Indoleamine 2,3-dioxygenase Levels Research Articles

Swimming exercise ameliorates depression-like behavior in chronically stressed rats: Relevant to proinflammatory cytokines and IDO activation

Chronic stress is involved in development of depression and causes immune alterations. Indoleamine-2,3-dioxygenase (IDO) plays a pivotal role in mediating the depression-like behaviors in response to immune activation. Physical exercise has been shown to reduce the stress impairment and ameliorate depressive symptoms. The objectives of present study were to confirm that chronic unpredictable mild stress (CUMS) induces depression-like behavior and inflammatory responses within the brain, and then investigate whether swimming exercise alleviates the depression-like behaviors induced by CUMS through proinflammatory cytokine-induced alteration of IDO in brain. It has been found that CUMS exposure induced depression-like behavior, increased serum corticosterone (CORT) level, decreased 5-HT level, increased IFN-γ and TNF-α levels and elevated IDO activity in prefrontal cortex. Moreover, the level of 5-HT was inversely correlated with IDO level. Regular swimming exercise ameliorated depressive symptoms induced by CUMS. The exercise reduced serum CORT level, increased 5-HT level as well as decreased levels of IFN-γ, TNF-α and IDO in prefrontal cortex in CUMS rats. These findings suggested that CUMS activate HPA axis and induce immune activation, which may stimulate IDO activity, leading to the reduction of 5-HT level in brain, thereby resulting in depression. Swimming exercise may inhibit activation of inflammation/IDO pathways induced by CUMS, thereby ameliorating depression.

Indoleamine 2,3-Dioxygenase (IDO) Is Associated with High Incidence of Chemorefractory Disease in Acute Myeloid Leukemia (AML) Patients

Abstract 4787Indoleamine 2,3-dioxygenase (IDO) is a heme-containing enzyme that catalyzes the first and rate-limiting step in tryptophan degradation along the kynurenine pathway. IDO is able to inhibit T-cell function and to induce the transformation of T-cells into regulatory T-cells. Several studies demonstrated that IDO expression is involved in immune tolerance induction during pregnancy, infection, transplantation, autoimmune diseases and neoplasias, including acute myeloid leukemia (AML). In particular, our and other groups demonstrated that IDO is expressed in a significant proportion of AML patients and that it increases along with disease progression. Here, we addressed the correlation between IDO expression by AML cells, risk factors at diagnosis and patients' outcome.Adult AML patients from the Hematology Institute “L. and A. Seràgnoli” in Bologna were analyzed for risk characteristics at diagnosis and for IDO expression by RT-PCR and by Western-Blot analysis. Patients were stratified according to age at diagnosis, de novo or secondary disease (pre-existing myelodysplastic syndrome or radio-chemotherapy), leucocytosis, cytogenetics (on the basis of cytogenetic characteristics patients were divided into low, intermediate and high risk groups) and FLT3 and NPM mutational status.Fifty-two patients with AML at diagnosis were analyzed for IDO expression both at gene and protein level. According to IDO transcript levels, patients were divided into IDO-negative (21%) and IDO positive (79%). Positive patients were further subdivided into three different subgroups according to IDO level: IDO-low expression (78%), IDO-intermediate expression (10%) and IDO-high expression (12%) patients. When IDO protein was assessed, we found a correlation between IDO mRNA level and the detection of IDO protein. In particular, IDO protein was detectable only in IDO-high-expressing patients.No statistically significant differences in the recurrence of prognostic characteristics at diagnosis among the groups considered were observed, even though IDO-negative and IDO-low expressing patients showed a higher median age at diagnosis than IDO-intermediate and IDO-high expressing patients and an increased frequency of high-risk cytogenetics was found in IDO-high expressing patients. Response to induction chemotherapy regimen was then analyzed among the four groups of patients. Only patients who received cytotoxic chemotherapy were evaluated for response. Intriguingly, we found that refractory patients were 60% among patients who express IDO at high level and 27% among IDO-negative patients.In conclusion, IDO-high expressing patients show an increased proportion of refractory disease than IDO negative patients. To support our preliminary findings, a multivariate analysis on a larger cohort of patients is currently ongoing. Disclosures:No relevant conflicts of interest to declare.

