Immune cell proliferation is suppressed by the interferon-gamma-induced indoleamine 2,3-dioxygenase expression of fibroblasts populated in collagen gel (FPCG)

The multifaceted role of the stroma in the healthy prostate and prostate cancer

Prostate cancer (PC) is an age-related disease and represents, after lung cancer, the second cause of cancer death in males worldwide. Mortality is due to the metastatic disease, which mainly involves the bones, lungs, and liver. In the last 20 years, the incidence of metastatic PC has increased in Western Countries, and a further increase is expected in the near future, due to the population ageing. Current treatment options, including state of the art cancer immunotherapy, need to be more effective to achieve long-term disease control. The most significant anatomical barrier to overcome to improve the effectiveness of current and newly designed drug strategies consists of the prostatic stroma, in particular the fibroblasts and the extracellular matrix, which are the most abundant components of both the normal and tumor prostatic microenvironment. By weaving a complex communication network with the glandular epithelium, the immune cells, the microbiota, the endothelium, and the nerves, in the healthy prostatic microenvironment, the fibroblasts and the extracellular matrix support organ development and homeostasis. However, during inflammation, ageing and prostate tumorigenesis, they undergo dramatic phenotypic and genotypic changes, which impact on tumor growth and progression and on the development of therapy resistance. Here, we focus on the characteristics and functions of the prostate associated fibroblasts and of the extracellular matrix in health and cancer. We emphasize their roles in shaping tumor behavior and the feasibility of manipulating and/or targeting these stromal components to overcome the limitations of current treatments and to improve precision medicine's chances of success.

Host-Microbiome Interactions: Tryptophan Metabolism and Aromatic Hydrocarbon Receptors after Traumatic Brain Injury

Traumatic brain injury refers to the damage caused to intracranial tissues by an external force acting on the head, leading to both immediate and prolonged harmful effects. Neuroinflammatory responses play a critical role in exacerbating the primary injury during the acute and chronic phases of TBI. Research has demonstrated that numerous neuroinflammatory responses are mediated through the "microbiota-gut-brain axis," which signifies the functional connection between the gut microbiota and the brain. The aryl hydrocarbon receptor (AhR) plays a vital role in facilitating communication between the host and microbiota through recognizing specific ligands produced directly or indirectly by the microbiota. Tryptophan (trp), an indispensable amino acid in animals and humans, represents one of the key endogenous ligands for AhR. The metabolites of trp have significant effects on the functioning of the central nervous system (CNS) through activating AHR signalling, thereby establishing bidirectional communication between the gut microbiota and the brain. These interactions are mediated through immune, metabolic, and neural signalling mechanisms. In this review, we emphasize the co-metabolism of tryptophan in the gut microbiota and the signalling pathway mediated by AHR following TBI. Furthermore, we discuss the impact of these mechanisms on the underlying processes involved in traumatic brain injury, while also addressing potential future targets for intervention.

Tryptophan metabolites kynurenine and serotonin regulate fibroblast activation and fibrosis

Fibrosis is a pathological form of aberrant tissue repair, the complications of which account for nearly half of all deaths in the industrialized world. All tissues are susceptible to fibrosis under particular pathological sets of conditions. Though each type of fibrosis has characteristics and hallmarks specific to that particular condition, there appear to be common factors underlying fibrotic diseases. One of these ubiquitous factors is the paradigm of the activated myofibroblast in the promotion of fibrotic phenotypes. Recent research has implicated metabolic byproducts of the amino acid tryptophan, namely serotonin and kynurenines, in the pathology or potential pharmacologic therapy of fibrosis, in part through their effects on development of myofibroblast phenotypes. Here, we review literature underlying what is known mechanistically about the effects of these compounds and their respective pathways on fibrosis. Pharmacologic administration of kynurenine improves scarring outcomes in vivo likely not only through its well-characterized immunosuppressive properties but also via its demonstrated antagonism of fibroblast activation and of collagen deposition. In contrast, serotonin directly promotes activation of fibroblasts via activation of canonical TGF-β signaling, and overstimulation with serotonin leads to fibrotic outcomes in vivo. Recently discovered feedback inhibition between serotonin and kynurenine pathways also reveals more information about the cellular physiology of tryptophan metabolism and may also underlie possible paradigms for anti-fibrotic therapy. Together, understanding of the effects of tryptophan metabolism on modulation of fibrosis may lead to the development of new therapeutic avenues for treatment through exploitation of these effects.

Traumatic Injury Leads to Inflammation and Altered Tryptophan Metabolism in the Juvenile Rabbit Brain

Neuroinflammation after traumatic brain injury (TBI) contributes to widespread cell death and tissue loss. Here, we evaluated sequential inflammatory response in the brain, as well as inflammation-induced changes in brain tryptophan metabolism over time, in a rabbit pediatric TBI model. On post-natal days 5-7 (P5-P7), New Zealand white rabbit littermates were randomized into three groups: naïve (no injury), sham (craniotomy alone), and TBI (controlled cortical impact). Animals were sacrificed at 6 h and 1, 3, 7, and 21 days post-injury for evaluating levels of pro- and anti-inflammatory cytokines, as well as the major components in the tryptophan-kynurenine pathway. We found that 1) pro- and anti-inflammatory cytokine levels in the brain injury area were differentially regulated in a time-dependent manner post-injury; 2) indoleamine 2,3 dioxygeenase 1 (IDO1) was upregulated around the injury area in TBI kits that persisted at 21 days post-injury; 3) mean length of serotonin-staining fibers was significantly reduced in the injured brain region in TBI kits for at least 21 days post-injury; and 4) kynurenine level significantly increased at 7 days post-injury. A significant decrease in serotonin/tryptophan ratio and melatonin/tryptophan ratio at 21 days post-injury was noted, suggesting that tryptophan metabolism is altered after TBI. A better understanding of the temporal evolution of immune responses and tryptophan metabolism during injury and repair after TBI is crucial for the development of novel therapeutic strategies targeting these pathways.

