The importance of myeloid-derived suppressor cells in the regulation of autoimmune effector cells by a chronic contact eczema

Interleukin-4 enhances trafficking and functional activities of GM-CSF-stimulated mouse myeloid-derived dendritic cells at late differentiation stage

Mouse bone marrow-derived dendritic cells (BMDCs) are being employed as an important model for translational research into the development of DC-based therapeutics. For such use, the localization and specialized mobility of injected BMDCs within specific immune tissues are known to define their immunity and usefulness in vivo. In this study, we demonstrate that IL-4, a key driving factor for in vitro propagation and differentiation of BMDCs, when added during a late culture stage can enhance the in vivo trafficking activity of granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced BMDCs. It suggests that the temporal control of IL-4 stimulation during the in vitro generation of DCs drastically affects the DC trafficking efficiency in vivo. With this modification of IL-4 stimulation, we also show that much less cytokine was needed to generate BMDCs with high purity and yield that secrete a high level of cytokines and possess a good capacity to induce proliferation of allogeneic CD4+ T cells, as compared to the conventional method that uses a continuous supplement of GM-CSF and IL-4 throughout cultivation. These results provide us with an important know-how for differentiation of BMDCs from myeloid stem cells, and for use of other immune cells in related medical or stem cell applications.

Role of NKT cells in autoimmune liver disease

The three main broad categories of autoimmune liver disease are autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC). The etiologies of these diseases are still incompletely understood, but seem to involve a combination of immune, genetic and environmental factors. Although each of these diseases has relatively distinct clinical, serologic and histological profiles, all of them share common pathways of immune-mediated liver injury. The development of autoimmune liver diseases is thought to be due to an imbalance of proinflammatory and anti-inflammatory immune responses within the liver, with proinflammatory immune responses being upregulated and anti-inflammatory ones downregulated. The available evidence, suggest that during autoimmune responses within the liver, "self" antigens are presented by antigen presenting cells (APCs) which then activate, directly and/or indirectly, NKT cells and other innate immune cells within the liver. Importantly, the hepatic innate immune system plays an increasingly recognized role in the development and propagation of autoimmune liver injury. NKT cells predominantly reside in the liver sinusoids, and through their ability to rapidly produce a wide variety of cytokines (e.g. Th1, TH2, Th17 cytokine patterns), are a critical checkpoint that bridges innate and adaptive immune responses. Specifically, activated NKT cells are capable of transactivating other innate and adaptive immune cells within the liver to amplify and regulate subsequent immune responses within the liver. It has been hypothesized that NKT cells in the setting of autoimmune liver disease can play diverse roles, including driving both anti-inflammatory and proinflammatory responses, as well as regulating the hepatic recruitment of other types of immunoregulatory cells, including regulatory T cells.

The role of interleukin-12 on modulating myeloid-derived suppressor cells, increasing overall survival and reducing metastasis

Myeloid-derived suppressor cells (MDSC) are important to the tumour microenvironment as they actively suppress the immune system and promote tumour progression and metastasis. These cells block T-cell activation in the tumour microenvironment, preventing anti-tumour immune activity. The ability of a treatment to alter the suppressive function of these cells and promote an immune response is essential to enhancing overall therapeutic efficacy. Interleukin-12 (IL-12) has the potential not only to promote anti-tumour immune responses but also to block the activity of cells capable of immune suppression. This paper identifies a novel role for IL-12 as a modulator of MDSC activity, with implications for IL-12 as a therapeutic agent. Treatment with IL-12 was found to alter the suppressive function of MDSC by fundamentally altering the cells. Interleukin-12-treated MDSC exhibited up-regulation of surface markers indicative of mature cells as well as decreases in nitric oxide synthase and interferon-γ mRNA both in vitro and in vivo. Treatment with IL-12 was also found to have significant therapeutic benefit by decreasing the percentage of MDSC in the tumour microenvironment and increasing the percentage of active CD8(+) T cells. Treatment with IL-12 resulted in an increase in overall survival accompanied by a reduction in metastasis. The findings in this paper identify IL-12 as a modulator of immune suppression with significant potential as a therapeutic agent for metastatic breast cancer.

