Interleukin (IL)-22, a novel human cytokine that signals through the interferon receptor-related proteins CRF2-4 and IL-22R

A novel method for screening viral interferon-resistance genes

Many viruses have evolved mechanisms to antagonize the interferon (IFN) system, targeting all the major components involved in receptor binding and signaling. Although a number of these vital proteins are homologous to cellular proteins involved in IFN downregulation (e.g., viral IFN regulatory factors [vIRFs]), many share little resemblance to known proteins. To determine the IFN-blocking properties of these proteins, functional assays are required. Here, we present a new and rapid functional screening method, based on the 2fTGH cell line, which is able to determine viral gene products that inhibit the IFN-alpha/Jak-Stat signaling pathway. Expression cloning of viral IFN-blocking genes into 2fTGH and consequent selection with IFN-alpha and 6-thioguanine result in the outgrowth of cells that are no longer responsive to IFN-alpha. We also demonstrate that selection occurs if members of the Jak-Stat signaling pathway are lost. To show the utility of our system, we have used a known suppressor of IFN signaling, the human papillomavirus (HPV) E7 gene. Expression of E7 causes the loss of ability of 2fTGH cells to respond to IFN-alpha treatment because of a functional disruption of the signaling pathway. This approach offers a new strategy for identifying novel viral genes or new functions of already described viral genes that have a role in IFN-alpha signaling inhibition.

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.

Conservation of the genomic structure and receptor-mediated signaling between human and rat IL-24

IL-24/MDA-7 is a new member of the IL-10 family of cytokines, which signals through two heterodimeric receptor complexes (IL-20R1/IL-20R2 and IL-22R/IL-20R2). Previously, we identified a rat gene named mob-5, which encodes a secreted protein that shares a high degree of homology with human IL-24. Expression of mob-5 and its putative cell surface receptors was shown to be upregulated by oncogenic ras. Here we show that not only do rat mob-5 and human IL-24 share a strikingly similar genomic structure but also that the rat MOB-5 protein can bind to and signal through the human IL-24 receptors. Like human IL-24, binding of the rat MOB-5 protein to the human IL-24 receptors leads to activation of the JAK/STAT pathway, which in turn supports receptor-dependent survival and proliferation of Ba/F3 cells. Furthermore, using human colon cancer cell lines with somatic knockout of either the mutant or the wild-type k-ras allele, we demonstrate that the human IL-24 receptors also are upregulated by oncogenic ras. Taken together, these results provide strong experimental evidence that MOB-5 is indeed the rat homolog of human IL-24.

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.

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.

IL-22 increases the innate immunity of tissues

Interleukin 22 (IL-22) is mainly produced by activated Th1 cells. The data presented here indicate that neither resting nor activated immune cells express IL-22 receptor, and IL-22 did not have any effects on these cells in vitro and in vivo. In contrast, cells of the skin and the digestive and respiratory systems represent putative targets of this cytokine. The expression of IL-22 receptor in keratinocytes was upregulated by Interferon-gamma. In these cells, IL-22 activated STAT3 and directly and transcriptionally increased the expression of beta-Defensin 2 and beta-Defensin 3. High levels of IL-22 were associated with strongly upregulated beta-Defensin expression in skin from patients with T cell-mediated dermatoses. Taken together, IL-22 does not serve the communication between immune cells but is a T cell mediator that directly promotes the innate, nonspecific immunity of tissues.

Association of vitamin D receptor gene polymorphisms with childhood and adult asthma

Vitamin D receptor (VDR) polymorphisms have been associated with several immune-related diseases, and VDR and vitamin D itself modulate T cell differentiation. VDR maps to chromosome 12q, near a region commonly linked to asthma. We evaluated VDR as part of a 12q positional candidate survey, and in response to observations of VDR polymorphism associations with asthma and atopy in a founder population of Quebec. Twenty-eight loci in 7 positional candidates (7 in VDR) were genotyped in 582 families. Whereas other candidates demonstrated no association, the VDR ApaI polymorphism demonstrated significant transmission distortion, with undertransmission of the C allele in a ratio of 4:5 (p = 0.01). This association was most prominent in girls, in whom distortion was more marked (p = 0.009). Sex-specific associations between multiple VDR polymorphisms and immunoglobulin E levels were also observed (p = 0.006-0.01). Asthma associations were replicated in a second cohort (517 females with asthma and 519 matched control subjects): 4 of 6 VDR variants demonstrated significant association (p = 0.02-0.04). The direction of association in this second cohort was opposite to the effects seen in the trios, but similar to findings in the Quebec study. These results suggest that VDR influences asthma and allergy susceptibility in a complex manner.

