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

Regulatory activity of autocrine IL-10 on dendritic cell functions

IL-10 is a critical cytokine that blocks the maturation of dendritic cells (DCs), but the relevance of autocrine IL-10 on DC functions has not been investigated. In this study, we found that immature monocyte-derived DCs released low but sizeable amounts of IL-10. After stimulation with bacteria, LPS, lipoteichoic acid, or soluble CD40 ligand, DCs secreted high levels of IL-10. Addition of an anti-IL-10-neutralizing Ab to immature DCs as well as to soluble CD40 ligand- or LPS-maturing DCs led to enhanced expression of surface CD83, CD80, CD86, and MHC molecules and markedly augmented release of TNF-alpha and IL-12, but diminished IL-10 mRNA expression. Moreover, DCs treated with anti-IL-10 Ab showed an increased capacity to activate allogeneic T cells and primed naive T cells to a more prominent Th1 polarization. DC maturation and IL-10 neutralization were associated with enhanced accumulation of the IL-10 receptor binding chain (IL-10R1) mRNA and intracellular IL-10R1 protein. In contrast, surface IL-10R1 and IL-10 binding activity diminished in mature DCs. These results indicate that autocrine IL-10 prevents spontaneous maturation of DCs in vitro, limits LPS- and CD40-mediated maturation, and increases IL-10 production by DCs. Moreover, IL-10R expression appears to be regulated by both transcriptional and posttranscriptional mechanisms. Endogenous IL-10 and IL-10R can be relevant targets for the manipulation of DC functions.

Interleukin-10 and the Interleukin-10 Receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Regulation of the IL-10 production by human T cells

Interleukin (IL)-10, an immunomodulatory cytokine predominantly produced by monocytes/macrophages and T cells, inhibits several functions of dendritic cells (DC), monocytes and T cells including their cytokine production, but it stimulates B cell immunoglobulin (Ig) production and cytotoxic T lymphocyte (CTL) generation. A precise knowledge of the mechanisms that control the IL-10 production is therefore highly important for understanding the immunoregulation. The IL-10 production was studied in cultures of freshly isolated human T cells. A rise in intracellular calcium as well as the common gamma-chain containing cytokine receptor triggering or CD28 triggering were found to be important signals for IL-10 induction. CD80, CD58, rIL-12 and rIFN-alpha all had efficacious and independent costimulatory activities on the IL-10 production, while PGE2 was inhibitory. Dependence on autocrine IL-2 signalling was shown by the effects of anti-IL-2 and anti-IL-2R monoclonal antibodies (MoAb), but the IL-10 production proceeded partly IL-2-independent when CD80 provided costimulation. Sensitivity to inhibition by CsA was not removed by CD80 or CD58 costimulation and/or by addition of rIL-12 or rIFN-alpha, pointing to the absolute requirement for calcineurin activity. These data reveal important differences in the regulatory pathways between IL-10 (a cytokine-inhibitory interleukin) and IL-2 (a cytokine-inducing interleukin), which can potentially be exploited therapeutically. The fact that CsA blocks the production of IL-10, which itself has important immunosuppressive properties, should be taken into account in defining immunosuppressive treatment schedules which include the use of CsA.

Identification of the functional interleukin-22 (IL-22) receptor complex: the IL-10R2 chain (IL-10Rbeta ) is a common chain of both the IL-10 and IL-22 (IL-10-related T cell-derived inducible factor, IL-TIF) receptor complexes

Interleukin-10 (IL-10)-related T cell-derived inducible factor (IL-TIF; provisionally designated IL-22) is a cytokine with limited homology to IL-10. We report here the identification of a functional IL-TIF receptor complex that consists of two receptor chains, the orphan CRF2-9 and IL-10R2, the second chain of the IL-10 receptor complex. Expression of the CRF2-9 chain in monkey COS cells renders them sensitive to IL-TIF. However, in hamster cells both chains, CRF2-9 and IL-10R2, must be expressed to assemble the functional IL-TIF receptor complex. The CRF2-9 chain (or the IL-TIF-R1 chain) is responsible for Stat recruitment. Substitution of the CRF2-9 intracellular domain with the IFN-gammaR1 intracellular domain changes the pattern of IL-TIF-induced Stat activation. The CRF2-9 gene is expressed in normal liver and kidney, suggesting a possible role for IL-TIF in regulating gene expression in these tissues. Each chain, CRF2-9 and IL-10R2, is capable of binding IL-TIF independently and can be cross-linked to the radiolabeled IL-TIF. However, binding of IL-TIF to the receptor complex is greater than binding to either receptor chain alone. Sharing of the common IL-10R2 chain between the IL-10 and IL-TIF receptor complexes is the first such case for receptor complexes with chains belonging to the class II cytokine receptor family, establishing a novel paradigm for IL-10-related ligands similar to the shared use of the gamma common chain (gamma(c)) by several cytokines, including IL-2, IL-4, IL-7, IL-9, and IL-15.

Interleukin 20: discovery, receptor identification, and role in epidermal function

A structural, profile-based algorithm was used to identify interleukin 20 (IL-20), a novel IL-10 homolog. Chromosomal localization of IL-20 led to the discovery of an IL-10 family cytokine cluster. Overexpression of IL-20 in transgenic (TG) mice causes neonatal lethality with skin abnormalities including aberrant epidermal differentiation. Recombinant IL-20 protein stimulates a signal transduction pathway through STAT3 in a keratinocyte cell line, demonstrating a direct action of this ligand. An IL-20 receptor was identified as a heterodimer of two orphan class II cytokine receptor subunits. Both receptor subunits are expressed in skin and are dramatically upregulated in psoriatic skin. Taken together, these results demonstrate a role in epidermal function and psoriasis for IL-20, a novel cytokine identified solely by bioinformatics analysis.

The IL-10 gene is not involved in the predisposition to inflammatory bowel disease

Although genetic predisposition for inflammatory bowel disease (IBD) is well established, little is known about the accountable genes. The pathogenesis of IBD is characterized by an imbalanced activation of Th1- and Th2-lymphocytes. IL-10 represents an anti-inflammatory cytokine which downregulates the production of Th1-derived cytokines. To evaluate the role of the IL-10 gene in IBD, two polymorphisms in the promoter region (G/A at position -1082 and C/A at position -592) were genotyped in 142 patients with Crohn's disease (CD), 104 patients with ulcerative colitis (UC), and 400 healthy controls. Significant differences were not apparent, neither in the allele frequencies of either polymorphism, nor in the haplotype frequencies. Screening of the coding region of the IL-10 gene by polymerase chain reaction--single strand conformation polymorphism (PCR-SSCP) analysis revealed a rare sequence variation in exon 1 leading to an amino acid exchange (G-->A; G15R) in two patients with CD and five healthy controls. Therefore, polymorphisms of the IL-10 gene are not demonstrably involved in the predisposition of IBD in our cohorts of patients.