Acute Rejection as Key Predictor for Long-Term Outcomes after Kidney Transplantation?

Introduction: Type, severity, timing, and clinical course of acute rejection each influence the impact of a rejection episode, and if renal function recovers fully, there appears to be no survival disadvantage (CTS-Study, Opelz). With modern immunosuppressive regimens, the overall incidence of acute rejection may no longer be the most accurate surrogate marker for long-term kidney graft survival. We investigated the specificity of (subclinical) chronic inflammatory responses (SCAR) induced either by not successful treated rejection episodes, by using different CNI's or ongoing activated innate immune responses. We used the high sensitive parameter for inflammation, indoleamine 2,3 dioxygenase (IDO), in patients after renal transplantation in correlation to graft survival and graft function. Patients and methods: In a retro- (A, n=224, up to 12 years) and prospective study (B, n=124, up to 3 years) of renal transplant recipients we evaluated the IDO behavior for the long-term run. Both groups were comparable concerning the basic demographic data (age, time on dialysis, PRA and waiting time). Estimation of IDO was performed via kynurenine measurement. Results: IDO in normal controls (n=257) was 2,5±0,4 μmol/L Kyn, in stabile renal transplanted patients (n=248) 5,8 ±1,8μmol/L. We identified in both groups already end of the first week posttransplant a statistically significant difference (A:17,2 vs. 7,0 (week 1, median, p< .005; 8,1vs.4,8 (w.6, median, p< .001; B:12,3 vs. 7,0 (w.1, median, p< .001); 6,7 vs. 4,2 (w.6, median, p< .001)) in the IDO levels between patients with/without acute rejection. Patients with an IDO-level > 5, 5 in the follow up (min.3 weeks) and after rejection treatment showed a significant lower graft survival. In the cohort A (IDO < 5,0) 1/5/10 year graft survival was 98/88/69% compared to 88/57/34% (survival data death censored). There was no difference between both CNI's. Rejection rate in A was allover 18%, in B 19,5 % (BPAR). Patients with induction or polyclonal rejection treatment showed lower IDO levels and a better long-term survival. Conclusion: Supported by recent publications we found that chronic transplant nephropathy may not be related solely to CNI toxicity. Our data supporting the results, that not the rejection episode itself is leading to a reduced long-term outcome but a subclinical ongoing inflammatory processes. Once the rejection episode is treated successfully - meaning the reestablishment of the inflammatory homeostasis - the chance for a long graft survival is still given. IDO monitoring might be a helpful tool to identify very early subclinical acute rejection, the best rejection treatment and the optimization of immunsuppressive regimen in sense of rejection prophylaxis.

Increased Plasma Indoleamine 2,3-Dioxygenase Activity and Interferon-γ Levels Correlate with the Severity of Acute Graft-versus-Host Disease after Allogeneic Hematopoietic Stem Cell Transplantation