Molecular modeling of the interleukin-19 receptor complex. Novel aspects of receptor recognition in the interleukin-10 cytokine family

The interleukin-10 (IL-10) cytokine family consists of several viral and human homologs that exhibit distinct receptor binding specificities. In the present study, the complex between interleukin-19 (IL-19) and its physiological receptor-the interleukin-20 receptor alpha-chain (IL-20R1)-was modeled. The most prominent feature of this complex is an extended binding interface formed by a long loop of IL-20R1 and a bulge region of IL-19. The two regions exhibit complementary charges and have no structural counterparts in the IL-10/IL-10R1 complex but show some resemblance to the complex between interferon-gamma (IFN-gamma) and its receptor. Sequence comparison of the three cytokines (IL-19, IL-20, IL-24) that bind the IL-20R1 reveals a considerable conservation of the length of the interacting loops. One residue suggested to play a key role in receptor binding specificity is a conserved glutamate. The binding interface of IL-20R1 is rich in aromatic residues while the interfaces of its cytokine ligands are mainly formed by more flexible aliphatic amino acids. This structural feature might play an important role for the specific recognition of a single receptor chain by three different cytokines. [Figure: see text]. Comparison of the ligand/receptor interfaces in theA IL-10/IL-10R1,B IL-19/IL-20R1 andC IFN-gamma/receptor complexes. The translucent Connolly surfaces of the receptor and the ligand are shown in yellow and white, respectively. The backbone of the receptor and ligand are highlighted by a red and blue/green tube, respectively. For clarity, only one domain of the intertwined dimes is shown for IL-10 and IFN-gamma. Arrows denote the location of helix B and the corresponding structural elements in IL-19 and IFN-gamma as well as the location of receptor loop L2. As evident fromB andC an extended interaction surface is created in the IL-19/IL-20R1 and IFN-gamma/receptor complexes by the interaction of this structural element with a long loop of the respective receptor.

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.

Interleukin-22 activates STAT3 and induces IL-10 by colon epithelial cells

Human interleukin-22 (IL-22), a cytokine with structural homology to IL-10, is produced by activated T cells. The IL-22 receptor complex consists of a ligand-binding chain, the IL-22R1 and a signal-transducing chain, the IL-10R2. The aim of this study is to identify potential target cells and associated biological activity of IL-22 by identifying cell types that specifically express high levels of IL-22R1 as the expression of IL-10R2 is ubiquitous. Expression of IL-22R1 mRNA, as analyzed by real time quantitative polymerase chain reaction (PCR), was observed in human tumor cell lines of stromal or epithelial origin derived from liver, pancreas, colon and lung tissue. Furthermore, we examined the ability of IL-22 to activate the JAK-Signal Transducer and Activator of Transcription (STAT) pathway in epithelial cells of the colon. IL-22 induced the phosphorylation of STAT1 and STAT3 in Colo205, a colon epithelial cell line. Consequently, IL-22 upregulated mRNA for Suppressor of Cytokine Signaling 3 (SOCS3), a STAT3-responsive gene. Further analyses, by real time quantitative PCR, on a panel of chemokines and immune function related genes revealed that IL-22 induced expression of the acute phase proteins alpha-Antichymotrypsin and Serum Amyloid A, as well as IL-10 mRNA and protein production by Colo205. Induction of IL-10 by IL-22, in Colo205 cells, could be inhibited in the presence of a neutralizing antibody against IL-10R2. IL-22-mediated effects on the Colo205 cells were also inhibited in the presence of IL-22 binding protein (IL-22BP), a soluble receptor with structural similarity to IL-22R1. The high levels of expression of IL-22R1 observed in epithelial cells of the colon and the ability of IL-22 to upregulate production of acute phase proteins and IL-10 in Colo205 cells, suggest a functional role for IL-22 in intestinal inflammation.

IL-22, a Th1 cytokine that targets the pancreas and select other peripheral tissues

IL-22, also termed IL-TIF, is a member of the IL-10 family of cytokines. Its principal source appears to be memory CD4 T cells with a Th1 polarized phenotype. IL-22 induces its signals through a two-component receptor comprised of IL-22R1 and CRF2-4/IL10Rb. Both of these receptor components also participate in separate receptor complexes specific for other IL-10 family cytokines. Because CRF2-4 exhibits ubiquitous expression, the tropism of IL-22 action appears to be dictated by the expression of IL-22R1. IL-22R1 has a highly restricted expression pattern. Its highest expression, by far, is in the acinar cell population of the pancreas. Lower, but still functional, levels of expression are also observed in skin, colon, liver, and kidney. The responses that have been observed to date for IL-22 resemble the "acute phase" type responses elicited by IL-6, suggesting that IL-22 might be appropriately considered as a T cell-derived IL-6-like activity having distinct target cell specificity. The functional role of this system remains unclear, but it is likely that the responses elicited by this cytokine serve to contribute both to acute host defense against pathogens and to safeguard vulnerable target tissues under conditions of stress.

Temporal associations between interleukin 22 and the extracellular domains of IL-22R and IL-10R2

Interleukin 22 (IL-22) is a cytokine induced during both innate and adaptive immune responses. It can effect an acute phase response, implicating a role for IL-22 in mechanisms of inflammation. IL-22 requires the presence of the IL-22 receptor (IL-22R) and IL-10 receptor 2 (IL-10R2) chains, two members of the class II cytokine receptor family (CRF2), to effect signal transduction within a cell. We studied the interaction between human IL-22 and the extracellular domains (ECD) of its receptor chains in an enzyme-linked immunoabsorbant assay (ELISA)-based format, using biotinylated IL-22 (bio-IL-22) and receptor-fusions containing the ECD of a receptor fused to the Fc of hIgG1 (IL-22R-Fc and IL-10R2-Fc). IL-22 has measurable affinity for IL-22R-Fc homodimer and undetectable affinity for IL-10R2. IL-22 has substantially greater affinity for IL-22R/IL-10R2-Fc heterodimers. Further analyses involving sequential additions of receptor homodimers and cytokine indicates that the IL-10R2(ECD) binds to a surface created by the interaction between IL-22 and the IL-22R(ECD), and thereby further stabilizes the association of IL-22 within this cytokine-receptor-Fc complex. Both a neutralizing rat monoclonal antibody, specific for human IL-22, and human IL-22BP-Fc, an Fc-fusion of the secreted IL-22 binding-protein and proposed natural antagonist for IL-22, bind to similar cytokine epitopes that may overlap the binding site for IL-22R(ECD). Another rat monoclonal antibody, specific for IL-22, binds to an epitope that may overlap a separate binding site for IL-10R2(ECD). We propose, based on this data, a temporal model for the development of a functional IL-22 cytokine-receptor complex.

