Modulation of indoleamine-2,3-dioxygenase expression and activity by HIV-1 in human macrophages

Anti-inflammatory activities of Coleus forsteri (formerly Plectranthus forsteri) extracts on human macrophages and chemical characterization

Introduction: Formerly named Plectranthus forsteri, Coleus forsteri (Benth.) A.J.Paton, 2019 is a Lamiaceae traditionally used to treat flu-like symptoms and shock-related ecchymosis, especially in the Pacific region. Few studies investigated chemical composition and anti-inflammatory potential of this plant. Method: Herein, we investigated anti-inflammatory potential of C. forsteri ethanolic (ePE) and cyclohexane (cPE) plant extract on LPS-induced human macrophages models and quantified cytokines and quinolinic acid (QUIN) as inflammatory markers. Results: Our results show that extract of ePE and cPE significantly inhibit inflammatory cytokine IL-6 and TNF-α induced by LPS on PMA-derived THP-1 macrophages. QUIN production is also diminished under ePE and cPE treatment in activated human monocyte-derived macrophages (MDMs). Seven abietane diterpenes were characterized from C. forsteri cPE including coleon U (1), coleon U-quinone (2), 8α,9α-epoxycoleon U-quinone (3), horminone or 7α-hydroxyroyleanone (4), 6β,7α-dihydroxyroyleanone (5), 7α-acetoxy-6β-hydroxyroyleanone (6) and 7α-formyloxy-6β-hydroxyroyleanone (7). Discussion: We discussed potential contributions of these molecules from C. forsteri extracts for their anti-inflammatory activities.

T cell-tropic HIV efficiently infects alveolar macrophages through contact with infected CD4+ T cells

Alveolar macrophages (AMs) are critical for defense against airborne pathogens and AM dysfunction is thought to contribute to the increased burden of pulmonary infections observed in individuals living with HIV-1 (HIV). While HIV nucleic acids have been detected in AMs early in infection, circulating HIV during acute and chronic infection is usually CCR5 T cell-tropic (T-tropic) and enters macrophages inefficiently in vitro. The mechanism by which T-tropic viruses infect AMs remains unknown. We collected AMs by bronchoscopy performed in HIV-infected, antiretroviral therapy (ART)-naive and uninfected subjects. We found that viral constructs made with primary HIV envelope sequences isolated from both AMs and plasma were T-tropic and inefficiently infected macrophages. However, these isolates productively infected macrophages when co-cultured with HIV-infected CD4+ T cells. In addition, we provide evidence that T-tropic HIV is transmitted from infected CD4+ T cells to the AM cytosol. We conclude that AM-derived HIV isolates are T-tropic and can enter macrophages through contact with an infected CD4+ T cell, which results in productive infection of AMs. CD4+ T cell-dependent entry of HIV into AMs helps explain the presence of HIV in AMs despite inefficient cell-free infection, and may contribute to AM dysfunction in people living with HIV.

Metabolic reprograming of LPS-stimulated human lung macrophages involves tryptophan metabolism and the aspartate-arginosuccinate shunt

Lung macrophages (LM) are in the first line of defense against inhaled pathogens and can undergo phenotypic polarization to the proinflammatory M1 after stimulation with Toll-like receptor agonists. The objective of the present work was to characterize the metabolic alterations occurring during the experimental M1 LM polarization. Human LM were obtained from resected lungs and cultured for 24 hrs in medium alone or with 10 ng.mL-1 lipopolysaccharide. Cells and culture supernatants were subjected to extraction for metabolomic analysis with high-resolution LC-MS (HILIC and reverse phase -RP- chromatography in both negative and positive ionization modes) and GC-MS. The data were analyzed with R and the Worklow4Metabolomics and MetaboAnalyst online infrastructures. A total of 8,741 and 4,356 features were detected in the intracellular and extracellular content, respectively, after the filtering steps. Pathway analysis showed involvement of arachidonic acid metabolism, tryptophan metabolism and Krebs cycle in the response of LM to LPS, which was confirmed by the specific quantitation of selected compounds. This refined analysis highlighted a regulation of the kynurenin pathway as well as the serotonin biosynthesis pathway, and an involvement of aspartate-arginosuccinate shunt in the malate production. Macrophages M1 polarization is accompanied by changes in the cell metabolome, with the differential expression of metabolites involved in the promotion and regulation of inflammation and antimicrobial activity. The analysis of this macrophage immunometabolome may be of interest for the understanding of the pathophysiology of lung inflammatory disesases.