Indoleamine 2,3-dioxygenase (IDO) is a rate-limiting enzyme for the tryptophan catabolism that plays an important role in the induction of immune tolerance. To evaluate the expression levels of IDO and interferon (IFN)-γ in patients receiving allogeneic hematopoietic stem cell transplantation (allo-HSCT) and to identify the correlation between IDO activity, IFN-γ, and acute graft-versus-host disease (aGVHD), we measured IDO mRNA expression in peripheral blood mononuclear cells in 89 allo-HSCT patients by reverse transcription-polymerase chain reaction. The IDO activity in plasma was also performed by reverse-phase high-performance liquid chromatography; plasma IFN-γ was detected by a standard enzyme-linked immunosorbent assay. IDO mRNA was detected in 55 of 74 patients (74.32%) with aGVHD. Of patients without aGVHD, only 2 of 26 expressed IDO mRNA (7.69%); none of 8 healthy volunteers was positive for IDO expression. Plasma IDO activity was much higher in aGVHD patients than in those without aGVHD (4.74 ± 3.35 vs 1.79 ± 1.02, respectively; P < .0001) or in healthy control subjects (4.74 ± 3.35 vs 1.77 ± .22; P < .0001). Patients with severe (grade III/IV) aGVHD had much higher IDO activity than those with mild (grade I/II) aGVHD (6.57 ± 3.34 vs 2.46 ± 1.41; P < .0001). Meanwhile, there was a significant increase in plasma IFN-γ level in aGVHD patients (P = .0043). IDO activity decreased after alleviation of aGVHD, whereas fluctuation of plasma IDO was also observed upon the recurrence of aGVHD. Plasma IDO activity was correlated with the level of plasma IFN-γ (r = .8288; P < .0001). Using receiver-operating characteristic curves analysis, the sensitivity and specificity for evaluation of aGVHD were determined. The area under the curve of IDO activity was higher than that of IFN-γ (.852 vs .694) with a sensitivity and specificity for IDO of 81% and 78%, respectively, whereas the sensitivity and specificity for IFN-γ were 41% and 93%, respectively. IDO mRNA was expressed in blood mononuclear cells of patients with aGVHD. Plasma IDO activity was elevated in aGVHD patients and was correlated with the severity of aGVHD. In combination with plasma IFN-γ, IDO activity may represent a potential biomarker for the diagnosis and evaluation of aGVHD after allo-HSCT. Intervention of the IDO pathway may also represent an alternative way to overcome steroid-resistant aGVHD.

P.2.d.006 How does amitriptyline treatment affect coenzyme Q levels and oxidative stress in patients diagnosed with depressive disorder?

We investigated the activation and pathophysiological roles of indoleamine 2,3-dioxygenase (IDO) and kynurenine aminotransferase (KAT) in patients with ischemic stroke. Patients were recruited from the acute stroke unit of a general hospital within 24 hours post-stroke. The immune transmission turbidity method was used to determine the concentration of serum high-sensitivity C-reactive protein (hsCRP), apolipoprotein A-1 and apolipoprotein B. The concentrations of triglyceride, cholesterol, high density lipoprotein (HDL), low density lipoprotein and non-esterified fatty acids were determined using an enzymatic method. Tryptophan (TRP), kynurenine (KYN) and kynurenine acid (KYNA) concentrations were determined by high performance liquid chromatography. The National Institutes of Health Stroke Scale (NIHSS) was used to assess the neurological deficits at admission and 3 weeks post-stroke. The IDO and KAT activity ratio were calculated by KYN/TRP and KYNA/KYN, respectively. The correlation between hsCRP and IDO, KAT and NIHSS score was also analyzed. A total of 81 patients with ischemic stroke and 35 normal controls were recruited. Lower TRP, KYNA, HDL and KAT activity ratio were found in the stroke group compared to the control group (p < 0.05). The levels of hsCRP and IDO activity ratio were much higher in the stroke group than the control group (p < 0.01). The IDO activity in patients with ischemic stroke showed a positive correlation with hsCRP (r = 0.425, p = 0.027). In addition, hsCRP and IDO levels were positively associated with the NIHSS score both at admission and 3 weeks post-stroke. These data suggest an inflammatory response characterized by up-regulated IDO activation in ischemic stroke, which might be closely relevant to its pathophysiology.

Plasma Indoleamine 2,3-Dioxygenase and Arginase Type I May Contribute to Decreased Blood T-Cell Count in Hemodialysis Patients

