Indoleamine 2,3-dioxygenase-expressing myeloid dendritic cells and macrophages in infectious and noninfectious cutaneous granulomas

Macrophage Biology in Human Granulomatous Skin Inflammation

Cutaneous granulomatoses represent a heterogeneous group of diseases, which are defined by macrophage infiltration in the skin. Skin granuloma can be formed in the context of infectious and non-infectious conditions. Recent technological advances have deepened our understanding of the pathophysiology of granulomatous skin inflammation, and they provide novel insights into human tissue macrophage biology at the site of ongoing disease. Here, we discuss findings on macrophage immune function and metabolism derived from three prototypic cutaneous granulomatoses: granuloma annulare, sarcoidosis, and leprosy.

Pathogenesis of annular lesions: Why a ring presentation?

Annular lesions represent a distinct morphology which characterizes many well-known dermatologic conditions. Little is definitively known regarding the pathogenesis of annular lesions, however there a few well-regarded hypotheses. Lesions that clear centrally while enlarging peripherally may result from a local central tissue anergy, or tolerance. The central area in lesions due to dermatophyte infections or subacute cutaneous lupus erythematous may have a central immunity to the antigen that trigged the lesion. The peripheral spread of inflammatory mediators may also contribute to lesions that expand centrifugally. In a highly active immune response, some of the inflammatory mediators may spread to adjacent tissue, which can propagate the inflammatory reaction. The additional hypotheses regarding pathogenesis are disease specific with individual mechanisms having been proposed. This chapter will describe both general and disease specific mechanisms that may contribute to the formation of annular lesions.

Increased Indoleamine 2, 3-Dioxygenase expression modulates Th1/Th17/Th22 and Treg pathway in humans with Helicobacter Pylori-Infected gastric mucosa

INTRODUCTION AND PURPOSE

Indoleamine 2, 3- dioxygenase (IDO) plays an importantrole in immunosuppressive pathway, as inhibits responsesof T cells and promotes immune tolerance. Host responsetoHelicobacter pylori (H. pylori) is involved in the infection persistenceand it is also associatedwith different clinical outcomes. The aim of this study was to investigate the role of IDO in H. pylori-infected patients with gastritis diseases and peptic ulcer diseases (PUD) through the assessment of the relationship among IDO protein expression and the numbers of T helper (Th)-1, Th17, Th22, and T regulator (Treg) cells.

MATERIALS AND METHODS

Antrum biopsy was obtained from H. pylori-negative patients (n = 48) and H. pylori-positive subjects (55 patients with gastritis and 47 patients with PUD), for performing H. pylori status and histopathological assessments. IDO protein expression was evaluated by Western blotting.

RESULTS

IDO protein expression was significantly higher in gastric biopsies from H. pylori-positive subjects compared to the H. pylori-negative subjects, and also in H. pylori-positive subjects with gastritis disease compared to H. pylori-positive subjects with PUD. Moreover, in H. pylori-positive subjects, a positive correlation was observed between IDO protein expression and the frequency of Treg cells. In addition, a negative correlation was observed between IDO protein expression and the number of Th1, Th17, and Th22.

CONCLUSION

Increased IDO protein expression is able to change the number of Th1, Th17, Th22, and Treg cells and these changes are possibly associated with an increase in the risk of PUD development in H. pylori-infected patients.

The expression of Indoleamine 2, 3-dioxygenase (IDO) is reduced in granulomas from BCG vaccinated cattle compared to granulomas from unvaccinated controls after experimental challenge with Mycobacterium bovis