Genetic variation in IRF4 expression modulates growth characteristics, tyrosinase expression and interferon-gamma response in melanocytic cells

A SNP within intron4 of the interferon regulatory factor4 (IRF4) gene, rs12203592*C/T, has been independently associated with pigmentation and age-specific effects on naevus count in European-derived populations. We have characterized the cis-regulatory activity of this intronic region and using human foreskin-derived melanoblast strains, we have explored the correlation between IRF4 rs12203592 homozygous C/C and T/T genotypes with TYR enzyme activity, supporting its association with pigmentation traits. Further, higher IRF4 protein levels directed by the rs12203592*C allele were associated with increased basal proliferation but decreased cell viability following UVR, an etiological factor in melanoma development. Since UVR, and accompanying IFNγ-mediated inflammatory response, is associated with melanomagenesis, we evaluated its effects in the context of IRF4 status. Manipulation of IRF4 levels followed by IFNγ treatment revealed a subset of chemokines and immuno-evasive molecules that are sensitive to IRF4 expression level and genotype including CTLA4 and PD-L1.

Exosomes derived from atorvastatin-modified bone marrow dendritic cells ameliorate experimental autoimmune myasthenia gravis by up-regulated levels of IDO/Treg and partly dependent on FasL/Fas pathway

Background

Previously, we have demonstrated that spleen-derived dendritic cells (DCs) modified with atorvastatin suppressed immune responses of experimental autoimmune myasthenia gravis (EAMG). However, the effects of exosomes derived from atorvastatin-modified bone marrow DCs (BMDCs) (statin-Dex) on EAMG are still unknown.

Methods

Immunophenotypical characterization of exosomes from atorvastatin- and dimethylsulfoxide (DMSO)-modified BMDCs was performed by electron microscopy, flow cytometry, and western blotting. In order to investigate whether statin-DCs-derived exosomes (Dex) could induce immune tolerance in EAMG, we administrated statin-Dex, control-Dex, or phosphate-buffered saline (PBS) into EAMG rats via tail vein injection. The tracking of injected Dex and the effect of statin-Dex injection on endogenous DCs were performed by immunofluorescence and flow cytometry, respectively. The number of Foxp3⁺ cells in thymuses was examined using immunocytochemistry. Treg cells, cytokine secretion, lymphocyte proliferation, cell viability and apoptosis, and the levels of autoantibody were also carried out to evaluate the effect of statin-Dex on EAMG rats. To further investigate the involvement of FasL/Fas in statin-Dex-induced apoptosis, the underlying mechanisms were studied by FasL neutralization assays.

Results

Our data showed that the systemic injection of statin-Dex suppressed the clinical symptoms of EAMG rats. These statin-Dex had immune regulation functions in immune organs, such as the spleen, thymus, and popliteal and inguinal lymph nodes. Furthermore, statin-Dex exerted their immunomodulatory effects in vivo by decreasing the expression of CD80, CD86, and MHC class II on endogenous DCs. Importantly, the therapeutic effects of statin-Dex on EAMG rats were associated with up-regulated levels of indoleamine 2,3-dioxygenase (IDO)/Treg and partly dependent on FasL/Fas pathway, which finally resulted in decreased synthesis of anti-R97–116 IgG, IgG2a, and IgG2b antibodies.

Conclusions

Our data suggest that atorvastatin-induced immature BMDCs are able to secrete tolerogenic Dex, which are involved in the suppression of immune responses in EAMG rats. Importantly, our study provides a novel cell-free approach for the treatment of autoimmune diseases.

Respiratory syncytial virus induces indoleamine 2,3-dioxygenase activity: a potential novel role in the development of allergic disease

BACKGROUND

Infants that develop severe bronchiolitis due to respiratory syncytial virus (RSV) are at increased risk of developing asthma later in life. We investigated a potential immunological mechanism for the association between RSV and the development of allergic inflammation. The enzyme indoleamine 2,3-dioxygenase (IDO) has been reported to induce selective apoptosis of T helper 1 (Th1) cells and contributed to Th2-biased immune responses.

OBJECTIVE

To determine whether RSV infection in vitro could induce IDO expression and bioactivity in human dendritic cells, leading to a Th2-biased immune response.

METHODS

Human peripheral blood monocytes from healthy adult donors were isolated, differentiated to dendritic cells (moDC), in vitro. We studied RSV infection and mechanisms of IDO activation in moDC with subsequent effect on T-bet expression.

RESULTS

We found that moDC were infected by RSV and that this induced IDO activation. RSV-induced IDO activity was inhibited by palivizumab, UV inactivation, TL4R inhibition, and ribavirin. However, blocking endosomal TLR function with chloroquine did not inhibit IDO activity. Selective inhibitors suggested that RSV-induced IDO activity was dependent on the retinoic acid-inducible gene-I (RIG-I) related pathway via NF-κB and p38 MAPK. Coculture of RSV-infected moDC with activated T cells, in a transwell system, suppressed expression of T-bet (a Th1-associated factor) but not GATA3 (a Th2 regulator). Inhibition of IDO activity with the competitive inhibitor, 1-methyl tryptophan, blocked the effect on T-bet expression.

