Tryptophan Catabolism by Indoleamine 2,3-Dioxygenase 1 Alters the Balance of TH17 to Regulatory T Cells in HIV Disease

Division of Experimental Medicine, Department of Medicine, University of California, San Francisco, CA 94110, USA.
Science translational medicine (Impact Factor: 15.84). 05/2010; 2(32):32ra36. DOI: 10.1126/scitranslmed.3000632
Source: PubMed


The pathogenesis of human and simian immunodeficiency viruses is characterized by CD4(+) T cell depletion and chronic T cell activation, leading ultimately to AIDS. CD4(+) T helper (T(H)) cells provide protective immunity and immune regulation through different immune cell functional subsets, including T(H)1, T(H)2, T regulatory (T(reg)), and interleukin-17 (IL-17)-secreting T(H)17 cells. Because IL-17 can enhance host defenses against microbial agents, thus maintaining the integrity of the mucosal barrier, loss of T(H)17 cells may foster microbial translocation and sustained inflammation. Here, we study HIV-seropositive subjects and find that progressive disease is associated with the loss of T(H)17 cells and a reciprocal increase in the fraction of the immunosuppressive T(reg) cells both in peripheral blood and in rectosigmoid biopsies. The loss of T(H)17/T(reg) balance is associated with induction of indoleamine 2,3-dioxygenase 1 (IDO1) by myeloid antigen-presenting dendritic cells and with increased plasma concentration of microbial products. In vitro, the loss of T(H)17/T(reg) balance is mediated directly by the proximal tryptophan catabolite from IDO metabolism, 3-hydroxyanthranilic acid. We postulate that induction of IDO may represent a critical initiating event that results in inversion of the T(H)17/T(reg) balance and in the consequent maintenance of a chronic inflammatory state in progressive HIV disease.

