Biomedical subjects

Osamu Takikawa

Publications and source records attributed to Osamu Takikawa.

At least 19 recordsLinked to original sources

PubMed2006

Cloning and functional characterization of a novel up-regulator, cartregulin, of carnitine transporter, OCTN2.

Acetylcarnitine exerts therapeutic effects on some neurological disorders including Alzheimer's disease. OCTN2 is known as a transporter for acetylcarnitine, but its expression in the brain is very low. To examine a brain-specific transporter for acetylcarnitine, we screened a rat brain cDNA library by hybridization using a DNA probe conserved among an OCTN family. A cDNA homologous to OCTN2 cDNA was isolated. The cDNA encoded a novel 146-amino acid protein with one putative transmembrane domain. The mRNA was expressed not only in rat brain but also in some other tissues. The novel protein was localized in endoplasmic reticulum when expressed in COS-7 cells but exhibited no transport activity for acetylcarnitine. However, when co-expressed with OCTN2, it enhanced the OCTN2-mediated transport by about twofold. The enhancement was accompanied by an increase in the levels of mRNA and protein. When OCTN2 was expressed in Xenopus oocytes by injection of its cRNA, its transport activity was enhanced by co-expression of the novel protein. These data suggest that the novel protein increases OCTN2 by stabilizing the mRNA in endoplasmic reticulum. The protein may be an up-regulator of OCTN2 and is tentatively designated cartregulin.

Acetylcarnitine↗

PubMed2006

Inhibition of indoleamine 2,3 dioxygenase activity by H2O2.

Indoleamine 2,3-dioxygenase is the first and rate limiting enzyme of the kynurenine pathway of tryptophan metabolism, has potent effects on cell proliferation and mediates antimicrobial, antitumorogenic, and immunosuppressive effects. As a potent cytotoxic effector, the mechanisms of indoleamine 2,3-dioxygenase inhibition deserve greater attention. The work presented here represents the first systematic study exploring the mechanisms by which low levels of hydrogen peroxide (10-100 microM) inhibit indoleamine 2,3-dioxygenase in vitro. Following brief peroxide exposure both enzyme inhibition and structural changes were observed. Loss of catalysis was accompanied by oxidation of several cysteine residues to sulfinic and sulfonic acids, observed by electrospray and MALDI mass spectrometry. Enzyme activity could in part be preserved in the presence of sulfhydryl containing compounds, particularly DTT and methionine. However, these structural alterations did not prevent substrate (l-tryptophan) binding. Some enzyme activity could be recovered in the presence of thioredoxin, indicating that the inhibitory effect of H(2)O(2) is at least partially reversible in vitro. We present evidence that cysteine oxidation represents one mechanism of indoleamine 2,3-dioxygenase inhibition.

Dose-Response Relationship, Drug↗

PubMed2006

IDO expression on decidual and peripheral blood dendritic cells and monocytes/macrophages after treatment with CTLA-4 or interferon-gamma increase in normal pregnancy but decrease in spontaneous abortion.

Recent data demonstrated that CD4+CD25+ regulatory T (Treg) cells and an enzyme called indoleamine 2,3-dioxygenase (IDO) mediate maternal tolerance to the fetus. Interestingly, Treg cells express the CTLA-4 molecule on their surface, and B7 (CD80/86) ligation by CTLA-4 enhanced IDO activity of dendritic cells (DCs) and monocytes by the induction of interferon gamma (IFN-gamma) production. In this study, we studied the IDO expression on peripheral blood monocytes and decidual monocytes or DCs after treatment with CTLA-4/Fc fusion protein or IFN-gamma using flow cytometry. IDO expressions on both peripheral blood DC and decidual DC and monocytes were up-regulated during normal pregnancy. On the other hand, both IDO expression on DC and monocytes after IFN-gamma treatment or CTLA-4 treatment were decreased in spontaneous abortion cases. The expression of CD86 on peripheral blood and decidual monocytes and DC in spontaneous abortion cases was lower compared with those in normal pregnancy subjects. Also, IFN-gamma production by decidual and peripheral blood mononuclear cells after CTLA-4/Fc treatment in spontaneous abortion cases was significantly lower than those in normal pregnancy subjects. These data suggest that CTLA-4 on Treg cells up-regulates IDO expression on decidual and peripheral blood DC and monocytes by the induction of IFN-gamma production.