CONCLUSION AND CLINICAL RELEVANCE

Our data show for the first time that RSV can induce the expression and bioactivity of IDO in human moDC, in a virus replication-dependant fashion. We suggest that RSV activation of IDO could be a potential mechanism for the development of allergic diseases.

A novel regulation of PD-1 ligands on mesenchymal stromal cells through MMP-mediated proteolytic cleavage

Whether fibroblasts regulate immune response is a crucial issue in the modulation of inflammatory responses. Herein, we demonstrate that foreskin fibroblasts (FFs) potently inhibit CD3⁺ T cell proliferation through a mechanism involving early apoptosis of activated T cells. Using blocking antibodies, we demonstrate that the inhibition of T cell proliferation occurs through cell-to-cell interactions implicating PD-1 receptor expressed on T cells and its ligands, PD-L1 and PD-L2, on fibroblasts. Dual PD-1 ligand neutralization is required to abrogate (i) binding of the PD-1-Fc fusion protein, (ii) early apoptosis of T cells, and (iii) inhibition of T cell proliferation. Of utmost importance, we provide the first evidence that PD-1 ligand expression is regulated through proteolytic cleavage by endogenous matrix metalloproteinases (MMPs) without transcriptional alteration during culture-time. Using (i) different purified enzymatic activities, (ii) MMP-specific inhibitors, and (iii) recombinant human MMP-9 and MMP-13, we demonstrated that in contrast to CD80/CD86, PD-L1 was selectively cleaved by MMP-13, while PD-L2 was sensitive to broader MMP activities. Their cleavage by exogenous MMP-9 and MMP-13 with loss of PD-1 binding domain resulted in the reversion of apoptotic signals on mitogen-activated CD3⁺ T cells. We suggest that MMP-dependent cleavage of PD-1 ligands on fibroblasts may limit their immunosuppressive capacity and thus contribute to the exacerbation of inflammation in tissues. In contrast, carcinoma-associated fibroblasts appear PD-1 ligand-depleted through MMP activity that may impair physical deletion of exhausted defective memory T cells through apoptosis and facilitate their regulatory functions. These observations should be considered when using the powerful PD-1/PD-L1 blocking immunotherapies.

Activation of the kynurenine pathway and increased production of the excitotoxin quinolinic acid following traumatic brain injury in humans

Abstract

During inflammation, the kynurenine pathway (KP) metabolises the essential amino acid tryptophan (TRP) potentially contributing to excitotoxicity via the release of quinolinic acid (QUIN) and 3-hydroxykynurenine (3HK). Despite the importance of excitotoxicity in the development of secondary brain damage, investigations on the KP in TBI are scarce. In this study, we comprehensively characterised changes in KP activation by measuring numerous metabolites in cerebrospinal fluid (CSF) from TBI patients and assessing the expression of key KP enzymes in brain tissue from TBI victims. Acute QUIN levels were further correlated with outcome scores to explore its prognostic value in TBI recovery.

Methods

Twenty-eight patients with severe TBI (GCS ≤ 8, three patients had initial GCS = 9–10, but rapidly deteriorated to ≤8) were recruited. CSF was collected from admission to day 5 post-injury. TRP, kynurenine (KYN), kynurenic acid (KYNA), QUIN, anthranilic acid (AA) and 3-hydroxyanthranilic acid (3HAA) were measured in CSF. The Glasgow Outcome Scale Extended (GOSE) score was assessed at 6 months post-TBI. Post-mortem brains were obtained from the Australian Neurotrauma Tissue and Fluid Bank and used in qPCR for quantitating expression of KP enzymes (indoleamine 2,3-dioxygenase-1 (IDO1), kynurenase (KYNase), kynurenine amino transferase-II (KAT-II), kynurenine 3-monooxygenase (KMO), 3-hydroxyanthranilic acid oxygenase (3HAO) and quinolinic acid phosphoribosyl transferase (QPRTase) and IDO1 immunohistochemistry.

Results

In CSF, KYN, KYNA and QUIN were elevated whereas TRP, AA and 3HAA remained unchanged. The ratios of QUIN:KYN, QUIN:KYNA, KYNA:KYN and 3HAA:AA revealed that QUIN levels were significantly higher than KYN and KYNA, supporting increased neurotoxicity. Amplified IDO1 and KYNase mRNA expression was demonstrated on post-mortem brains, and enhanced IDO1 protein coincided with overt tissue damage. QUIN levels in CSF were significantly higher in patients with unfavourable outcome and inversely correlated with GOSE scores.

Conclusion

TBI induced a striking activation of the KP pathway with sustained increase of QUIN. The exceeding production of QUIN together with increased IDO1 activation and mRNA expression in brain-injured areas suggests that TBI selectively induces a robust stimulation of the neurotoxic branch of the KP pathway. QUIN’s detrimental roles are supported by its association to adverse outcome potentially becoming an early prognostic factor post-TBI.

The molecular mechanism of hypertrophic scar

Hypertrophic scar (HTS) is a dermal form of fibroproliferative disorder which often develops after thermal or traumatic injury to the deep regions of the skin and is characterized by excessive deposition and alterations in morphology of collagen and other extracellular matrix (ECM) proteins. HTS are cosmetically disfiguring and can cause functional problems that often recur despite surgical attempts to remove or improve the scars. In this review, the roles of various fibrotic and anti-fibrotic molecules are discussed in order to improve our understanding of the molecular mechanism of the pathogenesis of HTS. These molecules include growth factors, cytokines, ECM molecules, and proteolytic enzymes. By exploring the mechanisms of this form of dermal fibrosis, we seek to provide some insight into this form of dermal fibrosis that may allow clinicians to improve treatment and prevention in the future.

