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Objectives: Pediatric tuberculosis (TB) remains difficult to diagnose. The plasma kynurenine to tryptophan ratio (K/T ratio) is a potential biomarker for TB diagnosis and treatment response but has not been assessed in children., Methods: We performed a targeted diagnostic accuracy analysis of four biomarkers: kynurenine abundance, tryptophan abundance, the K/T ratio, and IDO-1 gene expression. Data were obtained from transcriptome and metabolome profiling of children with confirmed tuberculosis and age- and sex-matched uninfected household contacts of pulmonary tuberculosis patients. Each biomarker was assessed as a baseline diagnostic and in response to successful TB treatment., Results: Despite non-significant between-group differences in unbiased analysis, the K/T ratio achieved an area under the receiver operator characteristic curve (AUC) of 0.667 and 81.5% sensitivity for TB diagnosis. Kynurenine, tryptophan, and IDO-1 demonstrated diagnostic AUCs of 0.667, 0.602, and 0.463, respectively. None of these biomarkers demonstrated high AUCs for treatment response. The AUC of the K/T ratio was lower than biomarkers identified in unbiased analysis, but improved sensitivity over existing commercial assays for pediatric TB diagnosis., Conclusions: Plasma kynurenine and the K/T ratio may be useful biomarkers for pediatric TB. Ongoing studies in geographically diverse populations will determine optimal use of these biomarkers worldwide., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Tornheim, Paradkar, Zhao, Kulkarni, Pradhan, Kinikar, Kagal, Gupte, Mave, Gupta and Karakousis.)

The obesity epidemic has contributed to an escalating prevalence of metabolic diseases in children. Overnutrition leads to increased tryptophan uptake and availability. An association between the induction of the tryptophan catabolic pathway via indoleamine 2,3-dioxygenase (IDO) activity and obesity-related inflammation has been observed. This study aimed to investigate the impact of pediatric obesity on tryptophan metabolism and the potential relationship with metabolic disease. In this prospective cohort study, plasma kynurenine, tryptophan, and serotonin levels were measured by ELISA, and IDO activity was estimated by calculating the kynurenine/tryptophan ratio in a clinically characterized population with severe obesity (BMI ≥ 97th percentile) aged 9 to 19 ( n = 125). IDO activity and its product kynurenine correlated with BMI z-score and body fat mass, whereas concentrations of serotonin, the alternative tryptophan metabolite, negatively correlated with these measures of adiposity. Kynurenine and tryptophan, but not serotonin levels, were associated with disturbed glucose metabolism. Tryptophan concentrations negatively correlated with adiponectin and were significantly higher in prediabetes and metabolically unhealthy obesity. In conclusion, BMI and body fat mass were associated with increased tryptophan catabolism via the kynurenine pathway and decreased serotonin production in children and adolescents with severe obesity. The resulting elevated kynurenine levels may contribute to metabolic disease in obesity.

Background: CKD, characterized by retained uremic solutes, is a strong and independent risk factor for thrombosis after vascular procedures . Urem ic solutes such as indoxyl sulfate (IS) and kynurenine (Kyn) mediate prothrombotic effect through tissue factor (TF). IS and Kyn biogenesis depends on multiple enzymes, with therapeutic implications unexplored. We examined the role of indoleamine 2,3-dioxygenase-1 (IDO-1), a rate-limiting enzyme of kynurenine biogenesis, in CKD-associated thrombosis after vascular injury., Methods: IDO-1 expression in mice and human vessels was examined. IDO-1 -/- mice, IDO-1 inhibitors, an adenine-induced CKD, and carotid artery injury models were used., Results: Both global IDO-1 -/- CKD mice and IDO-1 inhibitor in wild-type CKD mice showed reduced blood Kyn levels, TF expression in their arteries, and thrombogenicity compared with respective controls. Several advanced IDO-1 inhibitors downregulated TF expression in primary human aortic vascular smooth muscle cells specifically in response to uremic serum. Further mechanistic probing of arteries from an IS-specific mouse model, and CKD mice, showed upregulation of IDO-1 protein, which was due to inhibition of its polyubiquitination and degradation by IS in vascular smooth muscle cells. In two cohorts of patients with advanced CKD, blood IDO-1 activity was significantly higher in sera of study participants who subsequently developed thrombosis after endovascular interventions or vascular surgery., Conclusion: Leveraging genetic and pharmacologic manipulation in experimental models and data from human studies implicate IS as an inducer of IDO-1 and a perpetuator of the thrombotic milieu and supports IDO-1 as an antithrombotic target in CKD., (Copyright © 2021 by the American Society of Nephrology.)

Fibrosing chronic graft-versus-host disease (cGVHD) is a debilitating complication of allogeneic stem cell transplantation (alloSCT). A driver of fibrosis is the kynurenine (Kyn) pathway, and Kyn metabolism patterns and cytokines may influence cGVHD severity and manifestation (fibrosing versus gastrointestinal [GI] cGVHD). Using a liquid chromatography-tandem mass spectrometry approach on sera obtained from 425 patients with allografts, we identified high CXCL9, high indoleamine-2,3-dioxygenase (IDO) activity, and an activated Kyn pathway as common characteristics in all cGVHD subtypes. Specific Kyn metabolism patterns could be identified for non-severe cGVHD, severe GI cGVHD, and fibrosing cGVHD, respectively. Specifically, fibrosing cGVHD was associated with a distinct pathway shift toward anthranilic and kynurenic acid, correlating with reduced activity of the vitamin-B2-dependent kynurenine monooxygenase, low vitamin B6, and increased interleukin-18. The Kyn metabolite signature is a candidate biomarker for severe fibrosing cGVHD and provides a rationale for translational trials on prophylactic vitamin B2/B6 supplementation for cGVHD prevention., Competing Interests: The authors declare no competing interests., (© 2021 The Authors.)

Background: Indoleamine 2,3 dioxygenase (IDO), the rate-limiting enzyme in the kynurenine (Kyn) pathway of tryptophan (Trp) degradation, is modulated by inflammation, and is regarded as a key molecule driving immunotolerance and immunosuppressive mechanisms. Little is known about IDO activity in patients with active coronary artery disease (CAD)., Methods: We prospectively enrolled patients who were scheduled to undergo coronary angiography. Measurement of IDO, high-sensitivity troponin T (hs-TnT), and high-sensitivity C-reactive protein (hs-CRP) levels was performed at baseline, and IDO activity was monitored at the 6-month follow-up., Results: Three hundred and five patients were enrolled. Ninety-eight patients (32.1%) presented with recent acute coronary syndrome (ACS). Significant difference in IDO, kynurenine, and hs-TnT between patients with and without significant CAD was observed. Baseline IDO activity, kynurenine level, and hs-TnT level were all significantly higher in significant CAD patients with 3-vessel, 2-vessel, and 1-vessel involvement than in those with insignificant CAD [(0.17, 0.13, and 0.16 vs. 0.03, respectively; p = 0.003), (5.89, 4.58, and 5.24 vs. 2.74 µM/g, respectively; p = 0.011), and (18.27, 12.22, and 12.86 vs. 10.89 mg/dL, respectively; p < 0.001)]. One-year mortality was 3.9%. When we compared between patients who survived and patients who died, we found a significantly lower prevalence of left main (LM) disease by coronary angiogram (6.1% vs. 33.3%, p = 0.007), and also a trend toward higher baseline kynurenine (5.07 vs. 0.79 µM/g, p = 0.082) and higher IDO (0.15 vs. 0.02, p = 0.081) in patients who survived., Conclusion: Immunometabolic response mediated via IDO function was enhanced in patients with CAD, and correlated with the extent and severity of disease. Patients with LM disease had higher 1-year mortality. Lower level of IDO, as suggested by inadequate IDO response, demonstrated a trend toward predicting 1-year mortality. Trial registration TCTR Trial registration number TCTR20200626001. Date of registration 26 June 2020. "Retrospectively registered"., (© 2021. The Author(s).)

