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The dimeric cytokine interleukin (IL)-26 belongs to the IL-10 family. Whereas it was originally perceived as a T-helper (Th)17 cytokine, subsequent studies have shown that IL-26 is produced by several populations of leukocytes and structural cells. This cytokine binds to a heterodimeric receptor complex including IL-10R2 and -20R1 (IL-26R) and signals through STAT 1 and 3 to induce the release of chemokines and growth factors. Remarkably, IL-26 directly kills bacteria and inhibits viral replication. The most recent studies on human airways confirm multiple cellular sources in this critical interphase of host defense and demonstrate that stimulation of toll-like receptors (TLR) trigger the release of IL-26. Once released, it exerts a dualistic effect on cytokine production and up-regulates gene expression of IL-26R. It also potentiates chemotaxis and inhibits chemokinesis for neutrophils, thereby facilitating the accumulation of innate effector cells at the site of bacterial stimulation. The high levels of IL-26 in human airways are altered in inflammatory airway disorders such as asthma and chronic obstructive pulmonary disease. Thus, IL-26 emerges as an important mediator, providing direct and indirect actions on microbes, actions that are essential for host defense and inflammation and bears potential as a biomarker of disease.

IL-26 is a potentially important player in host defense and may be a pathogenic factor in the chronic inflammatory disorders of humans. However, the involvement of IL-26 in tuberculous pleural effusion (TPE) has not been investigated. The concentration of IL-26 was determined in pleural fluids and sera from patients with pleural effusions. Flow cytometry was performed to identify the cell origin of IL-26. The effects of tuberculosis-specific antigen (ESAT-6/CFP-10) on IL-26 expression of CD4+ T cell were explored. The impacts of IL-26 on modulating CD4+ T cell polarization were also investigated. The concentrations of IL-26 were much higher in tuberculous, malignant, and infectious PE than those in the corresponding serum. The expression of IL-26 on CD4+ T cells was much higher in tuberculous PE than those in the corresponding serum, and pleural Th1 and Th17 cells might be the major cell sources of IL-26. The addition of ESAT-6/CFP-10 to CD4+ T cells led to increasing the number of IL-26-producing CD4+ T cells and IL-26 expression on Th1 and Th17 cells. IL-26 could induce the differentiation and generation of IL-22 by memory and naive CD4+ T cells. IL-26 also upregulated the mRNA encoding CC-chemokine ligand 20 (CCL20) and CCL22 by mononuclear cells isolated from TPE. This study implies that pleural Th1 and Th17 cells are the major cell sources of IL-26, which could induce the differentiation and generation of Th22 cells by CD4+ T cells, suggesting the involvement of IL-26 in the pathogenesis of human TPE. KEY MESSAGES: IL-26 is overexpressed in TPE patients and presents a higher concentration in pleural effusion than the corresponding peripheral blood. Pleural Th1 and Th17 cells might be the major cell sources of IL-26 in TPE patients. IL-26 promotes IL-22 secretion and Th22 generation by CD4+ T cells isolated from TPE patients. IL-26 may play an active role in the pathogenesis of tuberculous pleurisy.

Long-term tobacco smokers with chronic obstructive pulmonary disease (COPD) or chronic bronchitis display an excessive accumulation of neutrophils in the airways; an inflammation that responds poorly to established therapy. Thus, there is a need to identify new molecular targets for the development of effective therapy. Here, we hypothesized that the neutrophil-mobilizing cytokine interleukin (IL)-26 (IL-26) is involved in airway inflammation amongst long-term tobacco smokers with or without COPD, chronic bronchitis or colonization by pathogenic bacteria. By analyzing bronchoalveolar lavage (BAL), bronchail wash (BW) and induced sputum (IS) samples, we found increased extracellular IL-26 protein in the airways of long-term smokers in vivo without further increase amongst those with clinically stable COPD. In human alveolar macrophages (AM) in vitro, the exposure to water-soluble tobacco smoke components (WTC) enhanced IL-26 gene and protein. In this cell model, the same exposure increased gene expression of the IL-26 receptor complex (IL10R2 and IL20R1) and nuclear factor κ B (NF-κB); a proven regulator of IL-26 production. In the same cell model, recombinant human IL-26 in vitro caused a concentration-dependent increase in the gene expression of NF-κB and several pro-inflammatory cytokines. In the long-term smokers, we also observed that extracellular IL-26 protein in BAL samples correlates with measures of lung function, tobacco load, and several markers of neutrophil accumulation. Extracellular IL-26 was further increased in long-term smokers with exacerbations of COPD (IS samples), with chronic bronchitis (BAL samples ) or with colonization by pathogenic bacteria (IS and BW samples). Thus, IL-26 in the airways emerges as a promising target for improving the understanding of the pathogenic mechanisms behind several pulmonary morbidities in long-term tobacco smokers.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of authors. The Journal received an expression of concern from a reader, which noted that: “The problem is that there is no IL-26 gene in the mouse. They claim they bought the KO mouse and the mouse IL-26 protein but given that there is no mouse IL-26 gene, a purchase is not possible and in fact no such reagents are available. Furthermore they do reference and anti-IL-26 antibody but the spec sheet clearly states that it is only reactive with the human protein…., the Enzo Life Sciences online catalog does not have a listing for recombinant IL-26 of any kind.” The authors apologize for their mistakes and have asked to retract the article.

Anti-microbial peptides are produced at outer and inner surfaces by epithelia and innate immune cells in response to bacterial infection. Staphylococcus aureus is an enterotoxin producing, Gram-positive pathogen, which is a major cause of soft tissue infections and life-threatening bacteremia and sepsis. Here we show that (i) skin T cells in chronic wounds infected with S. aureus express interleukin-26 (IL-26) in situ, (ii) staphylococcal enterotoxins (SE) trigger IL-26 expression in T cell lines and primary skin T cells, and (iii) IL-26 triggers death and inhibits biofilm formation and growth of S. aureus. Thus, we provide novel evidence that IL-26 is an anti-microbial peptide produced by T cells in response to SE. Accordingly, we propose that IL-26 producing T cells take part in the innate immune response to SE producing S. aureus and thus play a novel role in the primary innate immune defense in addition to their classical role in adaptive immunity. Published version

