Antigen-presenting dendritic cells provide the reducing extracellular microenvironment required for T lymphocyte activation

Targeting the glutamatergic system for the treatment of HIV-associated neurocognitive disorders

The accumulation of excess glutamate in the extracellular space as a consequence of CNS trauma, neurodegenerative diseases, infection, or deregulation of glutamate clearance results in neuronal damage by excessive excitatory neurotransmission. Glutamate excitotoxicity is thought to be one of several mechanisms by which HIV exerts neurotoxicity that culminates in HIV-associated neurocognitive disorders (HAND). Excess glutamate is released upon HIV infection of macrophage/microglial cells and has been associated with neurotoxicity mediated by gp120, transactivator of transcription (Tat) and other HIV proteins. Several strategies have been used over the years to try to prevent glutamate excitotoxicity. Since the main toxic effects of excess glutamate are thought to be due to excitotoxicity from over activation of glutamate receptors, antagonists of these receptors have been popular therapeutic targets. Early work to ameliorate the effects of excess extracellular glutamate focused on NMDA receptor antagonism, but unfortunately, potent blockade of this receptor has been fraught with side effects. One alternative to direct receptor blockade has been the inhibition of enzymes responsible for the production of glutamate such as glutaminase and glutamate carboxypeptidase II. Another approach has been to regulate the transporters responsible for modulation of extracellular glutamate such as excitatory amino acid transporters and the glutamate-cystine antiporter. There is preliminary experimental evidence that these approaches have potential therapeutic utility for the treatment of HAND. These efforts however, are at an early stage where the next steps are dependent on the identification of drug-like inhibitors as well as the development of predictive neuroAIDS animal models.

Changing the energy of an immune response

The breakdown of nutrients into the critical energy source ATP is the general purpose of cellular metabolism and is essential for sustaining life. Similarly, the immune system is composed of different cell subsets that are indispensable for defending the host against pathogens and disease. The interplay between metabolic pathways and immune cells leads to a plethora of different signaling pathways as well as cellular activities. The activation of T cells via glycolysis-mediated upregulation of surface markers, for example, is necessary for an appropriate effector response against an infection. However, tight regulation of immune cell metabolism is required for protecting the host and resuming homeostasis. An imbalance of immunological metabolic function and/or metabolic byproducts (reactive oxygen species) can oftentimes lead to diseases. In the case of cancer, overactive glucose metabolism can lead to hyperproliferation of cells and subsequent decreases in cytotoxic T cell activity, which attack and destroy the tumor. For this reason and many more, targeting metabolism in immune cells may be a novel therapeutic strategy for treatment of disease. The metabolic pathways of immune cells and the possibilities of immunometabolic therapies will be discussed.

Organoselenium compounds modulate extracellular redox by induction of extracellular cysteine and cell surface thioredoxin reductase

The effect of selenium compounds on extracellular redox modulating capacity was studied in murine macrophage RAW 264.7 cells and differentiated human THP-1 monocytes. The arylselenium compounds benzeneselenol (PhSeH), dibenzyl diselenide (DBDSe), diphenyl diselenide (DPDSe), and ebselen were capable of inducing extracellular cysteine accumulation via a cystine- and glucose-dependent process. Extracellular cysteine production was dose-dependently inhibited by glutamate, an inhibitor of cystine/glutamate antiporter (Xc(-) transporter), supporting the involvement of Xc(-) transporter for cystine uptake in the above process. These arylselenium compounds also induced cellular thioredoxin reductase (TrxR) expression, particularly at the exofacial surface of cells. TrxR1 knockdown using small interfering RNA attenuated TrxR increases and cysteine efflux induced in cells by DPDSe. Sodium selenite (Na2SeO3), selenomethionine (SeMet), seleno-l-cystine (SeCySS), and Se-methylselenocysteine (MeSeCys) did not have these effects on macrophages under the same treatment conditions. The effects of organoselenium compounds on extracellular redox may contribute to the known, but inadequately understood, biological effects of selenium compounds.

Metabolic switching and fuel choice during T-cell differentiation and memory development

Clearance or control of pathogens or tumors usually requires T-cell-mediated immunity. As such, understanding the mechanisms that govern the function, maintenance, and persistence of T cells will likely lead to new treatments for controlling disease. During an immune response, T-cell development is marked by striking changes in metabolism. There is a growing appreciation that these metabolic changes underlie the capacity of T cells to perform particular functions, and this has led to a recent focus on the idea that the manipulation of cellular metabolism can be used to shape adaptive immune responses. Although interest in this area has grown in the last few years, a full understanding of the metabolic control of T-cell functions, particularly during an immune response in vivo, is still lacking. In this review, we first provide a basic overview of metabolism in T cells, and then we focus on recent studies providing new or updated insights into the regulation of metabolic pathways and how they underpin T-cell differentiation and memory T-cell development.

Nitrosothiols in the immune system: signaling and protection

SIGNIFICANCE

In the immune system, nitric oxide (NO) has been mainly associated with antibacterial defenses exerted through oxidative, nitrosative, and nitrative stress and signal transduction through cyclic GMP-dependent mechanisms. However, S-nitrosylation is emerging as a post-translational modification (PTM) involved in NO-mediated cell signaling.

RECENT ADVANCES

Precise roles for S-nitrosylation in signaling pathways have been described both for innate and adaptive immunity. Denitrosylation may protect macrophages from their own S-nitrosylation, while maintaining nitrosative stress compartmentalized in the phagosomes. Nitrosothiols have also been shown to be beneficial in experimental models of autoimmune diseases, mainly through their role in modulating T-cell differentiation and function.

CRITICAL ISSUES

Relationship between S-nitrosylation, other thiol redox PTMs, and other NO-signaling pathways has not been always taken into account, particularly in the context of immune responses. Methods for assaying S-nitrosylation in individual proteins and proteomic approaches to study the S-nitrosoproteome are constantly being improved, which helps to move this field forward.

FUTURE DIRECTIONS

Integrated studies of signaling pathways in the immune system should consider whether S-nitrosylation/denitrosylation processes are among the PTMs influencing the activity of key signaling and adaptor proteins. Studies in pathophysiological scenarios will also be of interest to put these mechanisms into broader contexts. Interventions modulating nitrosothiol levels in autoimmune disease could be investigated with a view to developing new therapies.

Disruption of disulfide-restriction at integrin knees induces activation and ligand-independent signaling of α4β7

Control of integrin activation and signaling plays critical roles in cell adhesion, spreading, and migration. Here, we report that selective breakage of two conserved disulfide bonds located at the knees of integrin, α4C589–C594 and β7C494–C526, induced α4β7 activation. This activated α4β7 had a unique structure different from the typical extended conformation of active integrin. In addition, these activated α4β7 integrins spontaneously clustered on the cell membrane and triggered integrin downstream signaling independent of ligand binding. Although these disulfide bonds were not broken during α4β7 activation by inside-out signaling or Mn2+, they could be specifically reduced by 0.1 mM dithiothreitol, a reducing strength that could be produced in vivo under certain conditions. Our findings reveal a novel mechanism of integrin activation under specific reducing conditions by which integrin can signal and promote cell spreading in the absence of ligand.

