At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, how...

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Free Radicals in the Physiological Control of Cell Function

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

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Nitric Oxide and Peroxynitrite in Health and Disease

▪ Abstract Naturally occurring CD4+ regulatory T cells, the majority of which express CD25, are engaged in dominant control of self-reactive T cells, contributing to the maintenance of immunologic self-tolerance. Their depletion or functional alteration leads to the development of autoimmune disease in otherwise normal animals. The majority, if not all, of such CD25+CD4+ regulatory T cells are produced by the normal thymus as a functionally distinct and mature subpopulation of T cells. Their repertoire of antigen specificities is as broad as that of naive T cells, and they are capable of recognizing both self and nonself antigens, thus enabling them to control various immune responses. In addition to antigen recognition, signals through various accessory molecules and via cytokines control their activation, expansion, and survival, and tune their suppressive activity. Furthermore, the generation of CD25+CD4+ regulatory T cells in the immune system is at least in part developmentally and genetically contro...

Naturally Arising CD4+ Regulatory T Cells for Immunologic Self-Tolerance and Negative Control of Immune Responses

Authors Jan L. Brozek, MD, PhD – Department of Clinical Epidemiology & Biostatistics and Medicine, McMaster University, Hamilton, Canada Jean Bousquet, MD, PhD – Service des Maladies Respiratoires, Hopital Arnaud de Villeneuve, Montpellier, France, INSERM, CESP U1018, Respiratory and Environmental Epidemiology Team, France, and WHO Collaborating Center for Rhinitis and Asthma Carlos E. Baena-Cagnani, MD – Faculty of Medicine, Catholic University of Cordoba, Cordoba, Argentina Sergio Bonini, MD – Institute of Neurobiology and Molecular Medicine – CNR, Rome, Italy and Department of Medicine, Second University of Naples, Naples, Italy G. Walter Canonica, MD – Allergy & Respiratory Diseases, DIMI, Department of Internal Medicine, University of Genoa, Genoa, Italy Thomas B. Casale, MD – Division of Allergy and Immunology, Department of Medicine, Creighton University, Omaha, Nebraska, USA Roy Gerth van Wijk, MD, PhD – Section of Allergology, Department of Internal Medicine, Erasmus Medical Centre, Rotterdam, the Netherlands Ken Ohta, MD, PhD – Division of Respiratory Medicine and Allergology, Department of Medicine, Teikyo University School of Medicine, Tokyo, Japan Torsten Zuberbier, MD – Department of Dermatology and Allergy, Charite Universitatsmedizin Berlin, Berlin, Germany Holger J. Schunemann, MD, PhD, MSc – Department of Clinical Epidemiology & Biostatistics and Medicine, McMaster University, Hamilton, Canada

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Allergic Rhinitis and Its Impact on Asthma

T cell exhaustion is a state of T cell dysfunction that arises during many chronic infections and cancer. It is defined by poor effector function, sustained expression of inhibitory receptors and a transcriptional state distinct from that of functional effector or memory T cells. Exhaustion prevents optimal control of infection and tumors. Recently, a clearer picture of the functional and phenotypic profile of exhausted T cells has emerged and T cell exhaustion has been defined in many experimental and clinical settings. Although the pathways involved remain to be fully defined, advances in the molecular delineation of T cell exhaustion are clarifying the underlying causes of this state of differentiation and also suggest promising therapeutic opportunities.

T cell exhaustion

Regulation of immune system is of paramount importance to prevent immune attacks against self-components. Mice deficient in the interleukin (IL)-2/IL-15 receptor β chain, CD122, are model animals of such immune attacks and characteristically have a high number of abnormally activated T cells. Here, we show that the transfer of CD8+CD122+ cells into CD122-deficient neonates totally prevented the development of abnormal T cells. Furthermore, recombination activating gene–2−/− mice that received wild-type mice–derived CD8+CD122− cells died within 10 wk after cell transfer, indicating that normal CD8+CD122− cells become dangerously activated T cells in the absence of CD8+CD122+ T cells. CD8+CD122+ cells could control activated CD8+ or CD4+ T cells both in vivo and in vitro. Our results indicate that the CD8+CD122+ population includes naturally occurring CD8+ regulatory T cells that control potentially dangerous T cells.

https://rupress.org/jem/article-pdf/200/9/1123/1152212/jem20091123.pdf

Essential roles of CD8+CD122+ regulatory T cells in the maintenance of T cell homeostasis.