Interleukin (IL)-26 is abundant in human airways and this cytokine is involved in the local immune response to a bacterial stimulus in vivo. Specifically, local exposure to the toll-like receptor (TLR) 4 agonist endotoxin does increase IL-26 in human airways and this cytokine potentiates chemotactic responses in human neutrophils. In addition to T-helper (Th) 17 cells, alveolar macrophages can produce IL-26, but it remains unknown whether this cytokine can also be produced in the airway mucosa per se in response to a viral stimulus. Here, we evaluated whether this is the case using primary bronchial epithelial cells from the airway epithelium in vitro and explored the signaling mechanisms involved, including the modulatory effects of additional Th17 cytokines. Finally, we assessed IL-26 and its archetype signaling responses in healthy human airways in vivo. We found increased transcription and release of IL-26 protein after stimulation with the viral-related double stranded (ds) RNA polyinosinic-polycytidylic acid (poly-IC) and showed that this IL-26 release involved mitogen-activated protein (MAP) kinases and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). The release of IL-26 in response to a viral stimulus was modulated by additional Th17 cytokines. Moreover, there was transcription of IL26 mRNA and expression of the protein in epithelial cells of bronchial brush and tissue biopsies respectively after harvest in vivo. In addition, the extracellular IL-26 protein concentrations in bronchoalveolar lavage (BAL) samples did correlate with increased epithelial cell transcription of an archetype intracellular signaling molecule downstream of the IL-26-receptor complex, STAT1, in the bronchial brush biopsies. Thus, our study suggests that viral stimulation causes the production of IL-26 in lining epithelial cells of human airways, structural cells that constitute a critical immune barrier and that this production is modulated by Th17 cytokines.

Aim To detect the possible role of interleukin (IL)-26 in diabetic retinopathy (DR) patients. Methods Subjects were divided into diabetes without retinopathy (DWR) group (n=20), non-proliferative diabetic retinopathy (NPDR) group (n=20), proliferative diabetic retinopathy (PDR) group (n=20) and normal control group (n=20). The protein expression of IL-26 in the serum and vitreous fluid were measured by enzyme-linked immunosorbent assay (ELISA). The mRNA change of IL-26 in peripheral blood mononuclear cells (PBMCs) was assessed by real-time polymerase chain reaction. Results The serum expression of IL-26 in PDR group was significantly elevated compared with the normal control group, DWR group and NPDR group. The vitreous fluid concentration of IL-26 in PDR patients (without anti-VEGF therapy) was also higher compared to normal controls. However, no obvious significance was found concerning the expression of IL-26 in vitreous fluid between PDR after anti-VEGF therapy and normal controls. In PDR group, the mRNA level of IL-26 significantly increased compared with the normal controls and DWR patients in the PBMCs. Conclusion Protein and mRNA expression of IL-26 are increased in serum, vitreous fluid and PBMCs in PDR patients, suggesting that IL-26 may be associated with the pathogenesis of PDR.

Background: The cellular sources of IL-26 in human airways include T-lymphocytes, bronchial epithelial cells and alveolar macrophages. Here, IL-26 is markedly increased in response to endotoxin, an archetype component of Gram-negative bacteria (GNB). However, the corresponding response to Gram-positive bacteria (GPB) in the airways is not known. Moreover, alveolar type II cells, which play a key role in innate immune responses to bacteria have not been investigated in terms of IL-26 release. Aims and Objectives: To characterize whether alveolar type II epithelial cells release IL-26 protein inherently, and in response to GNB and GPB. Methods: A model of human alveolar type II epithelial cells (A549 cells) was utilized. The TLR1/2 (Pam3CSK4) and TLR6 (Pam2CGDPKHPKSF) ligands represented a stimulus from GPB. The TLR4 ligand (LPS) represented a stimulus from GNB. Moreover, The TLR5 ligand (flagellin) represented a stimulus from both GPB and GNB. Cells were stimulated (0.1 & 1ug/mL) during 3-24 hours (h). We quantified IL-26 protein concentrations in cell-free conditioned media (ELISA). Results: There was a time-dependent increase release of inherent IL-26 protein in cell-free conditioned media. TLR1/2 stimulation (1µg/mL) increased IL-26 at the 24h time-point whereas TLR4 stimulation (1µg/mL) increased IL-26 at the 6h time-point. TLR5 (1ug/mL) and TLR6 (0. 1 & 1µg/mL) stimulation increased IL-26 at 3, 6 and 24h time points. Conclusions: A model of human alveolar type II cells releases IL-26 in response to stimuli from GNB and GPB. Further exploration of the involvement of alveolar type II cells and IL-26 in airway disease affecting host defense is warranted.

Background Sepsis is a serious syndrome that is caused by an unbalanced host inflammatory response to an infection. The cytokine network plays a pivotal role in the orchestration of inflammatory response during sepsis. IL-26 is an emerging proinflammatory member of the IL-10 cytokine family with multifaceted actions in inflammatory disorders. However, its role in the pathogenesis of sepsis remains unknown. Methods Serum IL-26 level was measured and analyzed in 52 septic patients sampled on the day of intensive care unit (ICU) admission, 18 non-septic ICU patient controls, and 30 healthy volunteers. In addition, the effects of recombinant human IL-26 on host inflammatory response in cecal ligation and puncture (CLP)-induced polymicrobial sepsis were determined. Results On the day of ICU admission, the patients with sepsis showed a significant increase in serum IL-26 levels compared with ICU patient controls and healthy volunteers, and the serum IL-26 levels were related to the severity of sepsis. Nonsurvivors of septic patients displayed significantly higher serum IL-26 levels compared with survivors. A high serum IL-26 level on ICU admission was associated with 28-day mortality, and IL-26 was found to be an independent predictor of 28-day mortality in septic patients by logistic regression analysis. Furthermore, administration of recombinant human IL-26 increased lethality in CLP-induced polymicrobial sepsis. Despite a lower bacterial load, septic mice treated with recombinant IL-26 had higher concentrations of IL-1β, IL-4, IL-6, IL-10, IL-17A, TNF-α, CXCL1, and CCL2 in peritoneal lavage fluid and blood and demonstrated more severe multiple organ injury (including lung, liver and kidney) as indicated by clinical chemistry and histopathology. Furthermore, septic mice treated with recombinant human IL-26 showed an increased neutrophil recruitment to the peritoneal cavity. Conclusions Septic patients had elevated serum IL-26 levels, which may correlate with disease severity and mortality. In experimental sepsis, we demonstrated a previously unrecognized role of IL-26 in increasing lethality despite promoting antibacterial host responses. Electronic supplementary material The online version of this article (10.1186/s13054-019-2574-7) contains supplementary material, which is available to authorized users.