The cystine/glutamate antiporter regulates indoleamine 2,3-dioxygenase protein levels and enzymatic activity in human dendritic cells

Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the tryptophan-catabolizing pathway and a key regulator of peripheral immune tolerance. As the suppressive effects of IDO are predominantly mediated by dendritic cells (DCs) and IDO-competent DCs promote long-term immunologic tolerance, a detailed understanding of how IDO expression and activity is regulated in these cells is central to the rational design of therapies to induce robust immune tolerance. We previously reported that the cystine/glutamate antiporter modulates the functional expression of IDO in human monocyte-derived DCs. Specifically, we showed that blocking antiporter uptake of cystine significantly increased both IDO mRNA and IDO enzymatic activity and that this correlated with impaired DC presentation of exogenous antigen to T cells via MHC class II and the cross-presentation pathway. The antiporter regulates intracellular and extracellular redox by transporting cystine into the cell in exchange for glutamate. Intracellular cystine is reduced to cysteine to support biosynthesis of the major cellular antioxidant glutathione and cysteine is exported from the cell where it functions as an extracellular antioxidant. Here we show that antiporter control of IDO expression in DCs is reversible, independent of interferon-γ, regulated by redox, and requires active protein synthesis. These findings highlight a role for antiporter regulation of cellular redox as a critical control point for modulating IDO expression and activity in DCs. Thus, systemic disease and aging, processes that perturb redox homeostasis, may adversely affect immunity by promoting the generation of IDO-competent DCs.

The pharmacologic inhibition of the xc- antioxidant system improves the antitumor efficacy of COX inhibitors in the in vivo model of 3-MCA tumorigenesis

The chemopreventive and therapeutic efficacy of the cyclooxygenase (COX) inhibitor ibuprofen (IB) and of sulfasalazine (SASP), a drug that targets the antioxidant xc- system, were exploited in the experimental model of 3-methylcholantrene (3-MCA)-induced mouse sarcoma. The chemopreventive treatments gave unsatisfactory results because administration of IB one day after the 3-MCA injection only slightly delayed the tumor development, whereas SASP dispensed under the same conditions resulted in accelerated tumorigenesis. Similarly, the therapeutic treatment with either drug, administrated daily from the tumor detection, decreased the proliferation rate of tumor cells and increased the survival of treated mice only at a low extent. Remarkably, the combined chemopreventive treatment with IB and therapeutic treatment with SASP displayed a better efficacy, with strong delay of sarcoma growth, reduced tumor size and increased survival of treated mice. The two drugs target not only tumor cells but also tumor-associated macrophages that were dramatically decreased in the tumor infiltrate of mice subjected to the combined treatment. The synergistic effects of the association between a broad anti-inflammatory compound, such as IB, and a redox-directed drug, such as SASP, shed new light in the role of inflammation and of the redox response in chemical tumorigenesis and point to the combined chemopreventive plus therapeutic treatment with IB and SASP as a promising novel approach for antitumor therapy.

A critical role for Mnt in Myc-driven T-cell proliferation and oncogenesis

Mnt (Max's next tango) is a Max-interacting transcriptional repressor that can antagonize both the proproliferative and proapoptotic functions of Myc in vitro. To ascertain the physiologically relevant functions of Mnt and to help define the relationship between Mnt and Myc in vivo, we generated a series of mouse strains in which Mnt was deleted in T cells in the absence of endogenous c-Myc or in the presence of ectopic c-Myc. We found that apoptosis caused by loss of Mnt did not require Myc but that ectopic Myc expression dramatically decreased the survival of both Mnt-deficient T cells in vivo and Mnt-deficient MEFs in vitro. Consequently, Myc-driven proliferative expansion of T cells in vitro and thymoma formation in vivo were prevented by the absence of Mnt. Consistent with T-cell models, mouse embryo fibroblasts (MEFs) lacking Mnt were refractory to oncogenic transformation by Myc. Tumor suppression caused by loss of Mnt was linked to increased apoptosis mediated by reactive oxygen species (ROS). Thus, although theoretically and experimentally a Myc antagonist, the dominant physiological role of Mnt appears to be suppression of apoptosis. Our results redefine the physiological relationship between Mnt and Myc and requirements for Myc-driven oncogenesis.

Increased synapse formation obtained by T cell epitopes containing a CxxC motif in flanking residues convert CD4+ T cells into cytolytic effectors

The nature of MHC class II-binding epitopes not only determines the specificity of T cell responses, but may also alter effector cell functions. Cytolytic CD4+ T cells have been observed primarily in anti-viral responses, but very little is known about the conditions under which they can be elicited. Their potential as regulators of immune responses, however, deserves investigations. We describe here that inclusion of a thiol-disulfide oxidoreductase motif within flanking residues of class II-restricted epitopes results, both in vitro and in vivo, in elicitation of antigen-specific cytolytic CD4+ T cells through increased synapse formation. We show that both naïve and polarized CD4+ T cells, including Th17 cells, can be converted by cognate recognition of such modified epitopes. Cytolytic CD4+ T cells induce apoptosis on APCs by Fas-FasL interaction. These findings potentially open the way towards a novel form of antigen-specific immunosuppression.

Amino acid metabolism related to immune tolerance by MDSCs

Myeloid-derived suppressor cells (MDSCs) are present in most cancer patients. Due to their significant role in blocking immune responses, MDSCs are strategic obstacles to immunotherapy that require activation of the host's cell-mediated and innate immune responses. Following a brief description of the immunosuppressive MDSCs, the authors review the discovered mechanisms of amino acid metabolism that MDSCs use to suppress the activation of T cells. Given the heterogeneity of MDSCs and the variety of suppressive mechanisms employed by MDSCs, it is essential to understand which group of these cells and mechanisms are dominant.

P2X7 receptor regulation of non-classical secretion from immune effector cells

P2X7 receptors (P2X7R) are extracellular ATP-gated ion channels expressed in the immune effector cells that carry out critical protective responses during the early phases of microbial infection or acute tissue trauma. P2X7R-positive cells include monocytes, macrophages, dendritic cells and T cells. Given its presence in all host and pathogen cell types, ATP can be readily released into extracellular compartments at local sites of tissue damage and microbial invasion. Thus, extracellular ATP and its target receptors on host effector cells can be considered as additional elements of the innate immune system. In this regard, stimulation of P2X7R rapidly triggers a key step of the inflammatory response: induction of NLRP3/caspase-1 inflammasome signalling complexes that drive the proteolytic maturation and secretion of the proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18). IL-1β (and IL-18) lacks a signal sequence for compartmentation within the Golgi and classical secretory vesicles and the proIL-1β precursor accumulates within the cytosol following translation on free ribosomes. Thus, ATP-induced accumulation of the mature IL-1β cytokine within extracellular compartments requires non-classical mechanisms of export from the cytosolic compartment. Five proposed mechanisms include: (i) exocytosis of secretory lysosomes that accumulate cytosolic IL-1β via undefined protein transporters; (ii) release of membrane-delimited microvesicles derived from plasma membrane blebs formed by evaginationsof the surface membrane that entrap cytosolic IL-β; (iii) release of membrane-delimited exosomes secondary to the exocytosis of multivesicular bodies formed by invaginations of recycling endosomes that entrap cytosolic IL-β; (iv) exocytosis of autophagosomes or autophagolysosomes that accumulate cytosolic IL-1β via entrapment during formation of the initial autophagic isolation membrane or omegasome and (v) direct release of cytosolic IL-1β secondary to regulated cell death by pyroptosis or necroptosis. These mechanisms are not mutually exclusive and may represent engagement of parallel or intersecting membrane trafficking responses to P2X7R activation.

