Nitric oxide mediates apoptosis through formation of peroxynitrite and Fas/Fas-ligand interactions in experimental autoimmune uveitis

Accumulation of immunosuppressive CD11b+ myeloid cells correlates with the failure to prevent tumor growth in the anterior chamber of the eye

The purpose of these studies is to determine why an immunogenic tumor grows unchecked in the anterior chamber (a.c.) of the eye. The OVA-expressing EL4 tumor, E.G7-OVA, was injected into the a.c. or skin of immunocompetent and immunodeficient mice. Tumor growth and tumor-specific immune responses were monitored. Ocular tumor-infiltrating leukocytes were characterized phenotypically and functionally. Growth of E.G7-OVA was inhibited when limiting numbers of cells were injected in the skin but not in the a.c. of C57BL/6 mice, although both routes primed OVA-specific immune responses, which prevented the growth of a subsequent injection with E.G7-OVA in the skin or opposite eye. Tumor regression was OVA-specific because growth of the parental EL-4 tumor was not inhibited in primed mice. E.G7-OVA growth in the skin was not inhibited in immunodeficient Rag(-/-) or CD8 T cell-deficient mice, suggesting that CD8(+) CTLs mediate tumor elimination. CD8(+) T cell numbers were significantly increased in eyes of mice primed with E.G7-OVA, but few were detected in primary ocular tumors. Nevertheless, growth of E.G7-OVA was retarded in the a.c. of TCR-transgenic OT-I mice, and CD8(+) T cell numbers were increased within eyes, suggesting that tumor-specific CD8(+) CTLs migrated into and controlled primary ocular tumor growth. E.G7-OVA did not lose antigenicity or become immunosuppressive after 13 days of growth in the eye. However, CD11b(+) cells accumulated in primary ocular tumors and contained potent immunosuppressive activity when assayed in vitro. Thus, CD11b(+) cells that accumulate within the eye as tumors develop in the a.c. may contribute to immune evasion by primary ocular tumors by inhibiting CTLs within the eye.

Regulatory T cells control uveoretinitis induced by pathogenic Th1 cells reacting to a specific retinal neoantigen

In many clinical cases, uveitis develops secondary to an infection. This could result from peripheral activation followed by ocular penetration and reactivation of T cells specific for microbial Ags expressed in the retina. To gain insights into the pathophysiology of uveitis, we developed a new mouse model based on stable retinal expression of influenza virus hemagglutinin (HA) neoantigen by adeno-associated virus-mediated gene transfer. One month thereafter, we adoptively transferred HA-specific T cells, which were activated in vitro or in vivo. Intraocular inflammation was clinically and histologically observed in all animals within 15 days. The ocular infiltrate was composed mostly of macrophages and HA-specific T cells with a proinflammatory cytokine profile. Depletion of CD4(+)CD25(+) regulatory T cells exacerbated the disease, whereas HA-specific CD4(+)CD25(+) T cells given i.v. controlled the disease. This novel model should allow to better study the pathophysiology and therapeutic of uveitis.

Nitric oxide synthases are associated with bronchial dysplasia

Recent studies suggest that reactive oxygen (ROS) and nitrogen species (RNS) are highly associated with the pathogenesis of cigarette smoke related lung diseases but their role in the malignant conversion of bronchial epithelium is unclear. The immunohistochemical expression of inducible, endothelial and neuronal nitric oxide synthases (iNOS, eNOS and nNOS) and nitrotyrosine as a biomarker of oxidative/nitrosative stress was evaluated in 79 cases including 13 non-smokers, 20 smokers without chronic obstructive pulmonary disease (COPD), 22 with COPD and 24 with metaplasia-dysplasia-sequence of the bronchial epithelium. Normal lung of non-smokers was mainly negative for nitrotyrosine, while it was higher in the alveolar macrophages of cigarette smokers and COPD than in non-smokers (p=0.025, p<0.001), and in the alveolar epithelium of smokers and COPD than in non-smokers (p=0.049). There were no major differences in the nitrotyrosine immunoreactivity between the metaplastic/dysplastic lesions and bronchial epithelium of cigarette smokers. Inducible NOS and nNOS were mainly non-detectable or weak in the normal looking bronchial epithelium of smokers and COPD, whereas metaplasia and dysplasia showed positivity for iNOS (22/24) and nNOS (14/24) in the majority of cases. Strong immunoreactivity for iNOS and nNOS was also found more often in dysplastic than metaplastic (p=0.011 and p=0.049, respectively) specimens. Thus, smoking can cause protein nitration also in normal lung. Prominent iNOS and nNOS immunoreactivity in the metaplasia-dysplasia-lesions suggests a divergent role of NOSs in lung carcinogenesis.