MDSC in autoimmunity

Myeloid derived suppressor cells (MDSC) were first described nearly two decades ago. Until recently, however, descriptions of MDSC populations were found almost exclusively in animal models of cancer or in cancer patients. Over the last few years, an increasing number of reports have been published describing populations of myeloid cells with MDSC-like properties in murine models of autoimmune disease. In contrast to the proposed deleterious role of MDSC in cancer--where these cells likely inhibit tumor immunity--in the context of autoimmunity, MDSC have the potential to suppress the autoimmune response, thereby limiting tissue injury. A logical corollary of this hypothesis is that a failure of endogenous MDSC to appropriately control autoimmune T cell responses in vivo may actually contribute to the pathogenesis of autoimmune disease.

In vivo suppressive function of myeloid-derived suppressor cells is limited to the inflammatory site

Current paradigms suggest that, despite the heterogeneity of myeloid-derived suppressor cells (MDSC), all Gr-1(+) CD11b(+) cells can exert suppressive function when exposed to inflammatory stimuli. In vitro evaluation shows that MDSC from multiple tissue sites have suppressive activity, and in vivo inhibition of MDSC enhances T-cell function; however, the relative capacity of MDSC present at localized inflammatory sites or in peripheral tissues to suppress T-cell responses in vivo has not been directly evaluated. In the current study, we observed that during a tissue-specific inflammatory response, MDSC inhibition of CD8(+) T-cell proliferation and IFN-γ production was restricted to the inflammatory site. Using a prostate-specific inflammatory model and a heterotopic prostate tumor model, we showed that MDSC from inflammatory sites or from tumor tissue possess immediate capacity to inhibit T-cell function, whereas those isolated from peripheral tissues (spleens and liver) were not suppressive without activation of iNOS by exposure to IFN-γ. These data suggest that MDSC are important regulators of immune responses in the prostate during acute inflammation and the chronic inflammatory setting of tumor growth, and that regulation of T-cell function by MDSC during a localized inflammatory response is restricted in vivo to the site of an ongoing immune response.

Involvement of CD11b+ GR-1 low cells in autoimmune disorder in MRL-Fas lpr mouse

OBJECTIVE

Myeloid-derived suppressor cells (MDSCs) have been identified as immunosuppressive cells in tumor-related inflammation. However, the pathogenesis of MDSCs for autoimmune disease has not been investigated as yet. The aim of this study was to address whether MDSCs contribute to autoimmune organ injury in lupus-prone mice.

METHODS

MDSCs were analyzed by flow cytometric staining of CD11b(+) GR-1(+) in MRL-Fas ( lpr ) mice. CD4(+) T-cell proliferation assay was performed by coculture with CD11b(+) GR-1(+) splenocytes. The percentage of immunosuppressive cells was examined during disease progression. Expression of chemokine receptor on immunosuppressive cells was analyzed, and chemotaxis assay was performed.

RESULTS

CD11b(+) GR-1(low) cells had a suppressive effect on CD4(+) T-cell proliferation, which was restored by an arginase-1 inhibitor. CD11b(+) GR-1(low) cells increased in percentage during disease progression in kidney and blood. The number of migrated CD11b(+) GR-1(low) cells increased in the presence of monocyte chemoattractant protein-1/CCL2.

CONCLUSION

We assessed the involvement of CD11b(+) GR-1(low) cells in autoimmune disorder in MRL-Fas(lpr) mice. These cells regulate immunological responses via CCL2/CCR2 signaling. The regulation of immunosuppressive monocytes may provide novel therapeutic strategy for organ damage in autoimmune diseases.