Bovine tuberculosis (bTB), mainly caused by Mycobacterium bovis (M. bovis), is a major economic disease of livestock worldwide. Vaccination is considered as a potentially sustainable adjunct to the current control strategy. Cattle vaccination with the live attenuated M. bovis bacillus Calmette-Guerin (BCG) confers variable protection; the reasons for this variability are not understood. Indoleamine 2, 3-dioxygenase (IDO), through the catalysis of tryptophan, is thought to have an immunoregulatory role in the immune response to Mycobacterium tuberculosis (M. tuberculosis). In this work, we used immunohistochemistry and digital image analysis to evaluate the presence of IDO in granulomas at different stages of development in cattle that had been BCG-vaccinated or not and then challenged with M. bovis. Our results show that the expression of IDO in granulomas from non-vaccinated M. bovis challenged animals is higher than in granulomas from BCG-vaccinated M. bovis challenged animals. Thus, it is possible that vaccination with BCG prevents the induction of what are thought to be host immunosuppressive pathways by M. bovis, which contribute to pathology during the disease.

Innate Immune Responses in Leprosy

Leprosy is an infectious disease that may present different clinical forms depending on host immune response to Mycobacterium leprae. Several studies have clarified the role of various T cell populations in leprosy; however, recent evidences suggest that local innate immune mechanisms are key determinants in driving the disease to its different clinical manifestations. Leprosy is an ideal model to study the immunoregulatory role of innate immune molecules and its interaction with nervous system, which can affect homeostasis and contribute to the development of inflammatory episodes during the course of the disease. Macrophages, dendritic cells, neutrophils, and keratinocytes are the major cell populations studied and the comprehension of the complex networking created by cytokine release, lipid and iron metabolism, as well as antimicrobial effector pathways might provide data that will help in the development of new strategies for leprosy management.

Indoleamine 2,3-Dioxygenase Expression in Primary Cutaneous Melanoma Correlates with Breslow Thickness and Is of Significant Prognostic Value for Progression-Free Survival

The enzyme indoleamine 2,3-dioxygenase (IDO) is emerging as a facilitator of cancer development through its effects on cancer-associated inflammation. Recent studies report a significant improvement of the response rates in melanoma patients to PD-1 antibodies when IDO inhibitors were added to the regimen. Data on IDO expression in primary human melanomas are, however, incomplete and conflicting. Here, we show that the level of IDO expression in primary human melanoma cells significantly correlates with Breslow thickness (P = 0.003), the presence of tumor-infiltrating lymphocytes (P = 0.029), and the intensity of the peritumoral inflammatory infiltrate (P = 0.001). The expression of IDO in melanoma cells predicted independently of Breslow thickness and tumor stage (P = 0.04). We further show that CD11c⁺ dendritic cells and CD68⁺ macrophages in the microenvironment of melanomas express IDO. The level of IDO expression in antigen-presenting cells correlated positively to peritumoral inflammation (P = 0.001) but not to tumor-infiltrating lymphocytes. Significant negative correlation with progression-free survival was found for patients for whom antigen-presenting cells were very strongly IDO positive. These results suggest that IDO induction within melanoma cells may directly reflect tumor progression, whereas IDO in antigen-presenting cells may determine immune surveillance with impact on local and systemic tolerance.

Response of iNOS and its relationship with IL-22 and STAT3 in macrophage activity in the polar forms of leprosy

Leprosy is a chronic granulomatous infection that manifests as different clinical forms related to the immunological response. The aim of the study was to evaluated the response of IL-22, STAT3, CD68 and iNOS in leprosy skin lesions. The mean number IL-22 positive cells was 12.12±1.90cells/field in the TT form and 31.31±2.91cells/field in the LL form. STAT3 positive cells was 5.29±1.96 cells/field in the TT form, while this number was 11.13±3.48cells/field in the LL form. The mean number of CD68 positive cells was 25.18±6.21cells/field in the TT form and 62.81±8.13cells/field in the LL form. Quantitative analysis of iNOS revealed a significant difference, with the mean number of cells expressing the enzyme being 30.24±2.88cells/field in the TT form compared to 35.44±4.69cells/field in the LL form. Linear correlations in lesions of TT patients showed a moderate positive correlations between CD68 and iNOS, STAT3 and Inos, IL-22 and STAT3, and IL-22 and iNOS. Our results demonstrate that these factors can act synergistically to induce a microbicidal activity in the population of macrophages in the leprosy lesions.