Mechanism underlying defective interferon gamma-induced IDO expression in non-obese diabetic mouse fibroblasts

Indoleamine 2,3-dioxygenase (IDO) can locally suppress T cell-mediated immune responses. It has been shown that defective self-tolerance in early prediabetic female non-obese diabetic (NOD) mice can be attributed to the impaired interferon-gamma (IFN-γ)- induced IDO expression in dendritic cells of these animals. As IFN-γ can induce IDO in both dendritic cells and fibroblasts, we asked the question of whether there exists a similar defect in IFN-γ-induced IDO expression in NOD mice dermal fibroblasts. To this end, we examined the effect of IFN-γ on expression of IDO and its enzymatic activity in NOD dermal fibroblasts. The results showed that fibroblasts from either prediabetic (8 wks of age) female or male, and diabetic female or male (12 and 24 wks of age respectively) NOD mice failed to express IDO in response to IFN-γ treatment. To find underlying mechanisms, we scrutinized the IFN- γ signaling pathway and investigated expression of other IFN-γ-modulated factors including major histocompatibility complex class I (MHC-I) and type I collagen (COL-I). The findings revealed a defect of signal transducer and activator of transcription 1 (STAT1) phosphorylation in NOD cells relative to that of controls. Furthermore, we found an increase in MHC-I and suppression of COL-I expression in fibroblasts from both NOD and control mice following IFN-γ treatment; indicating that the impaired response to IFN-γ in NOD fibroblasts is specific to IDO gene. Finally, we showed that an IFN-γ-independent IDO expression pathway i.e. lipopolysaccharide (LPS)-mediated-c-Jun kinase is operative in NOD mice fibroblast. In conclusion, the findings of this study for the first time indicate that IFN-γ fails to induce IDO expression in NOD dermal fibroblasts; this may partially be due to defective STAT1 phosphorylation in IFN-γ-induced-IDO signaling pathway.

Dermal fibroblasts display similar phenotypic and differentiation capacity to fat-derived mesenchymal stem cells, but differ in anti-inflammatory and angiogenic potential

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent stem cells able to differentiate into different cell lineages. However, MSCs represent a subpopulation of a more complex cell composition of stroma cells contained in mesenchymal tissue. Due to a lack of specific markers, it is difficult to distinguish MSCs from other more mature stromal cells such as fibroblasts, which, conversely, are abundant in mesenchymal tissue. In order to find more distinguishing features between MSCs and fibroblasts, we studied the phenotypic and functional features of human adipose-derived MSCs (AD-MSCs) side by side with normal human dermal fibroblasts (HNDFs) in vitro

METHODS

AD-MSCs and HNDFs were cultured, expanded and phenotypically characterized by flow cytometry (FC). Immunofluorescence was used to investigate cell differentiation. ELISA assay was used to quantify angiogenic factors and chemokines release. Cultures of endothelial cells (ECs) and a monocyte cell line, U937, were used to test angiogenic and anti-inflammatory properties.

RESULTS

Cultured AD-MSCs and HNDFs display similar morphological appearance, growth rate, and phenotypic profile. They both expressed typical mesenchymal markers-CD90, CD29, CD44, CD105 and to a minor extent, the adhesion molecules CD54, CD56, CD106 and CD166. They were negative for the stem cell markers CD34, CD146, CD133, CD117. Only aldehyde dehydrogenase (ALDH) was expressed. Neither AD-MSCs nor HNDFs differed in their multi-lineage differentiation capacity; they both differentiated into osteoblast, adipocyte, and also into cardiomyocyte-like cells. In contrast, AD-MSCs, but not HNDFs, displayed strong angiogenic and anti-inflammatory activity. AD-MSCs released significant amounts of VEGF, HGF and Angiopoietins and their conditioned medium (CM) stimulated ECs proliferation and tube formations. In addition, CM-derived AD-MSCs (AD-MSCs-CM) inhibited adhesion molecules expression on U937 and release of RANTES and MCP-1. Finally, after priming with TNFα, AD-MSCs enhanced their anti-inflammatory potential; while HNDFs acquired pro-inflammatory activity.

CONCLUSIONS

AD-MSCs cannot be distinguished from HNDFs in vitro by evaluating their phenotypic profile or differentiation potential, but only through the analysis of their anti-inflammatory and angiogenic properties. These results underline the importance of evaluating the angiogenic and anti-inflammatory features of MSCs preparation. Their priming with inflammatory cytokines prior to transplantation may improve their efficacy in cell-based therapies for tissue regeneration.