Interleukin (IL)-26, known as a Th17 cytokine, acts on various cell types and has multiple biological functions. Although its precise role still remains to be elucidated, IL-26 is suggested to be associated with the pathology of diverse chronic inflammatory diseases such as psoriasis, inflammatory bowel diseases and rheumatoid arthritis. To develop novel neutralizing anti-human IL-26 monoclonal antibodies (mAbs) for therapeutic use in the clinical setting, we immunized mice with human IL-26 protein. Hybridomas producing anti-IL-26 mAbs were screened for various in vitro functional assays, STAT3 phosphorylation and antibiotic assays. Although the IL-20RA/IL-10RB heterodimer is generally believed to be the IL-26 receptor, our data strongly suggest that both IL-20RA-dependent and -independent pathways are involved in IL-26-mediated stimulation. We also investigated the potential therapeutic effect of anti-IL-26 mAbs in the imiquimod-induced psoriasis-like murine model using human IL-26 transgenic mice. These screening methods enabled us to develop novel neutralizing anti-human IL-26 mAbs. Importantly, administration of IL-26-neutralizing mAb did not have an effect on the antimicrobial activity of IL-26. Taken together, our data strongly suggest that our newly developed anti-human IL-26 mAb is a potential therapeutic agent for the treatment of diverse chronic inflammatory diseases including psoriasis.

Background The inflammatory cascade in the rheumatoid arthritis (RA) synovium is modulated by a variety of cytokine and chemokine networks; however, the roles of IL-26, in RA pathogenesis, are poorly defined. Here, we investigated the functional role of interleukin-26 (IL)-26 in osteoclastogenesis in RA. Methods We analyzed levels of IL-20 receptor subunit A (IL-20RA), CD55, and receptor activator of nuclear factor kappaB (NF-κB) ligand (RANKL) in RA fibroblast-like synoviocytes (FLSs) using confocal microscopy. Recombinant human IL-26-induced RANKL expression in RA-FLSs was examined using real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Human peripheral blood monocytes were cultured with macrophage colony-stimulating factor (M-CSF) and IL-26, after which osteoclastogenesis was evaluated by counting the number of tartrate-resistant acid phosphatase-positive multinucleated cells. Additionally, osteoclastogenesis was evaluated by monocytes co-cultured with IL-26-prestimulated FLSs. Results The expression of IL-20RA in RA-FLSs was higher than that in osteoarthritis-FLSs. Additionally, in IL-26-pretreated RA-FLSs, the expression of IL-20RA (but not IL-10 receptor subunit B) and RANKL increased in a dose-dependent manner, with IL-26-induced RANKL expression reduced by IL-20RA knockdown. Moreover, IL-26-induced RANKL expression was significantly downregulated by inhibition of signal transducer and activator of transcription 1, mitogen-activated protein kinase, and NF-κB signaling. Furthermore, IL-26 promoted osteoclast differentiation from peripheral blood monocytes in the presence of low dose of RANKL, with IL-26 exerting an additive effect. Furthermore, co-culture of IL-26-pretreated RA-FLSs with peripheral blood monocytes also increased osteoclast differentiation in the absence of addition of RANKL. Conclusions IL-26 regulated osteoclastogenesis in RA through increased RANKL expression in FLSs and direct stimulation of osteoclast differentiation. These results suggest the IL-26/IL-20RA/RANKL axis as a potential therapeutic target for addressing RA-related joint damage.

International audience; Interleukin 26 (IL-26) is the most recently identified member of the IL-20 cytokine subfamily, and is a novel mediator of inflammation overexpressed in activated or transformed T cells. Novel properties have recently been assigned to IL-26, owing to its non-conventional cationic, and amphipathic features. IL-26 binds to DNA released from damaged cells and, as a carrier molecule for extracellular DNA, links DNA to inflammation. This observation suggests that IL-26 may act both as a driver and an effector of inflammation, leading to the establishment of a deleterious amplification loop and, ultimately, sustained inflammation. Thus, IL-26 emerges as an important mediator in local immunity/inflammation. The dysregulated expression and extracellular DNA carrier capacity of IL-26 may have profound consequences for the chronicity of inflammation. IL-26 also exhibits direct antimicrobial properties. This review summarizes recent advances on the biology of IL-26 and discusses its roles as a novel kinocidin. Cytokines are a class of signaling molecules expressed by many cell types, and especially those of the immune system. They are classified in seven major families: the type I cytokine, the type II cytokine (1), the IL-1 (2), and the TGF-β (3) families, the TNF superfamily (4), the receptor tyrosine kinase cytokine family (5), and the chemokine family (6). Although exhibiting pleiotropic properties, they are pivotal regulators of innate and adaptive immune defenses, inflammation, and hematopoiesis. The term "interleukin" (IL) originally refers to a group of cytokines expressed by leukocytes. To date, interleukins have been reported expressed by a wide variety of immune and non-immune cells and exhibit a large panel of properties (e.g., affecting proliferation, activation, differentiation, maturation, migration, and adhesion). Although agonist/antagonist activities and redundancy make any classification particularly complicated, different classifications have been proposed based on their functions, receptor usage or structure. As an example, a functional classification distinguishes eight subgroups of interleukins (IL-1, common γ chain receptor cytokine, cytokines of type 2 immune responses, interleukins with chemokine activity, the IL-10, IL-12, and IL-17 families and, others) (7). A structure-based classification has been also proposed, dividing interleukins into four major groups: IL-1-like cytokines, class I helical cytokines (IL-4-, IL-6-, and IL-12-like ILs, common γ chain receptor cytokines), class II helical cytokines (IL-10-and IL-28-like molecules) and the IL17-like cytokines (8).