4-Hydroxynonenal (HNE), a diffusible product of lipid peroxidation, has been suggested to be a key mediator of oxidative stress-induced cell death. In this study, we partially characterized the mechanism of HNE-mediated cytotoxicity. Incubation of human T lymphoma Jurkat cells with 20-50 microM HNE led to cell death accompanied by DNA fragmentation. Western blot analysis showed that HNE-treatment induced time- and dose-dependent activation of caspase-8, caspase-9 and caspase-3. HNE-induced caspase-3 processing was confirmed by a flow cytometric demonstration of increased catalytic activity on the substrate peptide. HNE treatment also led to remarkable cleavage of poly(ADP-ribose) polymerase (PARP), which was prevented by pretreatment of cells with DEVD-FMK as a caspase-3 inhibitor. The HNE-mediated activation of caspases, cleavage of PARP and DNA fragmentation were blocked by antioxidants cysteine, N-acety-L-cysteine and dithiothreitol, but not by two other HNE-reactive amino acids lysine and histidine, or by cystine, the oxidized form of cysteine. HNE rapidly decreased levels of intracellular reduced glutathione (GSH) and its oxidized form GSSG, and these were also attenuated by the reductants. Coincubation of Jurkat cells with a blocking anti-Fas antibody prevented Fas-induced but not HNE-induced activation of caspase-3. HNE also activated caspase-3 in K562 cells that do not express functional Fas. Our results thereby demonstrate that HNE triggers oxidative stress-linked apoptotic cell death through activation of the caspase cascade. The results also suggest a possible mechanism involving a direct scavenge of intracellular GSH by HNE.

4-hydroxynonenal induces a cellular redox status-related activation of the caspase cascade for apoptotic cell death.

We report here on a novel metallothionein-I (MT)/ret transgenic mouse line in which skin melanosis, benign melanocytic tumor and malignant melanoma metastasizing to distant organs develop stepwise. The process of tumor development and its malignant transformation in this line may resemble that of the human giant congenital melanocytic nevus that is present at birth and that frequently gives rise to malignant melanoma during aging. We observed an increase in the expression level and activity of the ret transgene during the disease progression. That increase in transgene expression accompanied an activation of mitogen-activated protein kinases (MAPKs) and c-Jun as well as matrix metalloproteinases. These results suggest that progressive dysregulation of the expression level of the ret transgene might play a crucial role in the malignant transformation of melanocytic tumors developed in the MT/ret transgenic mouse line.

Transgenic mouse model for skin malignant melanoma

Eighty-two Klebsiella O1 strains belonging to various K types were tested for virulence for mice by intraperitoneal inoculation. They comprised 49 strains newly isolated from various clinical specimens, 31 reference strains, and 2 laboratory strains. Of 9 Klebsiella O1:K2 strains, 7 were highly virulent inasmuch as their 50% lethal doses per mouse were less than 10 CFU, whereas the other 2 strains were avirulent even when encapsulated just like the virulent strains as revealed by the quellung test. Klebsiella K2 reference strain B5055 and strain Chedid, which were maintained in vitro for a long time, were highly virulent. Of 8 Klebsiella O1:K1 strains, 2 showed moderate virulence, and the other 6 strains had relatively low or no virulence. We found no definite correlation between the virulence of Klebsiella K1 and K2 strains for mice and the kind of clinical specimens in which they originated. All of the Klebsiella O1 strains tested belonging to K types other than K1 and K2 showed very low or no virulence for mice.

https://iai.asm.org/content/iai/40/1/56.full.pdf

Virulence for mice of Klebsiella strains belonging to the O1 group: relationship to their capsular (K) types.

We demonstrated that products of the L-arginine-dependent pathway of human alveolar macrophages (AM) effectively kill the Mycobacterium bovis bacillus Calmette-Guerin (BCG) in vitro. The formation of products was triggered by inoculation with BCG itself. Many reports have shown that activated rodent AM could produce an amount of nitric oxide (NO) sufficient to suppress the growth of mycobacteria. However, there have been no definitive results as to whether human AM might have the NO-dependent mechanism for the killing of mycobacteria. Therefore, we have undertaken some experiments to answer this question. Immunofluorescence assays showed an increased production of inducible nitric oxide synthase (iNOS) and peroxynitrite in BCG-inoculated AM from patients with pulmonary fibrosis. Reverse transcriptase-PCR also revealed the higher expression of iNOS-coding mRNA. Colony assays demonstrated that these human AM effectively killed BCG in their cytoplasm. However, treatment of AM with N(G)-monomethyl-L-arginine monoacetate resulted in markedly reduced killing activity. These results clearly show that BCG-induced NO and its reactive product with the oxygen radical peroxynitrite could play an important role in the killing of BCG in human AM.

Izumi Nakashima

Papers

Essential roles of CD8+CD122+ regulatory T cells in the maintenance of T cell homeostasis.

4-hydroxynonenal induces a cellular redox status-related activation of the caspase cascade for apoptotic cell death.

Transgenic mouse model for skin malignant melanoma

Virulence for mice of Klebsiella strains belonging to the O1 group: relationship to their capsular (K) types.

Mechanism of nitric oxide-dependent killing of Mycobacterium bovis BCG in human alveolar macrophages.