Abortion, Spontaneous↗

PubMed2006

Nitration and inactivation of IDO by peroxynitrite.

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

Amino Acid Sequence↗

PubMed2006

Systemic application of CpG-rich DNA suppresses adaptive T cell immunity via induction of IDO.

CpG-rich oligonucleotides (CpG-ODN) bind to Toll-like receptor 9 (TLR9) and are used as powerful adjuvants for vaccination. Here we report that CpG-ODN not only act as immune stimulatory agents but can also induce strong immune suppression depending on the anatomical location of application. In agreement with the adjuvant effect, subcutaneous application of antigen plus CpG-ODN resulted in antigen-specific T cell activation in local lymph nodes. In contrast, systemic application of CpG-ODN resulted in suppression of T cell expansion and CTL activity in the spleen. The suppressive effect was mediated by indoleamine 2,3-dioxygenase (IDO) as indicated by the observation that CpG-ODN induced IDO in the spleen and that T cell suppression could be abrogated by 1-methyl-tryptophan (1-MT), an inhibitor of IDO. No expression of IDO was observed in lymph nodes after injection of CpG-ODN, explaining why suppression was restricted to the spleen. Studies with a set of knockout mice demonstrated that the CpG-ODN-induced immune suppression is dependent on TLR9 stimulation and independent of type I and type II interferons. The present study shows that for the use of CpG-ODN as an adjuvant in vaccines, the route of application is crucial and needs to be considered. In addition, the results indicate that down-modulation of immune responses by CpG-ODN may be possible in certain pathological conditions.

Adenoviridae↗

PubMed2005

Neuronal localization of indoleamine 2,3-dioxygenase in mice.

Indoleamine 2,3-dioxygenase (IDO) catabolizes tryptophan to kynurenine. In the immune system, the reduction in tryptophan and increase in kynurenine act to suppress T-cell function. In the nervous system, kynurenine can be further metabolized to quinolinic acid, which can be neurotoxic. IDO is known to be expressed by microglia and its levels are upregulated by interferon-gamma (IFNgamma). We report here that IDO immunoreactivity is also localized in neurons, and that IDO is upregulated by IFNgamma in neurons of the hippocampus. Thus, neuronal IDO could contribute to the vulnerability of neurons to inflammatory conditions.

Animals↗

PubMed2005

Biochemical and medical aspects of the indoleamine 2,3-dioxygenase-initiated L-tryptophan metabolism.

Indoleamine 2,3-dioxygenase (EC 1.13.11.42) is a heme-containing dioxygenase which catalyzes the first and rate-limiting step in the major pathway of L-tryptophan catabolism in mammals. Much attention has recently been focused on the dioxygenase because this metabolic pathway is involved not only in a variety of physiological functions but also in many diseases. In this review, the discovery and unique catalytic properties of dioxygenase are described first, and then the recent findings regarding the dioxygenase-initiated tryptophan metabolism are summarized, with special emphasis on the detrimental role of dioxygenase in side effects of interferon-gamma and interleukin-12 (by systemic tryptophan depletion), the escape of malignant tumors from immune surveillance (by immunosuppression caused by tryptophan depletion), several neurodegenerative disorders including Alzheimer's disease (by an aberrant production of neurotoxin, quinolinic acid), and age-related cataract (due to "Kynurenilation," a novel post-translational modification of lens proteins with tryptophan-derived UV filters).

Animals↗

PubMed2005

Indoleamine 2,3-dioxygenase serves as a marker of poor prognosis in gene expression profiles of serous ovarian cancer cells.