Background: Acquired immunity is impaired in hemodialysis (HD) patients, and decreased T-cell number may contribute. Indoleamine 2,3-dioxygenase (IDO) and arginase type I (ARG) catabolize tryptophane and arginine, respectively, and exert proapoptotic and antiproliferative effects on T-cells. Plasma levels of IDO and ARG and their relation to blood T-cell number were evaluated in HD patients. Methods: Thirty-two HD patients and 20 healthy controls participated in the study. Plasma IDO and ARG were measured by means of enzyme-linked immunosorbent assay. T-cell number was assessed by means of flow cytometry. Results: IDO concentration was significantly higher in HD patients than in healthy volunteers (44.30 ± 31.83 ng/mL vs. 21.28 ± 26.21 ng/mL, p = 0.009). There was a trend for higher ARG concentration in HD patients (13.43 ± 11.91 ng/mL) than in healthy volunteers (9.56 ± 4.03 ng/mL), which, however, did not reach statistic significance (p = 0.099). Absolute T-cell count was significantly lower in HD patients than in healthy controls (1176.99 ± 567.71 cells/mm3 vs. 1519.85 ± 594.96 cells/mm3, p = 0.040). Absolute blood T-cell number was inversely related to plasma IDO (r = −0.490, p = 0.004) and to plasma ARG (r = −0.387, p = 0.029) concentrations. Conclusions: Plasma IDO and ARG may contribute to decreased blood T-cell count in HD patients.

Pharmacodynamic assessment of INCB024360, an inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1), in advanced cancer patients.

2500^ Background: The ineffectiveness of the immune system to control tumor growth is, in part, a result of immunosuppression imposed by negative regulatory mechanisms. Indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme that catabolizes the first and rate-limiting step in the degradation of the essential amino acid tryptophan (Trp) to kynurenine (Kyn), has been shown preclinically to play an important role in tumor-mediated immunosuppression. In cancer patients (pts), elevated IDO1 levels are associated with poor prognosis and shortened survival in a number of tumor types. Here we describe the pharmacodynamic (PD) assessment of INCB024360, a novel inhibitor of IDO1. Methods: Plasma samples were obtained from consented pts in study INCB 24360-101, a phase I dose-escalation study in patients with advanced malignancies. Trp and Kyn levels in plasma were determined by LC/MS/MS. IDO1 activity in activated peripheral blood cells was also monitored. Results: Using anti-IDO1 specific antisera and archived tumor samples, we found IDO1 expression in various human tumors, including ovarian, colorectal, breast and prostate. Consistent with this result, higher Kyn/Trp ratios (1.5-3.4 fold above healthy volunteers) were detected in archived plasma samples from pts, indicative of higher IDO1 activity in cancer pts. To date, 23 pts have been treated with the selective IDO1 inhibitor INCB024360. When plasma samples from patients were collected pre- and post-INCB024360 treatment, significant dose-dependent reductions in plasma Kyn/Trp ratios and Kyn levels were detected. As an additional biomarker measurement, whole blood samples collected from pts at various times after dosing were stimulated ex vivo with interferon-γ and lipopolysaccharide to increase IDO1 activity and also showed dose-dependent decreases in IDO activity. With the current dose regimens and assays we have successfully achieved sustained inhibition of &gt;90% at a well tolerated dose of INCB024360. Conclusions: This is the first demonstration of PD activity of an IDO1-specific inhibitor in cancer pts. Our study also confirms that IDO1 is frequently activated in cancer pts. The methods described will be used to establish a phase II dose.

Dynamic Changes of Indoleamine 2,3-Dioxygenase of Kupffer Cells in Rat Liver Transplant Rejection and Tolerance

AimsTo study the dynamic changes and the immunologic role of indoleamine 2, 3-dioxygenase (IDO) in Kupffer cells (KCs) after rat liver transplantation. MethodsAnimals were randomly divided into two groups: a rejection group (REJ; LEW to BN) and a tolerance group (TOL; BN to LEW). Liver morphological changes were observed optically with hematoxylin/eosin staining. KCs were isolated from recipients. mRNA and protein expressions of IDO were detected by real-time polymerase chain reaction and Western blotting at 1, 3, 5, and 7 days after transplantation. ResultsThe levels of IDO mRNA and protein in KCs of TOL groups were similar to those in REJ groups at day 1 posttransplantation. However, the expression of IDO mRNA and protein time-dependently increased to much higher levels in the TOL than the in REJ groups at 3, 5, and 7 days posttransplantation (P < .05). The peak was observed at 7 days. ConclusionsThe IDO level of KCs was closely associated with immune tolerance induction. IDO-mediated immune modulation appears to be an attractive means to assess transplant tolerance induction.

