Myeloid-derived suppressive cells (MDSCs) have been a focus of recent study on tumor-mediated immune suppression. However, its role in type 17 helper T (Th17) cell differentiation and the pathogenesis of autoimmune diseases (e.g., multiple sclerosis) has not been determined. We show here that development of experimental autoimmune encephalomyelitis (EAE) in mice is associated with a profound expansion of CD11b+Gr-1+ MDSCs, which display efficient T cell inhibitory functions in vitro. Unexpectedly, these MDSCs enhance the differentiation of naïve CD4+ T cell precursors into Th17 cells in a highly efficient manner under Th17 polarizing conditions, as indicated by significantly increased number of Th17 cell, elevation of IL-17A production, and upregulation of the orphan nuclear receptor RORA and RORC. Mechanistic studies show that IL-1β represents a major mediator of MDSC-facilitated Th17 differentiation, which depends on the IL-1 receptor on CD4+ T cells but not MDSCs. Selective depletion of MDSCs using gemcitabine results in a marked reduction in the severity of EAE (e.g., decreased clinical scores and myelin injury), which correlates with reduced Th17 cells and inflammatory cytokines (IL-17A and IL-1β) in the lymphoid tissues and spinal cords. Adoptively transfer of MDSCs after gemcitabine treatment restores EAE disease progression. Together, we demonstrate for the first time that excessive and prolonged presence of MDSCs can drive a Th17 response and consequently contributes to the pathogenesis of EAE. These new findings provide unique insights into the pleiotropic functions of MDSCs, and may help explain the failure of immunosuppressive MDSCs to control Th17/IL-17-dependent autoimmune disorders.

Objectives Although myeloid-derived suppressive cells (MDSCs) have been linked to T-cell tolerance, their role in autoimmune rheumatoid arthritis (RA) remains elusive. Here we investigate the potential association of MDSCs with the disease pathogenesis using a preclinical model of RA and specimen collected from RA patients. Methods The frequency of MDSCs in blood, lymphoid tissues, inflamed paws, or synovial fluid and their association with disease severity, tissue inflammation, and the levels of pathogenic T-helper (Th) 17 cells was examined in arthritic mice or in patients with RA (n=35) and osteoarthritis (OA, n=15). The MDSCs in arthritic mice were also characterized for their phenotype, inflammation status, T-cell suppressive activity, and their capacity of pro-Th17 cell differentiation. The involvement of MDSCs in the disease pathology and a Th17 response was examined by adoptive transfer or antibody depletion of MDSCs in arthritic mice or by co-culturing mouse or human MDSCs with naïve CD4+ T cells under Th17-polarizing conditions. Results MDSCs significantly expanded in arthritic mice and in RA patients, which correlated positively with disease severity and an inflammatory Th17 response. While displaying T-cell suppressive activity, MDSCs from arthritic mice produced high levels of inflammatory cytokines (e.g., IL-1β, TNF-α). Both mouse and human MDSCs promoted Th17 cell polarization ex vivo. Transfer of MDSCs facilitated disease progression, whereas their elimination in arthritic mice ameliorates disease symptoms concomitant with reduction of IL-17A/Th17 cells. Conclusions Our studies suggest that proinflammatory MDSCs with their capacity to drive Th17 cell differentiation may be a critical pathogenic factor in autoimmune arthritis.

Class A scavenger receptor (SRA), also known as CD204, has been shown to participate in the pathogenesis of atherosclerosis and the pattern recognition of pathogen infection. However, its role in adaptive immune responses has not been well defined. In this study, we report that the lack of SRA/CD204 promotes Toll-like receptor (TLR)4 agonist-augmented tumor-protective immunity, which is associated with en-

No abstract

The collaboration and cross-talk between different classes of innate pattern recognition receptors are crucial for a well coordinated inflammatory response and host defense. Here we report a previously unrecognized role of scavenger receptor A (SRA; also known as CD204) as a signaling regulator in the context of Toll-like receptor 4 (TLR4) activation. We show that SRA/CD204 deficiency leads to greater sensitivity to LPS-induced endotoxic shock. SRA/CD204 down-regulates inflammatory gene expression in dendritic cells by suppressing TLR4-induced activation of the transcription factor NF-B. For the first time, we demonstrate that SRA/CD204 executes its regulatory functions by directly interacting with the TRAF-C domain of TNF receptor-associated factor 6 (TRAF6), resulting in inhibition of TRAF6 dimerization and ubiquitination. The attenuation of NF-B activity by SRA/CD204 is independent of its ligand-binding domain, indicating that the signaling-regulatory feature of SRA/CD204 can be uncoupled from its conventional endocytic functions. Collectively, we have identified the molecular linkage between SRA/CD204 and the TLR4 signaling pathways, and our results reveal a novel mechanism by which a non-TLR pattern recognition receptor restricts TLR4 activation and consequent inflammatory response. The scavenger receptors (SRs)2 constitute a large family of structurally diverse pattern recognition receptors (PRRs) (1). Scavenger receptor A (SRA), also termed CD204, is a prototypic member of the growing SR family. The role of SRA/CD204 in atherosclerosis has been extensively studied because it was the first receptor identified for modified lipoproteins (e.g. oxidized or acetylated low density lipoproteins) that are pertinent to the development of vascular disease (2). As a PRR primarily expressed on myeloid cells, such as dendritic cells (DCs) and macrophages, SRA/CD204 binds not only to altered or modified self macromolecules but also to a wide range of pathogenassociated molecular patterns, including lipopolysaccharide (LPS), bacterial CpG DNA, and double strand RNA (3). SRA/ CD204-deficient mice are significantly more susceptible than their wild type (WT) counterparts to infection with Listeria monocytogenes (2) and Staphyloccus aureus (4). Loss of SRA/ CD204 expression led to an increased mortality in Bacillus Calmette-Guérin primed animals, which has been partially attributed to the overproduction of proinflammatory cytokines by macrophages rather than impaired LPS clearance in vivo (5). Several lines of evidence suggest that SRA/CD204 on myeloid cells functions as a suppressor that can limit an inflammatory response (6, 7). However, the molecular basis underlying the SRA/CD204-mediated regulation of inflammation and production of inflammatory cytokines remains unexplored.The Toll-like receptors (TLRs) represent a family of evolutionarily conserved PRRs and are believed to play central roles in the induction of innate as well as adaptive immunity to pathogen infection (8). Binding of the microbial pattern molecules (i....