Objective: To explore the correlation of indoleamine-2,3-dioxygenase (IDO) and chronic kidney disease (CKD)., Methods: A total of 154 CKD patients and 42 non-CKD patients were recruited. Patients were grouped into ACR1~ACR3 (<30 mg/g, 30-300 mg/g, and >300 mg/g). Biomarkers in different groups were compared by ANOVA. Correlation was calculated by Pearson or Spearman analysis and binary logistic regression. The ROC curve was also performed., Results: The levels of albumin, serum creatinine (sCr), and IDO in non-CKD patients were significantly different from those in CKD3-CKD5 stages ( p < 0.05). IDO was correlated with age, proteinuria, ACR, and eGFR ( p < 0.01). After adjusting for CKD-related indices, ln(IDO) was an independent risk factor for CKD (3.48, p < 0.05). The analysis of ROC curve revealed a best cut-off for IDO was 0.0466 and yielded a sensitivity of 83.8% and a specificity of 75%. Hemoglobin, total protein, and albumin in the ACR1 group were significantly higher than those in the ACR2 and ACR3 groups ( p < 0.01), while sCr and IDO levels were significantly lower than those in the ACR2 and ACR3 groups ( p < 0.01 or p < 0.05). After adjusting for CKD-related indices, ln(IDO) was still an independent risk factor for ACR (OR = 2.7, p < 0.05). The analysis of ROC curve revealed a best cut-off for IDO was 0.075 and yielded a sensitivity of 71.9% and a specificity of 72.2%., Conclusion: IDO may be a promising biomarker to predict CKD and assess kidney function., Competing Interests: The authors have nothing to disclose., (Copyright © 2021 Binbin Pan et al.)

Background: Indoleamine 2, 3-dioxygenase-1 (IDO1) is a promising target for immunotherapy in bladder cancer (BC). IDO1 breaks-down tryptophan to generate kynurenine derivatives, which may activate the aryl hydrocarbon receptor (AHR). AHR is an important target for carcinogens, but its association with BC progression was unknown. Two IDO1 inhibitors used in clinical trials are 1-methyl-D-tryptophan (MT) and INCB240360. Because MT is an aromatic hydrocarbon, it may be a ligand for AHR. We hypothesized that AHR could be associated with BC progression and that MT could activate AHR in BC., Methods: BC patients (n = 165) were selected from the Gene Expression Omnibus database. A cut-off point for relative expression of AHR and cytochrome 450 enzymes (CYP1A1, CYP1A2, and CYP1B1; markers of AHR activation) was determined to compare with the grade, stage, and tumor progression. For in vitro experiments, RT4 (grade 1) and T24 (grade 3) BC cells were incubated with MT and INCB240360 to evaluate the expression of AHR and CYP1A1., Results: AHR activation was associated with grade, stage, and progression of BC. T24 cells express more CYP1A1 than RT4 cells. Although IDO1 expression and kynurenine production are elevated in T24 cells concomitantly to CYP1A1 expression, IDO1 inhibitors were not able to decrease CYP1A1 expression, in contrast, MT significantly increased it in both cell lines., Conclusion: In conclusion, it is rational to inhibit IDO1 in BC, among other factors because it contributes to AHR activation. However, MT needs to be carefully evaluated for BC because it is an AHR pathway agonist independently of its effects on IDO1.

Septic shock is associated with a strong inflammatory response that induces vasodilation and vascular hyporeactivity. We investigated the role for tryptophan-pathway catabolites of proinflammatory cytokines in septic shock.We prospectively included 30 patients with very recent-onset septic shock and 30 healthy volunteers. The following were assayed once in the controls and on days 1, 2, 3, 7, and 14 in each patient: plasma free and total tryptophan, platelet and plasma serotonin, total blood serotonin, urinary serotonin, plasma and urinary 5-hydroxyindolacetic acid, plasma kynurenine, monoamine oxidase activity, and total indole amine 2,3-dioxygenase activity. Organ-system failure and mortality were recorded.Compared with the healthy controls, the patients with septic shock had 2-fold to 3-fold lower total tryptophan levels throughout the 14-day study period. Platelet serotonin was substantially lower, while monoamine oxidase activity and 5-hydroxyindolacetic acid were markedly higher in the patients than in the controls, consistent with the known conversion of tryptophan to serotonin, which is then promptly and largely degraded to 5-hydroxyindolacetic acid. Plasma kynurenine was moderately increased and indole amine 2,3-dioxygenase activity markedly increased in the patients versus the volunteers, reflecting conversion of tryptophan to kynurenine. Changes over time in tryptophan metabolites were not associated with survival in the patients but were associated with the Sequential Organ Failure Assessment score and hemodynamic variables including hypotension and norepinephrine requirements.Our results demonstrate major tryptophan pathway alterations in septic shock. Marked alterations were found compared with healthy volunteers, and tryptophan metabolite levels were associated with organ failure and hemodynamic alterations. Tryptophan metabolite levels were not associated with surviving septic shock, although this result might be ascribable to the small sample size.Trial registration: ClinicalTrials.gov; No: NCT00684736; URL: www.clinicaltrials.gov.

Background: Although Th2 immune activation is predominant in allergic diseases, neopterinlevels and indoleamine 2,3-dioxygenase (IDO)-1 activity (kynurenine:tryptophan ratio), which reflect Th1 immune activity, increase with interferon-gamma (IFN-γ) stimulation. We investigated neopterin, tryptophan, and kynurenine levels as biomarkersof the Th1 immune system activation and changes in IDO-1 activityin children with asthma, allergic rhinitis, and atopic dermatitis, as well as the relationship between these biomarkers and the total IgE level, age, and disease severity., Methods: We divided 205 children (80 girls and 125 boys, four months to 17 years old) into four groups: controls, patients with asthma, patients with allergic rhinitis, and patients with atopic dermatitis. Peripheral venous blood samples were collected. Neopterin levels were determined by an enzyme immunoassay. Tryptophan and kynurenine levels were analyzed using HPLC. IDO-1 enzyme activity was calculated using tryptophan and kynurenine levels. IgE levels were measured. The Mann-Whitney U test, Kruskal-Wallis test, and Conover post-hoc method were used for statistical analysis., Results: Neopterin, tryptophan, and kynurenine levels were higher and IgE levels and IDO-1 enzyme activity were lower in patients with asthma and allergic rhinitis than in controls ( P <0.05). Patients with atopic dermatitis showed higher neopterin, tryptophan, and kynurenine levels, higher IDO-1 activity, and lower IgE levels thancontrols ( P <0.05)., Conclusions: The Th1/Th2 balance is disrupted in children with allergic diseases, concomitant with increased Th1-mediated immune response activation and reduced IgEproduction, which is promoted by Th2-type cytokines., Competing Interests: No potential conflicts of interest related to this article are reported., (© The Korean Society for Laboratory Medicine.)

Metabolic syndrome (MetS) is a cluster of conditions, increasing the risk of developing diseases that can lead to premature death. Interferon γ-inducible (the production of which is dependent on the IFNγ rs2430561 polymorphism) tryptophan-kynurenine inflammatory cascade helps to understand the increased association between inflammatory process and MetS, which is why we seek the relationship between the IFNγ gene polymorphisms and serum levels of markers of interferon-gamma (IFNγ)-inducible inflammatory cascade. The study sample consisted of 416 women, including 118 (28.4%) with MetS. The research procedure involved interview, anthropometric measurements, and blood collection. Kynurenine levels were significantly higher in the group of women with MetS. In the group with MetS, the A/T genotype of the IFNγ gene was accompanied by higher kynurenine levels. A direct relationship between the IFNγ gene polymorphisms and the rest of the markers of IFNγ-inducible inflammatory cascade was not confirmed with regard to MetS in 45 to 60-year-old women. A disparity in the kynurenine level, as well as the relationship between the presence of the A/T genotype of the IFNγ gene and a higher level of kynurenine in the group of women with MetS, may indicate an association between inflammation, metabolic disorders and tryptophan-kynurenine inflammatory cascade.