Sarcoidosis-Lymphoma Syndrome Associated with Folliculotropic Peripheral T Cell Lymphoma Not Otherwise Specified

Sarcoidosis is occasionally accompanied by hematologic malignancies, including cutaneous T-cell lymphoma, called sarcoidosis-lymphoma syndrome. Although the mechanism underlying the induction of lymphomas is still unknown, understanding the immunological background of sarcoidosis could help explain the possible mechanisms of the induction of lymphomas. In this report, we describe a case of sarcoidosis-lymphoma syndrome associated with folliculotropic peripheral T cell lymphoma not otherwise specified, which caused dense infiltration of CD30+ CD163+ tumor-associated macrophages (TAMs) only in the lesional skin. Our present case might suggest the significance of TAMs in developing sarcoid-lymphoma syndrome.

Immunotolerant indoleamine-2,3-dioxygenase is increased in condyloma acuminata

BACKGROUND

The tryptophan-depleting enzyme indoleamine-2,3-dioxygenase (IDO) is critical for the regulation of immunotolerance and plays an important role in immune-associated skin diseases.

OBJECTIVES

To analyse the level of IDO in condyloma acuminata (CA) and its role in this condition.

METHODS

IDO expression was assessed in the skin and peripheral blood of healthy controls and patients with CA. To assess the role of skin IDO in immunity, the ability of isolated epidermal cells to metabolize tryptophan and the influence on polyclonal T-cell mitogen (PHA)-stimulated T-cell proliferation were explored.

RESULTS

IDO median fluorescence intensities in peripheral blood mononuclear cells from patients with CA were similar to those from healthy controls. Immunohistochemistry showed that IDO⁺ cells were rare in normal skin and the control skin of patients with CA, but were greatly accumulated in wart tissue. Most fluorescence signals of IDO⁺ cells did not overlap with those of CD1a⁺ Langerhans cells. Human papillomavirus (HPV) DNA probe in situ hybridization showed a large number of IDO⁺ cells in the HPV^- site. Keratinocytes in the skin of healthy controls and the circumcised skin of patients with CA could minimally transform tryptophan into kynurenine, but IDO-competent epidermal cells from warts could transform tryptophan. In addition, these IDO-competent epidermal cells could inhibit PHA-stimulated T-cell proliferation. The addition of an IDO inhibitor, 1-methyl-d-tryptophan, restored the inhibited T-cell proliferation.

CONCLUSIONS

Abnormally localized high IDO expression might be involved in the formation of a local immunotolerant microenvironment.

M2-Polarized Macrophages Compose Lupus Vulgaris Arising from a Bacillus Calmette-Guérin Vaccination Site

Since bacillus Calmette-Guérin (BCG) is an attenuated strain of Mycobacterium bovis, lupus vulgaris (LV) is reported as one of the rare complications after BCG vaccination, correlating with immunosuppression in the lesional skin. In this report, we describe a case of LV arising from the BCG vaccination site 22 years after vaccination. Interestingly, in the present case, granuloma cells were composed of M2-polarized macrophages. Our case might explain the contribution of M2-polarized macrophages to the biology of LV arising from a BCG vaccination site.

Green Tea Epigallocatechin-3-Gallate Suppresses Autoimmune Arthritis Through Indoleamine-2,3-Dioxygenase Expressing Dendritic Cells and the Nuclear Factor, Erythroid 2-Like 2 Antioxidant Pathway

Background

The activity of one of the major catechins in Green Tea, the polyphenol (−)-epigallocatechin-3-gallate (EGCG), has been shown to have a variety of health benefits. Recent studies suggest that EGCG can modulate both the innate and adaptive arms of the immune system. The goal of the current studies was to examine the immunomodulatory effects and mechanisms of action of EGCG on experimental arthritis in mice.

