IL-20 receptor 2 signaling down-regulates antigen-specific T cell responses

CD200R activation on naïve T cells by B cells induces suppressive activity of T cells via IL-24

CD200 is an anti-inflammatory protein that facilitates signal transduction through its receptor, CD200R, in cells, resulting in immune response suppression. This includes reducing M1-like macrophages, enhancing M2-like macrophages, inhibiting NK cell cytotoxicity, and downregulating CTL responses. Activation of CD200R has been found to modulate dendritic cells, leading to the induction or enhancement of Treg cells expressing Foxp3. However, the precise mechanisms behind this process are still unclear. Our previous study demonstrated that B cells in Peyer's patches can induce Treg cells, so-called Treg-of-B (P) cells, through STAT6 phosphorylation. This study aimed to investigate the role of CD200 in Treg-of-B (P) cell generation. To clarify the mechanisms, we used wild-type, STAT6 deficient, and IL-24 deficient T cells to generate Treg-of-B (P) cells, and antagonist antibodies (anti-CD200 and anti-IL-20RB), an agonist anti-CD200R antibody, CD39 inhibitors (ARL67156 and POM-1), a STAT6 inhibitor (AS1517499), and soluble IL-20RB were also applied. Our findings revealed that Peyer's patch B cells expressed CD200 to activate the CD200R on T cells and initiate the process of Treg-of-B (P) cells generation. CD200 and CD200R interaction triggers the phosphorylation of STAT6, which regulated the expression of CD200R, CD39, and IL-24 in T cells. CD39 regulated the expression of IL-24, which sustained the expression of CD223 and IL-10 and maintained the cell viability. In summary, the generation of Treg-of-B (P) cells by Peyer's patch B cells was through the CD200R-STAT6-CD39-IL-24 axis pathway.

The interleukin-10 family: Major regulators of the immune response against Plasmodium falciparum infections

Malaria caused by the Plasmodium falciparum strain is more severe because of this protozoan's ability to disrupt the physiology of host cells during the blood stages of development by initiating the production of the interleukin-10 (IL-10) family of cytokines. P. falciparum feeds on hemoglobin and causes host cells to adhere to the walls of blood vessels by remodeling their composition. IL-10 is produced by CD4+ T cells that inhibits antigen-presenting cells' activity to prevent inflammation. This cytokine and its family members are crucial in promoting malarial infection by inhibiting the host's protective immune response, thus initiating Plasmodium parasitemia. IL-10 is also responsible for preventing severe pathology during Plasmodium infection and initiates several signaling pathways to alter the physiology of host cells during malarial infection. This review summarizes the critical aspects of P. falciparum infection, including its role in signaling pathways for cytokine exudation, its effect on microRNA, the human immune response in malaria, and the role played by the liver hormone hepcidin. Moreover, future aspects of vaccine development and therapeutic strategies to combat P. falciparum infections are also discussed in detail.

Interleukin 24 promotes cell death in renal epithelial cells and is associated with acute renal injury

Ischemia-reperfusion injury is a major cause of acute kidney injury. Many cytokines are involved in the pathogenesis of renal ischemia-reperfusion injury. IL24 is a member of the IL10 family and has gained importance because of its apoptosis-inducing effects in tumor disease besides its immunoregulative function. Littles is known about the role of IL24 in kidney disease. Using a mouse model, we found that IL24 is upregulated in the kidney after renal ischemia-reperfusion injury and that tubular epithelial cells and infiltrating inflammatory cells are the source of IL24. Mice lacking IL24 are protected from renal injury and inflammation. Cell culture studies showed that IL24 induces apoptosis in renal tubular epithelial cells, which is accompanied by an increased endoplasmatic reticulum stress response. Moreover, IL24 induces robust expression of endogenous IL24 in tubular cells, fostering ER-stress and apoptosis. In kidney transplant recipients with delayed graft function and patients at high risk to develop acute kidney injury after cardiac surgery IL24 is upregulated in the kidney and serum. Taken together, IL24 can serve as a biomarker, plays an important mechanistic role involving both extracellular and intracellular targets, and is a promising therapeutic target in patients at risk of or with ischemia-induced acute kidney injury.

Multifunctional Interleukin-24 Resolves Neuroretina Autoimmunity via Diverse Mechanisms

IL-24 is a multifunctional cytokine that regulates both immune cells and epithelial cells. Although its elevation is associated with a number of autoimmune diseases, its tolerogenic properties against autoreactive T cells have recently been revealed in an animal model of central nervous system (CNS) autoimmunity by inhibiting the pathogenic Th17 response. To explore the potential of IL-24 as a therapeutic agent in CNS autoimmunity, we induced experimental autoimmune uveitis (EAU) in wildtype mice and intravitreally injected IL-24 into the inflamed eye after disease onset. We found that the progression of ocular inflammation was significantly inhibited in the IL-24-treated eye when compared to the control eye. More importantly, IL-24 treatment suppressed cytokine production from ocular-infiltrating, pathogenic Th1 and Th17 cells. In vitro experiments confirmed that IL-24 suppressed both Th1 and Th17 differentiation by regulating their master transcription factors T-bet and RORγt, respectively. In addition, we found that intravitreal injection of IL-24 suppressed the production of proinflammatory cytokines and chemokines from the retinas of the EAU-inflamed eyes. This observation appears to be applicable in humans, as IL-24 similarly inhibits human retinal pigment epithelium cells ARPE-19. In conclusion, we report here that IL-24, as a multifunctional cytokine, is capable of resolving ocular inflammation in EAU mice by targeting both uveitogenic T cells and RPE cells. This study sheds new light on IL-24 as a potential therapeutic candidate for autoimmune uveitis.

IL-24 intrinsically regulates Th17 cell pathogenicity in mice

In certain instances, Th17 responses are associated with severe immunopathology. T cell–intrinsic mechanisms that restrict pathogenic effector functions have been described for type 1 and 2 responses but are less well studied for Th17 cells. Here, we report a cell-intrinsic feedback mechanism that controls the pathogenicity of Th17 cells. Th17 cells produce IL-24, which prompts them to secrete IL-10. The IL-10–inducing function of IL-24 is independent of the cell surface receptor of IL-24 on Th17 cells. Rather, IL-24 is recruited to the inner mitochondrial membrane, where it interacts with the NADH dehydrogenase (ubiquinone) 1 α subcomplex subunit 13 (also known as Grim19), a constituent of complex I of the respiratory chain. Together, Grim19 and IL-24 promote the accumulation of STAT3 in the mitochondrial compartment. We propose that IL-24–guided mitochondrial STAT3 constitutes a rheostat to blunt extensive STAT3 deflections in the nucleus, which might then contribute to a robust IL-10 response in Th17 cells and a restriction of immunopathology in experimental autoimmune encephalomyelitis.