The association between altered gut microbiota, intestinal permeability, inflammation and cardiometabolic diseases is becoming increasingly clear but remains poorly understood 1,2 . Indoleamine 2,3-dioxygenase is an enzyme induced in many types of immune cells, including macrophages in response to inflammatory stimuli, and catalyzes the degradation of tryptophan along the kynurenine pathway. Indoleamine 2,3-dioxygenase activity is better known for its suppression of effector T cell immunity and its activation of regulatory T cells 3,4 . However, high indoleamine 2,3-dioxygenase activity predicts worse cardiovascular outcome 5-9 and may promote atherosclerosis and vascular inflammation 6 , suggesting a more complex role in chronic inflammatory settings. Indoleamine 2,3-dioxygenase activity is also increased in obesity 10-13 , yet its role in metabolic disease is still unexplored. Here, we show that obesity is associated with an increase of intestinal indoleamine 2,3-dioxygenase activity, which shifts tryptophan metabolism from indole derivative and interleukin-22 production toward kynurenine production. Indoleamine 2,3-dioxygenase deletion or inhibition improves insulin sensitivity, preserves the gut mucosal barrier, decreases endotoxemia and chronic inflammation, and regulates lipid metabolism in liver and adipose tissues. These beneficial effects are due to rewiring of tryptophan metabolism toward a microbiota-dependent production of interleukin-22 and are abrogated after treatment with a neutralizing anti-interleukin-22 antibody. In summary, we identify an unexpected function of indoleamine 2,3-dioxygenase in the fine tuning of intestinal tryptophan metabolism with major consequences on microbiota-dependent control of metabolic disease, which suggests indoleamine 2,3-dioxygenase as a potential therapeutic target.

Low-grade gliomas (LGGs) are the most common brain tumor affecting children. We recently reported an early phase clinical trial of a peptide-based vaccine, which elicited consistent antigen-specific T cell responses in pediatric LGG patients. Additionally, we observed radiologic responses of stable disease (SD), partial response (PR), and near-complete/complete response (CR) following therapy. To identify biomarkers of clinical response in peripheral blood, we performed RNA sequencing on PBMC samples collected at multiple time points. Patients who showed CR demonstrated elevated levels of T cell activation markers, accompanied by a cytotoxic T cell response shortly after treatment initiation. At week 34, patients with CR demonstrated both IFN signaling and Poly-IC:LC adjuvant response patterns. Patients with PR demonstrated a unique, late monocyte response signature. Interestingly, HLA-V expression, before or during therapy, and an early monocytic hematopoietic response were strongly associated with SD. Finally, low IDO1 and PD-L1 expression before treatment and early elevated levels of T cell activation markers were associated with prolonged progression-free survival. Overall, our data support the presence of unique peripheral immune patterns in LGG patients associated with different radiographic responses to our peptide vaccine immunotherapy. Future clinical trials, including our ongoing phase II LGG vaccine immunotherapy, should monitor these response patterns.

Objective: To study the value of indoleamine 2,3-dioxygenase (IDO) in the early diagnosis of systemic inflammatory response syndrome (SIRS) after cardiopulmonary bypass in children with congenital heart disease., Methods: A total of 90 children with congenital heart disease who underwent cardiopumonary bypass surgery between May 2012 and January 2016 were enrolled. According to the prsence or absence of SIRS after surgery, they were divided into SIRS group (n=43) and control group (n=47). Peripheral blood samples were collected before surgery, during surgery, and after surgery. Serum levels of IDO, C-reactive protein (CRP), and interleukin-6 (IL-6) were measured and compared between the two groups. The receiver operating characteristic (ROC) curve was used to evaluate their diagnostic efficiency., Results: Compared with the control group, the SIRS group had higher serum CRP levels at 72 hours after surgery, higher IL-6 levels during surgery and at 72 hours after surgery, and higher IDO levels at 24 and 72 hours after surgery. IDO had a certain value in the diagnosis of SIRS at 24 hours after surgery with an area under the ROC curve (AUC) of 0.793, a specificity of 100%, and a sensitivity of 58.14%. CRP, IL-6, and IDO had a certain value in the diagnosis of SIRS at 72 hours after surgery. IDO had the highest diagnostic efficiency with an AUC of 0.927, a specificity of 95.74%, and a sensitivity of 76.74% at 72 hours after surgery., Conclusions: IL-6, CRP, and IDO have a certain value in the diagnosis of SIRS after surgery for congenital heart disease, and IDO has a higher diagnostic efficiency. IDO can predict the development of SIRS in children after surgery for congenital heart disease earlier.

This study investigates molecular and cellular mechanisms involved in mesenchymal stem cell (MSC)-mediated modulation of IL-17 signaling during liver fibrosis. Mice received CCl 4 (1 μl/g intraperitoneally) twice/week for 1 month. MSCs (1 × 10 6 ), or MSC-conditioned medium (MSC-CM), were intravenously injected 24 h after CCl 4 and on every 7th day. Liver fibrosis was determined by macroscopic examination, histological analysis, Sirius red staining, and RT-PCR. Serum levels of cytokines, indoleamine 2,3-dioxygenase (IDO), and kynurenine were determined by ELISA. Flow cytometry was performed to identify liver-infiltrated cells. In vitro, CD4 + T cells were stimulated and cultured with MSCs. 1-methyltryptophan was used for inhibition of IDO. MSCs significantly attenuated CCl 4 -induced liver fibrosis by decreasing serum levels of inflammatory IL-17, increasing immunosuppressive IL-10, IDO, and kynurenine, reducing number of IL-17 producing Th17 cells, and increasing percentage of CD4 + IL-10 + T cells. Injection of MSC-CM resulted with attenuated fibrosis accompanied with the reduced number of Th17 cells in the liver and decreased serum levels of IL-17. MSC-CM promoted expansion of CD4 + FoxP3 + IL-10 + T regulatory cells and suppressed proliferation of Th17 cells. This phenomenon was completely abrogated in the presence of IDO inhibitor. MSCs, in IDO-dependent manner, suppress liver Th17 cells which lead to the attenuation of liver fibrosis., (© 2017 Steunstichting ESOT.)

Indoleamine 2,3-dioxygenase 1 (IDO1) is an intracellular rate-limiting enzyme in the metabolism of tryptophan along the kynurenine pathway, subsequently mediating the immune response; however, the role of IDO1 in liver fibrosis and cirrhosis is still unclear. In this study, we investigated the role of IDO1 in the development of hepatic fibrosis and cirrhosis. Patients with hepatitis B virus-induced cirrhosis and healthy volunteers were enrolled. For animals, carbon tetrachloride (CCl4) was used to establish liver fibrosis in wild-type and IDO1 knockout mice. Additionally, an IDO1 inhibitor (1-methyl-D-tryptophan) was administered to WT fibrosis mice. Liver lesions were positively correlated with serum IDO1 levels in both the clinical subjects and hepatic fibrosis mice. A positive correlation between serum IDO1 levels and liver stiffness values was found in the cirrhosis patients. Notably, IDO1 knockout mice were protected from CCl4-induced liver fibrosis, as reflected by unchanged serum alanine transaminase and aspartate transaminase levels and lower collagen deposition, α-smooth muscle actin expression and apoptotic cell death rates. On the other hand, tryptophan 2,3-dioxygenase (TDO), another systemic tryptophan metabolism enzyme, exhibited a compensatory increase as a result of IDO1 deficiency. Moreover, hepatic interleukin-17a, a characteristic cytokine of T helper 17 (Th17) cells, and downstream cytokines' mRNA levels showed lower expression in the IDO1-/- model mice. IDO1 appears to be a potential hallmark of liver lesions, and its deficiency protects mice from CCl4-induced fibrosis mediated by Th17 cells down-regulation and TDO compensation.