Interleukin 22 (IL-22) plays a protective role in T cell-mediated murine hepatitis: IL-22 is a survival factor for hepatocytes via STAT3 activation

The central role of T cell activation in hepatocellular injury has been well documented. In this article, we provide evidence suggesting that T cells may also play a protective role in liver disease by releasing interleukin-22 (IL-22), a recently identified T cell-derived cytokine whose biological significance is unclear. IL-22 messenger RNA and protein expression are significantly elevated in T cell-mediated hepatitis induced by concanavalin A (ConA) but are less extensively elevated in the carbon tetrachloride-induced liver injury model. Activated CD3(+) T cells are likely responsible for the production of IL-22 in the liver after injection of ConA. The IL-22 receptor is normally expressed at high levels by hepatocytes and further induced after ConA injection. IL-22 blockade with a neutralizing antibody reduces signal transducer and activator of transcription factor 3 (STAT3) activation and worsens liver injury in T cell-mediated hepatitis, whereas injection of recombinant IL-22 attenuates such injury. In vitro treatment with recombinant IL-22 or overexpression of IL-22 promotes cell growth and survival in human hepatocellular carcinoma HepG2 cells. Stable overexpression of IL-22 in HepG2 cells constitutively activates STAT3 and induces expression of a variety of antiapoptotic (e.g., Bcl-2, Bcl-xL, Mcl-1) and mitogenic (e.g., c-myc, cyclin D1, Rb2, CDK4) proteins. Blocking STAT3 activation abolishes the antiapoptotic and mitogenic actions of IL-22 in hepatic cells. In conclusion, the T cell-derived cytokine IL-22 is a survival factor for hepatocytes; this suggests that T cell activation may also prevent and repair liver injury by releasing hepatoprotective cytokine IL-22 in addition to its previously documented central role in hepatocellular injury.

The Class II cytokine receptor (CRF2) family: overview and patterns of receptor–ligand interactions

Expanded genomic information has driven the discovery of new members of the human Class II family of cytokine receptors (CRF2), which now includes 12 proteins. The corresponding cytokines have been identified, paired with their receptors and initially characterized for function. These cytokines include: a new human Type I IFN, IFN-kappa; molecules related to IL-10 (IL-19, IL-20, IL-22, IL-24, IL-26); and IFN-lambdas (IL-28/29), which have antiviral and cell stimulatory activities reminiscent of Type I IFNs, but act through a distinct receptor. In response to ligand binding, the CRF2 proteins form heterodimers, leading to cytokine-specific cellular responses; these diverse physiological functions are just beginning to be explored. Progress in structural and mutational analysis of ligand-receptor interactions now presents a more reliable framework for understanding receptor-ligand interactions, and for predicting key regions in less well studied members of the CRF2 family. The relationships between the CRF2 proteins will be summarized, as will the progress in identifying patterns of receptor interactions with ligands.

Cytokine–receptor pairing: accelerating discovery of cytokine function

Over the past decade, advances in both gene discovery and ligand-receptor pairing techniques have led to the recognition that systematic pairing of 'orphan' database-derived cytokines and/or cytokine receptors with their cognate partners can lead to a marked acceleration in the elucidation of biological function. The sometimes-restricted tissue distribution of the receptor, coupled with the highly specific bioactivity of the corresponding ligand, can direct investigators rapidly towards regulatory function and site-of-action studies. The power of cytokine-receptor pairing to accelerate the understanding of function will be illustrated, citing several examples of candidate drug discoveries. Several of these discoveries, resulting from cytokine-receptor pairings, are at present advancing towards human clinical evaluation.

The secreted protein discovery initiative (SPDI), a large-scale effort to identify novel human secreted and transmembrane proteins: a bioinformatics assessment

A large-scale effort, termed the Secreted Protein Discovery Initiative (SPDI), was undertaken to identify novel secreted and transmembrane proteins. In the first of several approaches, a biological signal sequence trap in yeast cells was utilized to identify cDNA clones encoding putative secreted proteins. A second strategy utilized various algorithms that recognize features such as the hydrophobic properties of signal sequences to identify putative proteins encoded by expressed sequence tags (ESTs) from human cDNA libraries. A third approach surveyed ESTs for protein sequence similarity to a set of known receptors and their ligands with the BLAST algorithm. Finally, both signal-sequence prediction algorithms and BLAST were used to identify single exons of potential genes from within human genomic sequence. The isolation of full-length cDNA clones for each of these candidate genes resulted in the identification of >1000 novel proteins. A total of 256 of these cDNAs are still novel, including variants and novel genes, per the most recent GenBank release version. The success of this large-scale effort was assessed by a bioinformatics analysis of the proteins through predictions of protein domains, subcellular localizations, and possible functional roles. The SPDI collection should facilitate efforts to better understand intercellular communication, may lead to new understandings of human diseases, and provides potential opportunities for the development of therapeutics.