Indoleamine 2,3-Dioxygenase, Tryptophan Catabolism, and Mycobacterium avium subsp. paratuberculosis: a Model for Chronic Mycobacterial Infections

Virulent mycobacterial infections progress slowly, with a latent period that leads to clinical disease in a proportion of cases. Mycobacterium avium subsp. paratuberculosis is an intracellular pathogen that causes paratuberculosis or Johne's disease (JD), a chronic intestinal disease of ruminants. Indoleamine 2,3-dioxygenase (IDO), an enzyme that regulates tryptophan metabolism, was originally reported to have a role in intracellular pathogen killing and has since been shown to have an important immunoregulatory role in chronic immune diseases. Here we demonstrate an association between increased IDO levels and progression to clinical mycobacterial disease in a natural host, characterizing gene expression, protein localization, and functional effects. IDO mRNA levels were significantly increased in M. avium subsp. paratuberculosis-infected monocytic cells. Levels of both IDO gene and protein expression were significantly upregulated within the affected tissues of sheep with JD, particularly at the site of primary infection, the ileum, of animals with severe multibacillary disease. Lesion severity was correlated with the level of IDO gene expression. IDO gene expression was also increased in the peripheral blood cells of M. avium subsp. paratuberculosis-exposed sheep and cattle. IDO breaks down tryptophan, and systemic increases were functional, as shown by decreased plasma tryptophan levels, which correlated with the onset of clinical signs, a stage well known to be associated with Th1 immunosuppression. IDO may be involved in downregulating immune responses to M. avium subsp. paratuberculosis and other virulent mycobacteria, which may be an example of the pathogen harnessing host immunoregulatory pathways to aid survival. These findings raise new questions about the host-mycobacterium interactions in the progression from latent to clinical disease.

Potential immunosuppressive function of plasma indoleamine 2,3‐dioxygenase in patients with aGVHD after allo‐HSCT

Given the function of indoleamine 2,3-dioxygenase (IDO) in the induction of immune tolerance as a T-cell inhibitor, we investigated whether plasma IDO levels correlate with the biological activity of acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). Plasma levels of IDO were monitored by ELISA in 147 samples from 65 patients who fulfilled the diagnostic histopathological and/or clinical criteria of aGVHD and 16 episodes of infection after allo-HSCT. Elevated plasma IDO levels were associated with occurrence of infection or mild aGVHD (grade I-II). Most patients with grade III-IV aGVHD had relatively low levels of IDO compared to those with mild aGVHD or infection. Responses of aGVHD to immunosuppressive therapy were associated with a decrease in IDO levels in the majority of patients with mild aGVHD, whereas secondary infection was characterized by persistent or increased IDO levels after treatment. Although plasma IDO levels may indicate the severity and outcome of aGVHD and point to appropriate therapies through its function in immune tolerance, it is not aGVHD specific and may not be a distinguishing biomarker of aGVHD.

High activity of indoleamine 2,3-dioxygenase is associated with renal insufficiency in Puumala hantavirus induced nephropathia epidemica

Nephropathia epidemica (NE) is a hemorrhagic fever with renal syndrome caused by Puumala hantavirus. The severity of NE varies greatly. The aim of the present study was to evaluate whether serum indoleamine 2,3-dioxygenase (IDO) activity is associated with the severity of NE. A prospectively collected cohort of 102 consecutive patients with acute serologically confirmed NE was examined. Serum kynurenine, tryptophan, creatinine, CRP, and blood cell count were measured for up to 5 consecutive days after admission. The kynurenine to tryptophan (kyn/trp) ratio reflecting IDO activity was calculated. A maximum kyn/trp ratio >202 µmol/mmol had a sensitivity of 85% and a specificity of 75% for detecting maximum serum creatinine values >250 µmol/L by receiver operating characteristic (ROC) analysis. A maximum kyn/trp ratio >202 µmol/mmol (high IDO level) was also associated with other parameters reflecting the severity of the disease and renal impairment. Patients with high IDO levels had higher maximum serum creatinine (379 vs. 102 µmol/L, P<0.001), plasma C-reactive protein (104.1 vs. 72.1 mg/L, P=0.029), and blood leukocyte values (11.9 vs. 9.0 × 10(9) /L, P<0.001) compared to patients with kyn/trp ratio ≤ 202 µmol/mmol. They also had lower minimum urinary output (1,100 vs. 1,900 ml/day, P<0.001) and longer hospital stays (8 vs. 5 days, P<0.001). In conclusion, high serum IDO activity was associated with increased disease severity and renal impairment in NE.