USP18 is a significant driver of memory CD4 T-cell reduced viability caused by type I IFN signaling during primary HIV-1 infection

The loss of Memory CD4 T-cells (Mem) is a major hallmark of HIV-1 immuno-pathogenesis and occurs early during the first months of primary infection. A lot of effort has been put into understanding the molecular mechanisms behind this loss, yet they still have not been fully identified. In this study, we unveil the unreported role of USP18 in the deleterious effects of sustained type I IFN signaling on Mem, including HIV-1-specific CD4 T-cells. We find that interfering with IFN-I signaling pathway in infected patients, notably by targeting the interferon-stimulated gene USP18, resulted in reduced PTEN expression similar to those observed in uninfected control donors. We show that AKT activation in response to cytokine treatment, T-cell receptor (TcR) triggering, as well as HIV-1 Gag stimulation was significantly improved in infected patients when PTEN or USP18 were inhibited. Finally, our data demonstrate that higher USP18 in Mem from infected patients prevent proper cell survival and long-lasting maintenance in an AKT-dependent manner. Altogether, we establish a direct role for type I IFN/USP18 signaling in the maintenance of total and virus-specific Mem and provide a new mechanism for the reduced survival of these populations during primary HIV-1 infection.

In this study, we expend our knowledge of how type I interferons (IFN-I) leads to memory CD4 T-cell defective survival by unveiling the molecular mechanism behind such impairments, placing USP18 at its center. Our data further deciphers the specific USP18-related mechanism that is responsible for such impairments by implicating AKT inhibition in a PTEN-dependent manner. Our findings also point to a potential use of neutralizing anti-interferon α/β receptor antibodies to rescue the defective memory CD4 T-cell survival during HIV-1 infection, even in HIV-1 specific CD4 T-cell. To conclude, our findings provide the characterization of the molecular pathway leading to disturbances caused by sustained IFN-I signaling which occurs early during primary HIV-1 infection, complementing current knowledge which placed sustained IFN-I signaling as detrimental to the host during this infection.

Elevated indoleamine-2,3-dioxygenase enzyme activity in a novel mouse model of HIV-associated atherosclerosis

OBJECTIVE

HIV atherosclerosis and cardiovascular disease (CVD) represent a significant human health burden in the era of combination antiretroviral therapy (cART). The pathogenesis of HIV atherosclerosis is still poorly understood, due, in part, to the lack of a suitable small animal model. Indoleamine-2,3-dioxygenase (IDO) enzyme activity is the first and rate-limiting step in tryptophan catabolism and is measured by the kynurenine to tryptophan ratio (KTR). The serum KTR is a biomarker of inflammation and has recently been implicated as an important risk factor for CVD in patients living with HIV (PLWH) who are virologically suppressed under cART. However, IDO activity in HIV-associated CVD has not been studied in mouse model before.

DESIGN

A novel mouse model of HIV atherosclerosis (Tg26/ApoE) was generated and examined for IDO activity and atherogenesis throughout 8 weeks on a high-fat diet. Tg26/ApoE mice were compared with Tg26 and ApoE single transgenic mice, before and during a high-fat diet.

METHOD

Serum kynurenine, tryptophan and percentage of aortic plaque formation were measured. Additionally, levels of relevant cytokines were investigated in Tg26/ApoE and ApoE.

RESULTS

Tg26/ApoE developed an accelerated atherosclerosis with increasing levels of KTR that were associated with plaque progression. This accelerated plaque was potentially driven by elevated levels of circulating IL-6.

CONCLUSION

These results indicate that Tg26/ApoE serve as a new mouse model for HIV-induced atherogenesis, and aid in understanding the role of tryptophan catabolism in the pathogenesis of HIV atherosclerosis/CVD.

Comparison of fluoxetine and 1-methyl-L-tryptophan in treatment of depression-like illness in Bacillus Calmette-Guerin-induced inflammatory model of depression in mice

BACKGROUND

The inflammatory response system has been implicated in the pathophysiology of major depression. The pro-inflammatory cytokines like interferon-γ induce the enzyme indoleamine-2,3-dioxygenase (IDO) of the kynurenine pathway of tryptophan metabolism. The induction of IDO reduces the availability of tryptophan for serotonin synthesis. Furthermore, the metabolites of kynurenine pathway have neurotoxic property, which along with decreased serotonin may account for depression-like illness.