IL-20 Cytokines Are Involved in Epithelial Lesions Associated with Virus-Induced COPD Exacerbation in Mice

(1) Background: viral infections are a frequent cause of chronic obstructive pulmonary disease (COPD) exacerbations, which are responsible for disease progression and mortality. Previous reports showed that IL-20 cytokines facilitate bacterial lung infection, but their production and their role in COPD and viral infection has not yet been investigated. (2) Methods: C57BL/6 WT and IL-20 Rb KO mice were chronically exposed to air or cigarette smoke (CS) to mimic COPD. Cytokine production, antiviral response, inflammation and tissue damages were analyzed after PVM infection. (3) Results: CS exposure was associated with an increase in viral burden and antiviral response. PVM infection in CS mice enhanced IFN-γ, inflammation and tissue damage compared to Air mice. PVM infection and CS exposure induced, in an additive manner, IL-20 cytokines expression and the deletion of IL-20 Rb subunit decreased the expression of interferon-stimulated genes and the production of IFN-λ2/3, without an impact on PVM replication. Epithelial cell damages and inflammation were also reduced in IL-20 Rb^-/- mice, and this was associated with reduced lung permeability and the maintenance of intercellular junctions. (4) Conclusions: PVM infection and CS exposure additively upregulates the IL-20 pathway, leading to the promotion of epithelial damages. Our data in our model of viral exacerbation of COPD identify IL-20 cytokine as a potential therapeutic target.

Interleukin-24 regulates mucosal remodeling in inflammatory bowel diseases

Background

Recently, increased interleukin (IL)-24 expression has been demonstrated in the colon biopsies of adult patients with inflammatory bowel disease (IBD). However, the role of IL-24 in the pathomechanism of IBD is still largely unknown.

Methods

Presence of IL-24 was determined in the samples of children with IBD and in the colon of dextran sodium sulfate (DSS) treated mice. Effect of inflammatory factors on IL24 expression was determined in peripheral blood (PBMCs) and lamina propria mononuclear cells (LPMCs). Also, the impact of IL-24 was investigated on HT-29 epithelial cells and CCD-18Co colon fibroblasts. Expression of tissue remodeling related genes was investigated in the colon of wild type (WT) mice locally treated with IL-24 and in the colon of DSS treated WT and Il20rb knock out (KO) mice.

Results

 Increased amount of IL-24 was demonstrated in the serum and colon samples of children with IBD and DSS treated mice compared to that of controls. IL-1β, LPS or H₂O₂ treatment increased the expression of IL24 in PBMCs and LPMCs. IL-24 treatment resulted in increased amount of TGF-β and PDGF-B in HT-29 cells and enhanced the expression of extracellular matrix (ECM)-related genes and the motility of CCD-18Co cells. Similarly, local IL-24 treatment increased the colonic Tgfb1 and Pdgfb expression of WT mice. Moreover, expression of pro-fibrotic Tgfb1 and Pdgfb were lower in the colon of DSS treated Il20rb KO compared to that of WT mice. The disease activity index of colitis was less severe in DSS treated Il20rb KO compared to WT mice.

Conclusion

Our study suggest that IL-24 may play a significant role in the mucosal remodeling of patients with IBD by promoting pro-fibrotic processes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02890-7.

Interleukin-19 Abrogates Experimental Autoimmune Encephalomyelitis by Attenuating Antigen-Presenting Cell Activation

Interleukin-19 (IL-19) acts as a negative-feedback regulator to limit proinflammatory response of macrophages and microglia in autocrine/paracrine manners in various inflammatory diseases. Multiple sclerosis (MS) is a major neuroinflammatory disease in the central nervous system (CNS), but it remains uncertain how IL-19 contributes to MS pathogenesis. Here, we demonstrate that IL-19 deficiency aggravates experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, by promoting IL-17-producing helper T cell (Th17 cell) infiltration into the CNS. In addition, IL-19-deficient splenic macrophages expressed elevated levels of major histocompatibility complex (MHC) class II, co-stimulatory molecules, and Th17 cell differentiation-associated cytokines such as IL-1β, IL-6, IL-23, TGF-β1, and TNF-α. These observations indicated that IL-19 plays a critical role in suppression of MS pathogenesis by inhibiting macrophage antigen presentation, Th17 cell expansion, and subsequent inflammatory responses. Furthermore, treatment with IL-19 significantly abrogated EAE. Our data suggest that IL-19 could provide significant therapeutic benefits in patients with MS.

Deficiency of interleukin-19 exacerbates lipopolysaccharide/D-galactosamine-induced acute liver failure

Interleukin (IL)-19 is a cytokine clustered in the IL-20 cytokine superfamily with both anti-inflammatory and pro-inflammatory aspects depending on the etiology of inflammatory disease. The function of IL-19 has been evaluated in cutaneous and inflammatory bowel diseases, but has not been studied in liver diseases. Here, we examined the effect of IL-19 on acute liver failure (ALF) using two mouse models of ALF: lipopolysaccharide and D-galactosamine (LPS/GalN)-induced model and concanavalin A (ConA)-induced model. In the LPS/GalN-induced ALF model, which is mainly caused by the innate immune response of liver macrophages, IL-19 knockout (KO) mice showed increased plasma level of liver deviation enzymes, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) compared with wild-type (WT) mice. In histopathology of liver sections, IL-19 KO mice exacerbated liver injury with marked hemorrhagic lesions and hepatocellular death in the liver compared with WT mice. In this model, mRNA expressions of pro-inflammatory chemokines, CCL2 and CCL5 were increased in liver tissue from IL-19 KO mice compared with WT mice. Moreover, the mRNA expressions of IL-19 and its receptor subunit were induced in liver tissue by LPS/GalN administration. However, there is no difference in liver injury between WT and IL-19KO in the ConA-induced ALF model induced by CD4+ T cell activation. These data suggest that IL-19 has a protective effect against inflammation-mediated liver injury, which is dependent on the etiology.

Resolution of inflammation in immune and nonimmune cells by interleukin-19

The inflammatory response is a complex, tightly regulated process activated by tissue wounding, foreign body invasion, and sterile inflammation. Over the decades, great progress has been made to advance our understanding of this process. One often overlooked aspect of inflammation is its sequel: resolution. We know that dysregulated resolution often results in numerous chronic degenerative diseases such as arthritis, cancer, and asthma. However, identification of components and mechanisms of resolving pathways lags behind those of proinflammatory processes, yet represents overlooked therapeutic opportunities. One approach is identification of endogenous, negative compensatory mechanisms, which are activated in response to inflammation for the purpose of resolution of that inflammatory stimuli. This review will focus on literature that describes expression and function of interleukin-19, a proposed anti-inflammatory cytokine, in numerous inflammatory diseases. The literature concerning IL-19 is complex, context-dependent, and often contradictory. The expression and function of IL-19 in the inflammatory response are in no way settled. We will attempt to clarify the role that this interesting and understudied cytokine plays in resolution of inflammation and discuss its mechanisms of action in different cell types. We will present a hypothesis that endogenous IL-19 expression in response to inflammatory stimuli is a cellular compensatory mechanism to dampen inflammation. We further present studies suggesting that while endogenously expressed IL-19 may be a response to inflammation, pharmacological levels may be necessary to effectively resolve the inflammatory cascade.