Indoleamine 2,3-dioxygenase is increased in hemodialysis patients and affects immune response to hepatitis B vaccination

Background Acquired immunity is impaired in hemodialysis (HD) patients. Indoleamine 2,3-dioxygenase (IDO) is inducible by inflammation and through tryptophan depletion and generation of kynurenine pathway products suppresses adaptive immune response. In the present study plasma IDO levels were assessed in HD patients. Its effect on response to HBV vaccination program was evaluated. Patients and methods Sixty-six HD patients and twenty-four healthy volunteers enrolled into the study. All the HD patients were initially vaccinated with four double doses of recombinant HBV vaccine. All doses were repeated in patients who had not responded after complete first vaccination series. Only one boost dose was being administered in patients with initial adequate antibody levels against the HBV surface antigen (anti-HBs > 10 IU/L) who then presented with reduced anti-HBs levels. IDO, CRP, IL-6 and TNF-α were measured by means of ELISA. Results Compared to healthy volunteers, IDO levels were twice higher in HD patients. CRP, IL-6 and TNF-α were also much higher in HD patients. IDO levels were almost twice higher in HD patients with inadequate response to HBV vaccination, than in those with adequate immune response. CRP, IL-6 and TNF-α did not differ between the two patients’ groups. IDO was negatively correlated with all markers of inflammation in HD patients. Conclusion IDO is increased in HD patients. It is possible that after its initial upregulation due to chronic inflammation, IDO curtails its own provoking agent, i.e., inflammation. Increased IDO suppresses adaptive immunity in HD patients, as it is assessed by the response to HBV vaccination.

Matrix Metalloproteinase Inhibitors Attenuate Neuroinflammation Following Focal Cerebral Ischemia in Mice

The aim of this study was to investigate whether matrix metalloproteinase (MMP) inhibitors attenuate neuroinflammation in an ischemic brain following photothrombotic cortical ischemia in mice. Male C57BL/6 mice were anesthetized, and Rose Bengal was systemically administered. Permanent focal ischemia was induced in the medial frontal and somatosensory cortices by irradiating the skull with cold white light. MMP inhibitors, such as doxycycline, minocycline, and batimastat, significantly reduced the cerebral infarct size, and the expressions of monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), and indoleamine 2,3-dioxygenase (IDO). However, they had no effect on the expressions of heme oxygenase-1 and neuroglobin in the ischemic cortex. These results suggest that MMP inhibitors attenuate ischemic brain injury by decreasing the expression levels of MCP-1, TNF-α, and IDO, thereby providing a therapeutic benefit against cerebral ischemia.

Reduced expression of indoleamine 2,3-dioxygenase participates in pathogenesis of preeclampsia via regulatory T cells

Preeclampsia is a complex multi-organ disease and the leading cause of maternofetal morbidity and mortality. Low levels of indoleamine 2,3-dioxygenase (IDO) and diminished numbers of regulatory T cells (Tregs) have been separately reported to participate in the pathogenesis of preeclampsia. In the present study, we aimed to determine whether alterations in the expression of IDO, forkhead box P3 (Foxp3) and interleukin-18 (IL-18) contribute to the pathogenesis of preeclampsia, by measuring their levels in preeclamptic placentae and in placentae from healthy pregnant women as a control. IDO protein levels were determined by immunohistochemistry, while the mRNA levels of IDO, FoxP3 and IL-18 were measured by quantitative RT-PCR. The intensity of IDO immunostaining was lower in the preeclamptic placentae than in the normal controls, and was related to the clinical severity of the preeclampsia. Quantitative RT-PCR revealed that the IDO and IL-18 mRNA levels were reduced in a correlated manner the preeclamptic placentae compared to the controls, and that the levels of FoxP3 mRNA were consistently decreased in the preeclamptic group. A positive correlation betwen FoxP3 and IDO mRNA was found. The results of the study indicate that IL-18, IDO and FoxP3 mRNA levels were decreased in the preeclamptic placentae. Reduced IDO levels in preeclampsia may be partly influenced by IL-18, and result in the maladaptation of maternal tolerance and the pathogenesis of preeclampsia by directly reducing Tregs.

