL/6 and IL-10(-/-) mice fed dietary n-3 PUFA after 72 h of in vitro stimulation with alphaCD3/CD28. Enzyme-linked immunosorbent assay (ELISA) measurements revealed that C57BL/6 mice fed DHA had significantly reduced interferon (IFN)-gamma and IL-10 levels 48 h post-activation. However, CD4(+) T cells from IL-10(-/-) mice fed dietary n-3 PUFA produced significantly greater levels of IFN-gamma than the CO-fed group. Our data suggest that in the absence of IL-10, CD4(+) T cells from n-3 PUFA-fed mice may up-regulate IFN-gamma. Suppressed CD4(+) T cells from n-3 PUFA-fed C57BL/6 mice may use mechanisms other than IL-10 to down-regulate T cell function.

Immunoregulatory effects of regulated, lung-targeted expression of IL-10 in vivo

Regulation of pulmonary inflammation involves an intricate balance of both pro- and anti-inflammatory mediators. Acute lung injury can result from direct pulmonary insults that activate alveolar macrophages to respond with increased cytokine expression. Such cytokine gene expression is mediated in part via NF-κB. IL-10 has been previously identified as an important endogenous anti-inflammatory cytokine in vivo on the basis of inhibiting NF-κB activation; however, the mechanism of this inhibition remains incompletely defined. We hypothesized that IL-10 regulated NF-κB activation in vivo via IκK inhibition. A bitransgenic mouse that allowed for externally regulated, lung-specific human IL-10 overexpression was generated. In the bitransgenic mice, introduction of doxycycline induced lung-specific, human IL-10 overexpression. Acute induction of IL-10 resulted in significant decreases in bronchoalveolar lavage fluid neutrophils (48%, P = 0.03) and TNF (62%, P < 0.01) following intratracheal LPS compared with bitransgenic negative mice. In vitro kinase assays showed this decrease to correlate to diminished lung IκK activity. Furthermore, we also examined the effect of chronic IL-10 overexpression in these transgenic mice. Results show that IL-10 overexpression in lungs of mature mice increased the number of intrapulmonary cells the phenotype of which was skewed toward increased B220+/CD45+ B cells and CD4+ T cells and was associated with increased CC chemokine expression. Thus regulated, lung-specific IL-10 overexpression may have a variety of complex immunologic effects depending on the timing and duration of expression.

Melanoma differentiation-associated gene-7/IL-24 gene enhances NF-kappa B activation and suppresses apoptosis induced by TNF

Melanoma differentiation-associated gene-7 (mda-7), also referred to as IL-24, is a novel growth regulatory cytokine that has been shown to regulate the immune system by inducing the expression of inflammatory cytokines, such as TNF, IL-1, and IL-6. Whether the induction of these cytokines by MDA-7 is mediated through activation of NF-kappaB or whether it regulates cytokine signaling is not known. In the present report we investigated the effect of MDA-7 on NF-kappaB activation and on TNF-induced NF-kappaB activation and apoptosis in human embryonic kidney 293 cells. Stable or transient transfection with mda-7 into 293 cells failed to activate NF-kappaB. However, TNF-induced NF-kappaB activation was significantly enhanced in mda-7-transfected cells, as indicated by DNA binding, p65 translocation, and NF-kappaB-dependent reporter gene expression. Mda-7 transfection also potentiated NF-kappaB reporter activation induced by TNF receptor-associated death domain and TNF receptor-associated factor-2. Cytoplasmic MDA-7 with deleted signal sequence was as effective as full-length MDA-7 in potentiating TNF-induced NF-kappaB reporter activity. Secretion of MDA-7 was not required for the potentiation of TNF-induced NF-kappaB activation. TNF-induced expression of the NF-kappaB-regulated gene products cyclin D1 and cyclooxygenase-2, were significantly up-regulated by stable expression of MDA-7. Furthermore, MDA-7 expression abolished TNF-induced apoptosis, and suppression of NF-kappaB by IkappaBalpha kinase inhibitors enhanced apoptosis. Overall, our results indicate that stable or transient MDA-7 expression alone does not substantially activate NF-kappaB, but potentiates TNF-induced NF-kappaB activation and NF-kappaB-regulated gene expression. Potentiation of NF-kappaB survival signaling by MDA-7 inhibits TNF-mediated apoptosis.

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.

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.