Background Interleukin (IL)-26 is a signature T helper 17 cytokine described as a proinflammatory and antimicrobial mediator. So far, IL-26 has been reported in several immune-mediated inflammatory diseases, but its involvement in inflammatory skin disorders is poorly known. Objectives To investigate the role of IL-26 in hidradenitis suppurativa (HS), through its involvement in antimicrobial activity. Methods IL-26 was assessed in patients with HS through gene expression and protein analysis at skin and circulating levels. Ex vivo HS organ skin cultures, together with IL-26 antibody treatment, were performed to determine the IL-26 activity. Peripheral blood mononuclear cells (PBMCs) from patients with HS and healthy controls were either silenced or not with IL-26 small interfering (si)RNA in order to measure its antimicrobial, cytotoxic and phagocytic activities against Staphylococcus aureus. Results Firstly, we observed that IL-26 is able to modulate the proinflammatory response at the immune cell level. IL-26 was increased in the plasma of patients with HS compared with healthy controls. Subsequently, we explored the bactericidal, cytotoxic and phagocytic activities of PBMCs against S. aureus in patients with HS and healthy controls. These activities were lower in patients with HS than in controls. Remarkably, the killing activities were reduced when healthy control PBMCs were transfected with IL-26 siRNA. However, the transfection did not affect the killing activity of HS PBMCs, supporting the idea that IL-26 lacks efficacy in HS. Conclusions Our findings suggest that infection susceptibility in HS might be related to IL-26. Although the role of bacteria remains controversial in HS, this paper supports that there is a defect of antimicrobial response in these patients. What's already known about this topic? Interleukin (IL)-26 is a T helper 17 cytokine described as an antimicrobial and proinflammatory mediator. IL-26 has been reported in immune-mediated inflammatory diseases, but its involvement in inflammatory skin disorders remains unclear. Hidradenitis suppurativa (HS) is a chronic inflammatory skin disorder characterized by deficiency of IL-20 and IL-22 (a close homologue of IL-26), which causes antimicrobial peptide pauperization leading to severe and recurrent skin infections. What does this study add? IL-26 plasma levels are higher in patients with HS than in healthy control individuals. The antimicrobial activity of IL-26 might be ineffective in patients with HS. What is the translational message? Cutaneous antimicrobial incompetence in HS could be related to IL-26.

Objective IL-26 has been shown to have high expression in RA. However, the effects of IL-26 on bone destruction in RA have not been evaluated. The aim of this study was to investigate the effects and mechanisms of IL-26 on RANK ligand (RANKL)-induced osteoclastogenesis. Methods We treated cells with IL-26 in RANKL-induced oseteoclastogenesis to monitor osteoclast formation by tartrate-resistant acid phosphatase (TRAP) staining. Osteoclast activity was assessed by pit formation assay and F-actin ring formation. The mechanism of the inhibition was studied by biochemical analyses such as RT-PCR, immunofluorescence staining and immunoblotting. In addition, cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Results IL-26 inhibited RANKL-induced TRAP-positive multinucleated cells and inhibited RANKL-induced nuclear factor κB (NF-κB) activation and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) nuclear translocation in RAW264.7 cells. Also, IL-26 significantly inhibited the bone-resorbing activity and F-actin ring formation ability of mature osteoclasts. Moreover, IL-26 suppressed RANKL-induced mitogen-activated protein kinase activation and NFATc1 downstream gene expression. Conclusion We suggest that the inhibitory activity of IL-26 on osteoclastogenesis is via down-regulation of RANKL-induced NF-κB and NFATc1 expression. Our results suggest IL-26 as a possible new remedy against osteolytic bone destruction.

Objective To investigate the involvement of interleukin (IL)-26 in neuroinflammatory processes in multiple sclerosis (MS), in particular in blood-brain barrier (BBB) integrity. Methods Expression of IL-26 was measured in serum, CSF, in vitro differentiated T helper (T-H) cell subsets, and postmortem brain tissue of patients with MS and controls by ELISA, quantitative PCR, and immunohistochemistry. Primary human and mouse BBB endothelial cells (ECs) were treated with IL-26 in vitro and assessed for BBB integrity. RNA sequencing was performed on IL-26-treated human BBB ECs. Myelin oligodendrocyte glycoprotein(35-55) experimental autoimmune encephalomyelitis (EAE) mice were injected IP with IL-26. BBB leakage and immune cell infiltration were assessed in the CNS of these mice using immunohistochemistry and flow cytometry. Results IL-26 expression was induced in T-H lymphocytes by T(H)17-inducing cytokines and was upregulated in the blood and CSF of patients with MS. CD4(+)IL-26(+) T lymphocytes were found in perivascular infiltrates in MS brain lesions, and both receptor chains for IL-26 (IL-10R2 and IL-20R1) were detected on BBB ECs in vitro and in situ. In contrast to IL-17 and IL-22, IL-26 promoted integrity and reduced permeability of BBB ECs in vitro and in vivo. In EAE, IL-26 reduced disease severity and proinflammatory lymphocyte infiltration into the CNS, while increasing infiltration of Tregs. Conclusions Our study demonstrates that although IL-26 is preferentially expressed by T(H)17 lymphocytes, it promotes BBB integrity in vitro and in vivo and is protective in chronic EAE, highlighting the functional diversity of cytokines produced by T(H)17 lymphocytes. This work was funded by a grant from the Canadian Institutes of Health Research (MOP136980). A. Prat holds a senior Canada Research Chair in Multiple Sclerosis. M. Charabati held a postdoctoral studentship from the Fonds de recherche du Quebec-Sante (FRQS) and is now supported by a doctoral scholarship from the Multiple Sclerosis Society of Canada (MSSC). E. Peelen and S. Zandee held a postdoctoral studentship from the FRQS/MSSC Partnership Award. B. Broux held a postdoctoral studentship from Fonds Wetenschappelijk Onderzoek-Vlaanderen. L. Hachehouche held PhD studentships from the MSSC, FRQS, and Neuroinflammation Training Program. Prat, A (corresponding author), Univ Montreal, Fac Med, Multiple Sclerosis Clin, Res Ctr,Ctr Hosp Univ Montreal CRCHUM,Dept Neuros, Montreal, PQ, Canada. a.prat@umontreal.ca

The production of interleukin (IL)-26 was initially attributed to T cells, and in particular to Th17 cells. However, more recent findings indicate IL-26 production in natural killer (NK) cells, macrophages and fibroblast-like cells as well. It is known that IL-26 binds to the IL-20R1/IL-10R2 receptor complex on certain target cells, where it causes specific intracellular signaling and the secretion of IL-1β, IL-8 and TNF-α. In line with this type of proinflammatory role, IL-26 also increases chemotaxis of human neutrophils. Interestingly, high levels of IL-26 are present even in normal human airways, and endotoxin exposure further enhances these levels; this indicates involvement in antibacterial host defense. Studies on acute inflammatory disorders are few but there are studies showing the involvement of IL-26 in rheumatoid arthritis and inflammatory bowel disease. In conclusion, IL-26 is emerging as a potentially important player in host defense and may also be a pathogenic factor in the chronic inflammatory disorders of humans.