Immune responses regulation following antitumor dendritic cell-based prophylactic, concurrent, and therapeutic vaccination

There is ample evidence in favor of various immunosuppressive mechanisms that weaken antitumor immune responses and affect currently used immunotherapies. Induction of regulatory T cells (Treg) and secretion of indoleamine 2,3-dioxygenase (IDO) by tumor tissue are considered as two main mechanisms of tumor immune escape. However, little is known about the contribution of these mechanisms on the modulation of dendritic cell vaccine-mediated antitumor response. To address this concern, we assessed Treg's infiltration and the expression of Foxp3 and IDO genes in tumor microenvironment following dendritic cell-based antitumor immunotherapy of mice in different protocols of prophylactic, concurrent, and therapeutic vaccination. According to cytotoxicity assay, the vaccinated mice exposed efficient induction of splenic CTLs in all groups. However, only the mice immunized in prophylactic regimen significantly retarded the growth of tumor cells. Interestingly, the Treg content of tumor samples and transcriptional level of both Foxp3 and IDO genes were reduced in this group, while animals that received the vaccine in concurrent and therapeutic protocols showed increase in tumor-infiltrating Tregs and mRNA levels of Foxp3 and IDO. Accordingly, higher expression of these genes resulted in more inhibition of antitumor response. Our findings indicate that tumor progression may enhance the immunoregulatory response and hence emphasize to the effectiveness of vaccination in early stages of tumor growth for avoiding induction of such regulatory responses.

Pancreatic Islet Transplants and IDO: When Starving the Enemy Does You Good

Competition for essential nutrients and/or release of toxic metabolites are mechanisms highly conserved in both bacteria and higher organisms as innate defense systems from external pathogens. One such mechanism is based on the activation of indoleamine 2,3-dioxygenase (IDO), an enzyme that catalyzes the catabolism of the essential amino acid tryptophan (rev. in 1). By depleting tryptophan, IDO limits the ability of many pathogens to synthesize proteins. In addition, activation of the enzyme results in the accumulation of tryptophan breakdown products, collectively known as kynurenines, some of which are toxic to bacteria and parasites. Consistent with the enzyme effects on the containment of pathogens' replication and invasion, constitutive IDO expression in higher organisms is found at mucosal interfaces, such as the mucosa of the intestine and the lung, which are barriers to external microorganisms (2). However, chronic inflammatory processes, particularly those sustained by interferon-driven immune responses, can induce high levels of IDO in many cell types including epithelial, endothelial, and myeloid cells (3–7). Intriguingly, under these conditions, active IDO appears to mute lymphocyte immune responses by “starving” actively proliferating leukocytes, thereby limiting the uncontrolled spread of inflammation. Both high levels of IDO as well as activation of the enzyme by redox active compounds present in the inflammatory microenvironment are required for the immunosuppressive effect (8). The ability of IDO to regulate lymphocyte functions has prompted many investigators to test the effect of IDO overexpression at transplantation sites as a mean to avert destructive allogeneic immune responses against heart, skin, lung, cornea, and bone marrow grafts (9 …

Secretion of Indoleamine 2,3-Dioxygenase, an Immunomodulatory Substance, by Adipose-Derived Mesenchymal Stem Cell