Class II cytokine receptors and their ligands: key antiviral and inflammatory modulators

Class II cytokine receptors were originally defined on the basis of sequence homologies in the extracellular domains of receptors for interferons (IFNs) and interleukin-10 (IL-10), and the ligands, known as class II cytokines, also have a common structure. More recently, a series of new receptors and cytokines that belong to this family have been discovered. The therapeutic potential of the 'old' members of this family, IFNs and IL-1, is recognized in the clinic, and the existence of structurally related molecules is raising expectations for additional clinical applications. In this review, I discuss both structural and biological data that are emerging about this family of receptors and ligands, to highlight the potential applications of modulating the activity of these cytokines.

Interleukin-10 therapy--review of a new approach

Interleukin (IL)-10 is an important immunoregulatory cytokine produced by many cell populations. Its main biological function seems to be the limitation and termination of inflammatory responses and the regulation of differentiation and proliferation of several immune cells such as T cells, B cells, natural killer cells, antigen-presenting cells, mast cells, and granulocytes. However, very recent data suggest IL-10 also mediates immunostimulatory properties that help to eliminate infectious and noninfectious particles with limited inflammation. Numerous investigations, including expression analyses in patients, in vitro and animal experiments suggest a major impact of IL-10 in inflammatory, malignant, and autoimmune diseases. So IL-10 overexpression was found in certain tumors as melanoma and several lymphomas and is considered to promote further tumor development. Systemic IL-10 release is a powerful tool of the central nervous system to prevent hyperinflammatory processes by activation of the neuro-endocrine axis following acute stress reactions. In contrast, a relative IL-10 deficiency has been observed and is regarded to be of pathophysiological relevance in certain inflammatory disorders characterized by a type 1 cytokine pattern such as psoriasis. Recombinant human IL-10 has been produced and is currently being tested in clinical trials. This includes rheumatoid arthritis, inflammatory bowel disease, psoriasis, organ transplantation, and chronic hepatitis C. The results are heterogeneous. They give new insight into the immunobiology of IL-10 and suggest that the IL-10/IL-10 receptor system may become a new therapeutic target.

Cloning and characterization of mouse IL-22 binding protein

Interleukin-22 (IL-22), a member of IL-10 family, plays some important roles in immune response through activation of the STAT 3 signal transduction pathway. Two types of IL-22-binding receptor have been discovered, a membrane-bound receptor and a soluble receptor, both encoded by different genes. IL-22 may be involved in inflammatory processes specifically regulated by soluble receptors. By screening a mouse genomic library for a human IL-22 binding protein homologue, we identified the mouse genomic clone of IL-22 binding protein. Its coding sequence was verified and isolated by RT-PCR. The gene encodes a protein of 230 amino acids that share 67.1% amino-acid sequence identity with human IL-22 binding protein. We designated this receptor 'mouse IL-22 binding protein' (mIL-22BP). mIL-22BP could be upregulated by LPS stimulation in mouse monocytes. mIL-22BP binds to mouse and human IL-22 and neutralizes STAT3 activation induced by both cytokines in human and rat hepatoma cell lines. Treating B cells with mouse IL-22 induces production of reactive oxygen species, which mIL-22BP blocks.

IL-20: a new target for the treatment of inflammatory skin disease

The discovery of dramatic pro-inflammatory effects of IL-20 on skin highlighted a novel regulatory pathway in cutaneous inflammation. Specific receptor complexes for IL-20 are induced on keratinocytes and transmit potent signals via the signal transducer and activator of transcription-3. In response to IL-20, keratinocytes proliferate and express pro-inflammatory genes including TNF-alpha, which leads to activation of NF-kappaB. Recently, two related cytokines, IL-19 and IL-24, have been shown to trigger the IL-20 receptor, and a second receptor complex has also been found to respond to IL-20 and IL-24. IL-20 signalling appears to be a prominent component of cutaneous inflammation, but the extent to which inflammatory processes rely upon it is unknown. Nonetheless, the prevalence of diseases involving pathological cutaneous inflammation makes the identification of safe and effective anti-inflammatory therapies for the skin a priority. Detailed understanding of the signal transduction pathways by which the skin responds to IL-20 and related factors may make it possible to develop new pharmaceutical agents to selectively suppress cutaneous inflammation.

Cloning of a new type II cytokine receptor activating signal transducer and activator of transcription (STAT)1, STAT2 and STAT3

In the present paper, we report the identification of a new gene encoding a transmembrane protein of 520 amino acids, showing 22% amino acid identity with the extracellular domain of the interleukin (IL)-20 receptor. This gene, termed likely interleukin or cytokine receptor-2 ( LICR2 ), is located on chromosome 1, at 25 kb from the IL22R (IL-22 receptor) gene, and is constitutively expressed in most tissues. A chimaeric receptor, consisting of the extracellular domain of the IL-10 receptor alpha chain and the intracellular domain of LICR2, activated signal transducer and activator of transcription (STAT)1, STAT2, STAT3 and STAT5 upon IL-10 stimulation, in a Janus kinase 1-dependent manner. In contrast, none of the IL-10-related cytokines described so far could activate LICR2-transfected cells, suggesting that LICR2 is a signalling receptor for a new cytokine of the IL-10 family.