Interleukin 17-producing helper T cells (T(H)17 cells) have a major role in protection against infections and in mediating autoimmune diseases, yet the mechanisms involved are incompletely understood. We found that interleukin 26 (IL-26), a human T(H)17 cell-derived cytokine, is a cationic amphipathic protein that kills extracellular bacteria via membrane-pore formation. Furthermore, T(H)17 cell-derived IL-26 formed complexes with bacterial DNA and self-DNA released by dying bacteria and host cells. The resulting IL-26-DNA complexes triggered the production of type I interferon by plasmacytoid dendritic cells via activation of Toll-like receptor 9, but independently of the IL-26 receptor. These findings provide insights into the potent antimicrobial and proinflammatory function of T(H)17 cells by showing that IL-26 is a natural human antimicrobial that promotes immune sensing of bacterial and host cell death.

In superior vertebrates, Interleukin 4 (IL-4) and Interleukin 13 (IL-13) play key and diverse roles to support immune responses acting on cell surface receptors. When stimulated, receptors activate intracellular signalling cascades switching cell phenotypes according to stimuli. In teleost fish, Interleukin 4/13 (IL-4/13) is the ancestral family cytokine related to both IL-4 and IL-13. Every private and common receptor subunit for IL-4/13 have in fish at least two paralogues and, as in mammals, soluble forms are also part of the receptor system. Reports for findings of fish IL-4/13 receptors have covered comparative analysis, transcriptomic profiles and to a lesser extent, functional analysis regarding ligand-receptor interactions and their biological effects. This review addresses available information from fish IL-4/13 receptors and discusses overall implications on teleost immunity, summarized gene induction strategies and pathogen-induced gene modulation, which may be useful tools to enhance immune response. Additionally, we present novel coding sequences for Atlantic salmon (Salmo salar) common gamma chain receptor (γC), Interleukin 13 receptor alpha 1A chain (IL-13Rα1A) and Interleukin 13 receptor alpha 1B chain (IL-13Rα1B).

Behcet's disease (BD) is a multi-systemic inflammatory disorder characterized by the "triple symptom complex". Several pro-inflammatory cytokines, mainly derived from the immune Th17 axis, seem to be involved in different pathogenic pathways leading to development of the clinical manifestations. Here, we have analyzed the expression and role of IL-26 in active BD patients, an inflammatory disorder characterized by bronchoalveolar lavage fluid (BAL) and cerebrospinal fluid (CSF) inflammation. On this basis, the primary aim of our work was to study IL-26 levels in serum, BAL CSF) from active BD patients. Samples were collected from 95 BD patients (55 patients were in active stage) and 50 healthy controls (HC). They were investigated with ELISA for estimation of cytokines levels. Serum concentration of IL-26 resulted higher in both active [4.80±1.32] and inactive [2.77±1.026] BD than HC [0.31±0.14ng/ml; p

Interleukin IL26 supports killing of microbes and the innate sensing of bacterial-derived DNA (bactDNA). We evaluated the relationship between IL26 serum levels and bactDNA translocation in Crohn's disease (CD). We ran a prospective study on CD patients in remission. IL26 common polymorphisms, serum cytokines and complement protein, amplified-bactDNA, and anti-TNF-α were evaluated. In vitro PBMC analysis was performed. Three hundred and thirteen patients were included (mean CDAI: 83.6 ± 32.8; mean fecal calprotectin: 55.4 ± 35.3 μg/g). A total of 106 patients (33.8%) showed bactDNA and 223 patients (71%) had a varIL26 genotype. BactDNA significantly correlated with increased IL26 levels compared with bactDNA-negative patients. PBMCs from varIL26 patients significantly reduced E. coli killing capacity compared with wtIL26-genotyped patients. The stimulation with a recombinant IL26 protein reduced pro-inflammatory cytokines in response to E. coli in the varIL26 cell supernatants. Serum anti-TNF-α levels in varIL26 vs wtIL26-genotyped patients on biologics were significantly lower in the presence of bactDNA. Cells from varIL26 vs wtIL26-genotyped patients cultured with E. coli DNA and infliximab showed a significant decrease in free anti-TNF-α concentration. A varIL26 genotype was associated with the initiation of anti-TNF-α in CD patients during the 6-month follow-up. IL26 polymorphisms may prevent bactDNA clearance and identify CD patients with a worse inflammatory evolution and response to therapy.BactDNA translocation in CD is associated with an increased risk of relapse. IL26 is sensitive to bactDNA and modulates the inflammatory response in CD patients. The varIL26 genotype is associated with reduced PMN capacity to kill bacteria. A varIL26 genotype is associated with decreased levels of anti-TNF-α in CD patients. IL26 may help explain the role of bactDNA as a risk factor of flare in CD patients.

Aim To investigate interleukin (IL)-26 expression in the inflamed mucosa of patients with inflammatory bowel disease (IBD) and the function of IL-26. Methods Human colonic subepithelial myofibroblasts (SEMFs) were isolated from colon tissue surgically resected. The expression of IL-26 protein and its receptor complex was analyzed by immunohistochemistry. The gene expression induced by IL-26 was evaluated by real-time polymerase chain reaction. Intracellular signaling pathways were evaluated by immunoblotting and specific small interfering (si) RNA transfection. Results The mRNA and protein expression of IL-26 were significantly enhanced in the inflamed mucosa of patients with IBD. IL-26 receptor complex was expressed in colonic SEMFs in vivo and in vitro. IL-26 stimulated the mRNA expression of IL-6 and IL-8 in colonic SEMFs. The inhibitors of mitogen-activated protein kinases and phosphoinositide 3-kinase, and siRNAs for signal transducers and activator of transcription 1/3, nuclear factor-kappa B and activator protein-1 significantly reduced the mRNA expression of IL-6 and IL-8 induced by IL-26. Conclusion These results suggest that IL-26 plays a role in the pathophysiology of IBD through induction of inflammatory mediators.