PURPOSE: We aimed to find key molecules associated with chemoresistance in ovarian cancer using gene expression profiling as a screening tool. EXPERIMENTAL DESIGN: Using two newly established paclitaxel-resistant ovarian cancer cell lines from an original paclitaxel-sensitive cell line and four supersensitive and four refractory surgical ovarian cancer specimens from paclitaxel-based chemotherapy, molecules associated with chemoresistance were screened with gene expression profiling arrays containing 39,000 genes. We further analyzed 44 genes that showed significantly different expressions between paclitaxel-sensitive samples and paclitaxel-resistant samples with permutation tests, which were common in cell lines and patients' tumors. RESULTS: Eight of these genes showed reproducible results with real-time reverse transcription-PCR, of which indoleamine 2,3-dioxygenase gene expression was the most prominent and consistent. Moreover, by immunohistochemical analysis using a total of 24 serous-type ovarian cancer surgical specimens (stage III, n = 21; stage IV, n = 7), excluding samples used for GeneChip analysis, the Kaplan-Meier survival curve showed a clear relationship between indoleamine 2,3-dioxygenase staining patterns and overall survival (log-rank test, P = 0.0001). All patients classified as negative survived without relapse. The 50% survival of patients classified as sporadic, focal, and diffuse was 41, 17, and 11 months, respectively. CONCLUSION: The indoleamine 2,3-dioxygenase screened with the GeneChip was positively associated with paclitaxel resistance and with impaired survival in patients with serous-type ovarian cancer.

Animals↗

PubMed2005

Inhibition of indoleamine 2,3-dioxygenase (IDO) enhances elimination of virus-infected macrophages in an animal model of HIV-1 encephalitis.

Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the kynurenine pathway of tryptophan metabolism. IDO activity is linked with immunosuppression by its ability to inhibit lymphocyte proliferation, and with neurotoxicity through the generation of quinolinic acid and other toxins. IDO is induced in macrophages by HIV-1 infection, and it is up regulated in macrophages in human brain tissue with HIV-1 encephalitis (HIVE). Using a model of HIVE, we investigated whether IDO inhibitor 1-methyl-d-tryptophan (1-MT) could affect the generation of cytotoxic T lymphocytes (CTLs) and clearance of virus-infected macrophages from the brain. Severe combined immunodeficient mice were reconstituted with human peripheral blood lymphocytes, and encephalitis was induced by intracranial injection of autologous HIV-1-infected monocyte-derived macrophages (MDMs). Animals treated with 1-MT demonstrated increased numbers of human CD3+, CD8+, CD8+/interferon-gamma+ T cells, and HIV-1(gag/pol)-specific CTLs in peripheral blood compared with controls. At week 2 after MDM injection in the basal ganglia, mice treated with 1-MT showed a 2-fold increase in CD8+ T lymphocytes in the areas of the brain containing HIV-1-infected MDMs compared with untreated controls. By week 3, 1-MT-treated mice showed 89% reduction in HIV-infected MDMs in brain as compared with controls. Thus, manipulation of immunosuppressive IDO activity in HIVE may enhance the generation of HIV-1-specific CTLs, leading to elimination of HIV-1-infected macrophages in brain.

Animals↗

PubMed2005

Monocyte-mediated T-cell suppression and augmented monocyte tryptophan catabolism after human hematopoietic stem-cell transplantation.

T-cell dysfunction after human hematopoietic stem-cell transplantation (HSCT) is generally attributed to intrinsic T-cell defects. Here we show that the characteristic impaired proliferative responses to polyclonal stimulation of post-HSCT peripheral blood mononuclear cells (PB-MCs) were markedly (4-fold) improved by T-cell enrichment. Conversely, addback of post-HSCT monocytes to these enriched T cells dampened their proliferative responses, suggesting that post-HSCT monocytes effectively mediate T-cell suppression. As a mechanism possibly contributing to monocyte-mediated T-cell suppression, we investigated monocyte tryptophan catabolism by indoleamine 2,3-dioxygenase into kynurenine, which has been implicated in regulating T-cell responses. Compared with controls, all post-HSCT monocyte-containing cell cultures (total PBMCs, monocytes, and monocyte/T-cell cocultures), but not monocyte-depleted populations, secreted elevated amounts of kynurenine. Blockade of tryptophan catabolism improved the proliferative responses. The slightly increased kynurenine release and substantial release of neopterin by unstimulated post-HSCT monocytes suggests that they were in a state of continuous activation. Superimposed on this state, stimulation of these cells caused a striking, additional increase (10-fold) in kynurenine release, and they triggered marked apoptosis of autologous post-HSCT T cells. We conclude that the amplified kynurenine release by post-HSCT monocytes, particularly induced upon stimulation, may underlie their suppressor activity, which in turn may contribute to the depressed T-cell immune responses after HSCT.