Exploratory clinical trial of (4S)-4-(3-[18F]fluoropropyl)-L-glutamate for imaging xC- transporter using positron emission tomography in patients with non-small cell lung or breast cancer

PURPOSE

(4S)-4-(3-[(18)F]fluoropropyl)-l-glutamate (BAY 94-9392, alias [(18)F]FSPG) is a new tracer to image x(C)(-) transporter activity with positron emission tomography (PET). We aimed to explore the tumor detection rate of [(18)F]FSPG in patients relative to 2-[(18)F]fluoro-2-deoxyglucose ([(18)F]FDG). The correlation of [(18)F]FSPG uptake with immunohistochemical expression of x(C)(-) transporter and CD44, which stabilizes the xCT subunit of system x(C)(-), was also analyzed.

EXPERIMENTAL DESIGN

Patients with non-small cell lung cancer (NSCLC, n = 10) or breast cancer (n = 5) who had a positive [(18)F]FDG uptake were included in this exploratory study. PET images were acquired following injection of approximately 300 MBq [(18)F]FSPG. Immunohistochemistry was done using xCT- and CD44-specific antibody.

RESULTS

[(18)F]FSPG PET showed high uptake in the kidney and pancreas with rapid blood clearance. [(18)F]FSPG identified all 10 NSCLC and three of the five breast cancer lesions that were confirmed by pathology. [(18)F]FSPG detected 59 of 67 (88%) [(18)F]FDG lesions in NSCLC, and 30 of 73 (41%) in breast cancer. Seven lesions were additionally detected only on [(18)F]FSPG in NSCLC. The tumor-to-blood pool standardized uptake value (SUV) ratio was not significantly different from that of [(18)F]FDG in NSCLC; however, in breast cancer, it was significantly lower (P < 0.05). The maximum SUV of [(18)F]FSPG correlated significantly with the intensity of immunohistochemical staining of x(C)(-) transporter and CD44 (P < 0.01).

CONCLUSIONS

[(18)F]FSPG seems to be a promising tracer with a relatively high cancer detection rate in patients with NSCLC. [(18)F]FSPG PET may assess x(C)(-) transporter activity in patients with cancer.

Myeloid-derived suppressor cells: mechanisms of action and recent advances in their role in transplant tolerance

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature hematopoietic precursors known to suppress immune responses in infection, chronic inflammation, cancer, and autoimmunity. In this paper, we review recent findings detailing their mode of action and discuss recent reports that suggest that MDSC are also expanded during transplantation and that modulation of MDSC can participate in preventing graft rejection as well as graft-versus-host disease.

On the redox control of B lymphocyte differentiation and function

SIGNIFICANCE

On the one hand, redox emerges as a key mechanism in regulating intra- and intercellular signaling and homeostatic systems. On the other hand, cells of the B lineage provide powerful systems to unravel the intra- and intercellular mechanisms that coordinate the processes of development and terminal differentiation.

RECENT ADVANCES

This essay summarizes a few paradigmatic examples of redox regulation and signal modulation that emerged from, or were confirmed by, studies on the development, differentiation and function of B cells.

CRITICAL ISSUES

While a role for intra- and intercellular redox signaling has been firmly established for differentiating B cells, many fundamental questions remain open, including the cellular sources of reactive oxygen species (ROS), the spatial and temporal constraints of ROS signaling, and the functional role of the antioxidant response.

FUTURE DIRECTIONS

Given their robustness and biotechnological and clinical interest, cells of the B lineage continue to be fruitful goldmines from which redox biologists can dig novel mechanistic knowledge of general relevance.

Molecular characterization, expression, and functional analysis of two thioredoxins in the black rockfish (Sebastes schlegelii)

Thioredoxins (TRxs) are a family of small evolutionarily conserved proteins that are essential for the maintenance of cellular homeostasis. Two TRx homologue cDNAs were isolated from a black rockfish concanavalin A (Con A)/phorbol myristate acetate (PMA)-stimulated leucocyte cDNA library and named BrTPx1-1 and BrTPx1-2. As compared with other known TRx peptide sequences, the most conserved regions of both BrTRx1-1 and BrTRx1-2 peptides were found to be the redox-active site Trp-Cys-X-X-Cys (WCXXC). The TRx present in most species is a TRx1-2 protein with a Cys-Pro-Gly-Cys (CPGC) active site. However, in the larger 13 kDa BrTRx1-1 protein, a Cys-Pro-Pro-Cys (CPPC) active site was identified. Here, we report the identification of a new member of the TRx protein family from the teleost black rockfish, which defines a new subclass of 13-kDa TRx1-1 proteins. Phylogenetic analysis indicated that both BrTRx1-1 and BrTRx1-2 were grouped with other vertebrate TRx1 peptides. BrTRx1-1 expression was strongly induced in peripheral blood leucocytes (PBLs) 12-24 h following Con A/PMA stimulation, with peak expression at 24 h post-stimulation. BrTRx1-2 was induced in PBLs after stimulation with lipopolysaccharide (LPS), Con A/PMA, or poly I:C at 24 h. The BrTRx1-1 gene was predominantly expressed in the liver and gills, while BrTRx1-2 was expressed in PBLs and gills. After treatment with a high concentration (10 μg/mL) of rBrTRx1-1 or rBrTRx1-2, kidney leucocytes exhibited increased cell proliferation and viability under oxidative stress.

Lymphocytes from rheumatoid arthritis patients have elevated levels of intracellular peroxiredoxin 2, and a greater frequency of cells with exofacial peroxiredoxin 2, compared with healthy human lymphocytes

Peroxiredoxin 2 has immune regulatory functions, but its expression in human peripheral blood lymphocytes and levels in extracellular fluid in healthy subjects and rheumatoid arthritis patients are poorly described. In the present study, the median intracellular peroxiredoxin 2 protein content of lymphocytes from rheumatoid arthritis patients was more than two-fold higher compared with healthy subjects’ lymphocytes. Intracellular peroxiredoxin 3 levels were similar in healthy and rheumatoid arthritis lymphocytes. Flow cytometry detected peroxiredoxin 2 on the surface of ca. 8% of T cells and ca. 56% of B cells (median % values) of all subjects analyzed. Exofacial thioredoxin-1 was also observed. In the total lymphocyte population from rheumatoid arthritis patients, few cells (median, 6%) displayed surface peroxiredoxin 2. In contrast, a significantly increased proportion of interleukin-17^+ve lymphocytes were exofacially peroxiredoxin 2^+ve (median, 39%). Prdx2 was also detected in human extracellular fluids. We suggest that crucial inflammatory cell subsets, i.e. interleukin-17^+ve T cells, exhibit increased exofacial redox-regulating enzymes and that peroxiredoxin 2 may be involved in the persistence of pro-inflammatory cells in chronic inflammation.