Indoleamine 2,3-dioxygenase (IDO) has emerged as a pivotal enzyme for mediating immune tolerance. Because IDO metabolizes tryptophan into kynurenine, the plasma kynurenine/tryptophan (Kyn/Trp) ratio has been widely used as a marker of systemic IDO. Here, we evaluated the clinical value of using the plasma Kyn/Trp ratio to estimate cell-mediated immune responses to tuberculin skin testing and risk of new bacterial infection. We also compared the Kyn/Trp ratio to a novel IDO marker, the IDO median fluorescence index (MFI) of peripheral blood mononuclear cells, which was determined by flow cytometry. In 228 patients from two hemodialysis centers, the two IDO markers were higher in patients than in healthy controls but were not correlated with each other. In vitro experiments demonstrated that peripheral blood mononuclear cells could not metabolize tryptophan into kynurenine, indicating that the increased Kyn/Trp ratio was IDO-independent. Skin induration diameters of tuberculin skin testing were correlated with the IDO MFI (negatively), but not the Kyn/Trp ratio. Further, in a 24-month prospective cohort, the Kyn/Trp ratio was not correlated with clinical infection. Alternatively, patients with a higher IDO MFI had a lower accumulative infection-free survival rate. Using a Cox proportional hazard model, it was also revealed that a higher IDO MFI was significantly associated with new bacterial infection. Taken together, these results indicate that the Kyn/Trp ratio is not a reliable circulating IDO marker in hemodialysis patients. However, the IDO MFI reflects an immunocompromised state and thus might be a potential clinical marker of bacterial infection.

Background: The level and activity of indoleamine 2,3-dioxygenase (IDO) and the concentrations of L-tryptophan and its metabolite L-kynurenine were determined in association with various renal diseases. However, there have been no data regarding these parameters in patients on peritoneal dialysis compared to those undergoing hemodialysis or kidney transplantation., Methods: This study investigated the level and activity of IDO and determined oxidative balance by calculating the total oxidant status (TOS), total antioxidant status (TAS), and oxidative stress index (OSI). We enrolled 60 kidney disease patients, including 20 on peritoneal dialysis (PD group), 19 on hemodialysis (HD group), and 21 with kidney transplantation (KT group), as well as 21 control group., Results: IDO levels were increased in the PD, HD, and KT groups compared to the control group. The concentration of kynurenine was significantly increased in the PD group compared to the other groups (p < 0.01). The kynurenine/tryptophan ratio was increased in the PD group compared to the other groups (all p < 0.01). TAS levels in the PD and HD groups were significantly decreased compared to the control group (both p < 0.05). TAS levels in the PD group were significantly decreased compared to the KT group. TOS levels in the PD group were higher than in the HD and KT groups., Conclusion: The results showed that IDO levels were increased in peritoneal dialysis and hemodialysis patients and in renal transplant recipients, while oxidative stress was found to be related to IDO activity and was most increased in the patients on peritoneal dialysis.

Aim: To evaluate whether serum and tumor indoleamine 2,3-dioxygenase activities can predict lymphatic invasion (LI) or lymph node metastasis in colorectal carcinoma., Methods: The study group consisted of 44 colorectal carcinoma patients. The patients were re-grouped according to the presence or absence of LI and lymph node metastasis. Forty-three cancer-free subjects without any metabolic disturbances were included into the control group. Serum neopterin was measured by enzyme linked immunosorbent assay. Urinary neopterin and biopterin, serum tryptophan (Trp) and kynurenine (Kyn) concentrations of all patients were determined by high performance liquid chromatography. Kyn/Trp was calculated and its correlation with serum neopterin was determined to estimate the serum indoleamine 2,3-dioxygenase activity. Tissue sections from the studied tumors were re-examined histopathologically and were stained by immunohistochemistry with indoleamine-2,3-dioxygenase antibodies., Results: Neither serum nor urinary neopterin was significantly different between the patient and control groups (both P > 0.05). However, colorectal carcinoma patients showed a significant positive correlation between the serum neopterin levels and Kyn/Trp (r = 0.450, P < 0.01). Urinary biopterin was significantly higher in cancer cases (P < 0.05). Serum Kyn/Trp was significantly higher in colorectal carcinoma patients (P < 0.01). Lymphatic invasion was present in 23 of 44 patients, of which only 12 patients had lymph node metastasis. Eleven patients with LI had no lymph node metastasis. Indoleamine-2,3-dioxygenase intensity score was significantly higher in LI positive cancer group (44.56% ± 6.11%) than negative colorectal cancer patients (24.04% ± 6.90%), (P < 0.05). Indoleamine 2,3-dioxygenase expression correlated both with the presence of LI and lymph node metastasis (P < 0.01 and P < 0.05, respectively). A significant difference between the accuracy of diagnosis by using either total indoleamine-2,3-dioxygenase immunostaining score or of lymph node metastasis was found during the evaluation of cancer patients., Conclusion: Indoleamine-2,3-dioxygenase expression may predict the presence of unrecognized LI and lymph node metastasis and may be included in the histopathological evaluation of colorectal carcinoma cases.

Objective: To identify independent contributors of fatigue in primary Sjögren's syndrome (SS) patients, taking into account clinical, laboratory, and psychological features, and to explore the potential role of interferon (IFN)-induced gene indoleamine 2,3-dioxygenase (IDO-1), anti-21-hydroxylase (anti-21[OH]) antibodies, and soluble BAFF., Methods: Detailed clinical and laboratory characteristics were recorded for 106 primary SS patients. The Functional Assessment of Chronic Illness Therapy-Fatigue, Zung Depression Scale, State-Trait Anxiety Inventory, Eysenck Personality Questionnaire Scale, and Athens Insomnia Scale were adopted to assess fatigue, depression, anxiety, and sleep disturbances, respectively. Peripheral whole blood expression levels of IDO-1, as well as type I and II IFN-induced genes were calculated using quantitative reverse transcriptase-polymerase chain reaction. Serum anti-21(OH) antibodies and soluble BAFF levels were determined by a radioimmunoassay and an enzyme-linked immunosorbent assay, respectively. Univariate and multivariate models were performed to identify determinants of fatigue., Results: Fatigue was detected in 32 of 106 (30.2%) primary SS patients. In univariate analysis, fatigue was associated with arthralgias/myalgias, fibromyalgia hydroxychloroquine therapy, both state and trait anxiety scores, depression, and neuroticism, as well as impaired sleep patterns. Multivariate analysis revealed neuroticism (odds ratio [OR] 6.9, [95% confidence interval (95% CI) 1.7-28.0]), depression (OR 3.0 [95% CI 0.8-11.0]), and fibromyalgia (OR 5.5 [95% CI 1.1-27.7]) as independent fatigue contributors. Soluble BAFF levels, anti-21(OH) autoantibodies, and IDO-1 messenger RNA expression did not significantly differ between fatigued and nonfatigued primary SS patients., Conclusion: Depression, neuroticism, and fibromyalgia play a major role in primary SS-associated fatigue and should be addressed in clinical practice, with active collaboration between rheumatologists and mental health professionals. Further studies are warranted in order to explore underlying pathophysiologic pathways that might explain fatigue in the setting of primary SS., (© 2016, American College of Rheumatology.)