Adolescent↗

PubMed2005

Expression of indoleamine 2,3-dioxygenase and production of quinolinic acid by human microglia, astrocytes, and neurons.

There is good evidence that the kynurenine pathway (KP) and one of its end products, quinolinic acid (QUIN) play a role in the pathogenesis of several major neurological diseases. While QUIN has been shown to be produced in neurotoxic concentrations by macrophages and microglia, the capacity of astrocytes and neurons to produce QUIN is controversial. Using interferon gamma (IFN-gamma)-stimulated primary cultures of human mixed brain cells, we assayed expression of the KP regulatory enzyme indoleamine 2,3-dioxygenase (IDO) and QUIN production by immunocytochemistry. Using IFN-gamma-stimulated purified cultures of neurons, astrocytes, microglia and macrophages, we studied IDO expression by RT-PCR and production of QUIN using mass spectrometry. We found that astrocytes, neurons, and microglia expressed IDO but only microglia were able to produce detectable amounts of QUIN. However, astrocytes and neurons had the ability to catabolize QUIN. This study also provides the first evidence of IDO expression and lack of production of QUIN in culture of primary human neurons.

Astrocytes↗

PubMed2005

Reciprocal changes in endothelium-derived hyperpolarizing factor- and nitric oxide-system in the mesenteric artery of adult female rats following ovariectomy.

1. To explore the effects of estrogen on arterial functions, we examined endothelium-derived hyperpolarizing factor (EDHF)- and NO-mediated responses in isolated mesenteric arteries of female rats, 4 weeks after sham-operation (CON), ovariectomy (OVX) and OVX plus chronic estrogen treatment (OVX+E(2)). Tissue levels of connexins-40, 43 (major components of gap junction), inducible NOS (iNOS), endothelial NOS (eNOS) and eNOS regulator proteins such as calmodulin, heat shock protein 90 (hsp90) and caveolin-1 were also examined using Western blot. 2. In OVX, acetylcholine (ACh)-induced EDHF-mediated relaxation and membrane hyperpolarization of arterial smooth muscles were reduced, whereas ACh-induced NO-mediated relaxation was enhanced, leading to no change in ACh-induced relaxation. 3. In OVX, connexin-40 and 43 were decreased. Tissue levels of eNOS and its positive regulators (calmodulin and hsp90) were unchanged, but that of its negative regulator, caveolin-1, was decreased. The levels of iNOS in mesenteric artery and aorta and plasma levels of NO metabolites and cholesterol were elevated. 4. In OVX, contraction of the artery by phenylephrine was reduced, but augmented by nonspecific inhibitor of NOS to the comparable level as that in CON group. The contraction in OVX group unlike that in CON group was augmented by specific iNOS inhibitor, and the difference between contractions in the presence of nonspecific and specific inhibitor as an index of eNOS activity was increased. 5. In OVX+E(2), all these changes were recovered. 6. In all groups, EDHF-mediated relaxation was suppressed by 18beta-glycyrrhetinic acid, an inhibitor of gap junction. 7. These results indicate that estrogen deficiency does not change the diameter of mesenteric artery: it reduces EDHF-mediated relaxation by decreasing gap junction, whereas it augments NO-mediated relaxation via an increase in NO release. Increased NO result from increased activity of eNOS subsequent to a decrease in caveolin-1 and from induction of iNOS. However, excessive NO generation with elevated plasma cholesterol would raise a risk for atherosclerosis.

Acetylcholine↗

PubMed2004

Determination of the nature of the heme environment in nitrosyl indoleamine 2,3-dioxygenase using Multiple-scattering analyses of X-ray absorption fine structure.