The Cytokine IL-17A Limits Th17 Pathogenicity via a Negative Feedback Loop Driven by Autocrine Induction of IL-24

Dysregulated Th17 cell responses underlie multiple inflammatory and autoimmune diseases, including autoimmune uveitis and its animal model, EAU. However, clinical trials targeting IL-17A in uveitis were not successful. Here, we report that Th17 cells were regulated by their own signature cytokine, IL-17A. Loss of IL-17A in autopathogenic Th17 cells did not reduce their pathogenicity and instead elevated their expression of the Th17 cytokines GM-CSF and IL-17F. Mechanistic in vitro studies revealed a Th17 cell-intrinsic autocrine loop triggered by binding of IL-17A to its receptor, leading to activation of the transcription factor NF-κB and induction of IL-24, which repressed the Th17 cytokine program. In vivo, IL-24 treatment ameliorated Th17-induced EAU, whereas silencing of IL-24 in Th17 cells enhanced disease. This regulatory pathway also operated in human Th17 cells. Thus, IL-17A limits pathogenicity of Th17 cells by inducing IL-24. These findings may explain the disappointing therapeutic effect of targeting IL-17A in uveitis.

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IL-17A deficiency does not reduce the pathogenicity of Th17 cells in uveitis

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IL-17A binds to its own receptor on Th17 cells, activating NF-κB

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NF-κB induces IL-24 production, repressing the Th17 cytokine program through SOCS1/3

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Silencing or depleting IL-24 in Th17 cells exacerbates neuroinflammation

Characterization of IL-19, -20, and -24 in acute and chronic kidney diseases reveals a pro-fibrotic role of IL-24

BACKGROUND

Recently, the role of IL-19, IL-20 and IL-24 has been reported in renal disorders. However, still little is known about their biological role.

METHODS

Localization of IL-20RB was determined in human biopsies and in the kidneys of mice that underwent unilateral ureteral obstruction (UUO). Renal Il19, Il20 and Il24 expression was determined in ischemia/reperfusion, lipopolysaccharide, streptozotocin, or UUO induced animal models of kidney diseases. The effects of H₂O₂, LPS, TGF-β1, PDGF-B and IL-1β on IL19, IL20 and IL24 expression was determined in peripheral blood mononuclear cells (PBMCs). The extents of extracellular matrix (ECM) and α-SMA, Tgfb1, Pdgfb, and Ctgf expression were determined in the kidneys of Il20rb knockout (KO) and wild type (WT) mice following UUO. The effect of IL-24 was also examined on HK-2 tubular epithelial cells and NRK49F renal fibroblasts.

RESULTS

IL-20RB was present in the renal biopsies of patients with lupus nephritis, IgA and diabetic nephropathy. Amount of IL-20RB increased in the kidneys of mice underwent UUO. The expression of Il19, Il20 and Il24 increased in the animal models of various kidney diseases. IL-1β, H₂O₂ and LPS induced the IL19, IL20 and IL24 expression of PBMCs. The extent of ECM, α-SMA, fibronectin, Tgfb1, Pdgfb, and Ctgf expression was lower in the kidney of Il20rb KO compared to WT mice following UUO. IL-24 treatment induced the apoptosis and TGF-β1, PDGF-B, CTGF expression of HK-2 cells.

CONCLUSIONS

Our data confirmed the significance of IL-19, IL-20 and IL-24 in the pathomechanism of renal diseases. Furthermore, we were the first to demonstrate the pro-fibrotic effect of IL-24.

[Recent progress in the pathophysiological role of interleukin-19]

Cytokine signal is essential for the biological function including development, maintenance of homeostasis and progression of disease. There are growing evidences that signaling via pro-inflammatory cytokines underlie a variety of immunological diseases such as psoriasis, atopic dermatitis, inflammatory bowel disease, and metabolic syndromes, in which cytokine signals are known as a potential therapeutic target of antibody drugs. In contrast, anti-inflammatory cytokines, which is represented by IL-10, largely contribute to suppression of inflammation and restoration of injured tissues. IL-19 is a member of IL-10 cytokine family, which comprises IL-20 cytokine subfamily with IL-20, IL-22, IL-24, and IL-26. IL-19 is produced by myeloid and epithelial cells with stimulation of bacterial components and cytokines. Although IL-19 has been originally recognized as a potential Th2-related cytokine, in recent researches, it has been reported that this cytokine upregulates Th17 response to reflect and promote progression of Th17-related disease including psoriasis. On the other hand, IL-19 has anti-inflammatory effects on inflammatory diseases such as infectious skin disease, inflammatory bowel disease, and cardiovascular disease. Therefore, IL-19 may exert pleiotropic effects dependent on the pathological mechanism of inflammatory diseases. In this review, we summarize recent studies about IL-19 and introduce the pathophysiological and therapeutic role of IL-19 in inflammatory diseases.

IL-24 contributes to skin inflammation in Para-Phenylenediamine-induced contact hypersensitivity

Para-Phenylenediamine (PPD) is an aromatic amine used in hair dyes and in temporary black henna tattoos, which is a frequent cause of allergic contact dermatitis (ACD). ACD is a skin inflammatory reaction characterized by modifications such as spongiosis, exocytosis and acanthosis. The aim of this study is to characterize the expression and the role of IL-20-related cytokines, including IL-19, IL-20, IL-22 and IL-24, in ACD. The expression of IL19, IL20, IL22 and IL24 is increased in affected skin from PPD allergic patients compared with uninvolved skin. In addition, the expression of these cytokines positively correlates with clinical symptoms. To assess their role in ACD, we set up a mouse model of PPD-induced allergic contact dermatitis and we showed that, in contrast to Il22-deficient mice, Il22ra1-, Il20rb- and Il24-deficient mice are partially protected against development of PPD-induced contact hypersensitivity. These mice have decreased ear thickening and less acanthosis compared with WT mice after PPD treatment. In addition, the absence of IL-22R, IL-20R2 or IL-24 affects the recruitment of neutrophils into the skin but not the total IgE production. Taken together, these results demonstrate the implication of IL-24 via the IL-20R type II receptor in the inflammatory process of ACD.

The IL-20 Cytokine Family in Rheumatoid Arthritis and Spondyloarthritis

This review describes the IL-20 family of cytokines in rheumatoid arthritis (RA) and spondyloartrhitits (SpA) including psoriatic arthritis. The IL-20 receptor (R) cytokines IL-19, IL-20, and IL-24 are produced in both the peripheral blood and the synovial joint and are induced by Toll-like receptor ligands and autoantibody-associated immune complexes in monocytes. IL-19 seems to have anti-inflammatory functions in arthritis. In contrast, IL-20 and IL-24 increase the production of proinflammatory molecules such as monocyte chemoattractant protein 1 and are associated with bone degradation and radiographic progression. IL-22 is also associated with progression of bone erosions. This suggests that the IL-22RA1 subunit shared by IL-20, IL-22, and IL-24 is important for bone homeostasis. In line with this, the IL-22RA1 has been found on preosteoclasts in early RA. IL-26 is produced in high amounts by myofibroblasts and IL-26 stimulation of monocytes is an important inducer of Th17 cells in RA. This indicates a role for IL-26 as an important factor in the interactions between resident synovial cells and infiltrating leukocytes. Clinical trials that investigate inhibitors of IL-20 (fletikumab) and IL-22 (fezakinumab) in psoriasis and RA have been terminated. Instead, it seems that the strategy for modulating the IL-20 cytokine family should take the overlap in cellular sources and effector mechanisms into account. The redundancy encourages inhibition of more than one cytokine or one of the shared receptors. All IL-20 family members utilize the Janus kinase signaling pathway and are therefore potentially inhibited by drugs targeting these enzymes. Effects and adverse effects in ongoing clinical trials with inhibitors of IL-22 and the IL-22RA1 subunit and recombinant IL-22 fusion proteins will possibly provide important information about the IL-20 subfamily of cytokines in the future.