Ability of IDO to attenuate liver injury in alpha-galactosylceramide-induced hepatitis model

IDO converts tryptophan to l-kynurenine, and it is noted as a relevant molecule in promoting tolerance and suppressing adaptive immunity. In this study, we examined the effect of IDO in α-galactosylceramide (α-GalCer)-induced hepatitis. The increase in IDO expression in the liver of wild-type (WT) mice administered α-GalCer was confirmed by real-time PCR, Western blotting, and IDO immunohistochemical analysis. The serum alanine aminotransferase levels in IDO-knockout (KO) mice after α-GalCer injection significantly increased compared with those in WT mice. 1-Methyl-D-tryptophan also exacerbated liver injury in this murine hepatitis model. In α-GalCer-induced hepatitis models, TNF-α is critical in the development of liver injury. The mRNA expression and protein level of TNF-α in the liver from IDO-KO mice were more enhanced compared with those in WT mice. The phenotypes of intrahepatic lymphocytes from WT mice and IDO-KO mice treated with α-GalCer were analyzed by flow cytometry, and the numbers of CD49b(+) and CD11b(+) cells were found to have increased in IDO-KO mice. Moreover, as a result of the increase in the number of NK cells and macrophages in the liver of IDO-KO mice injected with α-GalCer, TNF-α secretion in these mice was greater than that in WT mice. Deficiency of IDO exacerbated liver injury in α-GalCer-induced hepatitis. IDO induced by proinflammatory cytokines may decrease the number of TNF-α-producing immune cells in the liver. Thus, IDO may suppress overactive immune response in the α-GalCer-induced hepatitis model.

Local expression of indoleamine 2,3 dioxygenase in syngeneic fibroblasts significantly prolongs survival of an engineered three-dimensional islet allograft

OBJECTIVE

The requirement of systemic immunosuppression after islet transplantation is of significant concern and a major drawback to clinical islet transplantation. Here, we introduce a novel composite three-dimensional islet graft equipped with a local immunosuppressive system that prevents islet allograft rejection without systemic antirejection agents. In this composite graft, expression of indoleamine 2,3 dioxygenase (IDO), a tryptophan-degrading enzyme, in syngeneic fibroblasts provides a low-tryptophan microenvironment within which T-cells cannot proliferate and infiltrate islets.

RESEARCH DESIGN AND METHODS

Composite three-dimensional islet grafts were engineered by embedding allogeneic mouse islets and adenoviral-transduced IDO-expressing syngeneic fibroblasts within collagen gel matrix. These grafts were then transplanted into renal subcapsular space of streptozotocin diabetic immunocompetent mice. The viability, function, and criteria for graft take were then determined in the graft recipient mice.

RESULTS

IDO-expressing grafts survived significantly longer than controls (41.2 +/- 1.64 vs. 12.9 +/- 0.73 days; P < 0.001) without administration of systemic immunesuppressive agents. Local expression of IDO suppressed effector T-cells at the graft site, induced a Th2 immune response shift, generated an anti-inflammatory cytokine profile, delayed alloantibody production, and increased number of regulatory T-cells in draining lymph nodes, which resulted in antigen-specific impairment of T-cell priming.

CONCLUSIONS

Local IDO expression prevents cellular and humoral alloimmune responses against islets and significantly prolongs islet allograft survival without systemic antirejection treatments. This promising finding proves the potent local immunosuppressive activity of IDO in islet allografts and sets the stage for development of a long-lasting nonrejectable islet allograft using stable IDO induction in bystander fibroblasts.

Human fibroblasts share immunosuppressive properties with bone marrow mesenchymal stem cells

INTRODUCTION

Bone marrow mesenchymal stem cells (BM-MSCs) and adipose tissue-derived stem cells share immunosuppressive capacities, suggesting that the latter could be a general property of stromal cells.

METHODS

To check this hypothesis, we compared human BM-MSC and fibroblasts for their in vitro multi-potentiality, expandability and their immunomodulatory properties under normalized optimized culture conditions.

RESULTS

We report that, unlike BM-MSCs, fibroblasts cannot differentiate in vitro into adipocytes and osteoblasts and differ from BM-MSCs by the expression of membrane CD106, CD10 and CD26 and by the expression of collagen VII mRNA. Like BM-MSCs, fibroblasts are unable to provoke in vitro allogeneic reactions, but strongly suppress lymphocyte proliferation induced by allogeneic mixed lymphocyte culture (MLC) or mitogens. We show that fibroblasts' immunosuppressive capacity is independent from prostaglandin E2, IL-10 and the tryptophan catabolising enzyme indoleamine 2,3-dioxygenase and is not abrogated after the depletion of CD8+ T lymphocytes, NK cells and monocytes.

CONCLUSION

Finally, fibroblasts and BM-MSCs act at an early stage through blockage of lymphocyte activation, as demonstrated by down-regulation of GZMB (granzyme B) and IL2RA (CD25) expression.

Indoleamine 2,3-dioxygenase in lung allograft tolerance

BACKGROUND

Indoleamine 2,3-dioxygenase (IDO), an enzyme involved in the degradation of tryptophan (Try) to kynurenine (Kyn), is thought to suppress T-cell activity. Although a few experimental studies have suggested a role for IDO in graft acceptance, human data are scarce and inconclusive. We sought to establish whether, in lung transplant recipients (LTRs), plasma IDO activity mirrors the level of graft acceptance.

METHODS

We measured the plasma Kyn/Try ratio, reflecting IDO activity, by high-performance liquid chromatography (HPLC) in 90 LTRs, including 26 patients who were still functionally/clinically stable for >36 post-transplant months (stable LTRs) and 64 LTRs with bronchiolitis obliterans syndrome (BOS, Grades 0-p to 3). Twenty-four normal healthy controls (NHCs) were also included.

RESULTS

The Kyn/Try ratio in stable LTRs resembled that observed in NHCs, whereas, unexpectedly, patients with BOS, who had lower counts of peripheral CD4(+) T-regulatory cells and tolerogenic plasmacytoid dendritic cells than stable LTRs, showed an increased plasma Kyn/Try ratio compared with both NHCs and stable LTRs. IDO expression by in vitro-stimulated peripheral blood mononuclear cells (PBMC) did not vary between BOS and stable LTRs. Furthermore, BOS patients displayed signs of chronic systemic inflammation (increased plasma levels of interleukin-8 and tumor necrosis factor-alpha) and higher T-cell activation (increased frequency of peripheral interferon-gamma-producing clones).