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

We report the identification of a novel human cytokine, distantly related to interleukin (IL)-10, which we term IL-22. IL-22 is produced by activated T cells. IL-22 is a ligand for CRF2-4, a member of the class II cytokine receptor family. No high affinity ligand has yet been reported for this receptor, although it has been reported to serve as a second component in IL-10 signaling. A new member of the interferon receptor family, which we term IL-22R, functions as a second component together with CRF2-4 to enable IL-22 signaling. IL-22 does not bind the IL-10R. Cell lines were identified that respond to IL-22 by activation of STATs 1, 3, and 5, but were unresponsive to IL-10. In contrast to IL-10, IL-22 does not inhibit the production of proinflammatory cytokines by monocytes in response to LPS nor does it impact IL-10 function on monocytes, but it has modest inhibitory effects on IL-4 production from Th2 T cells.

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

IL-10-related T cell-derived inducible factor (IL-TIF or IL-21) is a new cytokine structurally related to IL-10 and originally identified in the mouse as a gene induced by IL-9 in T cells and mast cells. Here, we report the cloning of the human IL-TIF cDNA, which shares 79% amino acid identity with mouse IL-TIF and 25% identity with human IL-10. Recombinant human IL-TIF was found to activate signal transducer and activator of transcription factors-1 and -3 in several hepatoma cell lines. IL-TIF stimulation of HepG2 human hepatoma cells up-regulated the production of acute phase reactants such as serum amyloid A, alpha1-antichymotrypsin, and haptoglobin. Although IL-10 and IL-TIF have distinct activities, antibodies directed against the beta chain of the IL-10 receptor blocked the induction of acute phase reactants by IL-TIF, indicating that this chain is a common component of the IL-10 and IL-TIF receptors. Similar acute phase reactant induction was observed in mouse liver upon IL-TIF injection, and IL-TIF expression was found to be rapidly increased after lipopolysaccharide (LPS) injection, suggesting that this cytokine contributes to the inflammatory response in vivo.

Signaling by covalent heterodimers of interferon-gamma. Evidence for one-sided signaling in the active tetrameric receptor complex

Interferon-gamma (IFN-gamma) and its receptor complex are dimeric and bilaterally symmetric. We created mutants of IFN-gamma that bind only one IFN-gammaR1 chain per dimer molecule (called a monovalent IFN-gamma) to see if the interaction of IFN-gamma with one-half of the receptor complex is sufficient for bioactivity. Mutating a receptor-binding sequence in either AB loop of a covalent dimer of IFN-gamma yielded two monovalent IFN-gammas, gamma(m)-gamma and gamma-gamma(m), which cross-link to only a single soluble IFN-gammaR1 molecule in solution and on the cell surface. Monovalent IFN-gamma competes fully with wild type IFN-gamma for binding to U937 cells but only at a greater than 100-fold higher concentration than wild type IFN-gamma. Monovalent IFN-gamma had anti-vesicular stomatitis virus activity and antiproliferative activity, and it induced major histocompatibility complex class I and class II (HLA-DR) expression. In contrast, the maximal levels of activated Stat1alpha produced by monovalent IFN-gammas after 15 min were never more than half of those produced by either wild type or covalent IFN-gammas in human cell lines. These data indicate that while monovalent IFN-gamma activates only one-half of a four-chain receptor complex, this is sufficient for Stat1alpha activation, major histocompatibility complex class I surface antigen induction, and antiviral and antiproliferative activities. Thus, while interaction with both halves of the receptor complex is required for high affinity binding of IFN-gamma and efficient signal transduction, interaction with only one-half of the receptor complex is sufficient to initiate signal transduction.

Viral subversion of the immune system

This review describes the diverse array of pathways and molecular targets that are used by viruses to elude immune detection and destruction. These include targeting of pathways for major histocompatibility complex-restricted antigen presentation, apoptosis, cytokine-mediated signaling, and humoral immune responses. The continuous interactions between host and pathogens during their coevolution have shaped the immune system, but also the counter measures used by pathogens. Further study of their interactions should improve our ability to manipulate and exploit the various pathogens.

Interleukin 10 modulation of tumour necrosis factor receptors requires tyrosine kinases but not the PI 3-kinase/p70 S6 kinase pathway

We have previously shown that interleukin (IL-)10-induced proliferation of the murine mast cell line D36, was dependent upon the activation of PI 3-kinase and p70 S6 kinase. Conversely, we were able to show that this pathway was not involved in the signal transduction pathway mediating IL-10 inhibition of pro-inflammatory cytokine release from monocytes. We have extended these studies to investigate the induction of p75 tumour necrosis factor receptor (TNF-R) shedding, another anti-inflammatory property of IL-10. Using the inhibitors of PI 3-kinase (LY294002 and wortmannin) and an inhibitor of p70 S6 kinase activation (rapamycin), we were able to show that this anti-inflammatory effect of IL-10 was not mediated by the PI 3-kinase/p70 S6 kinase pathway, indicating that another signalling cascade(s) was involved. Further studies also investigated the role of tyrosine kinases in the response to IL-10. Two distinct tyrosine kinase inhibitors, herbimycin and genistein affected the expression of TNF-R in response to IL-10 but, surprisingly, with opposite effects. However, both compounds inhibited the activation of both PI 3-kinase and p70 S6 kinase, with a concomitant inhibition of IL-10-induced proliferation. We observed that whilst tyrosine kinase activity was involved in the regulation of TNF-R expression, IL-10-induced activation of JAK kinases was not sensitive to inhibition by the tyrosine kinase inhibitors. These data suggest that multiple unknown tyrosine kinases are mediating the IL-10-induced signal transduction pathways leading to the regulation of TNF-R expression and IL-10-induced proliferation.

Jak-Stat signal transduction pathway through the eyes of cytokine class II receptor complexes

Cells of the immune system communicate with each other to initiate, establish and maintain immune responses. The communication occurs through cell-to-cell contact or through a variety of intercellular mediators that include cytokines, chemokines, growth factors and hormones. In the case of cytokines, the signal is transmitted from the outside to the inside of a cell through cell surface receptors specific for each cytokine. At this step the signal is also decoded and amplified: ligand binding causes recruitment and/or activation of numerous cytoplasmic proteins. One cytokine can activate a number of signal transduction pathways leading to regulation of a wide array of biological activities. One of these pathways, the Jak-Stat pathway, is briefly reviewed here with respect to the class II cytokine receptors. Signal transduction through receptors for interferons Type I (IFN-alpha, IFN-beta, IFN-omega) and Type II (IFN-gamma), and interleukin 10 (IL-10) is described in detail. In addition, a complex between tissue factor (TF) and coagulation factor VIIa, and two new receptors related to the class II cytokine receptor family are discussed. Oncogene (2000).