IL-20 receptor cytokines in autoimmune diseases

IL-19, IL-20, and IL-24 are the members of IL-10 family. They are also known as IL-20 receptor (IL-20R) cytokines as they all signal through the IL-20RA/IL-20RB receptor complex; IL-20 and IL-24 (but not IL-19) also signal through the IL-20RB/IL22RA1 receptor complex. Despite their protein structure homology and shared use of receptor complexes, they display distinct biological functions in immune regulation, tissue homeostasis, host defense, and oncogenesis. IL-20R cytokines can be expressed by both immune cells and epithelial cells, and are important for their interaction. In general, these cytokines are considered to be associated with pathogenesis of chronic inflammation and autoimmune diseases, including psoriasis, rheumatoid arthritis, and inflammatory bowel disease. However, a number of studies also highlighted their suppressive functions in regulating both innate and adaptive T cell responses and other immune cells, suggesting that the role of IL-20R cytokines in autoimmunity may be complex. In this review, we will discuss the immunobiological functions of IL-20R cytokines and how they are involved in regulating autoimmune diseases.

The Stimulation of Macrophages with TLR Ligands Supports Increased IL-19 Expression in Inflammatory Bowel Disease Patients and in Colitis Models

IL-19, a member of the IL-10 cytokine family that signals through the IL-20 receptor type I (IL-20Rα:IL-20Rβ), is a cytokine whose function is not completely known. In this article, we show that the expression of IL19 in biopsies of patients with active ulcerative colitis was increased compared with patients with quiescent ulcerative colitis and that colitis was attenuated in IL-19-deficient mice. The disruption of the epithelial barrier with dextran sodium sulfate leads to increased IL-19 expression. Attenuated colitis in IL-19-deficient animals was associated with reduced numbers of IL-6-producing macrophages in the inflamed colonic lamina propria. Microbial-driven expression of IL-19 by intestinal macrophages may contribute to the pathogenesis of inflammatory bowel disease.

Interleukin-19 is cardioprotective in dominant negative cyclic adenosine monophosphate response-element binding protein-mediated heart failure in a sex-specific manner

AIM

To investigate the role of interleukin-19 (IL-19) in a murine model of female-dominant heart failure (HF).

METHODS

Expression of one copy of a phosphorylation-deficient cyclic adenosine monophosphate response-element binding protein (dnCREB) causes HF, with accelerated morbidity and mortality in female mice compared to males. We assessed expression of IL-19, its receptor isoforms IL-20R α/β, and downstream IL-19 signaling in this model of female-dominant HF. To test the hypothesis that IL-19 is cardioprotective in dnCREB-mediated HF, we generated a novel double transgenic (DTG) mouse of dnCREB and IL-19 knockout and assessed cardiac morbidity by echocardiography and survival of male and female mice.

RESULTS

IL-19 is expressed in the murine heart with decreased expression in dnCREB female compared to male mice. Further, the relative expression of the two IL-19 receptor isoforms manifests differently in the heart by sex and by disease. Male DTG mice had accelerated mortality and cardiac morbidity compared to dnCREB males, while female DTG mice showed no additional detriment, supporting the hypothesis that IL-19 is cardioprotective in this model.

CONCLUSION

Together, these data suggest IL-19 is an important cytokine mediating sex-specific cardiac (dys) function. Ongoing investigations will elucidate the mechanism(s) of sex-specific IL-19 mediated cardiac remodeling.

Genome-wide association analysis of chronic lymphocytic leukaemia, Hodgkin lymphoma and multiple myeloma identifies pleiotropic risk loci

B-cell malignancies (BCM) originate from the same cell of origin, but at different maturation stages and have distinct clinical phenotypes. Although genetic risk variants for individual BCMs have been identified, an agnostic, genome-wide search for shared genetic susceptibility has not been performed. We explored genome-wide association studies of chronic lymphocytic leukaemia (CLL, N = 1,842), Hodgkin lymphoma (HL, N = 1,465) and multiple myeloma (MM, N = 3,790). We identified a novel pleiotropic risk locus at 3q22.2 (NCK1, rs11715604, P = 1.60 × 10-9) with opposing effects between CLL (P = 1.97 × 10-8) and HL (P = 3.31 × 10-3). Eight established non-HLA risk loci showed pleiotropic associations. Within the HLA region, Ser37 + Phe37 in HLA-DRB1 (P = 1.84 × 10-12) was associated with increased CLL and HL risk (P = 4.68 × 10-12), and reduced MM risk (P = 1.12 × 10-2), and Gly70 in HLA-DQB1 (P = 3.15 × 10-10) showed opposing effects between CLL (P = 3.52 × 10-3) and HL (P = 3.41 × 10-9). By integrating eQTL, Hi-C and ChIP-seq data, we show that the pleiotropic risk loci are enriched for B-cell regulatory elements, as well as an over-representation of binding of key B-cell transcription factors. These data identify shared biological pathways influencing the development of CLL, HL and MM. The identification of these risk loci furthers our understanding of the aetiological basis of BCMs.

Mechanism of Action and Applications of Interleukin 24 in Immunotherapy

Interleukin 24 (IL-24) is an important pleiotropic immunoregulatory cytokine, whose gene is located in human chromosome 1q32-33. IL-24's signaling pathways have diverse biological functions related to cell differentiation, proliferation, development, apoptosis, and inflammation, placing it at the center of an active area of research. IL-24 is well known for its apoptotic effect in cancer cells while having no such effect on normal cells. IL-24 can also be secreted by both immune and non-immune cells. Downstream effects of IL-24, after binding to the IL-20 receptor, can occur dependently or independently of the JAK/STAT signal transduction pathway, which is classically involved in cytokine-mediated activities. After exogenous addition of IL-24, apoptosis is induced in tumor cells independently of the JAK/STAT pathway. We have shown that IL-24 binds to Sigma 1 Receptor and this event induces endoplasmic reticulum stress, calcium mobilization, reactive oxygen species generation, p38MAPK activity, and ceramide production. Here we review IL-24's role in autoimmunity, infectious disease response, wound repair, and vascular disease. Detailed understanding of the pleiotropic roles of IL-24 signaling can assist in the selection of more accurate therapeutic approaches, as well as targeting of appropriate cell types in treatment strategy development, and ultimately achieve desired therapeutic effects.