Methods

EGCG (10 mg/kg) was administered by oral gavage after CIA induction, while control mice were administered phosphate buffered saline (PBS). Disease mechanisms were studied in both groups of mice. Phenotypes were examined using repeated measure analysis of variance (ANOVA) and data from in vitro and ex vivo experiments were analyzed for significance using the Mann-Whitney U test.

Results

EGCG treatment ameliorated clinical symptoms and reduced histological scores in arthritic mice. Serum type-II collagen-specific immunoglobulin (Ig) IgG2a antibodies were significantly lower in EGCG-fed mice compared to PBS-treated mice. EGCG significantly suppressed T cell proliferation and relative frequencies of CD4 T cells, CD8 T cells and B cell subsets including marginal zone B cells, T1 and T2 transitional B cells, while increasing the frequency of CD4⁺ Foxp3⁺ regulatory T cells (Tregs) and indoleamine‐2,3‐dioxygenase (IDO) expression by CD11b⁺ dendritic cells (DC). Splenic CD11b⁺ DC from EGCG fed mice induced an increased frequency of Tregs via an IDO-dependent mechanism in in vitro cultures. Importantly, joint homogenates from EGCG-fed mice exhibited significantly increased levels of Nuclear Factor, Erythroid 2-Like 2 (Nrf-2) and Heme oxygenase-1 (HO-1) compared with PBS-fed mice.

Conclusions

This is the first report of upregulation of the Nrf-2 antioxidant pathway in EGCG-mediated immunoregulation. EGCG ameliorated experimental arthritis in mice by eliciting IDO-producing DCs, increasing frequencies of T regs and inducing the activation of the Nrf-2 antioxidant pathway. It remains to be established whether EGCG is useful for the prevention and treatment of rheumatoid arthritis and other inflammatory disorders.

Granulomatous dysimmune reactions (sarcoidosis, granuloma annulare, and others) on differently injured skin areas

Granulomatous disorders are chronic cell-mediated immune responses histologically characterized by collections of macrophages, epithelioid cells, and multinucleated giant cells. This disease spectrum often has an infectious origin, but sometimes neither an infective agent nor an inciting antigenic stimulus can be identified. The skin may be a preferential target for these disorders, especially in the areas that have been damaged by various forms of skin injury (eg, herpetic infections, trauma, thermal or solar burns, vaccinations, tattoos). These damaged skin sites frame the new concept of an immunocompromised cutaneous district (ICD), which defines a skin area with acquired immune dysregulation that can pave the way for the local onset of opportunistic disorders, such as infections, tumors, and granulomatous disorders. Sarcoidosis, granuloma annulare (GA), and forms of granulomatous vasculitis, such as Churg-Strauss syndrome (CSS) and Wegener's granulomatosis (WG), are the most common granulomatous disorders that occur in an ICD and may share common pathogenic mechanisms. Recent studies have found clinical and pathologic overlapping features across noninfectious granulomas. Although no unifying etiology exists, the development of granulomatous processes in the ICD has often been reported and the literature contains various hypotheses to explain it: (1) overactive immune response in a previously injured region with or without loss of immune tolerance; (2) overall reduced immune response; (3) retention of an exogeneous antigen or foreign body; (4) altered neural signaling; and (5) a combination of all the aforementioned processes. T helper cells, T regulatory cells, and macrophages, as well as a number of antigenic proteins, have been identified as potential contributing factors. In addition, a genetic predisposition and an intact systemic immune system are both instrumental for the persistence of local granuloma formation in the ICD.

New Insights into IDO Biology in Bacterial and Viral Infections

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.