The expanded family of class II cytokines that share the IL-10 receptor-2 (IL-10R2) chain

Several novel interleukin (IL)-10-related cytokines have recently been discovered. These include IL-22, IL-26, and the interferon-lambda (IFN-lambda) proteins IFN-lambda1 (IL-29), IFN-lambda2 (IL-28A), and IFN-lambda3 (IL-28B). The ligand-binding chains for IL-22, IL-26, and IFN-lambda are distinct from that used by IL-10; however, all of these cytokines use a common second chain, IL-10 receptor-2 (IL-10R2; CRF2-4), to assemble their active receptor complexes. Thus, IL-10R2 is a shared component in at least four distinct class II cytokine-receptor complexes. IL-10 binds to IL-10R1; IL-22 binds to IL-22R1; IL-26 binds to IL-20R1; and IFN-lambda binds to IFN-lambdaR1 (also known as IL-28R). The binding of these ligands to their respective R1 chains induces a conformational change that enables IL-10R2 to interact with the newly formed ligand-receptor complexes. This in turn activates a signal-transduction cascade that results in rapid activation of several transcription factors, particularly signal transducer and activator of transcription (STAT)3 and to a lesser degree, STAT1. Activation by IL-10, IL-22, IL-26, or IFN-lambda can be blocked with neutralizing antibodies to the IL-10R2 chain. Although IL-10R2 is broadly expressed on a wide variety of tissues, only a subset of these tissues expresses the ligand-binding R1 chains. The receptors for these cytokines are often present on cell lines derived from various tumors, including liver, colorectal, and pancreatic carcinomas. Consequently, the receptors for these cytokines may provide novel targets for inhibiting the growth of certain types of cancer.

Interleukin-22: a potential immunomodulatory molecule in the lung

Interleukin (IL)-22 is a member of the human type I interferon family, which includes IL-10. IL-22 has the potential to interact with IL-10 because it binds to the IL-10R2c chain with IL-22R1 in its receptor complex. Binding can be blocked by the soluble receptor, IL-22 binding protein (IL-22BP). We hypothesize that IL-22 and IL-22BP are involved in inflammatory regulation and its subsequent role in the pathogenesis of inflammatory lung disease. We have demonstrated IL-22 mRNA expression in alveolar macrophages (AM), monocytes, and alveolar epithelial (AE) cells. IL-22BP mRNA is expressed in AM, AE cells, and neutrophils. In contrast, IL-22R1 is expressed in AE only. Immunohistochemistry on normal and interstitial lung disease lung sections has confirmed IL-22 protein expression. Western blotting for IL-22 in bronchoalveolar lavage fluid demonstrated that lower levels of IL-22 were present in patients with acute respiratory distress syndrome and sarcoidosis relative to control subjects (P = 0.0152 and P = 0.0213). Levels of IL-22 in idiopathic pulmonary fibrosis were not different than those of the control subjects (P = 0.5838). IL-22 did not affect IL-10 inhibition of tumor necrosis factor-alpha in monocytes, which do not express IL-22R1. By contrast, we demonstrated synergy between IL-10 and IL-22 in terms of IL-8 inhibition in IL-22R1-expressing A549 cells. These data suggest a role for IL-22 in the regulation of pulmonary inflammation.

Cutting edge: IL-26 signals through a novel receptor complex composed of IL-20 receptor 1 and IL-10 receptor 2

The receptor for IL-26 (AK155), a cytokine of the IL-10 family, has not previously been defined. We demonstrate that the active receptor complex for IL-26 is a heterodimer composed of two receptor proteins: IL-20R1 and IL-10R2. Signaling through the IL-26R results in activation of STAT1 and STAT3 which can be blocked by neutralizing Abs against IL-20R1 or IL-10R2. IL-10R2 is broadly expressed on a wide variety of tissues, whereas only a limited number of tissues express IL-20R1. Therefore, the ability to respond to IL-26 is restricted by the expression of IL-20R1. IL-10, IL-19, IL-20, IL-22, and IL-24 fail to signal through the combination of IL-10R2 and IL-20R1 proteins, demonstrating that this receptor combination is unique and specific for IL-26.

The T-cell lymphokine interleukin-26 targets epithelial cells through the interleukin-20 receptor 1 and interleukin-10 receptor 2 chains

The cellular members of the interleukin-10 (IL-10) cytokine family share sequence homology with IL-10, whereas their sites of expression and their functions are divergent. One of these factors, AK155 or IL-26, was discovered because of its overexpression in human T lymphocytes after growth transformation by the simian rhadinovirus herpesvirus saimiri. In addition, the gene is transcribed in various types of primary and immortalized T-cells. Here we describe epithelial cells, namely colon carcinoma cells and keratinocytes, as targets of this T-cellular lymphokine. Purified recombinant IL-26 induced the rapid phosphorylation of the signal transducer and activator of transcription factors 1 and 3. As a result, secretion of IL-10 and IL-8, as well as cell surface expression of CD54 were enhanced. Moreover, we show that the IL-26 protein binds to heparin, is released from the cell surface, and can be functionally inhibited by heparin. The sensitivity to recombinant IL-26 of various cell lines strictly correlated with the expression of the long chain of the IL-20 receptor. Because blocking antibodies against either the short chain of the IL-10 receptor or the long chain of the IL-20 receptor inhibited IL-26-dependent signal transduction, and transient expression of these receptor chains induced IL-26 responsivity in non-sensitive cells, we propose that the IL-20 receptor 1 and IL-10 receptor 2 chains participate in forming the IL-26 receptor. Targeting epithelial cells, the T-cell lymphokine IL-26 is likely to play a role in local mechanisms of mucosal and cutaneous immunity.