CONCLUSIONS

Our results suggest that, in vivo, in lung transplantation, plasma IDO activity does not reflect the degree of lung graft acceptance, but instead is correlated with the degree of chronic inflammation.

Mouse pancreatic islets are resistant to indoleamine 2,3 dioxygenase-induced general control nonderepressible-2 kinase stress pathway and maintain normal viability and function

Islet transplantation is a promising treatment for diabetes. However, it faces several challenges including requirement of systemic immunosuppression. Indoleamine 2,3-dioxygenase (IDO), a tryptophan degrading enzyme, is a potent immunomodulatory factor. Local expression of IDO in bystander fibroblasts suppresses islet allogeneic immune response in vitro. The aim of the present study was to investigate the impact of IDO on viability and function of mouse islets embedded within IDO-expressing fibroblast-populated collagen scaffold. Mouse islets were embedded within collagen matrix populated with IDO adenovector-transduced or control fibroblasts. Proliferation, insulin content, glucose responsiveness, and activation of general control nonderepressible-2 kinase stress-responsive pathway were then measured in IDO-exposed islets. In vivo viabilities of composite islet grafts were also tested in a syngeneic diabetic animal model. No reduction in islet cells proliferation was detected in both IDO-expressing and control composites compared to the baseline rates. Islet functional studies showed normal insulin content and secretion in both preparations. In contrast to lymphocytes, general control nonderepressible-2 kinase pathway was not activated in islets cocultured with IDO-expressing fibroblasts. When transplanted to diabetic mice, syngeneic IDO-expressing composite islet grafts were functional up to 100 days tested. These findings collectively confirm normal viability and functionality of islets cocultured with IDO-expressing cells and indicate the feasibility of development of a functional nonrejectable islet graft.

Suppression of islet allogeneic immune response by indoleamine 2,3 dioxygenase-expressing fibroblasts

Success of transplantation of pancreatic islets which is a promising way for restoring efficient insulin regulation in type 1 diabetes depends on lifelong use of immunosuppressive drugs. To eliminate the use of systemic immunosuppressive drugs for islet transplantation, we examined the potential use of a local immunosuppressive factor, indoleamine 2,3-dioxygenase (IDO). Thus, the aim of this study was to determine whether local expression of IDO in bystander syngeneic fibroblasts could prevent islet allogeneic immune response in vitro. C57BL/6 (B6) mouse fibroblasts were induced to express IDO by either IFN-gamma treatment or transduction with an adenoviral vector and were co-cultured with B6 mouse lymphocytes and BALB/c mouse pancreatic islets in the presence or absence of an IDO inhibitor. Proliferation of lymphocytes were then assessed using [(3)H]-thymidine incorporation assay. IDO-expression by co-cultured syngeneic fibroblasts resulted in a five-fold decrease in lymphocyte proliferation rate upon stimulation of lymphocytes by allogeneic mouse pancreatic islets (21.9% +/- 5.3 and 22.1% +/- 4.9 in the preparations with IFN-gamma treated and genetically modified IDO-expressing fibroblasts, respectively vs. 100% in control groups, P < 0.01). Allogeneic response was restored when IDO inhibitor was added to the culture indicating that suppression was due to IDO. In conclusion, this study shows that local expression of IDO by syngeneic bystander fibroblasts can suppress in vitro proliferation of lymphocytes in response to stimulation with allogeneic pancreatic islets. This local immunosuppressive function of IDO may be employed for development of a novel alternative strategy for preventing allogeneic islet graft rejection.

The pro- and anti-inflammatory potential of IL-12: the dual role of Th1 cells

The differentiation of T-helper (Th) lymphocytes into various types of T-helper effector and memory cells with distinct functions depending on the type of concomitant signals they receive upon activation is a critical event determining the course of an immune reaction. Th1 cells characterized by the expression of IFN-gamma and the recently described Th17 cells promote inflammation and are critically involved in the induction and maintenance of autoimmunity, whereas the secretion of IL-4 is a hallmark of Th2 cells mediating protection from parasites and allergy. Original stimulation in the presence of IL-12 results in the imprinting of Th1 memory cells for the expression of IFN-gamma by expression of the transcription factor T-bet and epigenetic modification of the ifngamma gene. It has been demonstrated that Th1 cells are potent inducers of inflammation. However, in the chronic phase of such inflammation, the regulatory potential of IL-12 and Th1 cells themselves may play an important role in limiting immunopathology.