Alternative splicing directs two IL-20R2 isoforms and is responsible for the incomplete gene knockout via the exon I ablation

Two heterodimeric receptors consisting of interleukin (IL)-20R2 are shared by three of the IL-20 family of cytokines, IL-19, IL-20 and IL-24. Along with IL-22, these cytokines are downstream effectors of IL-23 and have been implicated in keratinocyte functions and the pathogenesis of psoriasis. Surprisingly, whereas knocking out either the IL-23 or IL-22 gene abolished imiquimod-induced psoriatic phenotypes in mice, similar attempt for IL-20R2 had little effect. Here, we report that the apparent disparity may result from a new IL-20R2 isoform encoded by an alternatively spliced transcript which survived the previous attempt for IL-20R2 gene knockout via the exon I deletion.

Interleukin-19 induces angiogenesis in the absence of hypoxia by direct and indirect immune mechanisms

Neovascularization and inflammation are independent biological processes but are linked in response to injury. The role of inflammation-dampening cytokines in the regulation of angiogenesis remains to be clarified. The purpose of this work was to test the hypothesis that IL-19 can induce angiogenesis in the absence of tissue hypoxia and to identify potential mechanisms. Using the aortic ring model of angiogenesis, we found significantly reduced sprouting capacity in aortic rings from IL-19(-/-) compared with wild-type mice. Using an in vivo assay, we found that IL-19(-/-) mice respond to vascular endothelial growth factor (VEGF) significantly less than wild-type mice and demonstrate decreased capillary formation in Matrigel plugs. IL-19 signals through the IL-20 receptor complex, and IL-19 induces IL-20 receptor subunit expression in aortic rings and cultured human vascular smooth muscle cells, but not endothelial cells, in a peroxisome proliferator-activated receptor-γ-dependent mechanism. IL-19 activates STAT3, and IL-19 angiogenic activity in aortic rings is STAT3-dependent. Using a quantitative RT-PCR screening assay, we determined that IL-19 has direct proangiogenic effects on aortic rings by inducing angiogenic gene expression. M2 macrophages participate in angiogenesis, and IL-19 has indirect angiogenic effects, as IL-19-stimulated bone marrow-derived macrophages secrete proangiogenic factors that induce greater sprouting of aortic rings than unstimulated controls. Using a quantitative RT-PCR screen, we determined that IL-19 induces expression of angiogenic cytokines in bone marrow-derived macrophages. Together, these data suggest that IL-19 can promote angiogenesis in the absence of hypoxia by at least two distinct mechanisms: 1) direct effects on vascular cells and 2) indirect effects by stimulation of macrophages.

Microarray Expression Analysis for the Paradoxical Roles of Acanthopanax senticosus Harms in Treating α-Synucleinopathies

α-Synuclein is a key player in the pathogenesis of neurodegenerative disorders with Lewy bodies. Our previous studies have also showed that Acanthopanax senticosus harms (AS) could significantly suppress α-synuclein overexpression and toxicity. Identifying the RNAs related to α-synucleinopathies may facilitate understanding the pathogenesis of the diseases and the safe application of AS in the clinic. Microarray expression profiling of long non-coding RNAs (lncRNAs) and mRNAs was undertaken in control non-transgenic and human α-synuclein transgenic mice. The effects of AS on central nervous system (CNS) in pathology and physiology were investigated based on the lncRNA/mRNA targets analysis. In total, 341 lncRNAs and 279 mRNAs were differentially expressed by α-synuclein stimulus, among which 29 lncRNAs and 25 mRNAs were involved in the anti-α-synucleinopathies mechanism of AS. However, the levels of 19/29 lncRNAs and 12/25 mRNAs in AS group were similar to those in α-synuclein group, which may cause potential neurotoxicity analogous to α-synuclein. This study demonstrated that some of lncRNAs/mRNAs were involved in α-synuclein related pathophysiology, and AS produced the bidirectional effects on CNS under pathological and physiological conditions.

Interleukin 19 reduces inflammation in chemically induced experimental colitis

Inflammatory bowel disease results from chronic dysregulation of the mucosal immune system and aberrant activation of both the innate and adaptive immune responses. Interleukin (IL)-19, a member of the IL-10 family, functions as an anti-inflammatory cytokine. Here, we investigated the contribution of IL-19 to intestinal inflammation in a model of T cell-mediated colitis in mice. Inflammatory responses in IL-19-deficient mice were assessed using the 2,4,6-trinitrobenzene sulfonic acid (TNBS) model of acute colitis. IL-19 deficiency aggravated TNBS-induced colitis and compromised intestinal recovery in mice. Additionally, the exacerbation of TNBS-induced colonic inflammation following genetic ablation of IL-19 was accompanied by increased production of interferon-gamma, IL-12 (p40), IL-17, IL-22, and IL-33, and decreased production of IL-4. Moreover, the exacerbation of colitis following IL-19 knockout was also accompanied by increased production of CXCL1, G-CSF and CCL5. Using this model of induced colitis, our results revealed the immunopathological relevance of IL-19 as an anti-inflammatory cytokine in intestinal inflammation in mice.

Modulation of CD4+ and CD8+ T-Cell Function by Interleukin 19 and Interleukin 24 During Filarial Infections

Interleukin 19 (IL-19) and interleukin 24 (IL-24) are cytokines that are highly expressed in filarial infections. To study the role of IL-19 and IL-24 in regulating T-cell responses, we examined the frequency of T-helper type 1 (Th1)/Tc1, Th2/Tc2, Th9/Tc9, Th17/Tc17, Th22/Tc22, and Tr1 cells in 26 filariae-infected individuals stimulated with filarial antigen following IL-19 or IL-24 neutralization. IL-19 or IL-24 neutralization resulted in significantly enhanced frequencies of Th1/Tc1 and/or Th17/Tc17 cells and significantly reduced frequencies of Th2/Tc2, Tr1, and/or Th9/Tc9 cells. Thus, we demonstrate that IL-19 and IL-24 are associated with the modulation of T-cell responses in filarial infections.

Astrocytes produce IL-19 in response to bacterial challenge and are sensitive to the immunosuppressive effects of this IL-10 family member

There is growing appreciation that resident glial cells can initiate and/or regulate inflammation following trauma or infection in the central nervous system (CNS). We have previously demonstrated the ability of microglia and astrocytes to respond to bacterial pathogens or their products by rapid production of inflammatory mediators, followed by the production of the immunosuppressive cytokine interleukin (IL)−10. IL-19, another member of the IL-10 family of cytokines, has been studied in the context of a number of inflammatory conditions in the periphery and is known to modulate immune cell activity. In the present study, we demonstrate the constitutive and/or inducible expression of IL-19 and its cognate receptor subunits, IL-19Rα and IL-19Rβ (also known as IL-20R1 and IL-20R2, and IL-20RA and IL-20RB), in mouse brain tissue, and by primary murine and human astrocytes. We also provide evidence for the presence of a novel truncated IL-19Rα transcript variant in mouse brain tissue, but not glial cells, that shows reduced expression following bacterial infection. Importantly, IL-19R functionality in glia is indicated by the ability of IL-19 to regulate signaling component expression in these cells. Furthermore, while IL-19 itself had no effect on glial cytokine production, IL-19 treatment of bacterially infected or Toll-like receptor ligand stimulated astrocytes significantly attenuated pro-inflammatory cytokine production. The bacterially induced production of IL-19 by these resident CNS cells, the constitutive expression of its cognate receptor subunits, and the immunomodulatory effects of this cytokine, suggest a novel mechanism by which astrocytes can regulate CNS inflammation.