T regulatory cells in B-cell malignancy - tumour support or kiss of death?

It is well established that T regulatory (Treg) cells counteract tumour immunity. However, conflicting results describing the role of Treg cells in haematological tumours warrant further investigations to clarify the interactions between Treg cells and the tumour. B-cell malignancy derives from different stages of B-cell development and differentiation in which T cells play a profound role. The transformed B cell may still be in need of T-cell help to thrive but simultaneously they may be recognized and destroyed by cytotoxic lymphocytes. Recent reports demonstrate that Treg cells can suppress and even kill B cells as part of their normal function to rescue the body from autoimmunity. An emerging body of evidence points out that Treg cells not only inhibit tumour-specific T cells but may also have a role in suppressing the progression of the B-cell tumour. In this review, we discuss the origin and function of Treg cells and their role in patients with B-cell tumours.

Transplant tolerance is associated with reduced expression of cystathionine-γ-lyase that controls IL-12 production by dendritic cells and TH-1 immune responses

Antigen-activated T lymphocytes undergo an immune or tolerogeneic response in part according to the activation status of their antigen-presenting cells. However, factors controlling the activation of antigen-presenting cells are not fully understood. In this study, we demonstrate that immune tolerance after organ allotransplantation in the rat is associated with a repressed intragraft expression of several enzymes of the trans-sulfuration pathway, including cystathionine γ-lyase (CSE). The pharmacologic blockade of CSE with propargylglycine delayed heart allograft rejection and abrogated type IV hypersensitivity but did not modify antibody responses, and was associated with a selective inhibition of the TH-1 type factors T-bet, IL-12, and IFN-γ. IL-12 repression could also be induced by propargylglycine in vitro in monocytes and dendritic cells (DCs), a phenomenon not mediated by changes to nuclear factor-κ B or hydrogen sulfide but that occurred together with a modulation of intracellular cysteine content. Intracellular cysteine levels were predominantly controlled in DCs by CSE activity, together with extracellular import via the Xc− transporter. Our results indicate that CSE plays a critical role in regulating IL-12 in monocytes and DCs and is down-modulated in transplant tolerance, presumably participating in the maintenance of the tolerant state.

Mercury toxicity in beluga whale lymphocytes: limited effects of selenium protection

Increasing emissions of anthropogenic mercury represents a growing concern to the health of high trophic level marine mammals. In its organic form, this metal bioaccumulates, and can be toxic to several physiological endpoints, including the immune system. In this study, we (1) evaluated the effects of inorganic mercury (mercuric chloride, HgCl2) and organic mercury (methylmercuric chloride, MeHgCl) on the in vitro function of lymphocytes isolated from the peripheral blood of beluga whales (Delphinapterus leucas); (2) characterized the potential protective effects of sodium selenite (Na2SeO3) on cell proliferation of HgCl2 or MeHgCl-treated beluga whale lymphocytes; and (3) compared these dose-dependent effects to measurements of blood Hg in samples collected from traditionally harvested beluga whales in the western Canadian Arctic. Lymphocyte proliferative responses were reduced following exposure to 1 μM of HgCl2 and 0.33 μM of MeHgCl. Decreased intracellular thiol levels were observed at 10 μM of HgCl2 and 0.33 μM of MeHgCl. Metallothionein induction was noted at 0.33 μM of MeHgCl. Concurrent exposure of Se provided a degree of protection against the highest concentrations of inorganic Hg (3.33 and 10 μM) or organic Hg (10 μM) for T-lymphocytes. This in vitro protection of Se against Hg toxicity to lymphocytes may contribute to the in vivo protection in beluga whales exposed to high Hg concentrations. Current Hg levels in free-ranging beluga whales from the Arctic fall into the range of exposures which elicited effects on lymphocytes in our study, highlighting the potential for effects on host resistance to disease. The implications of a changing Arctic climate on Hg fate in beluga food webs and the consequences for the health of beluga whales remain pressing research needs.

Understanding the roles of gingival beta-defensins

Gingival epithelium produces β-defensins, small cationic peptides, as part of its contribution to the innate host defense against the bacterial challenge that is constantly present in the oral cavity. Besides their functions in healthy gingival tissues, β-defensins are involved in the initiation and progression, as well as restriction of periodontal tissue destruction, by acting as antimicrobial, chemotactic, and anti-inflammatory agents. In this article, we review the common knowledge about β-defensins, coming from in vivo and in vitro monolayer studies, and present new aspects, based on the experience on three-dimensional organotypic culture models, to the important role of gingival β-defensins in homeostasis of the periodontium.

Enhancement of postoperative recovery by preoperative oral co-administration of the amino acids, cystine and theanine, in a mouse surgical model

BACKGROUND & AIMS

Glutathione (GSH) is important in the control of immune responses, and its levels decline following trauma. We previously reported that the oral administration of cystine/theanine (CT) increased GSH synthesis and that CT intake inhibited intense exercise-induced inflammation. Based on these results, we hypothesised that CT inhibits surgically induced inflammation and promotes postoperative recovery. Our aim was to confirm this hypothesis using a mouse surgical model.

METHODS

CT or a vehicle (V) was administered orally to mice once a day for 5 days, until the day of surgery. On the day of surgery, a sham operation or an intestinal manipulation was performed 2 h after the oral administration of CT or V. Levels of IL-6 in the blood and GSH in the intestine were analysed 2 h after surgery. Behavioural analysis was also undertaken after surgery.

RESULTS

Treatment with CT inhibited the manipulation-induced increase in IL-6 in the blood and decrease in GSH in the intestine. There was a significant negative correlation between IL-6 in the blood and GSH in the intestine. In addition, behavioural analysis revealed that CT administration improved locomotor activity and food intake after surgery.

CONCLUSION

These results suggest that CT suppresses inflammatory responses by inhibiting the surgically induced decrease in GSH in the small intestine and promotes postoperative recovery.

Activated human CD4+ T cells express transporters for both cysteine and cystine

Because naïve T cells are unable to import cystine due to the absence of cystine transporters, it has been suggested that T cell activation is dependent on cysteine generated by antigen presenting cells. The aim of this study was to determine at which phases during T cell activation exogenous cystine/cysteine is required and how T cells meet this requirement. We found that early activation of T cells is independent of exogenous cystine/cysteine, whereas T cell proliferation is strictly dependent of uptake of exogenous cystine/cysteine. Naïve T cells express no or very low levels of both cystine and cysteine transporters. However, we found that these transporters become strongly up-regulated during T cell activation and provide activated T cells with the required amount of cystine/cysteine needed for T cell proliferation. Thus, T cells are equipped with mechanisms that allow T cell activation and proliferation independently of cysteine generated by antigen presenting cells.