Genomic structure and inducible expression of the IL-22 receptor alpha chain in mice

IL-22 is a newly identified member of the interferon/IL-10 family. In humans, IL-22 signals through a heteroduplex receptor consisting of IL-22R and CRF2-4/IL-10Rbeta. To investigate the physiological function of IL-22 and IL-22R, we isolated a cDNA encoding the mouse IL-22R, which has been a missing component of the functional receptor complex for mouse IL-22. Subsequently, we identified the genomic sequence of the mouse IL-22R gene by a database search. The gene consists of about 24 kb and is split into seven exons. Interestingly, intron 2 begins with a GC dinucleotide instead of the consensus GT, although otherwise the overall structure of the mouse IL-22R gene is strikingly similar to its human counterpart. The gene was mapped to mouse chromosome 4 in the region syntenic to the human IL-22R gene locus. In normal mice, IL-22R mRNA is detected at very low levels in restricted organs such as the kidney, liver, and lung. However, upon lipopolysaccharide stimulation, IL-22R mRNA expression is highly upregulated in the liver, in contrast to CRF2-4, which is expressed constitutively in a variety of tissues. Thus, the expression of the functional IL-22 receptor in the liver is regulated at the gene transcription level.

Melanoma differentiation associated gene-7, mda-7/IL-24, selectively induces growth suppression, apoptosis and radiosensitization in malignant gliomas in a p53-independent manner

Malignant gliomas are extremely aggressive cancers currently lacking effective treatment modalities. Gene therapy represents a promising approach for this disease. A requisite component for improving gene-based therapies of brain cancer includes tumor suppressor genes that exhibit cancer constrained inhibitory activity. Subtraction hybridization identified melanoma differentiation associated gene-7 (mda-7) as a gene associated with melanoma cell growth, differentiation and progression. Ectopic expression of mda-7 by means of a replication-incompetent adenovirus (Ad), Ad.mda-7, induces growth suppression and apoptosis selectively in diverse human cancers, without producing any apparent harmful effect in normal cells. We presently demonstrate that Ad.mda-7 induces growth inhibition and apoptosis in malignant human gliomas expressing both mutant and wild-type p53, and these effects correlate with an elevation in expression of members of the growth arrest and DNA damage (GADD) gene family. In contrast, infection with a recombinant Ad expressing wild-type p53, Ad.wtp53, specifically affects mutant p53 expressing gliomas. When tested in early passage normal and immortal human fetal astrocytes, growth inhibition resulting from infection with Ad.mda-7 or Ad.wtp53 is significantly less than in malignant gliomas and no toxicity is evident in these normal cells. Moreover, infection of gliomas with Ad.mda-7 or treatment with purified GST-MDA-7 protein sensitizes both wild-type and mutant p53 expressing tumor cells to the growth inhibitory and antisurvival effects of ionizing radiation, and this response correlates with increased expression of specific members of the GADD gene family. Since heterogeneity in p53 expression is common in evolving gliomas, the present findings suggest that Ad.mda-7 may, in many instances, prove more beneficial for the gene-based therapy of malignant gliomas than administration of wild-type p53.

MDA-7/IL-24: novel cancer growth suppressing and apoptosis inducing cytokine

The melanoma differentiation-associated gene-7 (mda-7) was cloned by subtraction hybridization as a molecule whose expression is elevated in terminally differentiated human melanoma cells. Current information based on structural and sequence homology, has led to the recognition of MDA-7 as an IL-10 family cytokine member and its renaming as IL-24. Northern blot analysis revealed mda-7/IL-24 expression in human tissues associated with the immune system such as spleen, thymus, peripheral blood leukocytes and normal melanocytes. The MDA-7/IL-24 mouse counterpart, FISP, appears to be a Th2-specific protein and the rat counterpart, C49A/MOB-5, is associated with wound healing and is also induced as a consequence of ras-transformation. A notable property of MDA-7/IL-24 is its ability to induce apoptosis in a large spectrum of human cancer derived cell lines, in mouse xenografts and upon intratumoral injection in human tumors (phase I clinical trials). Various aspects of this intriguing molecule including its cytokine and anti-tumoral effects are described and discussed.

IL-28, IL-29 and their class II cytokine receptor IL-28R

Cytokines play a critical role in modulating the innate and adaptive immune systems. Here, we have identified from the human genomic sequence a family of three cytokines, designated interleukin 28A (IL-28A), IL-28B and IL-29, that are distantly related to type I interferons (IFNs) and the IL-10 family. We found that like type I IFNs, IL-28 and IL-29 were induced by viral infection and showed antiviral activity. However, IL-28 and IL-29 interacted with a heterodimeric class II cytokine receptor that consisted of IL-10 receptor beta (IL-10Rbeta) and an orphan class II receptor chain, designated IL-28Ralpha. This newly described cytokine family may serve as an alternative to type I IFNs in providing immunity to viral infection.