The development of inhibitory antibodies to factor VIII (FVIII) is a major obstacle in using this clotting factor to treat individuals with hemophilia A. Patients with a congenital absence of FVIII do not develop central tolerance to FVIII, and therefore, any control of their FVIII-reactive lymphocytes relies upon peripheral tolerance mechanisms. Indoleamine 2,3-dioxygenase 1 (IDO1) is a key regulatory enzyme that supports Treg function and peripheral tolerance in adult life. Here, we investigated the association between IDO1 competence and inhibitor status by evaluating hemophilia A patients harboring F8-null mutations that were either inhibitor negative (n = 50) or positive (n = 50). We analyzed IDO1 induction, expression, and function for any relationship with inhibitor occurrence by multivariable logistic regression and determined that defective TLR9-mediated activation of IDO1 induction is associated with an inhibitor-positive status. Evaluation of experimental hemophilic mouse models with or without functional IDO1 revealed that tryptophan metabolites, which result from IDO1 activity, prevent generation of anti-FVIII antibodies. Moreover, treatment of hemophilic animals with a TLR9 agonist suppressed FVIII-specific B cells by a mechanism that involves IDO1-dependent induction of Tregs. Together, these findings indicate that strategies aimed at improving IDO1 function should be further explored for preventing or eradicating inhibitors to therapeutically administered FVIII protein.

Background: Tryptophan is an essential amino acid for the synthesis of proteins and important metabolites such as serotonin, melatonin, tryptamine and niacin. After protein synthesis, more than 90 % of tryptophan catabolism occurs along the kynurenine pathway. The inflammation-inducible enzyme indoleamine 2,3 dioxygenase (IDO) is responsible for the first rate-limiting step in the kynurenine pathway, i.e., oxidation of tryptophan to kynurenine. Excessive IDO activity in conditions such as HIV/AIDS may lead to tryptophan depletion and accumulation of metabolites downstream from kynurenine. Little is known about the kynurenine pathway of HIV/AIDS patients in sub-Saharan regions. This study, in a low income sub-Saharan HIV/AIDS population, examined the effects of activities in the kynurenine pathway on plasma levels of tryptophan, kynurenine and the neurotoxin quinolinic acid, and on de novo synthesis of nicotinamide., Methods: Plasma samples were obtained from a cohort of 105 HIV patients and 60 controls. Kynurenine pathway metabolites were analysed using gas chromatography - mass spectrometry. ELISA and flow cytometry were used to assess plasma inflammatory markers., Results: IDO activity, depletion of tryptophan, as well as accumulation of kynurenine and the neurotoxin quinolinic acid, were not only significantly greater in the patients than in the controls, but also markedly greater than in HIV/AIDS patients from developed countries. Tryptophan levels were 12.3 % higher, kynurenine levels 16.2 % lower, quinolinic acid levels 43.2 % lower and nicotinamide levels 27,2 % lower in patients on antiretroviral treatment than in antiretroviral-naïve patients. Patients' kynurenine pathway metabolites correlated with the levels of inflammatory markers, including that of the major IDO-inducer, interferon-gamma. Indications are that the rate of de novo synthesis of nicotinamide in the kynurenine pathway correlates with increases in quinolinic acid levels up to a point where saturation of the enzyme quinolinate phosphoribosyl transferase occurs., Conclusions: Higher levels of inflammatory activity in this low income sub-Saharan HIV/AIDS population than in patients from developed countries lead to greater tryptophan depletion and greater accumulation of metabolites downstream from tryptophan with quinolinic acid levels often reaching levels associated with the development of HIV/AIDS-associated neurocognitive dysfunction. De novo synthesis of nicotinamide from quinolinic acid contributes to the maintenance of nicotinamide, and by implication NAD levels, in HIV/AIDS patients from low income populations. Antiretroviral treatment partially corrects disturbances in the kynurenine pathway.

Background: Interferon gamma (IFN-γ) production induces the transcription of indoleamine 2,3 dioxygenase (IDO) resulting in the reduction of T-cell activation and proliferation through the depletion of tryptophan and the elicitation of Treg lymphocytes. IDO was shown to be involved in the pathogenesis of autoimmune diseases; we investigated whether changes in IDO gene expression and activity could be indicative of onset of relapse in multiple sclerosis (MS) patients., Methods: IDO and interferon-γ (IFN-γ) gene expression, serum IDO activity (Kynurenine/Tryptophan ratio) and serum neopterin concentration--a protein released by macrophages upon IFN-γ stimulation--were measured in 51 individuals: 36 relapsing remitting (RR)-MS patients (21 in acute phase--AMS, 15 in stable phase--SMS) and 15 healthy controls (HC). PBMCs samples in AMS patients were collected before (BT-AMS) and during glucocorticoids-based therapy (DT-AMS)., Results: IDO expression was increased and IFN-γ was decreased (p<0.001) in BT-AMS compared to SMS patients. Glucocorticoids-induced disease remission resulted in a significant reduction of IDO and IFN-γ gene expression, IDO catalytic activity (p<0.001). Serum neopterin concentration followed the same trend as IDO expression and activity., Conclusions: Measurement of IDO gene expression and activity in blood could be a useful marker to monitor the clinical course of RR-MS. Therapeutic interventions modulating IDO activity may be beneficial in MS.

Serotonin, a highly pro-inflammatory molecule released by activated platelets, is formed by tryptophan. Tryptophan is also needed in the production of kynurenine, a process mediated by the type I interferon (IFN)-regulated rate-limiting enzyme indoleamine 2,3-dioxygenase (IDO). The aim of this study was to investigate levels of serotonin in patients with the autoimmune disease systemic lupus erythematosus (SLE), association to clinical phenotype and possible involvement of IDO in regulation of serotonin synthesis. Serotonin levels were measured in serum and plasma from patients with SLE (n=148) and healthy volunteers (n=79) by liquid chromatography and ELISA, as well as intracellularly in platelets by flow cytometry. We found that SLE patients had decreased serotonin levels in serum (p=0.01) and platelets (p<0.0001) as compared to healthy individuals. SLE patients with ongoing type I IFN activity, as determined by an in-house reporter assay, had decreased serum levels of serotonin (p=0.0008) as well as increased IDO activity (p<0.0001), as determined by the kynurenine/tryptophan ratio measured by liquid chromatography. Furthermore, SLE sera induced IDO expression in WISH cells in a type I IFN-dependent manner (p=0.008). Also platelet activation contributed to reduce overall availability of serotonin levels in platelets and serum (p<0.05). Decreased serum serotonin levels were associated with severe SLE with presence of anti-dsDNA antibodies and nephritis. In all, reduced serum serotonin levels in SLE patients were related to severe disease phenotype, including nephritis, suggesting involvement of important immunopathological processes. Further, our data suggest that type I IFNs, present in SLE sera, are able to up-regulate IDO expression, which may lead to decreased serum serotonin levels.