Design and analysis of an engineered human interleukin-10 monomer

A monomeric form of human interleukin 10 (IL-10M1) has been engineered for detailed structure-function studies on IL-10 and its receptor complexes. Wild type IL-10 (wtIL-10) is a domain swapped dimer whose structural integrity depends on the intertwining of two peptide chains. wtIL-10 was converted to a monomeric isomer by inserting 6 amino acids into the loop connecting the swapped secondary structural elements. Characterization of IL-10M1 by mass spectroscopy, size exclusion chromatography, cross-linking, and circular dichroism shows that IL-10M1 is a stable alpha-helical monomer at physiological pH whose three-dimensional structure closely resembles one domain of wtIL-10. As previously reported, incubation of wtIL-10 with a soluble form of the IL-10Ralpha (sIL-10Ralpha) generates a complex that consists of 2 wtIL-10 molecules and 4 sIL-10Ralphas. In contrast, IL-10M1 forms a 1:1 complex with the sIL-10Ralpha. Characterization of the interaction using isothermal titration calorimetry confirmed the 1:1 stoichiometry and yielded a dissociation constant of 30 nm with an apparent binding enthalpy of -12.2 kcal/mol. Despite forming a 1:1 complex, IL-10M1 is biologically active in cellular proliferation assays. These results indicate that the 1:1 interaction between IL-10M1 and IL-10Ralpha is sufficient for recruiting the signal transducing receptor chain (IL-10Rbeta) into the signaling complex and eliciting IL-10 cellular responses.

Stat3-dependent induction of p19INK4D by IL-10 contributes to inhibition of macrophage proliferation

We have previously reported that IL-10 inhibits proliferation of normal bone marrow-derived macrophages and of the monocyte/macrophage cell line J774. Activation of Stat3 was shown to be necessary and sufficient to mediate inhibition of proliferation. To investigate further the mechanism of growth arrest, we examined the effect of IL-10 on expression of cell cycle inhibitors. We found that IL-10 treatment increases expression of the cyclin-dependent kinase inhibitors p19INK4D and p21CIP1 in macrophages. IL-10 cannot induce p19INK4D expression or block proliferation when Stat3 signaling is blocked by a dominant negative Stat3 or a mutant IL-10Ralpha which does not recruit Stat3 in J774 cells, whereas p21CIP1 induction is not affected. An inducibly active Stat3 (coumermycin-dimerizable Stat3-Gyrase B), which suppresses J774 cell proliferation, also induced p19INK4D expression. Sequencing of the murine p19INK4D promoter revealed two candidate Stat3 binding sites, and IL-10 treatment activated a reporter gene controlled by this promoter. These data suggest that Stat3-dependent induction of p19INK4D mediates inhibition of proliferation. Enforced expression of murine p19INK4D cDNA J774 cells significantly reduced their proliferation. Use of antisense p19INK4D and analysis of p19INK4D-deficient macrophages confirmed that p19INK4D is required for optimal inhibition of proliferation by IL-10, and indicated that additional IL-10 signaling events contribute to this response. These data indicate that Stat3-dependent induction of p19INK4D and Stat3-independent induction of p21CIP1 are important components of the mechanism by which IL-10 blocks proliferation in macrophages.

Induction of a novel cellular homolog of interleukin-10, AK155, by transformation of T lymphocytes with herpesvirus saimiri

Although herpesvirus saimiri-transformed T lymphocytes retain multiple normal T-cell functions, only a few changes have been described. By subtractive hybridization, we have isolated a novel cellular gene, ak155, a sequence homolog of the interleukin-10 gene. Specifically herpesvirus saimiri-transformed T cells overexpress ak155 and secrete the protein into the supernatant. In other T-cell lines and in native peripheral blood cells, but not in B cells, ak155 is transcribed at low levels. AK155 forms homodimers similarly to interleukin-10. As a lymphokine, AK155 may contribute to the transformed phenotype of human T cells after infection by herpesvirus saimiri.

Kaposi's sarcoma-associated herpesvirus-encoded interleukin-6

Since the discovery of the virus in 1994, the rapid pace with which Karposi's sarcoma-associated herpesvirus (KSHV) research has progressed has quickly led to a broad understanding of the structure of the virus and its biology and pathology in humans. Molecular piracy of potentially useful cellular genes has emerged as a characteristic feature of this virus. The viral homolog of human IL-6, vIL-6 is an example in kind. Studies in vitro and in vivo have shown that vIL-6 can stimulate the growth of KSHV-infected primary infusion lymphoma (PEL) cells, can promote hematopoiesis, and act as an angiogenic factor through the induction of vascular endothelial growth factor (VEGF). It is not difficult to envision how vIL-6, through these properties and perhaps others yet to be identified, can contribute to KSHV survival and spread in the human population.

Systematic mutational mapping of sites on human interferon-beta-1a that are important for receptor binding and functional activity

A systematic mutational analysis of human interferon-beta-1a (IFN-beta) was performed to identify regions on the surface of the molecule that are important for receptor binding and for functional activity. The crystal structure of IFN-beta-1a was used to design a panel of 15 mutant proteins, in each of which a contiguous group of 2-8 surface residues was mutated, in most instances to alanine. The mutants were analyzed for activity in vitro in antiviral and in antiproliferation assays, and for their ability to bind to the type I IFN (ifnar1/ifnar2) receptor on Daudi cells and to a soluble ifnar2 fusion protein (ifnar2-Fc). Abolition of binding to ifnar2-Fc for mutants A2, AB1, AB2, and E established that the ifnar2 binding site on IFN-beta comprises parts of the A helix, the AB loop, and the E helix. Mutations in these areas, which together define a contiguous patch of the IFN-beta surface, also resulted in reduced affinity for binding to the receptor on cells and in reductions in activity of 5-50-fold in functional assays. A second receptor interaction site, concluded to be the ifnar1 binding site, was identified on the opposite face of the molecule. Mutations in this region, which encompasses parts of the B, C, and D helices and the DE loop, resulted in disparate effects on receptor binding and on functional activity. Analysis of antiproliferation activity as a function of the level of receptor occupancy allowed mutational effects on receptor activation to be distinguished from effects on receptor binding. The results suggest that the binding energy from interaction of IFN-beta with ifnar2 serves mainly to stabilize the bound IFN/receptor complex, whereas the binding energy generated by interaction of certain regions of IFN-beta with ifnar1 is not fully expressed in the observed affinity of binding but instead serves to selectively stabilize activated states of the receptor.