Interleukins 19, 20, and 24 signal through two distinct receptor complexes. Differences in receptor-ligand interactions mediate unique biological functions

Cytokines that signal through Class II receptors form a distinct family that includes the interferons and interleukin 10 (IL-10). Recent identification of several IL-10 homologs has defined a cytokine subfamily that includes AK155, IL-19, IL-20, IL-22, and IL-24. Within this subfamily, IL-19, IL-20, and IL-24 exhibit substantial sharing of receptor complexes; all three are capable of signaling through IL-20RA/IL-20RB, and IL-20 and IL-24 both can also use IL-22R/IL-20RB. However, the biological effects of these three cytokines appear quite distinct: immune activity with IL-19, skin biology with IL-20, and tumor apoptosis with IL-24. To more fully elucidate their interactions with the receptor complexes, we have performed a series of in vitro assays. Reporter, proliferation, and direct STAT activation assays using cell lines expressing transfected receptors revealed differences between the receptor complexes. IL-19 and IL-24 also exhibited growth inhibition on a cell line endogenously expressing all three receptor subunits, an effect that was seen at cytokine levels two orders of magnitude above those required for STAT activation or proliferation. These results demonstrate that, although this subclass exhibits receptor complex redundancy, there are differences in ligand/receptor interactions and in signal transduction that may lead to specificity and a distinct biology for each cytokine.

Linkage disequilibrium analysis of chromosome 12q14-15 in multiple sclerosis: delineation of a 118-kb interval around interferon-gamma (IFNG) that is involved in male versus female differential susceptibility

We have recently reported the association of a polymorphic intronic CA-repeat in the interferon-gamma gene (IFNG) with gender bias in susceptibility to multiple sclerosis (MS) in a Sardinian population. This association could refer to a functional polymorphism within IFNG or could be due to linkage disequilibrium between the IFNG marker and a neighbouring susceptibility locus. Within the average reach of linkage disequilibrium, various other candidate genes are located. Among these the most striking ones are the genes coding for the cytokines interleukin-22 (IL-22) and interleukin-26 (IL-26) that constitute together with IFNG a cytokine cluster on chromosome 12q14. To determine more precisely the location of this gender-associated susceptibility locus, we have now performed a more extensive linkage disequilibrium screen of this region using nine additional microsatellite markers. This locus appeared to be confined to a 118-kb interval that is bordered by the markers D12S313 and D12S2511, in which IFNG itself remains the main candidate gene. Haplotype analysis confirmed that this MS-associated locus protects males from developing MS according to a recessive or allele-dosage model. Our results indicate that the well-documented gender differences in susceptibility to MS are at least partially caused by genetic factors in the region surrounding IFNG.

Comparison of interleukin-22 and interleukin-10 soluble receptor complexes

Interleukin-22 (IL-22) is a cellular homolog of IL-10 that stimulates the production of acute-phase reactants. IL-22 and IL-10 require different ligand-specific receptor chains (IL-22R and IL-10R1) but share a second receptor chain (IL-10R2) to initiate cellular responses. The quaternary structures and the ability of IL-22 and IL-10 to engage soluble (s) IL-10R1, IL-22R, IL-10R2 receptor chains were analyzed using size exclusion chromatography and surface plasmon resonance techniques. In contrast to IL-10, which is a homodimer, IL-22 is a monomer in solution that forms a 1:1 interaction with sIL-22R. Kinetic binding data reveal sIL-22R and sIL-10R1 exhibit specific nanomolar binding constants for IL-22 (k(on)/k(off) = 14.9 nM) and a monomeric isomer of IL-10 (IL-10M1) (k(on)/k(off) = 0.7 nM), respectively. In contrast, IL-10R2 exhibits essentially no affinity for IL-22 (K(eq) approximately 1 mM) or IL-10M1 (K(eq) approximately 2 mM) alone but displays a substantial increase in affinity for the IL-10/sIL-10R1 (K(eq) approximately 350 microM) and IL-22/sIL-22R (K(eq) approximately 45 microM) complexes. Three-dimensional models of IL-22 and IL-10 receptor complexes suggest two receptor residues (Gly-44 and Arg-96) are largely responsible for the marked differences in ligand affinity observed for sIL-10R1 and sIL-22R vs. sIL-10R2.

Interleukin-22 (IL-22) activates the JAK/STAT, ERK, JNK, and p38 MAP kinase pathways in a rat hepatoma cell line. Pathways that are shared with and distinct from IL-10

IL (interleukin)-22 is an IL-10-related cytokine; its main biological activity known thus far is the induction of acute phase reactants in liver and pancreas. IL-22 signals through a receptor that is composed of two chains from the class II cytokine receptor family: IL-22R (also called ZcytoR11/CRF2-9) and IL-10Rbeta (CRF2-4), which is also involved in IL-10 signaling. In this report, we analyzed the signal transduction pathways activated in response to IL-22 in a rat hepatoma cell line, H4IIE. We found that IL-22 induces activation of JAK1 and Tyk2 but not JAK2, as well as phosphorylation of STAT1, STAT3, and STAT5 on tyrosine residues, extending the similarities between IL-22 and IL-10. However our results unraveled some differences between IL-22 and IL-10 signaling. Using antibodies specific for the phosphorylated form of MEK1/2, ERK1/2, p90RSK, JNK, and p38 kinase, we showed that IL-22 activates the three major MAPK pathways. IL-22 also induced serine phosphorylation of STAT3 on Ser(727). This effect, which is not shared with IL-10, was only marginally affected by MEK1/2 inhibitors, indicating that other pathways might be involved. Finally, by overexpressing a STAT3 S727A mutant, we showed that serine phosphorylation is required to achieve maximum transactivation of a STAT responsive promoter upon IL-22 stimulation.