Interleukin 26 (IL-26) gene has been identified in human, amphibian and teleost but not in rodents. It is well accepted that IL-26 was a crucial member of IL-10 family which acts as a pro-inflammatory cytokine in human. However, the role of IL-26 in regulating inflammation in lower vertebrates including teleost has not been defined yet. In the present study, grass carp IL-26 (gcIL-26) coding sequence was isolated and identified. Its chromosomal synteny was also analyzed, showing that gcIL-26 gene is flanked by IL-22 and IFN-γ genes with the same transcriptional orientation as seen in human, amphibian and zebrafish. Given that zebrafish and grass carp IL-26 shared relatively low amino acid identities with human IL-26, the functional roles of fish IL-26 are indispensable to be elucidated. Accordingly, recombinant gcIL-26 (rgcIL-26) was prepared by using Pichia pastoris expression system, and it was found to be partially glycosylated. Using grass carp head kidney leucocytes as cell model, rgcIL-26 displayed the bioactivity to stimulate the mRNA expression of some pro-inflammatory cytokines including IL-8, IL-1β and IL-6, while inhibit mRNA expression of an anti-inflammatory cytokine, IL-10. Moreover, rgcIL-26 also up-regulated inos expression and NO production in grass carp monocytes/macrophages, strengthening its pro-inflammatory properties in fish. Those results collectively demonstrated the functional role of IL-26 in regulating inflammatory response in fish.

Summary gp130 is a shared signal-transducing membrane-associated receptor for several hematopoietic cytokines. The 30 Å resolution cryo-electron microscopy (cryo-EM) structure of the Interleukin 11(IL-11)-IL-11 Receptor-gp130 extracellular complex reveals the architecture and dynamics of this gp130-containing signaling complex. Normal-mode analysis reveals a repertoire of conformational changes that could function in signal triggering. This suggests a concerted mechanism of signaling involving all the components of the complex. This could provide a general mechanism of signal transfer for cytokines utilizing the JAK-STAT signaling cascade.

In this pilot study, we examined associations between local interleukin (IL)-26, disease severity and biomarkers of Th2-mediated inflammation in a well-defined cohort of pediatric patients (14 years median age, 41 % females) with controlled (n = 28) or uncontrolled (n = 48) asthma. Sputum IL-26 protein concentrations (ELISA) reflected disease control in patients without local (low exhaled nitric oxide) or systemic (low blood eosinophils) signs of eosinophilic inflammation. Moreover, sputum-IL-26 concentrations correlated with those of blood neutrophils. Our study indicates that IL-26 is a potential biomarker of disease severity in pediatric asthma without signs of Th2-mediated inflammation.

IL-26 is classified as a member of the IL-10 cytokine family because it has limited sequence homology to IL-10 and the IL-10-related cytokines. The human IL-26 gene, IL26, is located on chromosome 12q15 between the genes for two other important class-2 cytokines, IFNG (IFN-γ) and IL22 (IL-22). IL-26 is often co-expressed with IL-22 by activated T cells, especially Th17 cells. It signals through a heterodimeric receptor complex composed of the IL-20R1 and IL-10R2 chains. IL-26 receptors are primarily expressed on non-hematopoietic cell types, particularly epithelial cells. Signaling through IL-26 receptor complexes results in the activation of STAT1 and STAT3 with subsequent induction of IL-26-responsive genes. The biological functions of IL-26 have only begun to be defined.

To construct a recombinant adenovirus vector for expressing the IL-18 binding protein (IL-18BP)/IL-4 fusion gene and confirm the anti-inflammatory effect of this gene.The recombinant virus expressing IL-18BP/IL-4 fusion protein (AD-IL-18BP/IL-4) was constructed. AD-IL-18BP/IL-4 was used to infect synovial fibroblasts (SF). ELISA and Western blot analysis were used to determine the expressions of the proteins IL-4 and IL-18BP. To investigate the protective effects of this vector on rheumatoid arthritis, SF were infected with AD-IL-18BP/IL-4 and stimulated by LPS (1 microg/ml) 4 h later. The expression levels of TNF-alpha, IL-6, IL-8, and IL-18 in the culture supernatant were detected by ELISA and production of PGE2 and NO was estimated. The protein expression of COX-2, iNOS, and NF-kappaB p50 in treated SF was analyzed by Western blot.AD-IL-18BP/IL-4 can effectively express the IL-18BP/IL-4 fusion protein. The expressions of TNF-alpha, IL-6, IL-8, and IL-18 were significantly inhibited in LPS-stimulated SF after treatment with AD-IL-18BP/IL-4. The production of PGE2 and NO was significantly decreased. Moreover, NF-kappaB p50, COX-2, and iNOS levels in SF were markedly suppressed by AD-IL-18BP/IL-4.AD-IL-18BP/IL-4 can suppress the production and expression of inflammatory cytokines such as COX-2, iNOS, and NF-kappaB in LPS-stimulated SF.

Expression of interleukin-1 receptor type II (IL1R2), a decoy receptor for pro-inflammatory interleukin 1 (IL-1), is enhanced by chronic exposure of the human uroepithelial cell line HUC-1 to arsenite. To explore the function of IL1R2, we ectopically expressed IL1R2 in HUC-1 cells. IL1R2 overexpression results in changes in cell morphology, actin rearrangement, and promoted cell migration. Ectopic expression of IL1R2 specifically blocked exogenous IL-1beta signaling but increased expression of the precursor form of IL-1alpha (pIL-1alpha) and its downstream targets, including interleukin 6 (IL-6), interleukin 8 (IL-8), and type I collagen alpha1 (COL1A1). However, depleting gene expression using small RNA interference specific to either pIL-1alpha or COL1A1, but not IL-6 or IL-8, significantly attenuated the migration of IL1R2-overexpressing cells. Furthermore, IL1R2 overexpression was associated with enhanced expression of Smad-interacting protein 1 (SIP-1) and reduced expression of E-cadherin. Because SIP-1 is a repressor of COL1A1-induced E-cadherin expression, the present results suggest that IL1R2 overexpression is likely through activation of the pIL-1alpha pathway to enhance cell migration.

Using bioinformatics approach, the genome locus containing interleukin (IL)-22, IL-26, and interferon gamma (IFN-gamma) genes has been identified in the amphibian, Xenopus tropicalis. Like that in other vertebrates such as fish, birds, and mammals, the Xenopus IL-22, IL-26, and IFN-gamma are clustered in the same chromosome and the adjacent genes are conserved. The genomic structures of the Xenopus IL-22, IL-26, and IFN-gamma gene were identical to that of their mammalian counterparts. The Xenopus IL-22 and IL-26 genes contained five exons and four introns while the Xenopus IFN-gamma gene consisted of four exons and three introns. The Xenopus IL-22, IL-26, and IFN-gamma share 14.1-41.6%, 14.6-31.2%, and 23.7-36.5% identity to their counterparts in other species, respectively. Reverse-transcription polymerase chain reaction (PCR) and real-time quantitative PCR analyses revealed that the expression of IL-22, IL-26, and IFN-gamma genes was significantly upregulated after simulation with bacterial polyliposaccharide and/or synthetic double-stranded poly(I:C), suggesting these cytokines like those in other vertebrates play an important role in regulating immune response in Xenopus.