Background: There is an urgent need for improved vaccines to protect against tuberculosis. The currently available vaccine Bacille Calmette-Guerin (BCG) has varying immunogenicity and efficacy across different populations for reasons not clearly understood. MVA85A is a modified vaccinia virus expressing antigen 85A from Mycobacterium tuberculosis which has been in clinical development since 2002 as a candidate vaccine to boost BCG-induced protection. A recent efficacy trial in South African infants failed to demonstrate enhancement of protection over BCG alone. The immunogenicity was lower than that seen in UK trials. The enzyme Indoleamine 2,3-dioxygenase (IDO) catalyses the first and rate-limiting step in the breakdown of the essential amino acid tryptophan. T cells are dependent on tryptophan and IDO activity suppresses T-cell proliferation and function., Methods: Using samples collected during phase I trials with MVA85A across the UK and South Africa we have investigated the relationship between vaccine immunogenicity and IDO using IFN-γ ELISPOT, qPCR and liquid chromatography mass spectrometry., Results: We demonstrate an IFN-γ dependent increase in IDO mRNA expression in peripheral blood mononuclear cells (PBMC) following MVA85A vaccination in UK subjects. IDO mRNA correlates positively with the IFN-γ ELISPOT response indicating that vaccine specific induction of IDO in PBMC is unlikely to limit the development of vaccine specific immunity. IDO activity in the serum of volunteers from the UK and South Africa was also assessed. There was no change in serum IDO activity following MVA85A vaccination. However, we observed higher baseline IDO activity in South African volunteers when compared to UK volunteers. In both UK and South African serum samples, baseline IDO activity negatively correlated with vaccine-specific IFN-γ responses, suggesting that IDO activity may impair the generation of a CD4+ T cell memory response., Conclusions: Baseline IDO activity was higher in South African volunteers when compared to UK volunteers, which may represent a potential mechanism for the observed variation in vaccine immunogenicity in South African and UK populations and may have important implications for future vaccination strategies., Trial Registration: Trials are registered at ClinicalTrials.gov; UK cohort NCT00427830, UK LTBI cohort NCT00456183, South African cohort NCT00460590, South African LTBI cohort NCT00480558.

Purpose: To investigate targeting of indoleamine 2,3 dioxygenase (IDO) enzyme using a synthetic peptide vaccine administered to patients with metastatic non-small cell lung cancer (NSCLC)., Experimental Design: In a clinical phase I study, we treated 15 HLA-A2-positive patients with stage III-IV NSCLC in disease stabilization after standard chemotherapy. Patients were treated with imiquimod ointment and subcutaneous vaccinations (100 μg IDO5 peptide, sequence ALLEIASCL, formulated in 900 μL Montanide). Primary endpoint was toxicity. Clinical benefit and immunity were assessed as secondary endpoints., Results: No severe toxicity was observed. One patient developed a partial response (PR) after one year of vaccine treatment, whereas long-lasting stable disease (SD) ≥ 8.5 months was demonstrated in another six patients. The median overall survival (OS) was 25.9 months. Patients demonstrated significant improved OS (P = 0.03) when compared with the group of patients excluded because of HLA-A2 negativity. IDO-specific CD8(+) T-cell immunity was demonstrated by IFN-γ Elispot and Tetramer staining. Fluorescence-activated cell sorting analyses demonstrated a significant reduction of the Treg population (P = 0.03) after the sixth vaccine (2.5 months) compared with pretreatment levels. Furthermore, expression of IDO was detected in nine of ten tumor biopsies by immunohistochemistry. High-performance liquid chromatography analyses of kynurenine/tryptophan (Kyn/Trp) ratio in sera were performed. In long-term analyses of two clinical responding patients, the ratio of Kyn/Trp remained stable., Conclusions: The vaccine was well tolerated with no severe toxicity occurring. A median OS of 25.9 months was demonstrated and long-lasting PR+SD was seen in 47% of the patients.

Introduction: There are very few strategies for the early detection of the patients who might develop the severe form of the illness., Objective: To evaluate the utility of serum levels of some immune response mediators as early biomarkers for the severe dengue prognosis during the early phase of the illness., Materials and Methods: Using a case-control design nested in a multicenter cohort from the AEDES network (a Colombian multicenter study), we compared TNF a, ST2, TRAIL and IDO levels in samples which were obtained during the early phase of the illness., Results: ST2, TRAIL and TNF a levels were higher in severe dengue patients compared with uncomplicated patients (p<0.0001), as follows: OR=24.8, CI95%= 6.1- 98.0; OR=18.0, CI95%= 4.6-69.1; OR=NC, CI95%= NC, respectively. We did not find statistically significant differences between IDO levels in severe dengue and uncomplicated dengue (p=1.000, OR=1.0, CI95%= 0.2-6.1)., Conclusions: In the early phase of the dengue infection (96 hours), ST2, TRAIL and TNF a quantifications could contribute to the prediction of complications of the illness.

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., (Copyright © 2013 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.)

Pain and depression are frequently comorbid disorders, but the mechanism underlying this association is unknown. Here, we report that brain indoleamine 2,3-dioxygenase 1 (IDO1), a rate-limiting enzyme in tryptophan metabolism, plays a key role in this comorbidity. We found that chronic pain in rats induced depressive behavior and IDO1 upregulation in the bilateral hippocampus. Upregulation of IDO1 resulted in the increased kynurenine/tryptophan ratio and decreased serotonin/tryptophan ratio in the bilateral hippocampus. We observed elevated plasma IDO activity in patients with both pain and depression, as well as in rats with anhedonia induced by chronic social stress. Intra-hippocampal administration of IL-6 in rats, in addition to in vitro experiments, demonstrated that IL-6 induces IDO1 expression through the JAK/STAT pathway. Further, either Ido1 gene knockout or pharmacological inhibition of hippocampal IDO1 activity attenuated both nociceptive and depressive behavior. These results reveal an IDO1-mediated regulatory mechanism underlying the comorbidity of pain and depression and suggest a new strategy for the concurrent treatment of both conditions via modulation of brain IDO1 activity.

Tuberculosis (TB) continues to be a major health problem, and there are few biomarkers for predicting prognosis. Indoleamine 2,3-dioxygenase (IDO), a potent immunoregulatory molecule, catalyzes the rate-limiting step of tryptophan (Trp) degradation in the kynurenine (Kyn) pathway. An increase in IDO activity determined by the serum Trp/Kyn ratio has been shown to be associated with poor prognosis in cancers and bacteremia. In TB, however, there are no studies measuring serum IDO activity to determine its clinical significance. We evaluated serum IDO activity with 174 pulmonary TB (PTB) patients and 85 controls, using liquid chromatography/electrospray ionization tandem mass spectrometry. IDO activity was estimated by calculating the serum Kyn-to-Trp ratio. PTB patients had significantly higher Kyn concentrations and IDO activity and significantly lower Trp concentrations (P < 0.0001, P < 0.0001, and P < 0.0001, respectively) than the controls. Of 174 PTB patients, 39 (22.4%) died. The patients who died had significantly higher concentrations of Kyn and significantly lower Trp concentrations, resulting in significantly higher IDO activity (P < 0.0001, P < 0.0001, and P < 0.0001, respectively). In a receiver operating characteristic (ROC) analysis, serum IDO activity had the highest area under the curve (0.850), and this activity was an independent prognostic factor in multivariate analysis. These results suggest that serum IDO activity can be used as a novel prognostic marker in PTB.

There is no specific marker to evaluate the immuno-suppressive status of cancer patients. Several markers, such as CD124, latency-associated peptide (LAP), arginase I, indole-amine-2,3-dioxygenase (IDO) and inducible nitric oxide synthase (iNOS), are known to be associated with immune suppression. However, there is little research regarding the change in these parameters after chemotherapy. The present study enrolled 23 chemo-naïve non-small cell lung cancer (NSCLC) patients and 19 healthy donors. From the 23 NSCLC patients, 11 post-chemotherapy samples were collected. Surface and functional markers were analyzed by flow-cytometry. The mean fluorescence intensities (MFI) of iNOS were higher and the MFI of LAP were lower in NSCLC patient than in healthy donors (P < 0.05). In a comparison of pre-chemotherapy and post-chemotherapy groups with NSCLC, the MFI of iNOS on granulocytes and monocytes and IDO on monocytes were significantly lower in the post-chemotherapy group than in the pre-chemotherapy group (P < 0.05). In a serial analysis with 10 patients who had paired samples and who showed clinical benefits from chemotherapy, the MFI of iNOS for both cell types, and of IDO and CD124 for monocytes decreased significantly after chemotherapy, compared with those before chemotherapy (iNOS, 4.79 ± 1.75 vs 2.83 ± 0.77, P = 0.005, for granulocytes and 6.15 ± 2.94 vs 2.76 ± 1.05, P = 0.005 for monocytes; IDO, 6.81 ± 3.43 vs 4.64 ± 1.55, P = 0.012 for monocytes; CD124, 2.31 ± 0.39 vs 1.94 ± 0.43, P = 0.008 for monocytes). The changes in arginase I and LAP expression were not significant. The changes in iNOS, IDO and CD124 expression were significant after chemotherapy in NSCLC. Further evaluation of the possibility of immune status monitoring using these parameters is needed., (© 2011 Japanese Cancer Association.)