Efficacy of gaseous nitric oxide in the treatment of skin and soft tissue infections

Bacterial burden significantly interferes with the healing process in chronic ulcers. Nitric oxide (NO) plays a key role in regulating skin's response to infection and wound healing. In previous studies, we demonstrated that exogenous NO gas (gNO) at 200 parts per million (ppm) exhibits potent antimicrobial effects against a representative range of pathogens. The aim of the present study is to explore the antimicrobial properties of gNO in vivo and to determine skin cells' sensitivity to the cytotoxic effects of gNO. To test gNO's antimicrobial effects, full-thickness wounds were infected with Staphylococcus aureus on the dorsal skin surface of New Zealand White rabbit and treated with 200 ppm gNO for 8 hours/day for 3 consecutive days. Significant reduction in wound bacterial content was observed in the presence of gNO. In a separate experiment, primary cultures of human fibroblasts, keratinocytes, and endothelial cells were established to test gNO's cytotoxicity in the skin. Methyl thiazolyl tetrazolium proliferation assays demonstrated that human skin cells, unlike bacterial cells, exhibited significant resistance toward gNO cytotoxicity. In vitro migration studies on keratinocytes and endothelial cells revealed that gNO treatment does not seem to interfere with reepithelialization and angiogenesis during the process of wound healing. Following 24 hours of gNO treatment, fibroblasts expressed significantly higher levels of procollagen and, to a lesser degree, a decrease in matrix metalloproteinase -1 mRNA. In conclusion, the present study provides evidence for the potential application of high doses of gNO as an antimicrobial agent for the treatment of infection in chronic nonhealing ulcers or burn patients, without compromising the viability, and function of skin cells.

Human bone marrow stromal cells hamper specific interactions of CD4 and CD8 T lymphocytes with antigen-presenting cells

Bone marrow stromal cells (BMSCs) may inhibit T-cell functions in vitro and thus have been proposed as immunoregulators to control in vivo graft-versus-host disease (GVHD) in haploidentical hemopoietic stem cell transplants. To better investigate this phenomenon, we used a defined experimental system in which responding T cells are antigen-specific and devoid of alloreactivity against BMSC from a different subject. Thus, we established antigen-specific human CD4 and CD8 T-cell lines as the readout system. Antigen-dependent proliferation was reduced with both T-cell subsets cultured on confluent BMSCs, and also on confluent human skin fibroblasts (HSF) inhibited T-cell proliferation with similar efficiency. Morphological observations of the cocultures showed impairment of physical interactions between T-cell and antigen-presenting cells in the presence of BMSC, with lack of formation of antigen-dependent clusters of T cells and antigen-presenting cells (APCs). In contrast, no effects were seen with BMSC-conditioned medium. Since suppression was seen only with confluent mesenchymal cells, this phenomenon may not be relevant in vivo, where BMSCs are at low frequency. In addition, if the reported suppressive effect of BMSCs on GVHD in vivo is confirmed, a different in vitro system should be envisaged to better understand and exploit the underlying mechanism.

Nitration and inactivation of IDO by peroxynitrite

IDO induction can deplete L-tryptophan in target cells, an effect partially responsible for the antimicrobial activities and antiallogeneic T cell responses of IFN-gamma in human macrophages, dendritic cells, and bone marrow cells. L-tryptophan depletion and NO production are both known to have an antimicrobial effect in macrophages, and the interaction of these two mechanisms is unclear. In this study we found that IDO activity was inhibited by the peroxynitrite generator, 3-(4-morpholinyl)sydnonimine, in PMA-differentiated cytokine-induced THP-1 (acute monocytic leukemia) cells and IFN-gamma-stimulated PBMCs, whereas IDO protein expression was unaffected compared with that in untreated cells. Nitrotyrosine was detected in immunoprecipitated (IP)-IDO from PMA-differentiated cytokine-induced THP-1 cells treated with 3-(4-morpholinyl)sydnonimine, but not from untreated cells. Treatment of IP-IDO and recombinant IDO (rIDO) with peroxynitrite significantly decreased enzyme activity. Nitrotyrosine was detected in both peroxynitrite-treated IP-IDO and rIDO, but not in either untreated IP-IDO or rIDO. Peptide analysis by liquid chromatography/electrospray ionization and tandem mass spectrometry demonstrated that Tyr15, Tyr345, and Tyr353 in rIDO were nitrated by peroxynitrite. The levels of Tyr nitration and the inhibitory effect of peroxynitrite on IDO activity were significantly reduced in the Tyr15-to-Phe mutant. These results indicate that IDO is nitrated and inactivated by peroxynitrite and that nitration of Tyr15 in IDO protein is the most important factor in the inactivation of IDO.

Cutting edge: human eosinophils regulate T cell subset selection through indoleamine 2,3-dioxygenase

Allergy involves eosinophilia and Th2 polarization. Indoleamine 2,3-dioxygenase (IDO)-catalyzed conversion of tryptophan to kynurenines (KYN) regulates T cell function. We show that human eosinophils constitutively express IDO. Eosinophils treated with IFN-gamma showed an 8-fold increase in IDO mRNA within 4 h; IL-3, IL-5, and GM-CSF had no effect on baseline IDO expression. IL-3 pretreatment of eosinophils reduced IFN-gamma-induced IDO mRNA expression below baseline. Conversely, GM-CSF, but not IL-5, resulted in a 2-fold increase in IFN-gamma-induced IDO. Treatment with IL-3, IL-5, GM-CSF, or IFN-gamma alone expressed IDO enzymatic activity (the presence of KYN in supernatants 48 h postculture). CD28 cross-linking resulted in measurable KYN in culture supernatants, inhibitable by a neutralizing anti-IFN-gamma. Coculture of eosinophils with an IFN-gamma-producing T cell line, but not IL-4-producing T cell clone, led to apoptosis and inhibition of CD3 or CD3/CD28-induced proliferation. Eosinophils infiltrating asthmatic lung and associated lymphoid tissue exhibited intracellular IDO immunoreactivity. Eosinophils may, therefore, maintain Th2 bias through IDO.