Human cytomegalovirus harbors its own unique IL-10 homolog (cmvIL-10)

We identified a viral IL-10 homolog encoded by an ORF (UL111a) within the human cytomegalovirus (CMV) genome, which we designated cmvIL-10. cmvIL-10 can bind to the human IL-10 receptor and can compete with human IL-10 for binding sites, despite the fact that these two proteins are only 27% identical. cmvIL-10 requires both subunits of the IL-10 receptor complex to induce signal transduction events and biological activities. The structure of the cmvIL-10 gene is unique by itself. The gene retained two of four introns of the IL-10 gene, but the length of the introns was reduced. We demonstrated that cmvIL-10 is expressed in CMV-infected cells. Thus, expression of cmvIL-10 extends the range of counter measures developed by CMV to circumvent detection and destruction by the host immune system.

Expression of IL-10 receptors on epithelial cells from the murine small and large intestine

The appearance of chronic intestinal inflammation in IL-10 knockout mice suggests IL-10 may inhibit adverse responses to luminal antigen. Moreover, this inflammation is associated with an increase in class II MHC molecule expression on intestinal epithelial cells. Thus, the role of IL-10 regulation in epithelial cell function was investigated. Using RT-PCR, it was shown that intestinal epithelial cells express mRNA for both subunits of the IL-10 receptor-signaling complex. In addition, biotinylated IL-10 was shown to bind to both cultured and freshly isolated intestinal epithelial cells prepared from the small or large intestine. This binding appeared specific as it was blocked by neutralizing antibodies to IL-10 but not the isotype control. Moreover, an excess of native IL-10 also inhibited the binding of radiolabeled IL-10. To evaluate whether IL-10 mediated any functions through this receptor, epithelial cells were cultured with IL-10 alone or with IFN-gamma plus IL-10. IL-10 alone had no detectable effects on epithelial cell growth or their expression of class II MHC molecules but it did antagonize the effect of IFN-gamma on the viability of cultured cells. In addition, IL-10 blocked the IFN-gamma-induced expression of class II MHC molecules on cultured epithelial cells. These results suggest that IL-10 binds to a specific receptor on intestinal epithelial cells and may regulate the contribution of epithelial cells to the inflammatory and immune response in the digestive tract.

A single amino acid determines the immunostimulatory activity of interleukin 10

Cellular interleukin 10s (cIL-10s) of human and murine origin have extensive sequence and structural homology to the Epstein-Barr virus BCRF-I gene product, known as viral IL-10 (vIL-10). Although these cytokines share many immunosuppressive properties, vIL-10 lacks several of the immunostimulatory activities of cIL-10 on certain cell types. The molecular and cellular bases for this dichotomy are not currently defined. Here, we show that the single amino acid isoleucine at position 87 of cIL-10 is required for its immunostimulatory function. Substitution of isoleucine in cIL-10 with alanine, which corresponds to the vIL-10 residue, abrogates immunostimulatory activity for thymocytes, mast cells, and alloantigenic responses while preserving immunosuppressive activity for inhibition of interferon gamma production and prolongation of cardiac allograft survival. Conversely, substitution of alanine with isoleucine in vIL-10 converts it to a cIL-10-like molecule with immunostimulatory activity. This single conservative residue alteration significantly affects ligand affinity for receptor; however, affinity changes do not necessarily alter specific activities for biologic responses in a predictable fashion. These results suggest complex regulation of IL-10 receptor-ligand interactions and subsequent biological responses. These results demonstrate that vIL-10 may represent a captured and selectively mutated cIL-10 gene that benefits viral pathogenesis by leading to ineffective host immune responses. The ability to manipulate the activity of IL-10 in either a stimulatory or suppressive direction may be of practical value for regulating immune responses for disease therapy, and of theoretical value for determining what aspects of IL-10 activity are important for normal T cell responses.

The treatment of psoriasis with IL-10: rationale and review of the first clinical trials

By virtue of its anti-inflammatory and immunosuppressive properties, IL-10 plays a crucial role in several immune reactions, including regulatory mechanisms in the skin. In psoriasis, a common cutaneous immune disease, a relative deficiency in cutaneous IL-10 expression is observed. Several lines of evidence suggest that IL-10 could have antipsoriatic abilities. One pilot and two Phase II trials with sc. IL-10 administration over 3 - 7 weeks in patients with moderate to severe psoriasis have supported this hypothesis. The therapy was well-tolerated and clinical efficiency was found in the majority of patients. Immunosuppressive effects (depressed monocytic HLA-DR expression, TNF-alpha and IL-12 secretion capacity, IL-12 plasma levels and responsiveness to recall antigens) as well as a shift towards a Type 2 cytokine pattern (increasing proportion of IL-4, IL-5, and IL-10 producing T-cells, selective increase in IgE serum levels) were observed. These investigations suggest that IL-10 is of major importance in psoriasis and show that IL-10 administration represents a new therapeutic approach. However, long-term administration of large recombinant protein limits the value of this novel therapeutic approach. As such, neither oral nor topical applications are possible; there is a risk of the development of neutralising antibodies.

Anti-inflammatory cytokine profile in human heart failure: behavior of interleukin-10 in association with tumor necrosis factor-alpha

Proinflammatory cytokines, i.e., tumor necrosis factor-alpha (TNFalpha), participate in the development and the progression of congestive heart failure (CHF). On the other hand, an anti-inflammatory cytokine may neutralize the proinflammatory cytokines of CHF. Interleukin-10 (IL-10) is known to suppress the synthesis of proinflammatory cytokines. IL-10 and the IL-10 receptor system was investigated in comparison with the behavior of TNFalpha in 68 patients with various causes of CHF (mean age: 61 years) and in 31 normal subjects (61 years). The circulating IL-10 level was higher in CHF patients than in normal subjects (p<0.05). The TNFalpha level was higher in CHF patients than in control subjects (p<0.005). The ratio of IL-10 to TNFalpha tended to be higher in control subjects than in patients with CHF (p = 0.09). With lipopolysaccharide treatment, the release of IL-10 was more enhanced from mononuclear leukocyte of patients with CHF than from control subjects (p<0.05). The expression of the IL-10 receptor estimated by flow cytometry of mononuclear leukocytes was higher in the CHF patients than in the normal subjects. The IL-10/IL-10 receptor system was activated, at least partly, to downregulate an excess of TNFalpha in patients with advanced CHF. IL-10 may be an important inherent component of the cytokine network of CHF.