Myeloid suppressor cells induced by hepatitis C virus suppress T-cell responses through the production of reactive oxygen species

Impaired T-cell responses in chronic hepatitis C virus (HCV) patients have been reported to be associated with the establishment of HCV persistent infection. However, the mechanism for HCV-mediated T-cell dysfunction is yet to be defined. Myeloid-derived suppressor cells (MDSCs) play a pivotal role in suppressing T-cell responses. In this study we examined the accumulation of MDSCs in human peripheral blood mononuclear cells (PBMCs) following HCV infection. We found that CD33(+) mononuclear cells cocultured with HCV-infected hepatocytes, or with HCV core protein, suppress autologous T-cell responses. HCV core-treated CD33(+) cells exhibit a CD14(+) CD11b(+/low) HLADR(-/low) phenotype with up-regulated expression of p47(phox) , a component of the NOX2 complex critical for reactive oxygen species (ROS) production. In contrast, immunosuppressive factors, arginase-1 and inducible nitric oxide synthase (iNOS), were not up-regulated. Importantly, treatment with an inactivator of ROS reversed the T-cell suppressive function of HCV-induced MDSCs. Lastly, PBMCs of chronic HCV patients mirror CD33(+) cells following treatment with HCV core where CD33(+) cells are CD14(+) CD11b(+) HLADR(-/low) , and up-regulate the expression of p47(phox).

CONCLUSION

These results suggest that HCV promotes the accumulation of CD33(+) MDSC, resulting in ROS-mediated suppression of T-cell responsiveness. Thus, the accumulation of MDSCs during HCV infection may facilitate and maintain HCV persistent infection.

Plasma glutathione of HIV⁺ patients responded positively and differently to dietary supplementation with cysteine or glutamine

OBJECTIVE

Patients with positivity for the human immunodeficiency virus (HIV⁺) present low concentrations of antioxidant nutrients, including total glutathione (GSH) and its precursors. We investigated the responses of the sulfur-containing amino acid pathway to cysteine and glutamine (Gln) dietary supplements in patients with HIV⁺ compared with healthy controls.

METHODS

Twelve treated patients (six men and six women, 22-45 y old) and 20 healthy controls (10 men and 10 women, 20-59 y old) were randomly assigned to 7-d dietary supplements containing N-acetylcysteine (NAC; 1 g/d) or Gln (20 g/d), with a 7-d washout period ingesting their usual diet. Blood samples were drawn after an overnight fast. High-performance liquid chromatographic plasma analysis of sulfur-containing amino acids (methionine, homocysteine, cysteine, and taurine), GSH, oxidized GSH, and serine, glycine, glutamic acid, and Gln was carried out moments before and after 7-d supplementations. Statistical comparisons were undertaken between groups and between dietary supplements (P < 0.05).

RESULTS

Patients with HIV⁺ showed higher oxidized GSH and lower concentrations of GSH and all amino acids except homocysteine. The HIV⁺ group responded to the NAC by increased levels of sulfur-containing amino acids and GSH and equalized taurine and GSH levels in the control group. The Gln supplements also equalized the levels of GSH, Gln, and glycine in the control group.

CONCLUSION

An increase in GSH may be attained by NAC or Gln supplementation, with NAC acting by increasing cysteine levels and Gln likely acting by replenishing the glycine pool (trial registered at http://www.clinicaltrials.gov, identifier NCT00910442).

Changes in the levels of thioredoxin and indoleamine-2,3-dioxygenase activity in plasma of patients with colorectal cancer treated with chemotherapy

Increased oxidative stress and indoleamine-2,3-dioxygenase (IDO) activity have been reported in cancer, but their relationship with chemotherapy remains unknown. The aim of the present study was to examine wether the chemotherapy treatments used in colorectal cancer had an additional effect on oxidative stress and on IDO activity. Plasma samples were collected from 27 colorectal cancer patients on cytostatic treatment, 27 with cytostatic drugs plus monoclonal antibodies (cytostatic-Mabs) and 15 non-treated patients. All patients with colorectal cancer had high plasma malondialdehyde (MDA), thioredoxin (Trx) levels, and elevated IDO activity in plasma (IDOp) and in dendritic cells (IDOc). This study shows that treatment with cytostatics have an effect on oxidative stress by increasing MDA levels and by decreasing Trx levels and IDO activity. However, treatment with cytostatic-Mabs showed no effect on MDA levels but decreased Trx levels, and the IDO activity showed values similar to the healthy group. Significant correlations between plasma IDO activity and the levels of Trx (r = 0.2062, p < 0.05) and MDA (r = 0.2873, p < 0.005) were observed. Furthermore, our study suggests that IDO activity measured as kynurenine levels could be used as a marker of the response to the chemotherapy treatments, although further studies are necessary.

Redox outside the box: linking extracellular redox remodeling with intracellular redox metabolism

Aerobic organisms generate reactive oxygen species as metabolic side products and must achieve a delicate balance between using them for signaling cellular functions and protecting against collateral damage. Small molecule (e.g. glutathione and cysteine)- and protein (e.g. thioredoxin)-based buffers regulate the ambient redox potentials in the various intracellular compartments, influence the status of redox-sensitive macromolecules, and protect against oxidative stress. Less well appreciated is the fact that the redox potential of the extracellular compartment is also carefully regulated and is dynamic. Changes in intracellular metabolism alter the redox poise in the extracellular compartment, and these are correlated with cellular processes such as proliferation, differentiation, and death. In this minireview, the mechanism of extracellular redox remodeling due to intracellular sulfur metabolism is discussed in the context of various cell-cell communication paradigms.

Protein energy malnutrition impairs homeostatic proliferation of memory CD8 T cells

Nutrition is a critical but poorly understood determinant of immunity. There is abundant epidemiological evidence linking protein malnutrition to impaired vaccine efficacy and increased susceptibility to infections; yet, the role of dietary protein in immune memory homeostasis remains poorly understood. In this study, we show that protein-energy malnutrition induced in mice by low-protein (LP) feeding has a detrimental impact on CD8 memory. Relative to adequate protein (AP)-fed controls, LP feeding in lymphocytic choriomeningitis virus (LCMV)-immune mice resulted in a 2-fold decrease in LCMV-specific CD8 memory T cells. Adoptive transfer of memory cells, labeled with a division tracking dye, from AP mice into naive LP or AP mice demonstrated that protein-energy malnutrition caused profound defects in homeostatic proliferation. Remarkably, this defect occurred despite the lymphopenic environment in LP hosts. Whereas Ag-specific memory cells in LP and AP hosts were phenotypically similar, memory cells in LP hosts were markedly less responsive to polyinosinic-polycytidylic acid-induced acute proliferative signals. Furthermore, upon recall, memory cells in LP hosts displayed reduced proliferation and protection from challenge with LCMV-clone 13, resulting in impaired viral clearance in the liver. The findings show a metabolic requirement of dietary protein in sustaining functional CD8 memory and suggest that interventions to optimize dietary protein intake may improve vaccine efficacy in malnourished individuals.