Enhanced sphingosine-1-phosphate receptor 2 expression underlies female CNS autoimmunity susceptibility

Multiple sclerosis (MS) is an inflammatory disease of the CNS that is characterized by BBB dysfunction and has a much higher incidence in females. Compared with other strains of mice, EAE in the SJL mouse strain models multiple features of MS, including an enhanced sensitivity of female mice to disease; however, the molecular mechanisms that underlie the sex- and strain-dependent differences in disease susceptibility have not been described. We identified sphingosine-1-phosphate receptor 2 (S1PR2) as a sex- and strain-specific, disease-modifying molecule that regulates BBB permeability by destabilizing adherens junctions. S1PR2 expression was increased in disease-susceptible regions of the CNS of both female SJL EAE mice and female patients with MS compared with their male counterparts. Pharmacological blockade or lack of S1PR2 signaling decreased EAE disease severity as the result of enhanced endothelial barrier function. Enhanced S1PR2 signaling in an in vitro BBB model altered adherens junction formation via activation of Rho/ROCK, CDC42, and caveolin endocytosis-dependent pathways, resulting in loss of apicobasal polarity and relocation of abluminal CXCL12 to vessel lumina. Furthermore, S1PR2-dependent BBB disruption and CXCL12 relocation were observed in vivo. These results identify a link between S1PR2 signaling and BBB polarity and implicate S1PR2 in sex-specific patterns of disease during CNS autoimmunity.

The Therapeutic Potential of Anti-Interleukin-20 Monoclonal Antibody

Interleukin (IL)-20, a member of the IL-10 family of cytokines, was discovered in 2001. IL-20 acts on multiple cell types by activating on a heterodimer receptor complex of either IL-20R1–IL-20R2 or IL-22R1–IL-20R2. Recent evidence indicates that IL-20's interaction with its receptors might have proinflammatory effects on chronic inflammatory diseases, particularly rheumatoid arthritis (RA), osteoporosis, and breast cancer. Updated information about IL-20, such as its identification, expression, receptors, signaling, and biological activities, is illustrated in this review based on our research and the data available in the literature. IL-20 is a pleiotropic cytokine, which promotes inflammation, angiogenesis, and chemotaxis. IL-20 also regulates osteoclast differentiation by altering the receptor activator of NF-κB (RANK) and RANK ligand (RANKL) axis. Inflammation, angiogenesis, and osteoclastogenesis are critical for the pathogenesis of RA, osteoporosis, and breast cancer-induced osteolysis. Based on the in vitro and in vivo data and clinical samples, we demonstrated that IL-20 plays pivotal roles in these three diseases. In experimental models, anti-IL-20 monoclonal antibody ameliorates arthritis severity, protects against ovariectomized-induced bone loss, and inhibits breast tumor-induced osteolysis. This review presents the clinical implications of IL-20, which will lead to a better understanding of the biological functions of IL-20 in these diseases and provide new therapeutic options in the future.

Interleukin-19 impairment in active Crohn's disease patients

The exact function of interleukin-19 (IL-19) on immune response is poorly understood. In mice, IL-19 up-regulates TNFα and IL-6 expression and its deficiency increases susceptibility to DSS-induced colitis. In humans, IL-19 favors a Th2 response and is elevated in several diseases. We here investigate the expression and effects of IL-19 on cells from active Crohn’s disease (CD) patient. Twenty-three active CD patients and 20 healthy controls (HC) were included. mRNA and protein IL-19 levels were analyzed in monocytes. IL-19 effects were determined in vitro on the T cell phenotype and in the production of cytokines by immune cells. We observed that unstimulated and TLR-activated monocytes expressed significantly lower IL-19 mRNA in active CD patients than in HC (logFC = −1.97 unstimulated; −1.88 with Pam3CSK4; and −1.91 with FSL-1; p<0.001). These results were confirmed at protein level. Exogenous IL-19 had an anti-inflammatory effect on HC but not on CD patients. IL-19 decreased TNFα production in PBMC (850.7±75.29 pg/ml vs 2626.0±350 pg/ml; p<0.01) and increased CTLA4 expression (22.04±1.55% vs 13.98±2.05%; p<0.05) and IL-4 production (32.5±8.9 pg/ml vs 13.5±2.9 pg/ml; p<0.05) in T cells from HC. IL-10 regulated IL-19 production in both active CD patients and HC. We observed that three of the miRNAs that can modulate IL-19 mRNA expression, were up-regulated in monocytes from active CD patients. These results suggested that IL-19 had an anti-inflammatory role in this study. Defects in IL-19 expression and the lack of response to this cytokine could contribute to inflammatory mechanisms in active CD patients.

Interleukin (IL)-19 promoted skin wound healing by increasing fibroblast keratinocyte growth factor expression

BACKGROUND

Interleukin (IL)-19, a member of the IL-10 cytokine family, is involved in keratinocyte proliferation in psoriasis.

OBJECTIVES

We investigated the role of IL-19 in the wound-healing process in vivo and in vitro.

METHODS

Two full-thickness circular wounds (4mm in diameter) were punched into the skin of BALB/C mice. IL-19 and keratinocyte growth factor (KGF) mRNA in wounded skin were determined using real-time PCR. The wounds were treated with PBS, vehicle, IL-19 (400ng/mL), or IL-20 (400ng/mL) (n=6 in each group) twice daily and the percentage of wound healing was measured daily for 7days. In vitro, human skin fibroblast CCD966-SK cells and keratinocyte HaCaT cells were treated with IL-19 or KGF. Cell proliferation and migration were determined using bromodeoxyuridine (BrdU) and transwell assays, respectively. The expression of IL-19 and KGF mRNA was also analyzed.

RESULTS

In wounded mouse skin, IL-19 mRNA was upregulated at 12h, and KGF at 24h after the injury. Both increases in gene expression declined 72h after the skin had been wounded. The percentage of wound healing in IL-19-treated mice was higher than in control mice. In vitro, IL-19 upregulated KGF expression in the CCD966-SK cells; IL-19 was upregulated in KGF-treated HaCaT cells. KGF but not IL-19 promoted HaCaT cell proliferation. However, IL-19 significantly increased the migration of HaCaT cells. HaCaT cells treated with the cultured supernatants of IL-19-stimulated CCD966-SK cells showed significantly more proliferation than in controls.

CONCLUSIONS

IL-19 is important for cutaneous wound healing because it upregulates KGF expression.