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    • "Another mechanism of IDO expression in APCs is mediated by regulatory T-cells (Treg) (39, 40). In HIV patients, an elevated enzymatic activity of IDO in APCs was associated with a reduced anti-viral T-cell response [reviewed elsewhere (41)], while depletion of Treg cells reconstituted anti-HIV immune responses (42). Similarly, in SIV-infected macaques, the expression of the Treg markers CTLA-4 and FoxP3 was increased in T-cells of mesenteric lymph nodes, spleen, and colon, organs with high viral load (43). "
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    ABSTRACT: Initially, indoleamine-2,3-dioxygenase (IDO) has been introduced as a bactericidal effector mechanism and has been linked to T-cell immunosuppression and tolerance. In recent years, evidence has been accumulated that IDO also plays an important role during viral infections including HIV, influenza, and hepatitis B and C. Moreover, novel aspects about the role of IDO in bacterial infections and sepsis have been revealed. Here, we review these recent findings highlighting the central role of IDO and tryptophan metabolism in many major human infections. Moreover, we also shed light on issues concerning human-specific and mouse-specific host-pathogen interactions that need to be considered when studying the biology of IDO in the context of infections.
    Frontiers in Immunology 08/2014; 5:384. DOI:10.3389/fimmu.2014.00384
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    • "It appears that CD16-positive monocytes (5% of monocyte population [2]) are both more susceptible to infection and preferentially harbor the virus long-term [26]in vitro. We have also reported that immunoregulatory enzymes like HO-1 and indoleamine 2, 3-dioxygenase (IDO), may have beneficial effects in HIV-seropositive subjects [27]. While HO-1 expression in CD14+ monocytes was not predictive of CD4+ T cell recovery when measured at time points early after ART-mediated viral suppression, (Figure  4C) suppressive ART did restore homeostatic levels of HMOX1 gene expression (Figure  3B). "
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    ABSTRACT: The level (or frequency) of circulating monocyte subpopulations such as classical (CD14(hi)CD16(-)) and non-classical (CD14(dim)CD16(+)) monocytes varies during the course of HIV disease progression and antiretroviral therapy (ART). We hypothesized that such variation and/or differences in the degree to which these cells expressed the immunoregulatory enzyme, heme oxygenase-1 (HO-1), would be associated with CD4(+) T cell recovery after the initiation of ART. This hypothesis was tested in a cross-sectional study of four groups of HIV-infected subjects, including those who were seronegative, untreated virologic controllers [detectable viral load (VL) of <1000 copies/mL], untreated virologic non-controllers [VL > 10,000 copies/mL], and ART-mediated virologic controllers [VL < 75 copies/mL]. A longitudinal analysis of ART-treated subjects was also performed along with regression analysis to determine which biomarkers were associated with and/or predictive of CD4(+) T cell recovery. Suppressive ART was associated with increased levels of classical monocyte subpopulations (CD14(hi)CD16(-)) and decreased levels of non-classical monocyte populations (CD14(dim)CD16(+)). Among peripheral blood mononuclear cells (PBMCs), HO-1 was found to be most highly up-regulated in CD14(+) monocytes after ex vivo stimulation. Neither the levels of monocyte subpopulations nor of HO-1 expression in CD14(+) monocytes were significantly associated with the degree of CD4(+) T cell recovery. Monocyte subpopulations and HO-1 gene expression were, however, restored to normal levels by suppressive ART. These results suggest that the level of circulating monocyte subpopulations and their expression of HO-1 have no evident relationship to CD4(+) T cell recovery after the initiation of ART.
    AIDS Research and Therapy 08/2014; 11(1):27. DOI:10.1186/1742-6405-11-27 · 1.46 Impact Factor
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    • "Alternatively, long-term, chronic expression of IDO in regulatory pDCs may be mediated by the anti-inflammatory cytokine TGFβ [35], [36]. IDO-expressing pDCs mediate suppressive effects on T cells via 1) degradation/depletion of local tryptophan which prevents T cell proliferation and 2) generation of kynurenine and downstream metabolites that block T cell proliferation [37], induce T cell apoptosis [38], [39], and convert naïve CD4+ cells and Th17 cells into Tregs [40], [41]. Thus, CTLA-4 and IDO work in tandem to increase the number and regulatory function of suppressive DCs and Tregs in lymphoid tissues. "
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    ABSTRACT: HIV immune pathogenesis is postulated to involve two major mechanisms: 1) chronic innate immune responses that drive T cell activation and apoptosis and 2) induction of immune regulators that suppress T cell function and proliferation. Both arms are elevated chronically in lymphoid tissues of non-natural hosts, which ultimately develop AIDS. However, these mechanisms are not elevated chronically in natural hosts of SIV infection that avert immune pathogenesis despite similarly high viral loads. In this study we investigated whether minocycline could modulate these pathogenic antiviral responses in non-natural hosts of HIV and SIV. We found that minocycline attenuated in vitro induction of type I interferon (IFN) and the IFN-stimulated genes indoleamine 2,3-dioxygenase (IDO1) and TNF-related apoptosis inducing ligand (TRAIL) in human plasmacytoid dendritic cells and PBMCs exposed to aldrithiol-2 inactivated HIV or infectious influenza virus. Activation-induced TRAIL and expression of cytotoxic T-lymphocyte antigen 4 (CTLA-4) in isolated CD4+ T cells were also reduced by minocycline. Translation of these in vitro findings to in vivo effects, however, were mixed as minocycline significantly reduced markers of activation and activation-induced cell death (CD25, Fas, caspase-3) but did not affect expression of IFNβ or the IFN-stimulated genes IDO1, FasL, or Mx in the spleens of chronically SIV-infected pigtailed macaques. TRAIL expression, reflecting the mixed effects of minocycline on activation and type I IFN stimuli, was reduced by half, but this change was not significant. These results show that minocycline administered after infection may protect against aspects of activation-induced cell death during HIV/SIV immune disease, but that in vitro effects of minocycline on type I IFN responses are not recapitulated in a rapid progressor model in vivo.
    PLoS ONE 04/2014; 9(4):e94375. DOI:10.1371/journal.pone.0094375 · 3.23 Impact Factor
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