Resistance of Rheumatoid Synovial Dendritic Cells to the Immunosuppressive Effects of IL-10

IL-10 down-regulates the APC function of many dendritic cells (DC), including human peripheral blood (PB) DC. In rheumatoid arthritis (RA), synovial fluid (SF) DC express markers of differentiation and are effective APC despite abundant synovial IL-10. The regulation of DC responsiveness to IL-10 was therefore examined by comparing the effect of IL-10 on normal PB and RA SF DC. Whereas IL-10 down-modulated APC function and MHC class II and B7 expression of PB DC, IL-10 had no such effect on SF DC. Since SF DC have differentiated in vivo in the presence of proinflammatory cytokines, PB DC were cocultured in the presence of IL-10 and either GM-CSF, IL-1β, TNF-α, IL-6, or TGF-β. GM-CSF, IL-1β, and TNF-α were all able to restore APC function. Whereas the effects of IL-10 on PB DC were shown to be mediated by IL-10R1, neither PB nor RA SF DC constitutively expressed IL-10R1 mRNA or detectable surface protein. In contrast, IL-10R1 protein was demonstrated in PB and SF DC whole cell lysates, suggestive of predominant intracellular localization of the receptor. Thus, DC responsiveness to IL-10 may be regulated through modulation of cell surface IL-10R1 expression or signaling.

The human homologue of the yeast proteins Skb1 and Hsl7p interacts with Jak kinases and contains protein methyltransferase activity

To expand our understanding of the role of Jak2 in cellular signaling, we used the yeast two-hybrid system to identify Jak2-interacting proteins. One of the clones identified represents a human homologue of the Schizosaccaromyces pombe Shk1 kinase-binding protein 1, Skb1, and the protein encoded by the Saccharomyces cerevisiae HSL7 (histone synthetic lethal 7) gene. Since no functional motifs or biochemical activities for this protein or its homologues had been reported, we sought to determine a biochemical function for this human protein. We demonstrate that this protein is a protein methyltransferase. This protein, designated JBP1 (Jak-binding protein 1), and its homologues contain motifs conserved among protein methyltransferases. JBP1 can be cross-linked to radiolabeled S-adenosylmethionine (AdoMet) and methylates histones (H2A and H4) and myelin basic protein. Mutants containing substitutions within a conserved region likely to be involved in AdoMet binding exhibit little or no activity. We mapped the JBP1 gene to chromosome 14q11.2-21. In addition, JBP1 co-immunoprecipitates with several other proteins, which serve as methyl group acceptors and which may represent physiological targets of this methyltransferase. Messenger RNA for JBP1 is widely expressed in human tissues. We have also identified and sequenced a homologue of JBP1 in Drosophila melanogaster. This report provides a clue to the biochemical function for this conserved protein and suggests that protein methyltransferases may have a role in cellular signaling.

Interleukin-10 (IL-10) Selectively Enhances CIS3/SOCS3 mRNA Expression in Human Neutrophils: Evidence for an IL-10–Induced Pathway That Is Independent of STAT Protein Activation

We have recently shown that, in human neutrophils, interleukin-10 (IL-10) fails to induce specific DNA-binding activities to the gamma-interferon response region (GRR), a regulatory element located in the FcγRI gene promoter, which is required for transcriptional activation by IL-10 and interferon γ (IFNγ) in monocytic cells. In this study, we report that IL-10 is also unable to induce the binding of STAT1 or STAT3 to the serum-inducible element (hSIE/m67), despite the fact that both proteins are expressed in neutrophils. Whereas IFNγ and granulocyte colony-stimulating factor (G-CSF) are efficient inducers of STAT1 and STAT3 tyrosine phosphorylation in polymorphonuclear neutrophils (PMN), IL-10 fails to trigger STAT1 and STAT3 tyrosine and serine phosphorylation, therefore explaining its inability to induce the FcγRI expression in these cells. By contrast, we demonstrate that IL-10 alone represents an efficient stimulus of CIS3/SOCS3 mRNA expression in neutrophils. CIS3/SOCS3 belongs to the recently cloned cytokine-inducible SH2-containing protein (CIS) gene family (which also includes CIS1, CIS2, CIS4, CIS5, and JAB) that is believed to be, at least in part, under the control of STAT transcription factors and whose products are potential modulators of cytokine signaling. Moreover, IL-10 synergizes with lipopolysaccharide (LPS) in upregulating CIS3/SOCS3 mRNA expression in PMN through a mechanism that involves mRNA stabilization. In contrast to CIS3/SOCS3, mRNA transcripts encoding other family members are unaffected by IL-10 in neutrophils. Finally, transfection of CIS3/SOCS3 in murine M1 myeloid cells suppresses LPS-induced growth arrest, macrophage-like differentiation, and nitric oxide synthesis, but not IL-6 mRNA expression. Collectively, our data suggest that, in neutrophils, the activation of STAT1 and STAT3 phosphorylation is neither required for CIS3/SOCS3 induction by IL-10 nor involved in the regulatory effects of IL-10 on cytokine production.

The type I interferon receptor: structure, function, and evolution of a family business

Recent results indicate that coherent models of how multiple interferons (IFN) are recognized and signal selectively through a common receptor are now feasible. A proposal is made that the IFN receptor, with its subunits IFNAR-1 and IFNAR-2, presents two separate ligand binding sites, and this double structure is both necessary and sufficient to ensure that the different IFN are recognized and can act selectively. The key feature is the duplication of the extracellular domain of the IFNAR-1 subunit and the configurational geometry that this imposes on the intracellular domains of the receptor subunits and their associated tyrosine kinases.

Characterization of a soluble ternary complex formed between human interferon-beta-1a and its receptor chains

The extracellular portions of the chains that comprise the human type I interferon receptor, IFNAR1 and IFNAR2, have been expressed and purified as recombinant soluble His-tagged proteins, and their interactions with each other and with human interferon-beta-1a (IFN-beta-1a) were studied by gel filtration and by cross-linking. By gel filtration, no stable binary complexes between IFN-beta-1a and IFNAR1, or between IFNAR1 and IFNAR2 were detected. However, a stable binary complex formed between IFN-beta-1a and IFNAR2. Analysis of binary complex formation using various molar excesses of IFN-beta-1a and IFNAR2 indicated that the complex had a 1:1 stoichiometry, and reducing SDS-PAGE of the binary complex treated with the cross-linking reagent dissucinimidyl glutarate (DSG) indicated that the major cross-linked species had an apparent Mr consistent with the sum of its two individual components. Gel filtration of a mixture of IFNAR1 and the IFN-beta-1a/IFNAR2 complex indicated that the three proteins formed a stable ternary complex. Analysis of ternary complex formation using various molar excesses of IFNAR1 and the IFN-beta-1a/IFNAR2 complex indicated that the ternary complex had a 1:1:1 stoichiometry, and reducing SDS-PAGE of the ternary complex treated with DSG indicated that the major cross-linked species had an apparent Mr consistent with the sum of its three individual components. We conclude that the ternary complex forms by the sequential association of IFN-beta-1a with IFNAR2, followed by the association of IFNAR1 with the preformed binary complex. The ability to produce the IFN-beta-1a/IFNAR2 and IFN-beta-1a/IFNAR1/IFNAR2 complexes make them attractive candidates for X-ray crystallography studies aimed at determining the molecular interactions between IFN-beta-1a and its receptor.