Multiple-scattering analysis of X-ray absorption fine structure data on the NO adducts of indoleamine 2,3-dioxygenase (IDO) and analysis of X-ray absorption near-edge structure (XANES) have provided the first direct structural information about the iron center for this ubiquitous mammalian metalloprotein. The IDO(II)NO adduct, which is likely to play a physiological role in the immune system, differs from similar adducts such as Mb(II)NO and Lb(II)NO in that the Fe-His bond is essentially broken. At 10 K, the Fe-N(p)(av) bond length = 2.00(2) A, Fe-NO bond length = 1.75 A, and angle = 140 degrees, which are typical of five-coordinate Fe(II)NO species. The XANES is also closer to that of five-coordinate model complexes than six-coordinate species. In addition to the Fe(II)NO species, there was a minor component of the Fe(III)NO adduct because of incomplete reduction of the Fe(II) species. This was also a five-coordinate center and consists of a linear Fe(II)NO(+) moiety with the Fe-N(p)(av) bond length = 2.00(2) A, Fe-NO bond length = 1.63(3) A, and angle = 179 degrees. The results indicate that both the blocking of the heme site to O(2) binding and conformational changes induced by breaking the Fe-N(epsilon) bond may be important mechanisms by which NO inhibits IDO in vitro and in vivo.

Binding Sites↗

PubMed2004

Mechanisms regulating the expression of indoleamine 2,3-dioxygenase during decidualization of human endometrium.

BACKGROUND: Expression of the tryptophan catabolizing enzyme, indoleamine 2,3-dioxygenase, in the mouse placenta has been shown to be critical in preventing immunological rejection of the fetal allograft. To clarify the physiological importance of indoleamine 2,3-dioxygenase in human pregnancy, we have studied how the expression of this enzyme changes during decidualization of human endometrium at both the cell and tissue level. METHODS AND RESULTS: The level of indoleamine 2,3-dioxygenase mRNA expression (determined by RT-PCR) was higher in decidual than in endometrial tissue. Uterine decidual tissue in ectopic pregnancy similarly showed increased mRNA expression. Immunohistochemistry demonstrated that indoleamine 2,3-dioxygenase protein immunoreactivity was found in glandular epithelium and in stromal cells. The intensity of this immunoreactivity was increased in decidualized tissue. In a cell culture model, the level of indoleamine 2,3-dioxygenase mRNA was suppressed specifically by progesterone-induced decidualization of isolated endometrial stromal cells. Indoleamine 2,3-dioxygenase protein abundance (determined by Western blot) was also decreased by progesterone-induced decidualization. However interferon-gamma, a potent stimulator of indoleamine 2,3-dioxygenase gene expression, increased the level of indoleamine 2,3-dioxygenase mRNA and protein in both non-decidualized and in decidualized cells. Indoleamine 2,3-dioxygenase activity (determined by measuring the concentration of tryptophan and its indoleamine 2,3-dioxygenase catabolite, kynurenine) was also decreased by progesterone-induced decidualization but enhanced following interferon-gamma treatment. Expression of other interferon-gamma inducible genes (STAT1 and tryptophanyl-tRNA synthetase) showed the same pattern as that of indoleamine 2,3-dioxygenase in tissue samples, but was not changed by decidualization in the cell culture model. CONCLUSIONS: These data suggest that despite suppression by progesterone, indoleamine 2,3-dioxygenase expression in endometrial stromal cells may increase during decidualization due to stimulation by interferon-gamma secreted by infiltrating leukocytes.

Decidua↗

PubMed2004

Increased expression of indoleamine 2,3-dioxygenase in murine malaria infection is predominantly localised to the vascular endothelium.

Products of the kynurenine pathway of tryptophan metabolism have been implicated in the pathogenesis of murine and human cerebral malaria. Indoleamine 2,3-dioxygenase is the first and rate-limiting enzyme in this pathway and we have developed an immunohistochemical method for its detection in tissues from normal and malaria-infected mice. Mice were infected with Plasmodium berghei ANKA, a murine model of cerebral malaria, or P. berghei K173, a non-cerebral malaria model. Vascular endothelial cells were the primary sites of indoleamine 2,3-dioxygenase expression in both types of malaria infection and this response was systemic, with positive staining of vascular endothelium in all tissues examined. No indoleamine 2,3-dioxygenase expression was detected in uninfected or interferon-gamma-/- mice. Corroborative data were obtained using quantitative reverse transcription PCR for indoleamine 2,3-dioxygenase mRNA. These results suggest that interferon-gamma-dependent indoleamine 2,3-dioxygenase expression is part of a normal systemic host response to the parasite, perhaps performing some tissue protective functions that may become deranged under some circumstances and contribute to the pathogenesis of cerebral malaria. On the other hand, constitutive indoleamine 2,3-dioxygenase expression in the epididymis and the placenta was detected in both C57Bl/6 wild-type and interferon-gamma-/- mice, suggesting a distinct regulatory mechanism for its induction in these normal physiological situations. Although increased indoleamine 2,3-dioxygenase production during murine malaria infection may not by itself cause cerebral pathology, metabolites of the kynurenine pathway may combine with other features of cerebral malaria, such as breakdown of the blood-brain barrier, to influence CNS function and contribute to the symptoms and pathology observed.