METHODS

The aim of this study was to compare the effects of treatment with fluoxetine and 1-methyl-L-tryptophan (1-MT) on Bacillus Calmette-Guerin (BCG)-induced inflammatory model of depression in mice. Behavioral tests included locomotor activity, forced swim test (FST) and tail suspension test (TST). Oxidative stress was assessed by examining the levels of thiobarbituric acid reactive species (TBARS) and non-protein thiols (NP-SH) in homogenized whole brain samples. Comet assays were performed to assess neurotoxicity.

RESULTS

The results of this study demonstrate that BCG treatment resulted in an increase in duration of immobility in FST and TST as compared to the saline group. Further, it produced a significant increase in the brain TBARS levels and decrease in the brain NP-SH levels. The hippocampal tissue from BCG group had significantly more comet cells than the saline group. 1-MT and fluoxetine were able to reverse the BCG-induced depression-like behavior and the derangement in oxidative stress parameters. Fluoxetine and 1-MT also reversed the BCG-induced neurotoxicity in such mice.

CONCLUSIONS

1-Methyl-L-tryptophan exhibits antidepressant-like effect comparable to that of fluoxetine in treating BCG-induced depression-like behavior in mice.

Tryptophan catabolism in acute exacerbations of chronic obstructive pulmonary disease

Introduction

Exacerbations are a leading cause of morbidity in COPD. The objective of this study was to identify metabolomic biomarkers of acute exacerbations of COPD (AECOPD).

Methods

We measured metabolites via mass spectrometry (MS) in plasma drawn within 24 hours of admission to the hospital for 33 patients with an AECOPD (day 0) and 30 days later and for 65 matched controls. Individual metabolites were measured via selective reaction monitoring with mass spectrometry. We used a mixed-effect model to compare metabolite levels in cases compared to controls and a paired t-test to test for differences between days 0 and 30 in the AECOPD group.

Results

We identified 377 analytes at a false discovery rate of 5% that differed between cases (day 0) and controls, and 31 analytes that differed in the AECOPD cases between day 0 and day 30 (false discovery rate: 5%). Tryptophan was decreased at day 0 of AECOPD compared to controls corresponding to an increase in indoleamine 2,3-dioxygenase activity.

Conclusion

Patients with AECOPD have a unique metabolomic signature that includes a decrease in tryptophan levels consistent with an increase in indoleamine 2,3-dioxygenase activity.

Kynurenine Reduces Memory CD4 T-Cell Survival by Interfering with Interleukin-2 Signaling Early during HIV-1 Infection

Early HIV-1 infection is characterized by enhanced tryptophan catabolism, which contributes to immune suppression and disease progression. However, the mechanism by which kynurenine, a tryptophan-related metabolite, induces immune suppression remains poorly understood. Herein, we show that the increased production of kynurenine correlates with defective interleukin-2 (IL-2) signaling in memory CD4 T cells from HIV-infected subjects. Defective IL-2 signaling in these subjects, which drives reduced protection from Fas-mediated apoptosis, was also associated with memory CD4 T-cell loss. Treatment of memory CD4 T cells with the concentration of kynurenine found in plasma inhibited IL-2 signaling through the production of reactive oxygen species. We further show that IL-2 signaling in memory CD4 T cells is improved by the antioxidant N-acetylcysteine. Early initiation of antiretroviral therapy restored the IL-2 response in memory CD4 T cells by reducing reactive oxygen species and kynurenine production. The study findings provide a kynurenine-dependent mechanism through IL-2 signaling for reduced CD4 T-cell survival, which can be reversed by early treatment initiation in HIV-1 infection.

IMPORTANCE

The persistence of functional memory CD4 T cells represents the basis for long-lasting immune protection in individuals after exposure to HIV-1. Unfortunately, primary HIV-1 infection results in the massive loss of these cells within weeks of infection, which is mainly driven by inflammation and massive infection by the virus. These new findings show that the enhanced production of kynurenine, a metabolite related to tryptophan catabolism, also impairs memory CD4 T-cell survival and interferes with IL-2 signaling early during HIV-1 infection.

Current topics in HIV-1 pathogenesis: The emergence of deregulated immuno-metabolism in HIV-infected subjects

HIV-1 infection results in long-lasting activation of the immune system including elevated production of pro-inflammatory cytokine/chemokines, and bacterial product release from gut into blood and tissue compartments, which are not fully restored by antiretroviral therapies. HIV-1 has also developed numerous strategies via viral regulatory proteins to hijack cell molecular mechanisms to enhance its own replication and dissemination. Here, we reviewed the relationship between viral proteins, immune activation/inflammation, and deregulated metabolism occurring in HIV-1-infected patients that ultimately dampens the protective innate and adaptive arms of immunity. Defining precisely the molecular mechanisms related to deregulated immuno-metabolism during HIV-1 infection could ultimately help in the development of novel clinical approaches to restore proper immune functions in these patients.