Structural basis for receptor sharing and activation by interleukin-20 receptor-2 (IL-20R2) binding cytokines

Interleukin 20 (IL-20) is a pleotropic IL-10 family cytokine that protects epithelial surfaces from pathogens. However, dysregulated IL-20 signaling is implicated in several human pathologies including psoriasis, rheumatoid arthritis, atherosclerosis, and osteoporosis. IL-20, and related cytokines IL-19 and IL-24, designated IL-20 subfamily cytokines (IL-20SFCs), induce cellular responses through an IL-20R1/IL-20R2 (type I) receptor heterodimer, whereas IL-20 and IL-24 also signal through the IL-22R1/IL-20R2 (type II) receptor complex. The crystal structure of the IL-20/IL-20R1/IL-20R2 complex reveals how type I and II complexes discriminate cognate from noncognate ligands. The structure also defines how the receptor-cytokine interfaces are affinity tuned to allow distinct signaling through a receptor complex shared by three different ligands. Our results provide unique insights into the complexity of IL-20SFC signaling that may be critical in the design of mechanistic-based inhibitors of IL-20SFC-mediated inflammatory disease.

Anti-inflammatory effects of interleukin-19 in vascular disease

Despite aggressive dietary modification, lipid-lowering medications, and other interventional medical therapy, vascular disease continues to be a leading cause of mortality in the western world. It is a significant medical and socioeconomic problem contributing to mortality of multiple diseases including myocardial infarction, stroke, renal failure, and peripheral vascular disease. Morbidity and mortality of vascular disease are expected to worsen with the increasing number of patients with comorbid conditions such as obesity, metabolic syndrome, and diabetes mellitus type 2. Vascular diseases such as atherosclerosis, restenosis, and allograft vasculopathy are recognized to be driven by inflammation, and as such, cytokines which mediate inflammation not only represent important targets of rational therapy, but also can be considered as possible therapeutic modalities themselves. In this paper, we will examine the role of inflammatory cytokines and lymphocyte T(h)1/T(h)2 polarity in vascular inflammation, with a focus on atherosclerotic vascular disease. We will then introduce a recently described T(h)2 interleukin, interleukin-19 (IL-19), as a previously unrecognized mediator of vascular inflammatory disorders. We will review our current understanding of this interleukin in health and disease and present the possibility that IL-19 could represent a potential therapeutic to combat vascular inflammatory disease.

Molecular Mechanisms Governing IL-24 Gene Expression

Interleukin-24 (IL-24) belongs to the IL-10 family of cytokines and is well known for its tumor suppressor activity. This cytokine is released by both immune and nonimmune cells and acts on non-hematopoietic tissues such as skin, lung and reproductive tissues. Apart from its ubiquitous tumor suppressor function, IL-24 is also known to be involved in the immunopathology of autoimmune diseases like psoriasis and rheumatoid arthritis. Although the cellular sources and functions of IL-24 are being increasingly investigated, the molecular mechanisms of IL-24 gene expression at the levels of signal transduction, epigenetics and transcription factor binding are still unclear. Understanding the specific molecular events that regulate the production of IL-24 will help to answer the remaining questions that are important for the design of new strategies of immune intervention involving IL-24. Herein, we briefly review the signaling pathways and transcription factors that facilitate, induce, or repress production of this cytokine along with the cellular sources and functions of IL-24.

Interleukin-19 downregulates interleukin-4-induced eotaxin production in human nasal fibroblasts

BACKGROUND

Interleukin-19 (IL-19), a member of the IL-10 family, is characterized as the cytokine suppressing the release and function of several proinflammatory cytokines. For regulation of local reaction in allergic rhinitis (AR), IL-19 might play an especially important role.

METHODS

We examined effects of IL-19 on IL-4-induced eotaxin production by human nasal fibroblasts. Early receptor-mediated events (expression of the suppressors of cytokine signaling (SOCS) and phosphorylation of signal transducer and activator of transcription 6 [STAT6]) by IL-19 was examined. Knockdown methods by RNAi were administered to investigate the involvement of those signal transductions.

RESULTS

Pretreatment with IL-19 downregulates IL-4-induced eotaxin production, but not interferon-γ(IFN-γ)-induced RANTES. Pretreatment with IL-19 suppressed the IL-4-induced STAT6 phosphorylation. The IL-19 induced SOCS-1, but not SOCS-3 or SOCS-5. The SOCS-1 knockdown by RNAi diminished pretreatment with IL-19-induced down-regulation of eotaxin production.

CONCLUSIONS

These results suggest that IL-19 down-regulates IL-4-induced eotaxin production via SOCS-1 in human nasal fibroblasts. In non-hematopoietic cells in AR, IL-19 might be an immunosuppressive factor.

Induced interleukin-19 contributes to cell-mediated immunosuppression in patients undergoing coronary artery bypass grafting with cardiopulmonary bypass

BACKGROUND

Coronary artery bypass graft (CABG) surgery with cardiopulmonary bypass (CPB) promotes immunosuppression, which predisposes patients to infectious complications. We investigated the role of interleukin (IL)-19 in the functions of CD4+ T cells in patients undergoing CABG with CPB.

METHODS

Blood samples were withdrawn from 42 patients undergoing elective CABG with CPB. Serum levels of IL-19 were analyzed by enzyme-linked immunosorbent assay (ELISA). The CD4+/CD25+ T-cell population was determined with flow cytometry. Isolated CD4+ T cells were cultured and assayed for proliferation and cytokine production under phorbol myristate acetate/ionomycin stimulation. Cytokine production and Foxp3 mRNA expression in CD4+ T cells from healthy volunteers with or without IL-19 treatment were determined with ELISA and real-time polymerase chain reaction, respectively.

RESULTS

Proliferation percentages were 162%, 48%, 34%, and 39%, and interferon (IFN)-γ production was 1.22 ng/mL, 0.56 ng/mL, 0.33 ng/mL, and 0.35 ng/mL in the CD4+ T cells of patients before CPB and at 24 hours, 48 hours, and 96 hours, respectively, after CPB. Serum levels of IL-19 were higher but negatively correlated with CD4+ T-cell proliferation and IFN-γ production. The populations of CD4+/CD25+ T cells and expression of Foxp3 mRNA in T cells were higher and were positively correlated with IL-19 levels after CPB. Treatment with IL-19 reduced T-cell proliferation and IFN-γ production, increased Foxp3 mRNA expression, and induced the regulatory activity of CD4+ T cells.

CONCLUSIONS

Interleukin-19 reduces T-cell responses and promotes the regulatory activity of CD4+ T cells. Induced IL-19 in patients undergoing CABG with CPB contributes to cell-mediated immunosuppression.

Interleukin-19: a constituent of the regulome that controls antigen presenting cells in the lungs and airway responses to microbial products

BACKGROUND

Interleukin (IL)-19 has been reported to enhance chronic inflammatory diseases such as asthma but the in vivo mechanism is incompletely understood. Because IL-19 is produced by and regulates cells of the monocyte lineage, our studies focused on in vivo responses of CD11c positive (CD11c+) alveolar macrophages and lung dendritic cells.