The cystine/cysteine cycle and GSH are independent and crucial antioxidant systems in malignant melanoma cells and represent druggable targets

AIMS

Cancer chemoresistance is often due to upregulation of antioxidant systems. Therapeutic targeting of these systems is however hampered by their redundancy. Here, we have performed a functional dissection of the antioxidant systems in different melanoma cases aimed at the identification of the most effective redox active drug.

RESULTS

We have identified two crucial antioxidant mechanisms: glutathione (GSH), the major intracellular redox buffer, and the cystine/cysteine cycle, which switches the extracellular redox state from an oxidized to a reduced state. The two mechanisms are independent in melanoma cells and may be substitutes for each other, but targeting both of them is lethal. Exposure to the pro-oxidant compound As(2)O(3) induces an antioxidant response. However, while in these cells the intracellular redox balance remains almost unaffected, a reduced environment is generated extracellularly. GSH depletion by buthioninesulfoximine (BSO), or cystine/cysteine cycle inhibition by (S)-4-carboxyphenylglycine (sCPG), enhanced the sensitivity to As(2)O(3). Remarkably, sCPG also prevented the remodeling of the microenvironment redox state.

INNOVATION

We propose that the definition of the prevalent antioxidant system(s) in tumors is crucial for the design of tailored therapies involving redox-directed drugs in association with pro-oxidant drugs.

CONCLUSION

In melanoma cells, BSO is the best enhancer of As(2)O(3) sensitivity. However, since the strong remodeling of the microenvironmental redox state caused by As(2)O(3) may promote tumor progression, the concomitant use of cystine/cysteine cycle blockers is recommended.

Labile disulfide bonds are common at the leucocyte cell surface

Redox conditions change in events such as immune and platelet activation, and during viral infection, but the biochemical consequences are not well characterized. There is evidence that some disulfide bonds in membrane proteins are labile while others that are probably structurally important are not exposed at the protein surface. We have developed a proteomic/mass spectrometry method to screen for and identify non-structural, redox-labile disulfide bonds in leucocyte cell-surface proteins. These labile disulfide bonds are common, with several classes of proteins being identified and around 30 membrane proteins regularly identified under different reducing conditions including using enzymes such as thioredoxin. The proteins identified include integrins, receptors, transporters and cell-cell recognition proteins. In many cases, at least one cysteine residue was identified by mass spectrometry as being modified by the reduction process. In some cases, functional changes are predicted (e.g. in integrins and cytokine receptors) but the scale of molecular changes in membrane proteins observed suggests that widespread effects are likely on many different types of proteins including enzymes, adhesion proteins and transporters. The results imply that membrane protein activity is being modulated by a 'redox regulator' mechanism.

Interplay between redox status and inflammasome activation

Several inflammation-related processes, including inflammasome activation and interleukin (IL)-1β secretion, are dependent on redox signaling. However, the type of redox response involved as well as the relevant role of pro-oxidant and antioxidant events are matters of intense debate. By comparing leukemic myeloid cells, healthy monocytes and macrophages, as well as monocytes from patients carrying mutations in members of the Nod-like receptor (NLR) gene family, we have drawn a model that reconciles previous conflicting hypotheses. We propose that the redox state of resting inflammatory cells determines the type and extent of redox response to pattern recognition receptor stimulation, which in turn dictates the efficiency of inflammasome activation. The impact on genetic and acquired inflammatory diseases will be discussed.

Activation of extracellular transglutaminase 2 by thioredoxin

The mechanism of activation of transglutaminase 2 (TG2) in the extracellular matrix remains a fundamental mystery in our understanding of the biology of this multifunctional mammalian enzyme. Earlier investigations have highlighted the role of a disulfide bond formed by vicinal Cys residues in maintaining calcium-bound TG2 in an inactive state. Here, we have shown that the redox potential of this disulfide bond is approximately -190 mV, a high value for a disulfide bond in proteins. Consistent with this observation, TG2 activity in a freshly wounded fibroblast culture depends upon the redox potential of the environment. We sought to identify a physiological mechanism for the activation of oxidized TG2. With a k(cat)/K(m) of 1.6 μm(-1) min(-1), human thioredoxin (Trx) was a highly specific activator of oxidized human TG2. Trx-mediated activation of TG2 was blocked by PX-12, a small molecule Trx inhibitor that is undergoing clinical trials as a cancer chemotherapeutic agent. In a mixed culture containing fibroblasts and monocytic cells, interferon-γ stimulated Trx release from monocytes, which in turn activated TG2 around the fibroblasts. Recombinant human Trx could also activate extracellular TG2 in cryosections of human and mouse small intestinal biopsies. In addition to explaining how TG2 can be activated by dietary gluten in the small intestinal mucosa of celiac sprue patients, our findings reveal a new strategy for inhibiting the undesirable consequences of TG2 activity in this widespread, lifelong disease.

Metabolomics of B to plasma cell differentiation

When small B lymphocytes bind antigen in the context of suitable signals, a profound geno-proteomic metamorphosis is activated that generates antibody-secreting cells. To study the metabolic changes associated with this differentiation program, we compared the exometabolome of differentiating murine B lymphoma cells and primary B cells by monodimensional proton nuclear magnetic resonance spectroscopy and mass spectrometry coupled to liquid chromatography. Principal component analysis, a multivariate statistical analysis, highlighted metabolic hallmarks of the sequential differentiation phases discriminating between the proliferation and antibody secreting phases and revealing novel metabolic pathways. During proliferation, lactate production increased together with consumption of essential amino acids; massive Ig secretion was paralleled by alanine and glutamate production, glutamine being used as carbon and energy sources. Notably, ethanol and 5'-methylthioadenosine were produced during the last phase of protein secretion and the proliferative burst, respectively. Our metabolomics results are in agreement with previous genoproteomics studies. Thus, metabolic profiling of extracellular medium is a useful tool to characterize the functional state of differentiating B cells and to identify novel underlying metabolic pathways.

Molecular cloning and expression analysis of a thioredoxin from rock bream, Oplegnathus fasciatus, and biological activity of the recombinant protein

Thioredoxins (TRxs) are a family of small, highly conserved proteins that are essential for the maintenance of cellular homeostasis. TRx1, which contains a conserved redox-active site, Cys-Gly-Pro-Cys, is a proinflammatory cytokine, B cell growth factor, macrophage migration inhibiting factor (MIF), and an immune regulatory cytokine. The TRx1 homologue cDNA was isolated from the rock bream LPS-stimulated liver cDNA library, RbTRx1. RbTRx1 consists of 730 bp full-length cDNA with a 324 bp open reading frame encoding 108 amino acids. When compared with other known TRx1 peptide sequences, the most conserved region of the RbTRx1 peptide was the redox-active site Cys-Gly-Pro-Cys. Phylogenetic analysis grouped the RbTRx1 with other vertebrate TRx1 peptides. Quantitative real-time PCR analysis revealed the presence of RbTRx1 transcripts in liver, gill, kidney, and muscle. The expression of RbTRx1 mRNA in kidney leukocytes was upregulated after bacterial and viral challenge. The kidney leukocytes were treated with a high concentration of rRbTRx1, which significantly enhanced cell proliferation (1 μg/ml and 10 μg/ml) and viability under oxidative stress (10 μg/ml).