Evidence for conformationally different states of interleukin-10: binding of a neutralizing antibody enhances accessibility of a hidden epitope

We present the mapping of two anti-human interleukin-10 (hIL-10) antibodies (CB/RS/2 and CB/RS/11) which have been described as binding their antigen cooperatively. The epitopes were identified using hIL-10-derived overlapping peptide scans prepared by spot synthesis. To identify residues essential for binding within the two epitopes, each position was replaced by all other L-amino acids. The epitope-derived peptides were further characterized with respect to antibody affinity and their inhibition of the antibody-hIL-10 interaction. One antibody (CB/RS/11) binds to residues which are completely buried in the X-ray structure of IL-10. Accessibility of this hidden epitope is enhanced upon binding of the antibody CB/RS/2, which recognizes a discontinuous epitope located nearby. The recognition of the hidden CB/RS/11 epitope, as well as the cooperative binding behaviour of the two antibodies, provides evidence that IL-10 can adopt a conformational state other than that observed in the crystal structure.

Interleukin-10 receptor signaling through the JAK-STAT pathway. Requirement for two distinct receptor-derived signals for anti-inflammatory action

Interleukin-10 (IL-10) is a cytokine that has pleiotropic effects on a variety of different cell types. Although many of the biologic responses induced by IL-10 are also induced by other cytokines, such as IL-6, IL-10 is relatively unique in its ability to potently inhibit production of pro-inflammatory cytokines in macrophages. In this study, we have used gain-of-function and loss-of-function genetic approaches to define the intracellular components involved in the different biologic actions of IL-10. Herein, we demonstrate that the ability of IL-10 to inhibit tumor necrosis factor alpha (TNFalpha) production in lipopolysaccharide-stimulated macrophages requires the presence of Stat3, Jak1, and two distinct regions of the IL-10 receptor intracellular domain. Macrophages deficient in Stat3 or Jak1 were unable to inhibit lipopolysaccharide-induced TNFalpha production following treatment with murine IL-10. Structure-function analysis of the intracellular domain of the IL-10 receptor alpha chain showed that whereas two redundant Stat3 recruitment sites (427YQKQ430 and 477YLKQ480) were required for all IL-10-dependent effects on either B cells or macrophages, expression of IL-10-dependent anti-inflammatory function required the presence on the intracellular domain of the IL-10 receptor of a carboxyl-terminal sequence containing at least one functionally critical serine. These results thus demonstrate that IL-10-induced inhibition of TNFalpha production requires two distinct regions of the IL-10 receptor intracellular domain and thereby establish a distinctive molecular basis for the developmental versus the anti-inflammatory actions of IL-10.

Interleukin-10 and Gp130 cytokines in human multiple myeloma

Interleukin (IL)-10 is a critical cytokine involved in the terminal differentiation of B cells into plasma cells. IL-10 is also involved in multiple myeloma, a malignant plasma cell disorder. IL-6 and, more generally the cytokines activating the gp130 IL-6 transducer, are major survival and proliferation factors of myeloma cells. IL-10 is also a growth factor of malignant plasma cells, produced by myeloma cells from about half the patients and is detected in the plasma of patients with plasma cell leukemia or solitary plasmacytoma. The myeloma cell growth activity of IL-10 is mediated through a gp130 cytokine, oncostatin M (OSM), that is frequently produced by myeloma cells. Myeloma cells fail to express OSM receptors but IL-10, by inducing it, confers on them the sensitivity to OSM.

Selective DNA-binding activity of interleukin-10-stimulated STAT molecules in human monocytes

It has been demonstrated that interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) have various reverse effects on macrophages; however, the molecular mechanism of this difference has not been fully understood. In this study, we analyzed the binding activity of IL-10- and IFN-gamma-activated STAT molecules to two kinds of GAS-motif sequences. IL-10-activated STAT1 could bind to the GAS-motif sequence in the promoter region of the Fcgamma receptor, but not to that in the promoter region of the COX-2 gene, whereas IFN-gamma-activated STAT1 and STAT5 could bind to both sequences. IL-10 inhibited IFN-gamma-induced STAT activation without newly synthesized protein. We further demonstrated that aspirin, but not dexamethasone, suppressed IFN-gamma-induced STAT activation. Taken together, these results suggest that IL-10-activated STAT1 has a specificity in binding to the GAS-motif sequences, whereas IFN-gamma-activated STAT1 and STAT5 have a broader spectrum in binding to the GAS-motif sequences. This may explain the difference between IL-10 and IFN-gamma in biological activity, and the inhibitory effect of IL-10 on IFN-gamma activities.

The interleukin-10 signal transduction pathway and regulation of gene expression in mononuclear phagocytes

Interleukin-10 (IL-10) activates a diverse array of functional responses in mononuclear phagocytes. Functional IL-10 receptor (IL-10R) complexes are tetramers consisting of two IL-10R1 polypeptide chains and two IL-10R2 chains. Binding of IL-10 to the extracellular domain of IL-10R1 activates phosphorylation of the receptor-associated Janus tyrosine kinases, JAK1 and Tyk2. These kinases then phosphorylate specific tyrosine residues (Y446 and Y496) on the intracellular domain of the IL-10R1 chain. Once phosphorylated, these tyrosine residues (and their flanking peptide sequences) serve as temporary docking sites for the latent transcription factor, STAT3 (signal transducer and activator of transcription-3). STAT3 binds to these sites via its SH2 (Src homology 2) domain, and is, in turn, tyrosine-phosphorylated by the receptor-associated JAKs. It then homodimerizes and translocates to the nucleus where it binds with high affinity to STAT-binding elements (SBE) in the promoters of various IL-10-responsive genes. One of these genes, SOCS-3 (Suppressor of Cytokine Signaling-3) is a member of a newly identified family of genes that inhibit JAK/STAT-dependent signaling. Moreover, the ability of IL-10 to induce de novo synthesis of SOCS-3 in monocytes correlates with its ability to inhibit expression of many genes in these cells, including endotoxin-inducible cytokines such as tumor necrosis factor-alpha (TNF-alpha) and IL-1. Thus, the ability of IL-10 to inhibit gene expression in monocytes is associated with its ability to rapidly induce synthesis of SOCS-3.

Purification of receptor complexes of interleukin-10 stoichiometry and the importance of deglycosylation in their crystallization

Interleukin-10 (IL-10) is a pleiotropic immunosuppressive cytokine that has a wide range of effects in controlling inflammatory responses. Viral IL-10 (vIL-10) is a homologue of human IL-10 (hIL-10) produced by Epstein-Barr virus (EBV). Both hIL-10 and vIL-10 bind to the soluble extracellular fragment of the cytokine receptor IL-10R1 (shIL-10R1). The stoichiometry of the vIL-10 : shIL-10R1 complex has been found to be the same as hIL-10 : shIL-10R1, with two vIL-10 dimers binding to four shIL-10R1 monomers. Complexes of both hIL-10 and vIL-10 with glycosylated shIL-10R1 could not be crystallized. Controlled deglycosylation using peptide : N-glycosidase F and endo-beta-N-acetylglucosaminidase F3 resulted in the formation of crystals of both hIL-10 : shIL-10R1 and vIL-10 : shIL-10R1 complexes, indicating that the difficulty in the crystal formation was largely due to the presence of complex carbohydrate side chains. The availability of the structure of the ligand-receptor complexes should facilitate our understanding of the basis of the interaction between IL-10 and the IL-10 receptor.