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.

To elucidate further the possible role of the tryptophan, rate-limiting enzyme indoleamine 2, 3-dioxygenase (IDO) in leprosy, the distribution of IDO-positive cells and IDO activity in the skin biopsies and sera of these patients representing the entire spectrum of the disease were studied. An increased number of macrophages/dendritic cells (DC-lineage IDO(+) cells were found in lepromatous (LL) compared to tuberculoid (BT) and reversal reaction (RR) patients. IDO-positive cells showing CD68 and CD86 surface markers predominated in LL lesions, while higher levels of IDO activity were observed in the sera of LL versus BT patients. Tests revealed an increased IDO message in Mycobacterium leprae-stimulated peripheral blood mononuclear cells (PBMC) by real-time polymerase chain reaction (PCR) and increased IDO expression in M. leprae-stimulated CD14(+) cells of both healthy controls (HC) and LL patients, as evaluated via flow cytometry. Increased M. leprae-induced IDO-protein synthesis was also confirmed by Western blot. Based on our in vitro studies, it was confirmed that M. leprae up-regulated IDO expression and activity in HC and LL monocytes. Interferon (IFN)-γ synergized with M. leprae in promoting IDO expression and activity in monocytes. IDO expression induced by both IFN-γ and M. leprae was abrogated by 1-methyltryptophan (1-MT). Our data suggest that M. leprae chronic infection activates the suppressive molecule IDO which, in turn, contributes to the specific immunosuppression observed in LL leprosy., (© 2011 The Authors; Clinical and Experimental Immunology © 2011 British Society for Immunology.)

Pentraxin 3 (PTX3) is a novel candidate immunoinflammatory marker that has been reported to be associated with cardiometabolic risk factors and to predict adverse outcomes in individuals with cardiovascular disease (CVD). Despite being a member of the same pentraxin protein family as C-reactive protein (CRP), PTX3 probably reflects different aspects of CVD pathogenesis. In this study, we assessed plasma PTX3 correlates and determinants in the Health 2000 Survey population, which comprised n = 403 insulin-resistant subjects, n = 845 hypercholesterolaemic subjects and n = 311 hypertensive subjects, all aged between 46 and 76 years. In insulin-resistant subjects the PTX3 concentration was found to correlate directly with age, pulse pressure and indoleamine 2,3-dioxygenase (IDO) enzyme activity and inversely with total and low-density lipoprotein (LDL) cholesterol. In hypercholesterolaemic subjects, the PTX3 concentration correlated directly with HDL cholesterol, systolic blood pressure and pulse pressure, whereas in hypertensive subjects, the PTX3 concentration correlated directly with systolic blood pressure, pulse pressure and IDO activity. No correlation was observed between the concentrations of PTX3 and CRP, adiposity indicators or indicators of subclinical atherosclerosis in any of the subject groups. PTX3 concentration variations were attributed to variations in LDL cholesterol and IDO activity in insulin-resistant subjects and to pulse pressure in hypercholesterolaemic and hypertensive subjects. These results indicate that, in individuals at high risk of CVD, the PTX3 concentration is associated with cardiovascular risk factors but not with subclinical atherosclerosis., (© 2011 The Authors. Clinical and Experimental Immunology © 2011 British Society for Immunology.)

Background: Although the rate of mother-to-child transmission of hepatitis C virus (HCV) is low, the effect of HCV exposure in utero on the fetal immune system is unknown., Methods: Umbilical cord blood was obtained from 7 neonates born to HCV-seropositive, HCV RNA-positive women and 8 neonates born to HCV-seronegative women. Cord blood mononuclear cells were analyzed by immunophenotyping and by intracellular cytokine staining after HCV-specific and polyclonal stimulation. Plasma was analyzed for anti-HCV immunoglobulin M (IgM), cytokine/granzyme concentrations, and indoleamine 2,3-dioxygenase (IDO) activity., Results: HCV-exposed neonates had significantly lower levels of regulatory T cells expressing HLA-DR, lower CD4(+) and CD8(+) T cell activation, and lower plasma levels of pro-inflammatory markers than did controls. However, CD4(+) and CD8(+) T cells from HCV-exposed neonates had higher IFN-γ production in response to polyclonal stimulation than did T cells from controls. IDO activity was similar between groups. No HCV-specific T cell responses or anti-HCV IgM were detected in any neonates., Conclusions: HCV-exposed neonates showed a relative suppression of immune activation and pro-inflammatory markers, which was counterbalanced by an increased production capacity for IFN-γ. These results suggest that HCV encounters the fetal immune system in utero, and alters the balance between suppressive and pro-inflammatory responses.

Background: Severe sepsis results in a sustained deleterious immune dysregulation. Indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme of tryptophan catabolism, plays a pivotal role in immune tolerance and is induced during various inflammatory conditions., Methods: Plasma samples obtained from patients with septic shock (n = 38), severe sepsis (n = 35), or sepsis (n = 10) and from healthy donors (n = 26) were analyzed for IDO activity by high-performance liquid chromatography. Lymphocyte, monocyte, and regulatory T cell counts as well as monocytic human leukocyte antigen DR (HLA-DR) expression were quantified by flow cytometry. Peripheral blood mononuclear cells and purified CD14(+) and CD14(-) fractions were assayed in vitro for spontaneous and inducible IDO expression and activity., Results: IDO activity gradually increased according to sepsis severity, and septic patients who died had higher IDO activity on admission than did survivors (P = .013). Monocytes were a major source of active IDO in normal peripheral blood. The percentage and absolute number of circulating CD14(+) cells were increased in septic patients, and their monocytes remained fully able to produce functional IDO after NF-kappaB-independent interferon gamma stimulation but not through NF-kappaB-dependent Toll-like receptor engagement., Conclusions: IDO activity is increased during severe sepsis and septic shock and is associated with mortality. IDO production could be used to better characterize monocyte reprogramming in sepsis.

Background: Tryptophan (Trp) is catabolized by indoleamine 2,3-dioxygenase (IDO). Changes in Trp metabolism and IDO activity in chronic kidney disease (CKD) have not been widely studied, and the impact of haemodialysis is uncertain. Here we investigate Trp catabolism, IDO activity and the role of inflammation in moderate to very severe CKD and haemodialysis., Methods: Eighty individuals were included in a prospective blinded endpoint analysis. Using tandem mass spectrometry, serum levels of Trp, kynurenine (Kyn), kynurenic-acid (Kyna), quinolinic-acid (Quin), 5-hydroxytryptophan (OH-Trp), serotonin (5-HT), estimated IDO activity and inflammatory markers were assessed in 40 CKD patients (age 57 +/- 14 years, 21 male, creatinine 4.5 +/- 2.7, n = 17 receiving haemodialysis), and in 40 healthy controls (age 34 +/- 9 years, 26 male)., Results: Trp levels were unchanged in CKD (P = 0.78 versus controls). Serum levels of Kyn, Kyna and Quin increased with CKD severity (stages 4, 5 versus controls all P < or = 0.01). IDO activity was significantly induced in CKD and correlated with disease severity (stages 3-5 versus controls, all P < or = 0.01) and inflammatory markers [high-sensitivity C-reactive protein (hsCRP), soluble TNF-receptor-1 (sTNFR-I); both P < or = 0.03]. IDO products (Kyn, Kyna, Quin) correlated also with hsCRP and sTNFR-I (all P < or = 0.04). Haemodialysis did not influence IDO activity (P = 0.26) and incompletely removed Kyn, Kyna, Quin, OH-Trp and 5-HT by 22, 26, 50, 44 and 34%, respectively. In multiple regression, IDO activity correlated with hsCRP and sTNFR-I (both P < or = 0.03) independent of serum creatinine, age and body weight., Conclusions: IDO activity and serum levels of tryptophan catabolites of the kynurenine pathway increase with CKD severity. In CKD, induction of IDO may primarily be a consequence of chronic inflammation.