Differential dependence on cysteine from transsulfuration versus transport during T cell activation

The synthesis of glutathione, a major cellular antioxidant with a critical role in T cell proliferation, is limited by cysteine. In this study, we evaluated the contributions of the x(C)(-) cystine transporter and the transsulfuration pathway to cysteine provision for glutathione synthesis and antioxidant defense in naïve versus activated T cells and in the immortalized T lymphocyte cell line, Jurkat. We show that the x(C)(-) transporter, although absent in naïve T cells, is induced after activation, releasing T cells from their cysteine dependence on antigen-presenting cells. We also demonstrate the existence of an intact transsulfuration pathway in naïve and activated T cells and in Jurkat cells. The flux through the transsulfuration pathway increases in primary but not in transformed T cells in response to oxidative challenge by peroxide. Inhibition of the transsulfuration pathway in both primary and transformed T cells decreases cell viability under oxidative-stress conditions.

Astrocytic redox remodeling by amyloid beta peptide

Astrocytes are critical for neuronal redox homeostasis providing them with cysteine needed for glutathione synthesis. In this study, we demonstrate that the astrocytic redox response signature provoked by amyloid beta (Aβ) is distinct from that of a general oxidant (tertiary-butylhydroperoxide [t-BuOOH]). Acute Aβ treatment increased cystathionine β-synthase (CBS) levels and enhanced transsulfuration flux in contrast to repeated Aβ exposure, which decreased CBS and catalase protein levels. Although t-BuOOH also increased transsulfuration flux, CBS levels were unaffected. The net effect of Aβ treatment was an oxidative shift in the intracellular glutathione/glutathione disulfide redox potential in contrast to a reductive shift in response to peroxide. In the extracellular compartment, Aβ, but not t-BuOOH, enhanced cystine uptake and cysteine accumulation, and resulted in remodeling of the extracellular cysteine/cystine redox potential in the reductive direction. The redox changes elicited by Aβ but not peroxide were associated with enhanced DNA synthesis. CBS activity and protein levels tended to be lower in cerebellum from patients with Alzheimer's disease than in age-matched controls. Our study suggests that the alterations in astrocytic redox status could compromise the neuroprotective potential of astrocytes and may be a potential new target for therapeutic intervention in Alzheimer's disease.

The rate of interleukin-1beta secretion in different myeloid cells varies with the extent of redox response to Toll-like receptor triggering

Human myeloid cells activate the NLRP3 inflammasome and secrete interleukin (IL)-1β in response to various Toll-like receptor (TLR) ligands, but the rate of secretion is much higher in primary human monocytes than in cultured macrophages or THP-1 cells. The different myeloid cells also display different redox status under resting conditions and redox response to TLR activation. Resting monocytes display a balanced redox state, with low production of reactive oxygen species (ROS) and antioxidants. TLR engagement induces an effective redox response with increased ROS generation followed by a sustained antioxidant response, parallelled by efficient IL-1β secretion. Drugs blocking ROS production or the antioxidant response prevent the secretion of mature IL-1β but not the biosynthesis of pro-IL-1β, indicating that redox remodeling is responsible for IL-1β processing and release. Unlike monocytes, THP-1 cells and cultured macrophages have up-regulated antioxidant systems that buffer the oxidative hit provided by TLR triggering and suppress the consequent redox response. This aborted redox remodeling is paralleled by low efficiency IL-1β processing and secretion. High doses (5 mM) of H(2)O(2) overcome the high antioxidant capacity of THP-1 cells, restore an efficient redox response, and increase the rate of IL-1β secretion. Together these data indicate that a tightly controlled redox homeostasis in resting cells is a prerequisite for a robust redox response to TLR ligands, in turn necessary for the efficient inflammasome activation. Inflammasome activation by bacterial DNA is not modulated by redox responses, suggesting that redox-dependent regulation of IL-1β secretion is restricted to some inflammasomes including NLRP3 but excluding AIM-2.

The oxidative stress-inducible cystine/glutamate antiporter, system x (c) (-) : cystine supplier and beyond

The oxidative stress-inducible cystine/glutamate exchange system, system x (c) (-) , transports one molecule of cystine, the oxidized form of cysteine, into cells and thereby releases one molecule of glutamate into the extracellular space. It consists of two protein components, the 4F2 heavy chain, necessary for membrane location of the heterodimer, and the xCT protein, responsible for transport activity. Previously, system x (c) (-) has been regarded to be a mere supplier of cysteine to cells for the synthesis of proteins and the antioxidant glutathione (GSH). In that sense, oxygen, electrophilic agents, and bacterial lipopolysaccharide trigger xCT expression to accommodate with increased oxidative stress by stimulating GSH biosynthesis. However, emerging evidence established that system x (c) (-) may act on its own as a GSH-independent redox system by sustaining a redox cycle over the plasma membrane. Hallmarks of this cycle are cystine uptake, intracellular reduction to cysteine and secretion of the surplus of cysteine into the extracellular space. Consequently, increased levels of extracellular cysteine provide a reducing microenvironment required for proper cell signaling and communication, e.g. as already shown for the mechanism of T cell activation. By contrast, the enhanced release of glutamate in exchange with cystine may trigger neurodegeneration due to glutamate-induced cytotoxic processes. This review aims to provide a comprehensive picture from the early days of system x (c) (-) research up to now.

Enhanced susceptibility of T lymphocytes to oxidative stress in the absence of the cellular prion protein

The cellular prion glycoprotein (PrP(C)) is ubiquitously expressed but its physiologic functions remain enigmatic, particularly in the immune system. Here, we demonstrate in vitro and in vivo that PrP(C) is involved in T lymphocytes response to oxidative stress. By monitoring the intracellular level of reduced glutathione, we show that PrP(-/-) thymocytes display a higher susceptibility to H(2)O(2) exposure than PrP(+/+) cells. Furthermore, we find that in mice fed with a restricted diet, a regimen known to increase the intracellular level of ROS, PrP(-/-) thymocytes are more sensitive to oxidative stress. PrP(C) function appears to be specific for oxidative stress, since no significant differences are observed between PrP(-/-) and PrP(+/+) mice exposed to other kinds of stress. We also show a marked evolution of the redox status of T cells throughout differentiation in the thymus. Taken together, our results clearly ascribe to PrP(C) a protective function in thymocytes against oxidative stress.