The intracellular domain of interferon-alpha receptor 2c (IFN-alphaR2c) chain is responsible for Stat activation

Type I IFNs activate the Jak-Stat signal transduction pathway. The IFN-alpha receptor 1 (IFN-alphaR1) subunit and two splice variants of the IFN-alphaR2 subunit, IFN-alphaR2c and IFN-alphaR2b, are involved in ligand binding. All these receptors have been implicated in cytokine signaling and, specifically, in Stat recruitment. To evaluate the specific contribution of each receptor subunit to Stat recruitment we employed chimeric receptors with the extracellular domain of either IFN-gammaR2 or IFN-gammaR1 fused to the intracellular domains of IFN-alphaR1, IFN-alphaR2b, and IFN-alphaR2c. These chimeric receptors were expressed in hamster cells. Because human IFN-gamma exhibits no activity on hamster cells, the use of the human IFN-gamma receptor extracellular domains allowed us to avoid the variable cross-species activity of the type I IFNs and eliminate the possibility of contributions of endogenous type I IFN receptors into the Stat recruitment process. We demonstrate that Stat recruitment is solely a function of the IFN-alphaR2c intracellular domain. When chimeric receptors with the human IFN-gammaR1 extracellular domain and various human IFN-alpha receptor intracellular domains were expressed in hamster cells carrying the human IFN-gammaR2 subunit, only the IFN-alphaR2c subunit was capable of supporting IFN-gamma signaling as measured by MHC class I induction, antiviral protection, and Stat activation. Neither the IFN-alphaR2b nor the IFN-alphaR1 intracellular domain was able to recruit Stats or support IFN-gamma-induced biological activities. Thus, the IFN-alphaR2c intracellular domain is necessary and sufficient to activate Stat1, Stat2, and Stat3 proteins.

Comparative genomic analysis of the interferon/interleukin-10 receptor gene cluster

Interferons and interleukin-10 are involved in key aspects of the host defence mechanisms. Human chromosome 21 harbors the interferon/interleukin-10 receptor gene cluster linked to the GART gene. This cluster includes both components of the interferon alpha/beta-receptor (IFNAR1 and IFNAR2) and the second components of the interferon gamma-receptor (IFNGR2) and of the IL-10 receptor (IL10R2). We report here the complete gene content of this GART-cytokine receptor gene cluster and the use of comparative genomic analysis to identify chicken IFNAR1, IFNAR2, and IL10R2. We show that the large-scale structure of this locus is conserved in human and chicken but not in the pufferfish Fugu rubripes. This establishes that the receptor components of these host defense mechanisms were fixed in an ancestor of the amniotes. The extraordinary diversification of the interferon ligand family during the evolution of birds and mammals has therefore occurred in the context of a fixed receptor structure.

Comparative Genomic Analysis of the Interferon/Interleukin-10 Receptor Gene Cluster

Interferons and interleukin-10 are involved in key aspects of the host defence mechanisms. Human chromosome 21 harbors the interferon/interleukin-10 receptor gene cluster linked to theGART gene. This cluster includes both components of the interferon α/β-receptor (IFNAR1 and IFNAR2) and the second components of the interferon γ-receptor (IFNGR2) and of the IL-10 receptor (IL10R2). We report here the complete gene content of this GART–cytokine receptor gene cluster and the use of comparative genomic analysis to identify chicken IFNAR1, IFNAR2, andIL10R2. We show that the large-scale structure of this locus is conserved in human and chicken but not in the pufferfish Fugu rubripes. This establishes that the receptor components of these host defense mechanisms were fixed in an ancestor of the amniotes. The extraordinary diversification of the interferon ligand family during the evolution of birds and mammals has therefore occured in the context of a fixed receptor structure.

[The sequence data described in this paper have been submitted to GenBank under accession nos.AF039904, AF039905, AF039906, AF039907, AF045606, AF082664, AF082665,AF082666, AF082667, and AF083221.]

A synthetic mimic of a discontinuous binding site on interleukin-10

We synthetically reconstructed a discontinuous binding site on interleukin-10 (IL-10) that recognizes the neutralizing anti-IL-10 antibody CB/RS/1. To design the 32-mer IL-10 mimic, a discontinuous interaction site on IL-10 was mapped, and binding studies with epitope-derived peptides led to specific replacement of several amino acids. Both parts of the interaction site were combined by addition of a linker molecule. Systematic analoging of the combined molecule then led to introduction of several additional substitutions in both regions and the linker. All possible disulfide bridge-containing variants of the 32-mer were tested by binding studies. Parallel syntheses were performed on continuous cellulose membranes by spot synthesis. As a result, a conformationally stabilized IL-10-derived molecule was obtained that both binds to and neutralizes the biological activity of CB/RS/1 in the low nanomolar range. This synthetic approach is a powerful alternative to phage display methods for the design of protein mimics.

The proximal tyrosines of the cytoplasmic domain of the beta chain of the type I interferon receptor are essential for signal transducer and activator of transcription (Stat) 2 activation. Evidence that two Stat2 sites are required to reach a threshold of interferon alpha-induced Stat2 tyrosine phosphorylation that allows normal formation of interferon-stimulated gene factor 3

The precise role of the different subunits (alpha/IFNAR1 and betaL/IFNAR2) of the type I interferon receptor (IFN-R) in the activation of signal transducer and activator of transcription (Stat) 1, Stat2, and Stat3 has not yet been established. In this report we demonstrate that there are functionally redundant phosphotyrosine-dependent and -independent binding sites for Stat2 in the alpha and beta subunits of the type I IFN-R. Expression of a type I IFN-R containing only the constitutive Stat2 site or the proximal tyrosines of betaL, but not the docking site on the alpha chain (Tyr466 and Tyr481), supported low levels of Stat2 activation. However, the presence of only one intact Stat2 site did not lead to induction of interferon-stimulated gene factor 3 (ISGF3) or an antiviral state. Normal levels of Stat2 tyrosine phosphorylation, induction of ISGF3, and an antiviral effect always required the proximal tyrosines of betaL and at least one of the other Stat2 sites (Tyralpha466, 481 or betaL404-462). These data suggest that a threshold of Stat2 tyrosine phosphorylation is required for complete activation of ISGF3. Interestingly, a receptor in which all tyrosines were mutated to phenylalanine shows normal Stat3 phosphorylation and low levels of activation of Stat1.