Anti-tat Hutat2:Fc mediated protection against tat-induced neurotoxicity and HIV-1 replication in human monocyte-derived macrophages

BACKGROUND

HIV-1 Tat is essential for HIV replication and is also a well-known neurotoxic factor causing HIV-associated neurocognitive disorder (HAND). Currently, combined antiretroviral therapy targeting HIV reverse transcriptase or protease cannot prevent the production of early viral proteins, especially Tat, once HIV infection has been established. HIV-infected macrophages and glial cells in the brain still release Tat into the extracellular space where it can exert direct and indirect neurotoxicity. Therefore, stable production of anti-Tat antibodies in the brain would neutralize HIV-1 Tat and thus provide an effective approach to protect neurons.

METHODS

We constructed a humanized anti-Tat Hutat2:Fc fusion protein with the goal of antagonizing HIV-1 Tat and delivered the gene into cell lines and primary human monocyte-derived macrophages (hMDM) by an HIV-based lentiviral vector. The function of the anti-Tat Hutat2:Fc fusion protein and the potential side effects of lentiviral vector-mediated gene transfer were evaluated in vitro.

RESULTS

Our study demonstrated that HIV-1-based lentiviral vector-mediated gene transduction resulted in a high-level, stable expression of anti-HIV-1 Tat Hutat2:Fc in human neuronal and monocytic cell lines, as well as in primary hMDM. Hutat2:Fc was detectable in both cells and supernatants and continued to accumulate to high levels within the supernatant. Hutat2:Fc protected mouse cortical neurons against HIV-1 Tat86-induced neurotoxicity. In addition, both secreted Hutat2:Fc and transduced hMDM led to reducing HIV-1BaL viral replication in human macrophages. Moreover, lentiviral vector-based gene introduction did not result in any significant changes in cytomorphology and cell viability. Although the expression of IL8, STAT1, and IDO1 genes was up-regulated in transduced hMDM, such alternation in gene expression did not affect the neuroprotective effect of Hutat2:Fc.

CONCLUSIONS

Our study demonstrated that lentivirus-mediated gene transfer could efficiently deliver the Hutat2:Fc gene into primary hMDM and does not lead to any significant changes in hMDM immune-activation. The neuroprotective and HIV-1 suppressive effects produced by Hutat2:Fc were comparable to that of a full-length anti-Tat antibody. This study provides the foundation and insights for future research on the potential use of Hutat2:Fc as a novel gene therapy approach for HAND through utilizing monocytes/macrophages, which naturally cross the blood-brain barrier, for gene delivery.

Cellular metabolism and macrophage functional polarization

Macrophages are a functionally heterogeneous cell population that is mainly shaped by a variety of microenvironmental stimuli. Interferon γ (IFN-γ), interleukin-1β (IL-1β), and lipopolysaccharide (LPS) induce a classical activation of macrophages (M1), whereas IL-4 and IL-13 induce an alternative activation program in macrophages (M2). Reprogramming of intracellular metabolisms is required for the proper polarization and functions of activated macrophages. Similar to the Warburg effect observed in tumor cells, M1 macrophages increase glucose consumption and lactate release and decreased oxygen consumption rate. In comparison, M2 macrophages mainly employ oxidative glucose metabolism pathways. In addition, fatty acids, vitamins, and iron metabolisms are also related to macrophage polarization. However, detailed metabolic pathways involved in macrophages have remained elusive. Understanding the bidirectional interactions between cellular metabolism and macrophage functions in physiological and pathological situations and the regulatory pathways involved may offer novel therapies for macrophage-associated diseases.