Interleukin 12 receptor beta1 (IL-12Rbeta1) and beta2 (IL-12Rbeta2) constitute the functional and high-affinity receptor complex for interleukin 12 (IL-12) and mediate important functions in activated T cells. In this study, we identified cyclin G associated kinase (GAK) as a new IL-12Rbeta2-interacting protein using yeast two-hybrid system and confirmed it by coimmunoprecipitation assays. Overexpression of GAK in activated T cells suppresses IL-12 induced IFN-gamma production but has no detectable effects on its proliferation, whereas knockdown of GAK by RNA interference (RNAi) increases IFN-gamma production. These results suggest that GAK associates with IL-12Rbeta2 and may play a role in regulating IL-12 signaling.

Rational: Improving the understanding of pulmonary host defense against bacteria in humans is vital for the development of effective therapy. Aim: To characterize the involvement of the presumed Th17 cytokine interleukin (IL)-26 in antibacterial host defense of the lungs. Methods: Intra-bronchial exposure of healthy volunteers to the TLR-4 agonist endotoxin and vehicle was performed during bronchoscopy and bronchoalveolar lavage (BAL) samples were harvested. Intracellular IL-26 was detected by immunocytochemistry and -cytofluorescence. This IL-26 was also detected by flow cytometry, as was its receptor complex. Cytokines and phosphorylated STAT1 plus -3 were quantified by ELISA. Gene expression was analyzed by real-time PCR and neutrophil migration was assessed in vitro. Results: Extracellular IL-26 was detected in BAL samples without prior exposure in vivo and was markedly increased after endotoxin exposure. Alveolar macrophages (AM), CD4 and 8 T-cells constituted cellular sources. Recombinant IL-26 potentiated chemotaxis induced by IL-8 and fMLP but decreased chemokinesis in neutrophils. The IL-26 receptor complex was detected in neutrophils and IL-26 decreased phosphorylated STAT3 in these cells. IL-26 increased gene expression of its receptor complex and STAT1 plus -3. Finally, IL-26 increased the release of neutrophil-mobilizing cytokines in BAL cells. Conclusion: Alveolar macrophages,stimulated through TLR-4 produce IL-26 that acts on neutrophil receptors and focuses their mobilization towards bacteria and accumulated immune cells in human lungs. This involvement of IL-26 in host defense in human lungs warrants further evaluation in local infections and inflammatory disorders.

Interleukin (IL)-17-producing T cells, especially T helper (Th)17 cells, play a critical role in the pathogenesis of a variety of autoimmune inflammatory diseases. The pathogenic function of Th17 cells results from their production of Th17 effector cytokines, namely IL-17 (or IL-17A), IL-17F, IL-22 and IL-26. The importance of IL-17 has been demonstrated by antibody neutralization studies in both animal models of autoimmune diseases as well as in human clinical trials. This review highlights the current knowledge of the clinical aspects of the Th17 cytokines as well as therapeutic antibodies against IL-17, IL-17F, IL-17 receptor, IL-22, IL-26 and granulocyte macrophage colony-stimulating factor for the future treatment of autoimmune inflammatory diseases.

Nowadays, multiple groups all over the world are being involved in the investigation of the impact of interleukin (IL)-10 superfamily members on cancer occurrence, development, and progression. Currently, the electronic database PubMed shows >4500 publications when one searches for the combination of the terms “interleukin-10/IL-10” and “cancer/tumor”; moreover, the amount of data on this topic has been growing every year. In this chapter, the authors summarize and review the key achievements of biomedicine in establishing the role of IL-10 in immunity and cancer biology. In addition, the authors discuss the relationship between IL-10 and multiple cancer-promoting agents, thereby trying to show an overall picture of IL-10 functioning in malignant disease. It was demonstrated that IL-10 may exert both procarcinogenic and anticarcinogenic activities depending on the condition of the immune system and tumor stage. The authors suggest that the most attractive and promising targets for further research on the IL-10 signaling in cancer are transforming growth factor-β, inducible isoform of nitric oxide synthase, E-selectin, cyclooxygenase 2/prostaglandin 2, and programed cell death ligands. Other representatives of the IL-10 superfamily include IL-19, IL-20, IL-22, IL-24, IL-26, and the unique type III interferon (IFN)-γ subfamily consisting of IL-28A (IFN-γ1), IL-28B (IFN-γ2), and IL-29 (IFN-γ3). The impact of these agents on cancer has been less investigated; however, their role is discussed briefly as well.

The interleukin 2 receptor alpha chain (IL-2Ralpha) is a component of high affinity IL-2 receptors and thus critically regulates T cell growth and other lymphoid functions. Five positive regulatory regions together control lineage-restricted and activation-dependent IL-2Ralpha induction in response to antigen and IL-2. We now show that TGF-beta cooperates with T cell receptor (TCR) signaling to increase IL-2Ralpha gene expression. Moreover, we identify a sixth positive regulatory region that regulates IL-2Ralpha expression in cells treated with anti-CD3 + anti-CD28 as well as TGF-beta and show that this region contains binding sites for Smad3, AP-1, and cAMP-responsive element-binding protein/ATF proteins. The importance of Smad complexes is indicated by impaired IL-2Ralpha induction by TGF-beta in CD4+ T cells from both Smad3-/- and Smad4-/- mice. Thus, we have identified a novel positive regulatory region in the IL-2Ralpha gene that mediates TGF-beta-dependent induction of the gene. These findings have implications related to IL-2Ralpha expression on activated T cells and regulatory T cells.

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.