Role of immune-regulatory cells in skin pathology

The skin harbors a complex and unique immune system that protects against various pathologies, such as infection and cancer. Although many of the mechanisms of immune activation in the skin have been investigated, it is likewise important to uncover the immune-regulatory components that limit effective immunity or prevent autoimmunity. Several cell populations are involved in this immune-regulatory function, including CD4+ T cells that coexpress the transcription factor Foxp3, known as Tregs, and cells with immune-regulatory function known as myeloid-derived suppressor cells (MDSCs). This review focuses on the role that immune-regulatory cells, such as MDSCs and Tregs, play in cutaneous pathology, such as malignancy, psoriasis, dermatitis, burn wounds, and transplantation. Although their depletion may serve to augment immunity, expansion of these cells may be used to suppress excessive immune reactions. These cells are attractive, therapeutic targets for various conditions and thus, deserve further exploration.

Tolerogenic dendritic cells and myeloid-derived suppressor cells: potential for regulation and therapy of liver auto- and alloimmunity

Organ transplantation is now established as an accepted treatment for end-stage liver disease, acute fulminant hepatic liver failure and hepatocellular carcinoma. While early graft acceptance rates have increased markedly due to improved immunosuppressive drug regimens, rates of late graft failure remain largely unchanged. Recent findings suggest that in addition to alloimmunity, chronic rejection of liver allografts may also reflect de novo autoimmune hepatitis or recurrence of pre-existing hepatic autoimmune disease. Dendritic cell (DC)- based therapy is a promising experimental approach to promotion of transplant tolerance and the treatment of autoimmune diseases. Newly emerging evidence also demonstrates the potential efficacy of myeloid-derived suppressor cells (MDSC) in the antigen (Ag)-specific regulation of T-cell responses. Herein, we discuss current understanding of liver autoimmunity post-transplantation, along with current approaches for the development of tolerogenic DC, and the potential use of MDSC for the development of stable, Ag-specific tolerance.

Subsets, expansion and activation of myeloid-derived suppressor cells

Tumor cells and microorganisms manipulate the immune system to minimize any counter response in order to survive. Myeloid-derived suppressor cells (MDSC) in the mouse represent activated Gr-1(+) CD11b(+) myeloid precursor cells. Activation may occur through endogenous or exogenous factors leading to the suppression of immune responses. Under steady state conditions the same precursors differentiate into dendritic cells, macrophages and neutrophils. Their linkage to tumor progression and several suppression mechanisms employing the arginine metabolism are well documented, but knowledge of their role in chronic infections, autoimmune diseases and graft-versus-host reactions is just emerging. Several factors have been described to promote MDSC expansion and activation in bone marrow, spleen and tumor sites. New evidence suggests that the Gr-1 antibody itself may differentially trigger myelopoiesis under steady state conditions or induce apoptosis in inflammatory situations after binding to a common epitope expressed on Ly-6C and Ly-6G molecules, respectively. Moreover, two subsets of neutrophil- and monocyte-related MDSC have been described in tumor-bearing and healthy mice. In the present review, we summarize some early work leading to recent findings on these two MDSC subsets, the factors supporting MDSC expansion and activation, as well as novel insights on Gr-1 antibody functions.

Galectin-9 expands immunosuppressive macrophages to ameliorate T-cell-mediated lung inflammation

Galectin-9 (Gal-9) plays pivotal roles in the modulation of innate and adaptive immunity to suppress T-cell-mediated autoimmune models. However, it remains unclear if Gal-9 plays a suppressive role for T-cell function in non-autoimmune disease models. We assessed the effects of Gal-9 on experimental hypersensitivity pneumonitis induced by Trichosporon asahii. When Gal-9 was given subcutaneously to C57BL/6 mice at the time of challenge with T. asahii, it significantly suppressed T. asahii-induced lung inflammation, as the levels of IL-1, IL-6, IFN-gamma, and IL-17 were significantly reduced in the BALF of Gal-9-treated mice. Moreover, co-culture of anti-CD3-stimulated CD4 T cells with BALF cells harvested from Gal-9-treated mice on day 1 resulted in diminished CD4 T-cell proliferation and decreased levels of IFN-gamma and IL-17. CD11b(+)Ly-6C(high)F4/80(+) BALF Mphi expanded by Gal-9 were responsible for the suppression. We further found in vitro that Gal-9, only in the presence of T. asahii, expands CD11b(+)Ly-6C(high)F4/80(+) cells from BM cells, and the cells suppress T-cell proliferation and IFN-gamma and IL-17 production. The present results indicate that Gal-9 expands immunosuppressive CD11b(+)Ly-6C(high) Mphi to ameliorate Th1/Th17 cell-mediated hypersensitivity pneumonitis.