Animals↗

PubMed2004

Indoleamine 2,3-dioxygenase: distribution and function in the developing human placenta.

Studies in mice have suggested that the placenta is protected from immune rejection by maternal T cells by means of localised indoleamine 2,3-dioxygenase dependent depletion of tryptophan. To determine whether such mechanisms might operate in the human placenta, we have studied the physiological importance of human placental indoleamine 2,3-dioxygenase immunohistochemically and functionally. Indoleamine 2,3-dioxygenase is detectable immunohistochemically from day 6 human blastocysts and thereafter throughout pregnancy in syncytiotrophoblasts, extravillous cytotrophoblasts and macrophages in the villous stroma and in the fetal membranes. Interferon-gamma added to villous explants markedly stimulates indoleamine 2,3-dioxygenase protein expression in macrophages. Indoleamine 2,3-dioxygenase-mediated tryptophan degradation in the first trimester villous and decidual tissue explants is stimulated by interferon-gamma and inhibited by 1-methyl-tryptophan (an inhibitor of indoleamine 2,3-dioxygenase). Peripheral blood mononuclear cell proliferation is controlled by indoleamine 2,3-dioxygenase-mediated tryptophan degradation. These results suggest the cellular basis of a mechanism present at the human maternal-fetal interface involved in regulating the maternal immune response to conceptus.

Antiviral Agents↗

PubMed2004

Macrophages of human first trimester decidua express markers associated to alternative activation.

PROBLEM: Depending on the type of their activation, macrophages may promote TH1- or TH2-type of immune responses. To date, not much is known about the activation phenotype of decidua macrophages, which - together with NK cells - constitute the majority of bone marrow derived cells at this location. METHOD OF STUDY: The study was based on analysis of healthy first trimester decidua by immunohistochemistry and flow cytometry. We analyzed expression of markers characteristic for alternatively activated macrophages (Mphi2). RESULTS: The markers MS-1 (stabilin-1) and coagulation factor XIIIa were found expressed in the interior of decidua macrophages (DMphi). In contrast, indoleamine 2,3-dioxygenase (IDO), an enzyme induced in macrophages by IFNgamma, was not present in DMphi. CONCLUSIONS: First trimester DMphi display phenotypic markers associated to alternatively activated macrophages. In addition, absence of IDO indicates that DMphi are not under a predominant influence of IFNgamma.

Biomarkers↗

PubMed2004

Human epidermal langerhans cells express the immunoregulatory enzyme indoleamine 2,3-dioxygenase.

Langerhans cells (LC) are a special subset of dendritic cells integrating cutaneous immunity. The study of LC function is of major interest not only for efforts of vaccine design and immunotherapy but also for gaining an insight into the pathogenesis of immune-mediated cutaneous diseases and neoplasias. Recently, defined antigen-presenting cells were described that express indoleamine 2,3-dioxygenase (IDO) and inhibit T cell proliferation in vitro and in vivo. Here, we show that stimulation with interferon-gamma (IFN-gamma) induces the expression of functionally active IDO in highly purified human epidermal LC. The induction of IDO after stimulation of LC with IFN-gamma seems to follow a defined kinetic with rapid upregulation followed by a downregulation after about 24 h of culture. Accordingly, proliferation of T cells induced by anti-CD3 antibodies was modulated by supernatants of IFN-gamma-activated human epidermal LC. Importantly, downregulation of T cell proliferation by supernatants of 24 h IFN-gamma-activated LC was prevented by inhibition of IDO. These results indicate that LC not only have the capacity to stimulate but also to inhibit T cells, and suggest that LC possess an immunoregulatory function in promoting T cell tolerance by production of IDO.

Antineoplastic Agents↗