Analysis of mRNA expression for genes associated with regulatory T lymphocytes (CD25, FoxP3, CTLA4, and IDO) after experimental infection with bovine viral diarrhea virus of low or high virulence in beef calves

Immunosuppression caused by bovine viral diarrhea virus (BVDV) has been associated with lymphocyte depletion, leukopenia and impairment of leukocyte function; however, no work has been done on the relationship between BVDV and regulatory T lymphocytes (Tregs). The objective of this study was to compare the mRNA expression of genes associated with Tregs (CD25, FoxP3, CTLA4, and IDO), after experimental infection of beef calves with low (LV) or high (HV) virulence BVDV. Thirty BVDV-naïve calves were randomly assigned to three groups. Calves were intra-nasally inoculated with LV (n=10, strain SD-1) or HV (n=10, strain 1373) BVDV or BVDV-free cell culture medium (control, n=10). Quantitative RT-PCR was used to determine the expression of target genes in tracheo-bronchial lymph nodes and spleen on day 5 post-infection. The mRNA expression of CD25 was up-regulated in tracheo-bronchial lymph nodes of LV (P<0.05), but not in HV compared to the control group. The expression of FoxP3 and CTLA4 was not increased in tracheo-bronchial lymph nodes of either of the BVDV-inoculated groups. A dramatic up-regulation of IDO mRNA was observed in tracheo-bronchial lymph nodes of LV (P<0.05), but not HV compared to the control calves. In conclusion, experimental infection with BVDV did not provide evidence of Treg activation based on expression of FoxP3 and CTL4. Differential expression of CD25 and IDO mRNA on day 5 post-infection with HV or LV BVDV might reflect temporal differences in transcription occurring during the immune response elicited by these viral strains, or differences in viral infectivity of the host cells.

The kynurenine pathway is involved in bacterial meningitis

BACKGROUND

Bacterial meningitis (BM) is characterized by an intense host inflammatory reaction, which contributes to the development of brain damage and neuronal sequelae. Activation of the kynurenine (KYN) pathway (KP) has been reported in various neurological diseases as a consequence of inflammation. Previously, the KP was shown to be activated in animal models of BM, and the association of the SNP AADAT + 401C/T (kynurenine aminotransferase II - KAT II) with the host immune response to BM has been described. The aim of this study was to investigate the involvement of the KP during BM in humans by assessing the concentrations of KYN metabolites in the cerebrospinal fluid (CSF) of BM patients and their relationship with the inflammatory response compared to aseptic meningitis (AM) and non-meningitis (NM) groups.

METHODS

The concentrations of tryptophan (TRP), KYN, kynurenic acid (KYNA) and anthranilic acid (AA) were assessed by HPLC from CSF samples of patients hospitalized in the Giselda Trigueiro Hospital in Natal (Rio Grande do Norte, Brazil). The KYN/TRP ratio was used as an index of indoleamine 2,3-dioxygenase (IDO) activity, and cytokines were measured using a multiplex cytokine assay. The KYNA level was also analyzed in relation to AADAT + 401C/T genotypes.

RESULTS

In CSF from patients with BM, elevated levels of KYN, KYNA, AA, IDO activity and cytokines were observed. The cytokines INF-γ and IL-1Ra showed a positive correlation with IDO activity, and TNF-α and IL-10 were positively correlated with KYN and KYNA, respectively. Furthermore, the highest levels of KYNA were associated with the AADAT + 401 C/T variant allele.

CONCLUSION

This study suggests a downward modulatory effect of the KP on CSF inflammation during BM.

Kynurenines in CNS disease: regulation by inflammatory cytokines

The kynurenine pathway (KP) metabolizes the essential amino acid tryptophan and generates a number of neuroactive metabolites collectively called the kynurenines. Segregated into at least two distinct branches, often termed the “neurotoxic” and “neuroprotective” arms of the KP, they are regulated by the two enzymes kynurenine 3-monooxygenase and kynurenine aminotransferase, respectively. Interestingly, several enzymes in the pathway are under tight control of inflammatory mediators. Recent years have seen a tremendous increase in our understanding of neuroinflammation in CNS disease. This review will focus on the regulation of the KP by inflammatory mediators as it pertains to neurodegenerative and psychiatric disorders.

M. tuberculosis induces potent activation of IDO-1, but this is not essential for the immunological control of infection

Indoleamine 2,3-dioxygenesae-1 (IDO-1) catalyses the initial, rate-limiting step in tryptophan metabolism, thereby regulating tryptophan availability and the formation of downstream metabolites, including picolinic and quinolinic acid. We found that Mycobacterium tuberculosis infection induced marked upregulation of IDO-1 expression in both human and murine macrophages in vitro and in the lungs of mice following aerosol challenge with M. tuberculosis. The absence of IDO-1 in dendritic cells enhanced the activation of mycobacteria-specific T cells in vitro. Interestingly, IDO-1-deficiency during M. tuberculosis infection in mice was not associated with altered mycobacteria-specific T cell responses in vivo. The bacterial burden of infected organs, pulmonary inflammatory responses, and survival were also comparable in M. tuberculosis-infected IDO-1 deficient and wild type animals. Tryptophan is metabolised into either picolinic acid or quinolinic acid, but only picolinic acid inhibited the growth of M. tuberculosis in vitro. By contrast macrophages infected with pathogenic mycobacteria, produced quinolinic, rather than picolinic acid, which did not reduce M. tuberculosis growth in vitro. Therefore, although M. tuberculosis induces robust expression of IDO-1 and activation of tryptophan metabolism, IDO-1-deficiency fails to impact on the immune control and the outcome of the infection in the mouse model of tuberculosis.