The neutrophil: one of the cellular targets of interleukin-10

Interleukin-10 exerts a wide spectrum of in vitro and in vivo biological activities implicated in the regulation of the inflammatory and immune responses. Among the different cell types affected by interleukin-10, monocyte/macrophages and lymphocytes appear to be particularly modified with regard to their function, morphology, and phenotype. However, recent studies performed in our laboratory, as well as by other groups, suggest that a number of functional activities of polymorphonuclear neutrophils are also subject to regulation by interleukin-10. In view of the central role of polymorphonuclear neutrophils in host defense processes and in amplifying inflammatory and immune reactions, the ability of interleukin-10 to act as a potent modulator of this cell type opens new perspectives as to the potential therapeutic utility of interleukin-10. This article reviews what is currently known about the effects of interleukin-10 on neutrophils.

Specific contribution of Tyk2 JH regions to the binding and the expression of the interferon alpha/beta receptor component IFNAR1

Cytokine signaling involves the activation of the Janus kinase (JAK) family of tyrosine kinases. These enzymes are physically associated with cytokine receptor components. Here, we sought to define the molecular basis of the interaction between Tyk2 and IFNAR1, a component of the interferon alpha/beta receptor, by delimiting a minimal IFNAR1 binding region in the Tyk2 protein. Using an in vitro assay system, we narrowed down the interaction domain to a region comprising the JH7 and part of the JH6 homology boxes (amino acids 22-221). When expressed in Tyk2-negative cells, the JH7-6 region was unable to stabilize IFNAR1 protein levels, a critical function that we previously attributed to the N region (amino acids 1-591) of Tyk2. Moreover, substitution of the JH7-JH6 domain in JAK1 with that of Tyk2 did not restore IFNAR1 level nor interferon alpha signaling in Tyk2-negative cells. Thus, the major interaction surface lies within JH7-6, but additional JH regions (JH5-4-3) contribute in a specific manner to the in vivo assembly of Tyk2 and IFNAR1. Evidence is also provided of the lack of specificity of the Tyk2 kinase-like and tyrosine kinase domains in interferon alpha/beta receptor signaling.

Cytokines: principles and prospects

Cytokines participate in the induction and effector phases of all immune and inflammatory responses. They are therefore obvious tools and targets for strategies designed to promote, inhibit or redirect these responses. However, the complexity of the cytokine network has hindered the widespread clinical application of many cytokines and it has become clear that a deeper understanding of the normal operation of this system in health and disease is needed for the therapeutic potential of cytokines to be fully realized. This review summarizes some of the principles that are now thought to underlie the diverse functions of the interleukins, interferons, colony-stimulating factors and tumour necrosis factors in immune and inflammatory reactions in vivo. Genetic and structural relationships between these cytokines, the regulation of their synthesis, and the structures and functions of their receptors are outlined. Current knowledge of these parameters suggests ways in which multiple positive and negative regulatory mechanisms are integrated to balance cytokine benefits and harm under physiological conditions and offers new prospects for rational exploitation of this system.

Viral strategies of immune evasion

The vertebrate body is an ideal breeding ground for viruses and provides the conditions that promote their growth, survival, and transmission. The immune system evolved and deals with this challenge. Mutually assured destruction is not a viable evolutionary strategy; thus, the study of host-virus interactions provides not only a glimpse of life at immunity's edge, but it has also illuminated essential functions of the immune system, in particular, the area of major histocompatibility complex-restricted antigen presentation.

Mapping of the interleukin-10/interleukin-10 receptor combining site

The discontinuous interleukin-10(IL-10)/interleukin-10 receptor (IL-10R) combining site was mapped using sets of overlapping peptides derived from both binding partners bound to continuous cellulose membranes. Low affinity binding of single regions of the discontinuous contact sites on IL-10 and IL-10R could be identified due to (1) high peptide density on the membrane support, (2) incubation with high protein concentrations, (3) indirect immunodetection of the ligates after electrotransfer onto polyvinylene difluoride membranes, and (4) use of highly overlapping peptide scans of different length (6-mers and 15-mers). The single binding regions identified for each protein species are separated in the protein sequences, but form continuous areas on the surface of IL-10 (X-ray structure) and IL-10R (computer model). Furthermore, four epitopes of neutralizing anti-IL-10 and anti-IL-10R antibodies were mapped and overlap with these binding regions. Soluble peptides (15- to 19-mers) each spanning one of the three identified IL-10-derived receptor binding regions displayed no significant affinity to IL-10R as expected, whereas a peptide (35-mer) comprising two of these regions had considerably higher binding activity. The data are consistent with a previously published computer model of the IL-10/IL-10R complex. This approach should be generally applicable for the mapping of non-linear protein-protein contact sites.

The orphan receptor CRF2-4 is an essential subunit of the interleukin 10 receptor

The orphan receptor CRF2-4 is a member of the class II cytokine receptor family (CRF2), which includes the interferon receptors, the interleukin (IL) 10 receptor, and tissue factor. CRFB4, the gene encoding CRF2-4, is located within a gene cluster on human chromosome 21 that comprises three interferon receptor subunits. To elucidate the role of CRF2-4, we disrupted the CRFB4 gene in mice by means of homologous recombination. Mice lacking CRF2-4 show no overt abnormalities, grow normally, and are fertile. CRF2-4 deficient cells are normally responsive to type I and type II interferons, but lack responsiveness to IL-10. By approximately 12 wk of age, the majority of mutant mice raised in a conventional facility developed a chronic colitis and splenomegaly. Thus, CRFB4 mutant mice recapitulate the phenotype of IL-10-deficient mice. These findings suggest that CRF2-4 is essential for IL-10-mediated effects and is a subunit of the IL-10 receptor.

The interferon gamma (IFN-gamma) receptor: a paradigm for the multichain cytokine receptor

With the purification and cloning of the interferon gamma (IFN-gamma) receptor chains the mechanism of IFN-gamma action and the resultant signal transduction events were delineated in remarkable detail. The interferon gamma (IFN-gamma) receptor complex consists of two chains: IFN-gammaR1, the ligand-binding chain, and IFN-gammaR2, the accessory chain. Binding of IFN-gamma causes oligomerization of the two IFN-gamma receptor subunits, IFN-gammaR1 and IFN-gammaR2, which initiates the signal transduction events: activation of Jak1 and Jak2 receptor associated protein tyrosine kinases, phosphorylation of the IFN-gammaR1 intracellular domain on Tyr440 followed by phosphorylation and activation of Stat1alpha, the latent transcriptional factor. With all these steps established, the IFN-gamma receptor complex has provided the basic model for understanding the receptors for other members of the family of class II cytokine receptors.