Alopecia areata update: part I. Clinical picture, histopathology, and pathogenesis

Alopecia areata (AA) is an autoimmune disease that presents as nonscarring hair loss, although the exact pathogenesis of the disease remains to be clarified. Disease prevalence rates from 0.1% to 0.2% have been estimated for the United States. AA can affect any hair-bearing area. It often presents as well demarcated patches of nonscarring alopecia on skin of overtly normal appearance. Recently, newer clinical variants have been described. The presence of AA is associated with a higher frequency of other autoimmune diseases. Controversially, there may also be increased psychiatric morbidity in patients with AA. Although some AA features are known poor prognostic signs, the course of the disease is unpredictable and the response to treatment can be variable. Part one of this two-part series on AA describes the clinical presentation and the associated histopathologic picture. It also proposes a hypothesis for AA development based on the most recent knowledge of disease pathogenesis.

LEARNING OBJECTIVES

After completing this learning activity, participants should be familiar with the most recent advances in AA pathogenesis, recognize the rare and recently described variants of AA, and be able to distinguish between different histopathologic stages of AA.

Myeloid-derived suppressor cells as regulators of the immune system

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that expand during cancer, inflammation and infection, and that have a remarkable ability to suppress T-cell responses. These cells constitute a unique component of the immune system that regulates immune responses in healthy individuals and in the context of various diseases. In this Review, we discuss the origin, mechanisms of expansion and suppressive functions of MDSCs, as well as the potential to target these cells for therapeutic benefit.

Myeloid-derived suppressor cells as regulators of the immune system

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that expand during cancer, inflammation and infection, and that have a remarkable ability to suppress T-cell responses. These cells constitute a unique component of the immune system that regulates immune responses in healthy individuals and in the context of various diseases. In this Review, we discuss the origin, mechanisms of expansion and suppressive functions of MDSCs, as well as the potential to target these cells for therapeutic benefit.

Analysis of retinal cellular infiltrate in experimental autoimmune uveoretinitis reveals multiple regulatory cell populations

Experimental autoimmune uveoretinitis (EAU) is an animal model for human intraocular inflammatory disease. EAU is induced in B10.RIII mice by immunization with RBP-3 161-180 peptide and intraperitoneal pertussis toxin and is mediated by CD4(+) T cells that generate a clinically monophasic disease peaking approximately 2 weeks post-immunization. Collagenase digestion of retinal tissue allowed the quantification and characterization of leukocytes in the inflamed retina during disease progression. Using this method we identified three stages of disease. Initially there is a prodromal phase where we found significant changes in the number of leukocytes in the eye as early as 5 days post-immunization. This effect was, in part, non-antigen specific as a small increase in retinal leukocytes was also observed following immunization with OVA peptide. Following the prodrome there is a primary peak of infiltration including both CD4(+) T cells and CD11b(+) cells. This coincides with an early influx of neutrophils and is associated with a peak in IL-17-producing T cells. The neutrophils in the eye are CD11b(+) and Gr1(+) but can be distinguished from other myeloid cells by their high expression of Ly6G. The remaining CD11b(+)Gr1(+) cells can suppress proliferation and are analogous to myeloid derived suppressor cells which are found in tumors. The inflamed eye also contains a considerable proportion of FoxP3(+) regulatory cells. Following peak disease, the retina does not return to its pre-disease phenotype. Instead, fluctuations in infiltrating leukocyte numbers and changes to their relative composition continue, indicating that clinical recovery does not equate to the restoration of a normal retinal leukocyte population.