New technologies for studying immune regulation in ruminants

There remains a great need for the development of reagents and techniques to study immune regulation in ruminants. These tools are fundamental to our understanding of the mechanisms of immune modulation and underpin the rational design of disease control strategies in livestock. Technological advances in molecular biology have resulted in the development of a new range of techniques to measure and quantify gene expression in normal and disease states. However, the ability to measure protein expression, produce proteins (usually in recombinant form) and to block receptor-ligand interactions remains essential for elucidating the function of the molecules of interest. The aims of this workshop were to look at the current status of reagents for studying ruminant immunology, the prospects for future developments, and also to discuss reagents availability between different groups worldwide.

Crystal structure of recombinant human interleukin-22

Interleukin-22 (IL-10-related T cell-derived inducible factor/IL-TIF/IL-22) is a novel cytokine belonging to the IL-10 family. Recombinant human IL-22 (hIL-22) was found to activate the signal transducers and activators of transcription factors 1 and 3 as well as acute phase reactants in several hepatoma cell lines, suggesting its involvement in the inflammatory response. The crystallographic structure of recombinant hIL-22 has been solved at 2.0 A resolution using the SIRAS method. Contrary to IL-10, the hIL-22 dimer does not present an interpenetration of the secondary-structure elements belonging to the two distinct polypeptide chains but results from interface interactions between monomers. Structural differences between these two cytokines, revealed by the crystallographic studies, clearly indicate that, while a homodimer of IL-10 is required for signaling, hIL-22 most probably interacts with its receptor as a monomer.

mda-7 (IL-24) Mediates selective apoptosis in human melanoma cells by inducing the coordinated overexpression of the GADD family of genes by means of p38 MAPK

Subtraction hybridization identified melanoma differentiation-associated gene-7 (mda-7) as a gene induced during terminal differentiation in human melanoma cells. On the basis of structure, chromosomal localization and cytokine-like properties, mda-7 is classified as IL-24. Administration of mda-7/IL-24 by means of a replication-incompetent adenovirus (Ad.mda-7) induces apoptosis selectively in diverse human cancer cells without inducing harmful effects in normal fibroblast or epithelial cells. The present studies investigated the mechanism underlying this differential apoptotic effect. Infection of melanoma cells, but not normal immortal melanocytes, with Ad.mda-7 induced a time- and dose-dependent increase in expression, mRNA and protein, of a family of growth arrest and DNA damage (GADD)-inducible genes, which correlated with induction of apoptosis. Among the members of the GADD family of genes, GADD153, GADD45 alpha, and GADD34 displayed marked, and GADD45 gamma showed minimal induction. Treatment of melanoma cells with SB203580, a selective inhibitor of the p38 mitogen-activated protein kinase (MAPK) pathway, effectively inhibited Ad.mda-7-induced apoptosis. Additional support for an involvement of the p38 MAPK pathway in Ad.mda-7-mediated apoptosis was documented by using an adenovirus expressing a dominant negative mutant of p38 MAPK. Infection with Ad.mda-7 increased the phosphorylation of p38 MAPK and heat shock protein 27 in melanoma cells but not in normal immortal melanocytes. In addition, SB203580 effectively inhibited Ad.mda-7-mediated induction of the GADD family of genes in a time- and dose-dependent manner, and it effectively blocked Ad.mda-7-mediated down-regulation of the antiapoptotic protein BCL-2. Inhibition of GADD genes by an antisense approach either alone or in combination also effectively blocked Ad.mda-7-induced apoptosis in melanoma cells. These results support the hypothesis that Ad.mda-7 mediates induction of the GADD family of genes by means of the p38 MAPK pathway, thereby resulting in the selective induction of apoptosis in human melanoma cells.

The conserved helix C region in the superfamily of interferon-gamma /interleukin-10-related cytokines corresponds to a high-affinity binding site for the HSP70 chaperone DnaK

HSP70 chaperones mediate protein folding by ATP-dependent interaction with short linear peptide segments that are exposed on unfolded proteins. The mode of action of the Escherichia coli homolog DnaK is representative of all HSP70 chaperones, including the endoplasmic reticulum variant BiP/GRP78. DnaK has been shown to be effective in assisting refolding of a wide variety of prokaryotic and eukaryotic proteins, including the alpha-helical homodimeric secretory cytokine interferon-gamma (IFN-gamma). We screened solid-phase peptide libraries from human and mouse IFN-gamma to identify DnaK-binding sites. Conserved DnaK-binding sites were identified in the N-terminal half of helix B and in the C-terminal half of helix C, both of which are located at the IFN-gamma dimer interface. Soluble peptides derived from helices B and C bound DnaK with high affinity in competition assays. No DnaK-binding sites were found in the loops connecting the alpha-helices. The helix C DnaK-binding site appears to be conserved in most members of the superfamily of interleukin (IL)-10-related cytokines that comprises, apart from IL-10 and IFN-gamma, a series of recently discovered small secretory proteins, including IL-19, IL-20, IL-22/IL-TIF, IL-24/MDA-7 (melanoma differentiation-associated gene), IL-26/AK155, and a number of viral IL-10 homologs. These cytokines belong to a relatively small group of homodimeric proteins with highly interdigitated interfaces that exhibit the strongly hydrophobic character of the interior core of a single-chain folded domain. We propose that binding of DnaK to helix C in the superfamily of IL-10-related cytokines may constitute the hallmark of a novel conserved regulatory mechanism in which HSP70-like chaperones assist in the formation of a hydrophobic dimeric "folding" interface.