Summary Multiple physiological and pathological conditions interfere with the function of Endoplasmic Reticulum (ER). However, much remains unknown regarding the impact of ER stress on inflammatory responses in dendritic cells (DCs) upon the recognition of pathogen molecules. We show that ER stress greatly potentiates the expression of inflammatory cytokines and IFN-β in murine DCs stimulated by polyIC, a synthetic mimic of virus dsRNA. Both toll-like receptor 3 and melanoma differentiation-associated gene-5 are involved in the enhanced IFN-β production, which is associated with increased activation of NF-κB and IRF3 signaling as well as the splicing of X-box binding protein-1 (XBP-1), an important regulator involved in ER stress response. Surprisingly, silencing of XBP-1 reduces polyIC-stimulated IFN-β expression in the presence or absence of ER stress, indicating that XBP-1 may be essential for polyIC signaling and ER stress-amplified IFN-β production. Overexpression of a spliced form of XBP-1(XBP-1s) synergistically augments polyIC-induced inflammatory response. For the first time we show that XBP-1s overexpression-enhanced IFN-β production in DCs markedly suppresses vesicular stomatitis virus infection, revealing a previously unrecognized role of XBP-1 in an antiviral response. Our findings suggest that evolutionarily conserved ER stress response and XBP-1 may function collaboratively with the innate immunity in maintaining cellular homeostasis.

Although hypoxia is accepted as an important microenvironmental factor influencing tumor progression and treatment response, it is usually regarded as a static global phenomenon. Consequently, less attention is given to the impact of dynamic changes in tumor oxygenation in regulating the behavior of cancer cells. Androgen receptor (AR) signaling plays a critical role in prostate cancer. We previously reported that hypoxia/ reoxygenation, an in vitro condition used to mimic an unstable oxygenation climate in a tumor, stimulates AR activation. In the present study, we showed that peroxiredoxin 1 (Prx1), a member of the peroxiredoxin protein family, acts as a key mediator in this process. We found that the aggressive LN3, C4-2, and C4-2B prostate cancer cell lines derived from LNCaP possess constitutively elevated Prx1 compared with parental cells, and display greater AR activation in response to hypoxia/ reoxygenation. Although the cell survival-enhancing property of Prx1 has traditionally been attributed to its antioxidant activity, the reactive oxygen species-scavenging activity of Prx1 was not essential for AR stimulation because Prx1 itself was oxidized and inactivated by hypoxia/reoxygenation. Increased AR transactivation was observed when wild-type Prx1 or mutant Prx1 (C52S) lacking antioxidant activity was introduced into LNCaP cells. Reciprocal immunoprecipitation, chromatin immunoprecipitation, and in vitro pull-down assays corroborated that Prx1 interacts with AR and enhances its transactivation. We also show that Prx1 is capable of sensitizing a ligand-stimulated AR. Based on the above information, we suggest that disrupting the interaction between Prx1 and AR may serve as a fruitful new target in the management of prostate cancer. [Cancer Res 2007;67(19):9294-303]

Converting the immunosuppressive tumor environment into one that is favorable to induction of antitumor immunity is indispensable for effective cancer immunotherapy. Here we strategically incorporate a pathogen (i.e., Flagellin)-derived, NF-κB-stimulating `danger' signal into the large stress protein or chaperone Grp170 (HYOU1/ORP150) that was previously shown to facilitate antigen cross-presentation. This engineered chimeric molecule (i.e., Flagrp170) is capable of transporting tumor antigens and concurrently inducing functional activation of dendritic cells. Intratumoral administration of adenoviruses expressing Flagrp170 induces a superior antitumor response against B16 melanoma and its distant lung metastasis compared to unmodified Grp170 and Flagellin. The enhanced tumor destruction is accompanied with significantly increased tumor infiltration by CD8+ cells as well as elevation of IFN-γ and IL-12 levels in the tumor sites. In situ Ad.Flagrp170 therapy provokes systemic activation of CTLs that recognize several antigens naturally expressing in melanoma (e.g., gp100/PMEL and TRP2/DCT). The mechanistic studies using CD11c-DTR transgenic mice and Batf3-deficient mice reveal that CD8α+ DCs are required for the improved T cell cross-priming. Antibody neutralization assays show that IL-12 and IFN-γ are essential for the Flagrp170-elicited antitumor response, which also involves CD8+ T cells and NK cells. The therapeutic efficacy of Flagrp170 and its immune stimulating activity are also confirmed in mouse prostate cancer and colon carcinoma. Together, targeting the tumor microenvironment with this chimeric chaperone is highly effective in mobilizing or restoring antitumor immunity, supporting the potential therapeutic use of this novel immune modulator in the treatment of metastatic diseases.