Adenosine A(2A) receptor activation limits chronic granulomatous disease-induced hyperinflammation

Chronic granulomatous disease (CGD) is caused by defects in the NADPH oxidase complex and is characterized by an increased susceptibility to infection. Other significant complications of CGD include autoimmunity and non-infectious hyperinflammatory disorders. We show that a gp91(phox) deficiency leads to the development of phenotypically altered T lymphocytes in mice and that this abnormal, hyperactive phenotype can be modulated by activation of the adenosine A(2A) receptor. T cells isolated from CGD mice produce significantly higher levels of the pro-inflammatory cytokines IFN-γ, IL-2, TNF-α, IL-4 and IL-13 than do WT cells after TCR-mediated activation; treatment with the selective adenosine A(2A) receptor agonist, CGS21680, potently inhibits this response. Additionally, the over exuberant inflammatory response elicited by thioglycollate challenge in gp91(phox) deficient mice is attenuated by CGS21680. These data suggest that treatment with A(2A)R agonists may be an effective therapy by which to regulate the immune system hyperactivity that results from a gp91(phox) deficiency.

Regulatory T cells interfere with glutathione metabolism in dendritic cells and T cells

Naturally occurring CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) suppress proliferation of CD4(+)CD25(-) effector T cells (Teffs) by mechanisms that are not well understood. We have previously demonstrated a novel mechanism of Treg suppression, i.e. interference with extracellular redox remodeling that occurs during activation of T cells by dendritic cells. In this study, we demonstrate that Treg-mediated redox perturbation is antigen-dependent but not antigen-specific, is CTLA-4-dependent, and requires cell-cell contact. Furthermore, we show that Tregs use multiple strategies for extracellular redox remodeling, including diminished GSH synthesis in dendritic cells via decreased expression of γ-glutamylcysteine synthetase, the limiting enzyme for GSH synthesis. Tregs also consume extracellular cysteine and partition it more proficiently to the oxidation product (sulfate), whereas Teffs divert more of the cysteine pool toward protein and GSH synthesis. Tregs appear to block GSH redistribution from the nucleus to the cytoplasm in Teffs, which is abrogated by the addition of exogenous cysteine. Together, these data provide novel insights into modulation of sulfur-based redox metabolism by Tregs, leading to suppression of T cell activation and proliferation.

The metabolic life and times of a T-cell

SUMMARY

The regulation of lymphocyte homeostasis is critical for the development and formation of productive immune responses. Cell numbers must be maintained to allow sufficient numbers of lymphocytes to combat foreign pathogens but prevent the accumulation of excess lymphocytes that may increase the risk of developing autoimmunity or neoplasia. Cell extrinsic growth factors are essential to maintain homeostasis and cell survival, and it has become increasingly apparent that a key mechanism of this control is through regulation of cell metabolism. The metabolic state of T cells can have profound influences on cell growth and survival and even differentiation. In particular, resting T cells utilize an energy efficient oxidative metabolism but shift to a highly glycolytic metabolism when stimulated to grow and proliferate by pathogen encounter. After antigen clearance, T cells must return to a more quiescent oxidative metabolism to support T-cell memory. This review highlights how these metabolic changes may be intricately involved with both T-cell growth and death in the control of homeostasis and immunity.

The impact of redox and thiol status on the bone marrow: Pharmacological intervention strategies

Imbalances in cancer cell redox homeostasis provide a platform for new opportunities in the development of anticancer drugs. The control of severe dose-limiting toxicities associated with redox regulation, including myelosuppression and immunosuppression, remains a challenge. Recent evidence implicates a critical role for redox regulation and thiol balance in pathways that control myeloproliferation, hematopoietic progenitor cell mobilization, and immune response. Hematopoietic stem cell (HSC) self-renewal and differentiation are dependent upon levels of intracellular reactive oxygen species (ROS) and niche microenvironments. Redox status and the equilibrium of free thiol:disulfide couples are important in modulating immune response and lymphocyte activation, proliferation and differentiation. This subject matter is the focus of the present review. The potential of redox modulating chemotherapeutics as myeloproliferative and immunomodulatory agents is also covered.

The mammalian target of rapamycin: linking T cell differentiation, function, and metabolism

In the two-signal model of T cell activation, the outcome of antigen recognition is determined by the integration of multiple cues in the immune microenvironment. mTOR is an evolutionarily conserved PI3-kinase family member that plays a central role in integrating environmental cues in the form of amino acids, energy, and growth factors. Recently, an increasingly important role for mTOR in directing T cell activation and differentiation has become apparent. Here we review recent findings demonstrating the ability of mTOR to interpret signals in the immune microenvironment and program the generation of CD4(+) effector versus regulatory T cells, the generation of CD8(+) effector versus memory cells, T cell trafficking, and T cell activation versus anergy. The key theme to emerge from these studies is that the central role of mTOR provides a direct link between T cell metabolism and function.

Redox remodeling allows and controls B-cell activation and differentiation

During their differentiation to antibody-secreting plasma cells, B lymphocytes undergo dramatic changes in metabolism, structure, and function. Here we show that this transition entails extensive intra- and extracellular redox changes. Lipopolysaccharide (LPS)-driven activation and differentiation of naïve murine B splenocytes is paralleled by increased production of reactive oxygen species (ROS) from different sources, followed by a strong antioxidant response. This response includes upregulation of thioredoxin and of the cystine transporter xCT, and increased production and extracellular release of nonprotein thiols, mainly glutathione (GSH) and cysteine. Although ROS levels are higher in late-differentiating B cells, an early oxidative step is likely required to start the differentiation program, because inhibition of NADPH oxidase-dependent early ROS production impairs B-cell activation and differentiation. Addition of reducing agents such as 2-ME results in increased IgM secretion per cell, suggesting that the antioxidant response not only is aimed at restoring the redox homeostasis but also plays a functional role. A highly reduced environment coincident with the presence of large ROS-producing cells is observed in histologic sections of spleens from immunized mice, indicating that the redox modifications observed in LPS-induced B-cell differentiation in vitro occur also in vivo during physiologic immune responses.

Extracellular/microenvironmental redox state

Extracellular redox (reduction-oxidation) state is a factor that serves as an important regulator of cell-microenvironmental interactions and is determined by several known variables; including redox-modulating proteins that are located on the plasma membrane or outside of cells, extracellular thiol/disulfide couples, and reactive oxygen species (ROS)/reactive nitrogen species (RNS) that are capable of traveling across plasma membranes into the extracellular space. The extracellular redox state works in concert with the intracellular redox state to control both the influx and efflux of ROS/RNS that may serve to modulate redox signaling or to perturb normal cellular processes or both. Under physiologic conditions, the extracellular space is known to have a relatively more-oxidized redox state than the interior of the cell. During pathologic conditions, such as cancer, the extracellular redox state may be altered, causing specific proteins such as proteases, soluble factors, or the extracellular matrix to have altered functions or activities. Recent studies have strongly supported an important relation between the extracellular redox state and cancer cell aggressiveness. The purpose of this review is to identify redox buffer networks in extracellular spaces and to emphasize the possible roles of the extracellular redox state in cancer, knowledge that may contribute to potential therapeutic interventions.