The protein product of the tumor suppressor gene, melanoma differentiation-associated gene 7, exhibits immunostimulatory activity and is designated IL-24

The melanoma differentiation-associated gene 7 (mda-7) has been studied primarily in the context of its tumor suppressor activity. Although mda-7 has been designated as IL-24 based on its gene location in the IL-10 locus and its mRNA expression in leukocytes, no functional evidence supporting this cytokine designation exists. To further characterize MDA-7/IL-24 expression patterns in the human immune system, MDA-7/IL-24 protein levels were examined in human PBMC. MDA-7/IL-24 was detected in PHA- and LPS-stimulated whole PBMC lysate by Western blot and in PHA-activated CD56 and CD19 subsets by immunohistochemistry. The biological function of MDA-7/IL-24, secreted from Ad-MDA7-transfected HEK 293 cells, was assessed by examining the effect of MDA-7/IL-24 on the cytokine secretion profile of PBMC. Within 48 h MDA-7/IL-24 induced secretion of high levels of IL-6, TNF-alpha, and IFN-gamma and low levels of IL-1beta, IL-12, and GM-CSF from human PBMC as measured by ELISA. The MDA-7/IL-24-mediated induction of these Th1-type cytokines was inhibited by the addition of IL-10 to the PBMC cultures, suggesting that these two related protein family members may provide antagonistic functions. Therefore, because human blood leukocytes can be stimulated to produce MDA-7/IL-24, as well as respond to MDA-7/IL-24 by expressing secondary cytokines, MDA-7/IL-24 has the expression profile and major functional attributes that justify its designation as an IL.

Cutting edge: immune cells as sources and targets of the IL-10 family members?

This study investigated the expression of five novel human IL-10-related molecules and their receptors in blood mononuclear cells. IL-19 and IL-20 were found to be preferentially expressed in monocytes. IL-22 and IL-26 (AK155) expression was exclusively detected in T cells, especially upon type 1 polarization, and in NK cells. IL-24 (melanoma differentiation-associated gene 7) expression was restricted to monocytes and T cells. Detection of these molecules in lymphocytes was predominantly linked to cellular activation. Regarding T cells, IL-26 was primarily produced by memory cells, and its expression was independent on costimulation. In contrast to the high expression of receptors for IL-10 homologs in different tissues and cell lines, monocytes and NK, B, and T cells showed clear expression only of IL-10R1, IL-10R2, and IL-20R2. In these cells, IL-20R2 might be part of a still-unknown receptor complex. Therefore, immune cells may represent a major source but a minor target of the novel IL-10 family members.

The family of IL-10-related cytokines and their receptors: related, but to what extent?

Five novel cytokines (IL-19, IL-20, IL-22 (IL-TIF), IL-24 (human MDA-7, mouse FISP, rat C49A/Mob-5), and IL-26 (AK155)) demonstrating limited primary sequence identity and probable structural homology to IL-10 have been identified. These cellular cytokines, as well as several cytokines encoded in viral genomes (viral cytokines), form a family of IL-10-related cytokines or the IL-10 family. These cytokines share not only homology but also receptor subunits and perhaps activities. Receptors for these cytokines belong to the class II cytokine receptor family. The receptors are IL-10R2 (CRF2-4), IL-22R1 (CRF2-9), IL-22BP (CRF2-10), IL-20R1 (CRF2-8) and IL-20R2 (CRF2-11). Biological activities of these cytokines, receptor utilization and signaling, as well as expression patterns for cytokines and their receptors are summarized. Although data indicate that these cytokines are involved in regulation of inflammatory and immune responses, their major functions remain to be discovered.

Type I-interferon signalling in fish

Type I interferon (IFN) signalling uses a dual mechanism of action. A Jak-Stat pathway extensively described in mammals involves a cascade of reactions from the interaction of the IFN molecule with its membrane receptor to the stimulation of IFN-induced gene promoters leading in turn to an antiviral state. Regulation of IFN activity is also mediated by two DNA-binding transcription factors called interferon regulatory factor (IRF)-1 and -2, that respectively stimulate and repress the promoter of IFN-induced genes. By gene walking with trout genomic DNA the regulatory sequence of the IRF-1 gene was cloned and sequenced. Sequence analysis showed that this 1 Kb 5' flanking region has a structure which is typical for an IFN-induced gene promoter. It contains a TATA box between -28 to -31, and a NF kappa B site between -41 and -52. No complete interferon stimulatory response element (ISRE) could be found, but ten GAAA motifs, which are characteristic of IFN-induced gene promoters, were found. In rainbow trout gonad (RTG) cells, IRF-1 is expressed constitutively and up-regulated by poly I:C but not by LPS. Transient transfections of RTG cells with a reporter construct based on the luciferase gene show that the IRF1 5' flanking region described above, is sufficient to allow the expression of luciferase and is capable of induction by dsRNA (poly I:C).

Cytokine signaling in 2002: new surprises in the Jak/Stat pathway

The importance of Jak-Stat pathway signaling in regulating cytokine-dependent gene expression and cellular development/survival is well established. Nevertheless, advances continue to be made in defining Jak-Stat pathway effects on different cellular processes and in different organisms. This review focuses on recent advances in the field and highlights some of the most active areas of Jak-Stat pathway research.