The depletion of l-tryptophan (L-Trp) has been associated with the inhibition of growth of micro-organisms and also has profound effects on T cell proliferation and immune tolerance. The enzyme indoleamine 2,3-dioxygenase (IDO) catalyses the rate-limiting step in the catabolic pathway of L-Trp. Gene expression analysis has shown upregulation of genes involved in L-Trp catabolism in in vitro models of dengue virus (DENV) infection. To understand the role of IDO during DENV infection, we measured IDO activity in sera from control and DENV-infected patients. We found increased IDO activity, lower levels of L-Trp and higher levels of l-kynurenine in sera from DENV-infected patients during the febrile days of the disease compared with patients with other febrile illnesses and healthy donors. Furthermore, we confirmed upregulation of IDO mRNA expression in response to DENV infection in vitro, using a dendritic cell (DC) model of DENV infection. We found that the antiviral effect of gamma interferon (IFN-gamma) in DENV-infected DCs in vitro was partially dependent on IDO activity. Our results demonstrate that IDO plays an important role in the antiviral effect of IFN-gamma against DENV infection in vitro and suggest that it has a role in the immune response to DENV infections in vivo.

Objective: To investigate the role of indoleamine 2,3-dioxygenase (IDO) in immune tolerance in patients with chronic hepatitis B (CHB)., Methods: Peripheral venous blood samples were collected from 50 CHB patients, and HBV viral load, T lymphocyte subsets and of IDO mRNA, protein and activity were detected with the blood samples from 50 healthy donors as the control. The correlations between HBV viral load, T lymphocyte subsets and IDO were statistically analyzed., Results: In CHB patients, the mRNA and protein levels and activity of IDO were all significantly higher than those in control group [mRNA: (2.110-/+0.615)x10(3) vs (0.143-/+0.026)x10(3); protein: 0.22-/+0.06 vs 0.02-/+0.0017; activity: 26.07-/+8.12 vs 4.98-/+1.65; P<0.05]. IDO mRNA level was positively correlated to HBV viral load (r=0.502, P<0.001) and ALT (r=0.65, P<0.01), and IDO mRNA, protein and activity were inversely correlated to CD4+ T cells (r=-0.622, -0.682, and -0.549, respectively, P<0.05), CD8+ T cells (r=-0.487, -367, and -294, respectively, P<0.05) and the ratio of CD4/CD8 (r=-0.426, -0.533, and -0.397, respectively, P<0.05)., Conclusion: IDO is closely correlated to HBV viral load and responsible for immunotolerance against HBV. Suppression of IDO can be a new therapeutic approach to reverse immunotolerance in CHB.

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-degrading enzyme which suppresses T lymphocyte activity. IDO activity can be determined by relating kynurenine, the main metabolite of tryptophan, to tryptophan (kyn/trp). We have demonstrated recently that systemic lupus erythematosus (SLE) is activated during the sunny season as measured by the European Consensus Lupus Activity Measurement Index (ECLAM) activity score. Our aim here was to establish whether IDO-dependent mechanisms are involved in the activation process of SLE. Kyn/trp was measured by reverse-phase high-performance liquid chromatography (HPLC) in 33 (30 female, three male) SLE patients in winter, spring and summer and in 309 healthy control subjects. At the same time-points the SLE patients were examined by a rheumatologist and a dermatologist and the activity of SLE assessed by the ECLAM score. IDO activity was higher in SLE patients than in healthy subjects. There was no seasonal variation in IDO activity in SLE patients and it did not correlate with the ECLAM activity score in winter. However, there was a significant correlation between IDO activity and the ECLAM score both in spring and in summer. High IDO activity in winter predicted subsequent activation of SLE in spring and summer. Our results indicate that IDO-dependent immunosuppressive mechanisms are activated in SLE patients. Exposure to sunlight or another factor causing seasonal variation in SLE activity leads to insufficiency of this suppression in a subgroup of patients, causing activation of SLE. High IDO activity in winter predicts activation of SLE in the sunny season.

Indoleamine 2,3 dioxygenase (IDO), an enzyme involved in the catabolism of tryptophan, suppresses T cell activity and is up-regulated by various inflammatory stimuli. The ratio of kynurenine, the main metabolite of tryptophan, to tryptophan (kyn/trp) reflects IDO activity. We calculated IDO activity and measured carotid intima-media thickness (IMT), a presymptomatic predictor of atherosclerosis, in 986 young adults (544 female, 442 male) for whom data on levels of high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglyceride, high sensitive C-reactive protein (CRP), body mass index (BMI), waist circumference, waist-to-hip ratio, systolic and diastolic blood pressure and smoking habits were available. IDO activity correlated significantly with IMT in female subjects, but not in males. In a multivariate linear regression model, IDO did not correlate independently with IMT in female subjects. However, IDO activity correlated significantly with several risk factors for atherosclerosis in females, i.e. with age, LDL-C, BMI, weakly with CRP and inversely with HDL-C and triglyceride. In males IDO activity correlated significantly with CRP and inversely with HDL-C. In conclusion, our results suggest that the IDO enzyme is involved in the immune regulation of early atherosclerosis, particularly in young female adults, and could constitute a novel marker of immune activation in early atherosclerosis in females.

Rationale: Clinical trials have demonstrated that probiotics may be effective in the treatment and prevention of atopic disease in children but there have been few reports of therapeutic effects of oral probiotics outside the gastrointestinal tract., Objectives: We investigated the effect of two probiotic organisms on the response to antigen challenge in a mouse model of allergic airway inflammation., Methods: We used an ovalbumin-sensitized asthma model in BALB/c and Toll-like receptor 9-deficient mice. Animals were treated with probiotic organisms via gavaging needle before antigen challenge. After antigen challenge, airway responsiveness to methacholine, influx of inflammatory cells to the lung, and cytokine levels in bronchoalveolar lavage fluid were assessed., Results: Oral treatment with live Lactobacillus reuteri but not Lactobacillus salivarius significantly attenuated the influx of eosinophils to the airway lumen and parenchyma and reduced the levels of tumor necrosis factor, monocyte chemoattractant protein-1, IL-5, and IL-13 in bronchoalveolar lavage fluid of antigen-challenged animals, but there was no change in eotaxin or IL-10. L. reuteri but not L. salivarius also decreased allergen-induced airway hyperresponsiveness. These responses were dependent on Toll-like receptor 9 and were associated with increased activity of indoleamine 2,3-dioxygenase. Killed organisms did not mimic the ability of the live L. reuteri to attenuate inflammation or airway hyperresponsiveness., Conclusion: Oral treatment with live L. reuteri can attenuate major characteristics of an asthmatic response in a mouse model of allergic airway inflammation. These results suggest that oral treatment with specific live probiotic strains may have therapeutic potential in the treatment of allergic airway disease.