METHODOLOGY/PRINCIPAL FINDINGS

IL-19-deficient (IL-19-/-) mice were studied at baseline (naïve) and following intranasal challenge with microbial products, or recombinant cytokines. Naïve IL-19-/- mixed background mice had a decreased percentage of CD11c+ cells in the bronchoalveolar-lavage (BAL) due to the deficiency in IL-19 and a trait inherited from the 129-mouse strain. BAL CD11c+ cells from fully backcrossed IL-19-/- BALB/c or C57BL/6 mice expressed significantly less Major Histocompatibility Complex class II (MHCII) in response to intranasal administration of lipopolysaccharide, Aspergillus antigen, or IL-13, a pro-allergic cytokine. Neurogenic-locus-notch-homolog-protein-2 (Notch2) expression by lung monocytes, the precursors of BAL CD11c+ cells, was dysregulated: extracellular Notch2 was significantly decreased, transmembrane/intracellular Notch2 was significantly increased in IL-19-/- mice relative to wild type. Instillation of recombinant IL-19 increased extracellular Notch2 expression and dendritic cells cultured from bone marrow cells in the presence of IL-19 showed upregulated extracellular Notch2. The CD205 positive subset among the CD11c+ cells was 3-5-fold decreased in the airways and lungs of naïve IL-19-/- mice relative to wild type. Airway inflammation and histological changes in the lungs were ameliorated in IL-19-/- mice challenged with Aspergillus antigen that induces T lymphocyte-dependent allergic inflammation but not in IL-19-/- mice challenged with lipopolysaccharide or IL-13.

CONCLUSIONS/SIGNIFICANCE

Because MHCII is the molecular platform that displays peptides to T lymphocytes and Notch2 determines cell fate decisions, our studies suggest that endogenous IL-19 is a constituent of the regulome that controls both processes in vivo.

Interleukin-19: multiple roles in immune regulation and disease

First reported in 1999, IL-19 remains a mystery in many ways. Despite appearing in many genome scans and candidate gene studies, and having been searched for specifically as part of the IL-10 family, its function is still to be defined. Nonetheless, a pattern of Th2 promotion is coalescing from this nebulous body of work, supported by increasing evidence for a role in asthma. Similarly, a clear but less intuitive role as a subtle immunomodulator is emerging in psoriasis and chronic inflammatory disorders in general. Indeed, several human diseases and their animal models have highlighted a role for IL-19. Key questions remain, relating to the nature of its receptor, its function (if any) on leukocytes and how its effects are distinguished by the cell from those of IL-20 and IL-24. In this review, I shall attempt to bring together a summary of the known work - disparate as it may be - as well as presenting a picture of these two important clinical disorders and the potential involvement of this somewhat enigmatic cytokine.

IL-20: biological functions mediated through two types of receptor complexes

IL-20 was discovered 10 years ago as a new member of the IL-10 family of cytokines. IL-20 shares the highest amino-acid sequence identity with IL-10, IL-24 and IL-19. IL-20 is secreted by immune cells and activated epithelial cells like keratinocytes. A high expression of the corresponding IL-20 receptor chains is detected on epithelial cells. In terms of function, IL-20 might therefore mediate a crosstalk between epithelial cells and tissue-infiltrating immune cells under inflammatory conditions. Transgenic and knockout mouse models for some cytokines and receptors of the IL-10-type cytokines have provided new insights into the biology of this family. This review will focus on the biological functions of IL-20 and its receptors within the IL-10 cytokine network.

IL-10 family of cytokines

In 2001, six immune mediators (IL-10, IL-19, IL-20, IL-22, IL-24, and IL-26) were grouped into the so-called IL-10 family of cytokines based on their similarities with respect to the structure and location of their encoding genes, their primary and secondary protein structures, and the receptor complexes used. Surprisingly, despite all these similarities, IL-10 family members possess different biological functions. The currently known facts regarding the biological effects of these six immune mediators give the impression that at least IL-10, IL-20, and IL-22 play an important role in the pathogenesis of some chronic inflammatory diseases. This review provides an overview of the most important and common aspects of the IL-10 family members.

Il-19 reduces VSMC activation by regulation of mRNA regulatory factor HuR and reduction of mRNA stability

While much is known about the deleterious effects of pro-inflammatory cytokines on development of vascular disease, little is reported on the direct effects of anti-inflammatory cytokines on the vascular smooth muscle cell (VSMC) response to injury. Interleukin-19 (IL-19) is a recently described Th2, anti-inflammatory interleukin. We have previously reported that IL-19 is absent in normal VSMC, but induced in VSMC by inflammatory cytokines and in arteries by injury. IL-19 is anti-proliferative for VSMC. The purpose of this study is to determine the molecular mechanism of these effects. In cultured, primary human VSMC, IL-19 reduces abundance of proliferative and inflammatory gene proteins and mRNA, including Cyclin D1, IL-1beta, IL-8, and COX2. IL-19 does not inhibit NF-kappaB, but does transiently reduce cytoplasmic abundance of the mRNA stability factor HuR. The mRNA stabilizing function of HuR is linked to its phosphorylation and cytoplasmic translocation. IL-19 reduces serine phosphorylation of HuR, and activation of PKCalpha, a known regulator of HuR translocation. Actinomycin D transcription blockade demonstrates that IL-19 treatment significantly reduces stability of proliferative and inflammatory mRNAs. Knock down of HuR with siRNA also reduces stability of these inflammatory mRNA transcripts. These data indicate that IL-19 has direct effects on VSMC mRNA stability. One potential mechanism whereby IL-19 reduces the VSMC response to injury is by regulation of HuR abundance and cytoplasmic translocation, with a subsequent decrease in mRNA half-life of proliferative and inflammatory mRNA transcripts.

IL-24 transgenic mice: in vivo evidence of overlapping functions for IL-20, IL-22, and IL-24 in the epidermis

IL-20 and IL-24 share two different heterodimeric receptors consisting of either IL-20R1 or IL-22R1 and a common IL-20R2 subunit, whereas IL-22 signals through IL-22R1/IL-10R2. However, until now, only IL-20 and IL-22 have been proven to play important roles in vivo in the epidermis where all four receptor subunits are expressed. In this study, we show that IL-24 transgenic mice manifest many similar phenotypes to that of IL-20 and IL-22, including neonatal lethality, epidermal hyperplasia, and abnormality in keratinocyte differentiation. These results support a largely redundant role in epidermal functions for IL-20, IL-22, and IL-24, which seem to be IL-22R1 dependent. Moreover, we show that IL-24 transgenic mice exhibit infiltrating macrophages in the dermis with concomitant increases in MCP-1 production from both keratinocytes in the epidermis and immune infiltrates in the adjacent dermal layer below. Furthermore, we demonstrate that the homodimeric IL-20R2 soluble receptor is a potent blocker for IL-24 and can be used to further dissect the crosstalk among the IL-20 family of cytokines in normal development as well as in autoimmune diseases.