Objective To determine whether polymorphisms in the interferon-γ (IFNγ)/interleukin-26 (IL-26; formerly, AK155) gene cluster contribute to sex-based differential susceptibility to rheumatoid arthritis (RA). Methods Four microsatellite markers, located in a 118-kb interval that contains both the IFNγ and IL-26 genes on chromosome 12q15, were typed in 251 patients with RA and 198 unrelated healthy controls (all of whom lived in Northern Ireland) by means of polymerase chain reaction–based fragment analysis. Results Marker D12S2510, which is located 3 kb 3′ from the IL-26 gene, was significantly associated with RA in women (corrected P [Pcorr] = 0.008, 2 degrees of freedom [2 df]) but not in men (P = 0.99, 2 df). A 3-marker haplotype, IFNGCA*13;D12S2510*8;D12S2511*9, was inferred that showed significant underrepresentation in women with RA (odds ratio 0.50, 95% confidence interval 0.32–0.78; P = 0.002, Pcorr = 0.03) but not in men with RA. Conclusion Our results demonstrate that common polymorphisms in the IFNγ/IL-26 gene region may contribute to sex bias in susceptibility to RA, by distorting the propensity of female carriers versus male carriers to contract this disease. These results conform to our recent observations of a role for this gene cluster in sex-based differential susceptibility to another Th1-type inflammatory disease, multiple sclerosis.

The role of the presumed Th17 cytokine IL-26 in antibacterial host defense of the lungs is not known.To characterize the role of IL-26 in antibacterial host defense of human lungs.Intrabronchial exposure of healthy volunteers to endotoxin and vehicle was performed during bronchoscopy and bronchoalveolar lavage (BAL) samples were harvested. Intracellular IL-26 was detected using immunocytochemistry and immunocytofluorescence. This IL-26 was also detected using flow cytometry, as was its receptor complex. Cytokines and phosphorylated signal transducer and activator of transcription (STAT) 1 plus STAT3 were quantified using ELISA. Gene expression was analyzed by real-time polymerase chain reaction and neutrophil migration was assessed in vitro.Extracellular IL-26 was detected in BAL samples without prior exposure in vivo and was markedly increased after endotoxin exposure. Alveolar macrophages displayed gene expression for, contained, and released IL-26. Th and cytotoxic T cells also contained IL-26. In the BAL samples, IL-26 concentrations and innate effector cells displayed a correlation. Recombinant IL-26 potentiated neutrophil chemotaxis induced by IL-8 and fMLP but decreased chemokinesis for neutrophils. Myeloperoxidase in conditioned media from neutrophils was decreased. The IL-26 receptor complex was detected in neutrophils and IL-26 decreased phosphorylated STAT3 in these cells. In BAL and bronchial epithelial cells, IL-26 increased gene expression of the IL-26 receptor complex and STAT1 plus STAT3. Finally, IL-26 increased the release of neutrophil-mobilizing cytokines in BAL but not in epithelial cells.This study implies that alveolar macrophages produce IL-26, which stimulates receptors on neutrophils and focuses their mobilization toward bacteria and accumulated immune cells in human lungs.

Background Interleukin 1 (IL-1) is implicated in neuroinflammation, an essential component of neurodegeneration. We evaluated the potential anti-inflammatory effect of a novel peptide antagonist of IL-1 signaling, Ilantide. Methods We investigated the binding of Ilantide to IL-1 receptor type I (IL-1RI) using surface plasmon resonance, the inhibition of Il-1β-induced activation of nuclear factor κB (NF-κB) in HEK-Blue cells that contained an IL-1β-sensitive reporter, the secretion of TNF-α in macrophages, protection against IL-1-induced apoptosis in neonatal pancreatic islets, and the penetration of Ilantide through the blood–brain barrier using competitive enzyme-linked immunosorbent assay (ELISA). We studied the effects of the peptide on social behavior and memory in rat models of lipopolysaccharide (LPS)- and amyloid-induced neuroinflammation, respectively, and its effect in a rat model of experimental autoimmune enchephalomyelitis. Results Ilantide bound IL-1RI, inhibited the IL-1β-induced activation of NF-κB, and inhibited the secretion of TNF-α in vitro. Ilantide protected pancreatic islets from apoptosis in vitro and reduced inflammation in an animal model of arthritis. The peptide penetrated the blood–brain barrier. It reduced the deficits in social activity and memory in LPS- and amyloid-treated animals and delayed the development of experimental autoimmune enchephalomyelitis. Conclusions These findings indicate that Ilantide is a novel and potent IL-1RI antagonist that is able to reduce inflammatory damage in the central nervous system and pancreatic islets.

Assembly of the cell surface IL-10 receptor complex is the first step in initiating IL-10 signaling pathways that regulate intestinal inflammation, viral persistence, and even tumor surveillance. The discovery of IL-10 homologs in the genomes of herpes viruses suggests IL-10 signaling pathways can be manipulated at the level of the receptor complex. This chapter will describe our current molecular understanding of IL-10 receptor assembly based on crystal structures and biochemical analyses of cellular and viral IL-10 receptor complexes.

cDNA coding for the alpha chain of the rat interleukin 10 (IL-10) receptor was amplified by polymerase chain reaction (PCR), cloned and sequenced. The nucleic acid coding sequence exhibited 88% and 68% homology with the mouse and human IL-10 receptor sequences, respectively. The translated protein exhibited 83% and 61% homology with the mouse and human IL-10 receptor proteins. Specific antibodies were raised to the extracellular domain of the rat IL-10 receptor expressed as a secreted protein in recombinant Drosophila S2 cells. Western blotting using these antibodies demonstrated the presence of the IL-10 receptor in five major regions of the rat brain (cortex, cerebellum, hippocampus, hypothalamus and pituitary), supporting a role for IL-10 as a central regulator of inflammation.

We have demonstrated that primary interleukin 13 (IL-13) binding protein IL-13 receptor (IL-13R) alpha chain plays an important role in IL-13 binding and internalization in the IL-13R system. Although IL-13R alpha chain is expressed on many cancer cell lines, some cancer types do not express or express low levels of this receptor chain. Consequently, these cells show no or low sensitivity to the cytotoxic effect of a recombinant chimeric protein composed of IL-13 and a mutated form of a Pseudomonas exotoxin, IL13-PE38QQR. Here we demonstrate that pancreatic cancer, renal cell carcinoma, head and neck cancer, and glioblastoma cell lines that were genetically altered to express high levels of IL-13R alpha chain increase their binding affinity for IL-13, and increase their sensitivity to IL13-PE38QQR by at least 6-fold to 1000-fold compared with mock-transfected control cells. This observation was made by protein synthesis inhibition assay and confirmed by clonogenic assay. Our studies provide a proof of principle for a novel strategy for cancer therapy that combines gene transfer and targeted cytotoxin therapy.