Lipoaspirate, a wasted by product from liposuction procedure recently has been shown to contain abundant adipose-derived-mesenchymal stem cells (MSCs). Mesenchymal stem cells (MSCs) have been studied in many research areas to regenerate many cell lineages. In addition, MSCs have immunomodulatory effect. This capability has been utilized in several clinical studies in hematopoetic stem cell and organ transplantation as a strategy to reduce the risk of Graft versus Host Disease (GvHD). It has been reported that the ‘stimulated’ MSC is able to secrete substances to suppress tissue rejection. One of the substances was known to be indoleamine 2,3-dioxygenase (IDO). A previous study has characterized the secretion of IDO by bone marrow-derived MSCs stimulated by an inflammatory mediator interferon gamma (IFN-γ). IDO has been detected using Western blot analysis and by High Performance Liquid Chromatography (HPLC) assay. The aim of this study was to detect the presence of IDO in AD-MSCs culture with and without INFγ stimulation. Our study showed that AD-MSC stimulated with IFN-γ significantly secreted high level of IDO as detected by Enzyme-Linked Immuno Sorbent Assay (ELISA). Despite its property as a proinflammatory mediator, IFN-γ has shown to be able to induce IDO secretion in MSC culture which suggests the immuno modulatory effect of MSC. This study clearly demonstrates the potential application of adipose-derived MSC in the immunomodulatory strategy for allogenic transplantation. Keyword : mesenchymal stem cell, indoleamine 2,3-dioxygenase, IFN-γ

Gut CD103+ dendritic cells express indoleamine 2,3-dioxygenase which influences T regulatory/T effector cell balance and oral tolerance induction

ObjectiveCD103+ gut dendritic cells (DCs) have been shown to be required for de novo conversion of adaptive T regulatory (Treg) cells. Indoleamine 2,3-dioxygenase (IDO) is an enzyme involved in tryptophan...

Indoleamine 2,3-Dioxygenase Tissue Distribution and Cellular Localization in Mice: Implications for Its Biological Functions

Earlier studies have suggested that indoleamine 2,3-dioxygenase (IDO) has a wide tissue distribution in mammals. However, detailed information on its cellular localization and also the levels of expression in various tissues is still scarce. In the present study, we sought to determine the cellular localization of IDO and also to quantify the level of its expression in various mouse tissues by using the branched DNA signal amplification assay, Western blotting, and immunohistochemical staining. The highest levels of constitutive IDO expression were found to be selectively present in the caput of epididymis, except for its initial segment. IDO expression was also detected inside the luminal compartment and even in the stereocilia within this region. In the prostate, high levels of IDO were selectively expressed in the capsular cells. In addition, high levels of IDO expression were also selectively detected in certain types of cells in the placenta, spleen, thymus, lung, and digestive tract. Notably, the morphological features of most of the positively stained cells in these organs closely resembled those of antigen-presenting cells. Based on the tissue distribution and cellular localization characteristics of IDO, it is hypothesized that its expression may serve two main functions: one is to deplete tryptophan in an enclosed microenvironment (such as in the epididymal duct lumen) to prevent bacterial or viral infection, and the other is to produce bioactive tryptophan catabolites that would serve to suppress T-cell-mediated immune responses against self-antigens, fetal antigens, or allogeneic antigens, in different situations.

Species Variation in the Mechanisms of Mesenchymal Stem Cell-Mediated Immunosuppression

Bone marrow-derived mesenchymal stem cells (MSCs) hold great promise for treating immune disorders because of their immunoregulatory capacity, but the mechanism remains controversial. As we show here, the mechanism of MSC-mediated immunosuppression varies among different species. Immunosuppression by human- or monkey-derived MSCs is mediated by indoleamine 2,3-dioxygenase (IDO), whereas mouse MSCs utilize nitric oxide, under the same culture conditions. When the expression of IDO and inducible nitric oxide synthase (iNOS) were examined in human and mouse MSCs after stimulation with their respective inflammatory cytokines, we found that human MSCs expressed extremely high levels of IDO, and very low levels of iNOS, whereas mouse MSCs expressed abundant iNOS and very little IDO. Immunosuppression by human MSCs was not intrinsic, but was induced by inflammatory cytokines and was chemokine-dependent, as it is in mouse. These findings provide critical information about the immunosuppression of MSCs and for better application of MSCs in treating immune disorders.