Intracerebroventricular administration of HIV-1 Tat induces brain cytokine and indoleamine 2,3-dioxygenase expression: a possible mechanism for AIDS comorbid depression

Human immunodeficiency virus (HIV) remains a major public health concern despite a large education effort during the past 25 years. A persistent problem with HIV infection is the high comorbity rate of clinical depression. We previously established that increasing proinflammatory cytokines within the brain of mice induces sickness that can culminate in depressive-like behavior. Here we investigated the role of the HIV transactivator of transcription (Tat) protein in activation of brain cytokine signaling and subsequent induction of depressive-like behavior in a murine model. Adult Balb/c mice were administered a single intracerebroventricular (ICV) injection of Tat (40 ng). Social investigation of a novel juvenile was measured at 2, 4, 8 and 24 h post-treatment. Mice treated with Tat did not display signs of sickness, as measured by either decreased social investigation or loss of body weight. At 24 h post-injection, mice were subjected to the forced swim test (FST). ICV administration of Tat to Balb/c mice increased immobility in the FST at 24 h post injection. A different strain of mice, C57BL/6J, responded similarly in the FST. Furthermore, adult C57BL/6J mice injected with Tat and tested in a two-bottle 1% sucrose preference test displayed reduced preference for sucrose during the 24 h post-injection period. Subsequently, brain tissues from Tat-treated and control C57BL/6J mice were collected at 4 and 24 h post injection. CNS tissue from Tat-treated mice had increased expression of IL-1β, TNF-α, IL-6, and IDO mRNAs at 4 h post injection. These data demonstrate that a single exposure to Tat in the brain is sufficient to induce brain cytokine signaling that culminates in depressive-like behavior. The results reveal a potential role for Tat in the development of comorbid depression in HIV-infected individuals.

HIV-1 Tat activates indoleamine 2,3 dioxygenase in murine organotypic hippocampal slice cultures in a p38 mitogen-activated protein kinase-dependent manner

Background

We have established that activation of the tryptophan degrading enzyme indoleamine 2,3 dioxygenase (IDO) mediates the switch from cytokine-induced sickness behavior to depressive-like behavior. Because human immunodeficiency virus type 1 (HIV-1) Tat protein causes depressive-like behavior in mice, we investigated its ability to activate IDO in organotypic hippocampal slice cultures (OHSCs) derived from neonatal C57BL/6 mice.

Methods

Depressive-like behavior in C57BL/6J mice was assessed by the forced swim test. Expression of cytokines and IDO mRNA in OHSCs was measured by real-time RT-PCR and cytokine protein was measured by enzyme-linked immunosorbent assays (ELISAs). p38 MAPK phosphorylation was analyzed by western blot.

Results

Intracerebroventricular (i.c.v.) administration of Tat (40 ng) induced depressive-like behavior in the absence of sickness. Addition of Tat (40 ng/slice) to the medium of OHSCs induced IDO steady-state mRNA that peaked at 6 h. This effect was potentiated by pretreatment with IFNγ. Tat also induced the synthesis and release of TNFα and IL-6 protein in the supernatant of the slices and increased expression of the inducible isoform of nitric oxide synthase (iNOS) and the serotonin transporter (SERT). Tat had no effect on endogenous synthesis of IFNγ. To explore the mechanisms of Tat-induced IDO expression, slices were pretreated with the p38 mitogen-activated protein kinase (MAPK) inhibitor SB 202190 for 30 min before Tat treatment. SB 202190 significantly decreased IDO expression induced by Tat, and this effect was accompanied by a reduction of Tat-induced expression of TNFα, IL-6, iNOS and SERT.

Conclusion

These data establish that Tat induces IDO expression via an IFNγ-independent mechanism that depends upon activation of p38 MAPK. Targeting IDO itself or the p38 MAPK signaling pathway could provide a novel therapy for comorbid depressive disorders in HIV-1-infected patients.

The role of indoleamine 2, 3-dioxygenase in lepromatous leprosy immunosuppression

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.