Induction of type I and type III interferons by Borrelia burgdorferi correlates with pathogenesis and requires linear plasmid 36

The capacity for Borrelia burgdorferi to cause disseminated infection in humans or mice is associated with the genotype of the infecting strain. The cytokine profiles elicited by B. burgdorferi clinical isolates of different genotype (ribosomal spacer type) groups were assessed in a human PBMC co-incubation model. RST1 isolates, which are more frequently associated with disseminated Lyme disease in humans and mice, induced significantly higher levels of IFN-α and IFN-λ1/IL29 relative to RST3 isolates, which are less frequently associated with disseminated infection. No differences in the protein concentrations of IFN-γ, IL-1β, IL-6, IL-8, IL-10 or TNF-α were observed between isolates of differing genotype. The ability of B. burgdorferi to induce type I and type III IFNs was completely dependent on the presence of linear plasmid (lp) 36. An lp36-deficient B. burgdorferi mutant adhered to, and was internalized by, PBMCs and specific dendritic cell (DC) subsets less efficiently than its isogenic B31 parent strain. The association defect with mDC1s and pDCs could be restored by complementation of the mutant with the complete lp36. The RST1 clinical isolates studied were found to contain a 2.5-kB region, located in the distal one-third of lp36, which was not present in any of the RST3 isolates tested. This divergent region of lp36 may encode one or more factors required for optimal spirochetal recognition and the production of type I and type III IFNs by human DCs, thus suggesting a potential role for DCs in the pathogenesis of B. burgdorferi infection.

The indoleamine 2,3-dioxygenase (IDO) pathway controls allergy

A series of recent studies have demonstrated that the immunoregulatory pathway of tryptophan catabolism, initiated by the enzyme indoleamine 2,3-dioxygenase (IDO), is a critical participant in allergic inflammation. Originally known for its regulatory function during pregnancy and during chronic inflammation in tumorigenesis and infection, the activity of IDO seems to positively modify the inflammatory state of atopy or allergy. The tryptophan degradation pathway is important for tolerance induction during systemic allergen immunotherapy. Here, we focus on recent findings that establish the IDO pathway as central to allergic inflammation.

Indoleamine 2,3-dioxygenase expression in human inflammatory bowel disease

OBJECTIVE

The study is carried out to identify the expression pattern of indoleamine 2,3-dioxygenase (IDO) in human Crohn's disease and ulcerative colitis and to investigate the effect of different therapies (salicylates, steroids, and antitumor necrosis factor antibody) on the intestinal expression of IDO.

METHODS

Immunohistochemistry was used. A total of 10 high power fields were counted for each patient.

RESULTS

IDO was expressed in the both lamina propria and epithelium. IDO expression increased in the lesions from ulcerative colitis and Crohn's disease and was positively related to the severity of inflammation. IDO-positive mononuclear cells also expressed CD11c, CD68, and TLR4. IDO expression decreased significantly after treatment with steroids and salicylates, but remained unchanged after infliximab therapy.

CONCLUSION

IDO was over-expressed in human inflammatory bowel disease. It may be a bridge between innate immunity and adaptive immunity. Steroids and salicylates may act through the inhibition of IDO expression. IDO upregulation may be a promising therapy to achieve inflammatory bowel disease remission.

Halofuginone and other febrifugine derivatives inhibit prolyl-tRNA synthetase

Febrifugine, one of the fifty fundamental herbs of traditional Chinese medicine, has been characterized for its therapeutic activity whilst its molecular target has remained unknown. Febrifugine derivatives have been used to treat malaria, cancer, fibrosis, and inflammatory disease. We recently demonstrated that halofuginone (HF), a widely studied derivative of febrifugine, inhibits the development of Th17-driven autoimmunity in a mouse model of multiple sclerosis by activating the amino acid response pathway (AAR). Here we show that HF binds glutamyl-prolyl-tRNA synthetase (EPRS) inhibiting prolyl-tRNA synthetase activity; this inhibition is reversed by the addition of exogenous proline or EPRS. We further show that inhibition of EPRS underlies the broad bioactivities of this family of natural products. This work both explains the molecular mechanism of a promising family of therapeutics, and highlights the AAR pathway as an important drug target for promoting inflammatory resolution.