Interferon-gamma-modified dendritic cells suppress B cell function and ameliorate the development of experimental autoimmune myasthenia gravis

This study was designed to investigate the therapeutic effects of interferon (IFN)-gamma-modulated dendritic cells (DC) in experimental autoimmune myasthenia gravis (EAMG). We induced EAMG in Lewis rats by immunization with Torpedo nicotinic acetylcholine receptor (nAChR) and adjuvant. On day 33 post-immunization (p.i.), splenic DC were prepared, exposed to IFN-gamma alone (IFN-gamma-DC) or to IFN-gamma in combination with 1-methyl-DL-tryptophan (1-MT), the specific inhibitor of indoleamine 2,3-dioxygenase (IDO) (IFN-gamma + 1-MT-DC), and injected subcutaneously into rats with incipient EAMG on day 5 p.i. A control group of EAMG rats received naive DC on day 5 p.i., while another group received 1-MT every other day, intraperitoneally (p.i.), from days 5 to 41 p.i. The severity of clinical signs of EAMG was reduced dramatically in IFN-gamma-DC-treated rats compared to rats receiving naive DC, IFN-gamma + 1-MT-DC or 1-MT alone. The number of plasma cells secreting nAChR antibodies was reduced and the expression of B cell activation factor (BAFF) on splenic and lymph node mononuclear cells (MNC) was down-regulated in rats treated with IFN-gamma-DC. In vitro co-culture of MNC derived from EAMG rats with IFN-gamma-DC produced relatively few cells secreting nAChR antibodies. Addition of 1-MT to the co-culture significantly increased the number of cells secreting nAChR antibodies. We conclude that IFN-gamma-DC reduced the number of plasma cells secreting nAChR antibodies in an IDO-dependent manner and ameliorated the development of EAMG in Lewis rats.

Expression of Indoleamine 2,3-Dioxygenase in Dermal Fibroblasts Functions as a Local Immunosuppressive Factor

As a possible way of making a non-rejectable skin substitute, here, we ask the question of whether the expression of indoleamine 2,3-dioxygenase (IDO) selectively suppresses immune, but skin, cell proliferation. To address this question, a series of experiments in which adenovirus (Ad-IDO) infected IDO expressing dermal fibroblasts were co-cultured with different types of immune cells were carried out. The immune cells were then harvested and evaluated for propidium iodide (PI) positive cells by FACS analysis. TUNEL assay was also carried out to determine the apoptotic status of these cells. The results showed that the expression of IDO in dermal fibroblasts significantly induces apoptotic death of PBMC, CD4(+)-, CD8(+)- and B cell-riched primary lymphocytes, Jurkat cells, and THP-1 cells. IDO-mediated damage of immune cells was restored by an addition of tryptophan and IDO inhibitor. Using the same approaches, we also demonstrated that skin cells and endothelial cells are remarkably resistant to tryptophan-deficient environment. Furthermore, no significant difference in cell proliferation between Ad-GFP (control)- and Ad-IDO-GFP-infected either keratinocytes or fibroblasts, was found. The results of this study, therefore, suggest that the expression of IDO by dermal fibroblasts mediates immune cell damage and this may shed a new light toward developing a non-rejectable skin substitute in the future.

Temperature-sensitive polymer-conjugated IFN-? induces the expression of IDO mRNA and activity by fibroblasts populated in collagen gel (FPCG)

Indoleamine 2,3-dioxygenase (IDO) is an intracellular tryptophan-catabolizing enzyme possessing various immunosuppressive properties. Here, we report the use of this enzyme to suppress the proliferation of peripheral blood mononuclear cells (PBMC) co-cultured with IDO-expressing fibroblasts of an allogeneic skin substitute in vitro. Fetal foreskin fibroblasts populated within collagen gel (FPCG) were treated with interferon-gamma (IFN-gamma) conjugated with a temperature-sensitive polymer to induce the expression of IDO mRNA and protein. SDS-PAGE showed successful conjugation of IFN-gamma with the temperature-sensitive polymer. Expression of IDO mRNA was evaluated by Northern analysis. IDO enzyme activity was evaluated by the measurement of kynurenine levels. The results of Northern blot analysis showed an induction of IDO mRNA expression when treated with polymer-conjugated IFN-gamma. Kynurenine levels, as a measure of IDO bioactivity, were significantly higher in IFN-gamma-treated fibroblasts than in controls (P < 0.001). In a lasting effect experiment, the expression of IDO mRNA in FPCG treated with polymer-conjugated IFN-gamma was significantly longer than in those treated with free (non-conjugated) IFN-gamma (P < 0.001). IFN-gamma radiolabeling showed a prolonged retention of IFN-gamma within collagen gel in its polymer-conjugated form, compared to its free form. Presence of IDO protein in FPCG was demonstrated by Western analysis even 16 days after removal of the conditioned medium (containing released IFN-gamma). To demonstrate the immunosuppressive effects of IDO on the proliferation of PBMC, IDO-expressing FPCG treated with polymer-conjugated IFN-gamma were co-cultured with PBMC for a period of 5 days. The results showed a significant reduction in proliferation of PBMC co-cultured with IFN-gamma-treated IDO-expressing fibroblasts, compared to those co-cultured with non-IDO-expressing fibroblasts (P < 0.001). The addition of an IDO inhibitor (1-methyl-D-tryptophan) reversed the suppressive effects of IDO on PBMC proliferation. In conclusion, IDO expression in FPCG suppresses the proliferation of immune cells in vitro. The use of a temperature-sensitive polymer further prolongs the effect of IFN-gamma on the expression of IDO. Therefore, modulating IDO levels in situ might be an alternative for prolonging the survival of skin allografts.