A selective role for the TNF p55 receptor in autocrine signaling following IFN-gamma stimulation in experimental autoimmune uveoretinitis

IFN-gamma stimulates macrophage activation and NO production, which leads to destruction of the retina in experimental autoimmune uveoretinitis. In this study, we investigate the mechanism of disease resistance in TNF p55 receptor-deficient animals. We show that although T cell priming is relatively unaffected, macrophages lacking the TNF p55 receptor fail to produce NO following IFN-gamma stimulation because of a requirement for autocrine TNF-alpha signaling through the TNF p55 receptor. In contrast to the impaired activation of NO synthesis, MHC class II up-regulation was indistinguishable in wild-type and TNFRp55-/- mice stimulated with IFN-gamma. These defects could be overcome by stimulating macrophages with LPS. Together, these results show that selected aspects of IFN-gamma activation are controlled by autocrine secretion of TNF-alpha, but that this control is lost in the presence of signals generated by pathogen-associated molecular patterns recognizing receptors.

Evaluation of MRI for in vivo monitoring of retinal damage and detachment in experimental ocular inflammation

Two quantitative methods were developed for investigation of the potential of MRI for in vivo monitoring of retinal damage and detachment in experimental autoimmune uveitis (EAU). Measurements of retinal thickness and detachment area were performed on matched MR and histologic (HIST) images of rat eyes at different stages of EAU. In vivo MR images of rat eyes were acquired at 4.7 T using a figure-of-eight surface coil and a spin echo pulse sequence. Ex vivo measurements were performed on HIST images acquired using a digital camera attached to a microscope. MR images mirrored the HIST appearance of inflamed eyes at each stage of disease. Retinal detachments as small as 0.1 mm(2) were measured in vivo by MRI and confirmed in the same eye ex vivo by histology. Measurements performed on corresponding MR and HIST images demonstrated a good agreement between the two techniques. The potential of MRI for in vivo visualization and for monitoring changes in the eye during development of EAU was demonstrated in this study.

Enhanced tolerance to autoimmune uveitis in CD200-deficient mice correlates with a pronounced Th2 switch in response to antigen challenge

A single exposure to inhaled Ag 10 days before immunization leads to long term, Ag-specific tolerance. Respiratory tract myeloid APCs are implicated, but how regulation is invoked, and how tolerance is sustained are unclear. This study examines the in vivo function of the myeloid regulatory molecule CD200 in the process of tolerance induction. Despite earlier onset of experimental autoimmune uveitis in sham-tolerized, CD200-deficient mice, disease incidence and subsequent severity were actually reduced compared with those in wild-type mice. Protection was more effective and long term, lasting at least 28 days. Halting disease progression and tolerance in CD200(-/-) mice correlated with a marked increase in Th2-associated cytokine production by Ag-challenged splenocytes. Reduced overall disease and enhanced tolerance in the CD200-deficient mice in this model system were unexpected and may be related to altered populations of MHC class II(low) APC in the respiratory tract compared with wild-type mice together with associated activation of STAT6 in draining lymph nodes of tolerized mice. These data indicate that in the absence of default inhibitory CD200 receptor signaling, alternative, powerful regulatory mechanisms are invoked. This may represent either permissive dominant Th2 activation or an altered hierarchy of negative signaling by other myeloid cell-expressed regulatory molecules.

The role of tumour necrosis factor (TNF-alpha) in experimental autoimmune uveoretinitis (EAU)

The pleiotropic cytokine tumour necrosis factor-alpha (TNF-alpha) is released from cells that include macrophages and T-cells during inflammatory responses, orchestrating the initiation of further leucocytic infiltration via adhesion molecule upregulation, dendritic cell maturation and survival, macrophage activation and driving Th1 T-cells responses within tissues. Exposure to TNF also plays a role in maintaining tissue homeostasis, particularly relating to resident cell responses of both microglia and retinal pigment epithelium. Depending on the balance between duration and dose of TNF exposure, an environment where full expression of inflammatory and autoimmune responses within tissues may occur. In experimental autoimmune uveoretinitis (EAU), increased tissue concentrations of TNF facilitate the on-going T-cell effector responses and macrophage activation. These are responsible for targeted and bystander tissue damage and can be suppressed by anti-TNF therapies, in particular, those directed at the p55 TNF receptor. The ability to suppress disease experimentally has led to the successful translation of anti-TNF therapy for treatment of uveitis in cohort studies and phase I/II trials where, additionally, altered peripheral blood CD4(+) T-cell profiles can be demonstrated following each treatment.

Enhancement of apoptosis by nitric oxide released from α-phenyl-tert-butyl nitrone under hyperthermic conditions

The aim of this study was to examine whether a neuroprotector, PBN (alpha-phenyl-tert-butyl nitrone), enhances apoptosis induced by hyperthermia, which generates superoxide (O2-) intracellularly, since the release of nitric oxide (NO) from PBN under oxidative stress has been reported. When human myelomonocytic lymphoma U937 cells were treated with hyperthermia (44 degrees C, 10 min) and PBN, an increase in the concentration of nitrite in the culture medium, and a decrease in the hyperthermia-induced production of O2- was observed. Imaging using a fluorescence dye for intracellular NO, diaminofluorescein-2 diacetate (DAF-2 DA), revealed the formation of NO in the apoptotic cells treated with hyperthermia and PBN combined. Apoptotic endpoints were significantly enhanced by the combined treatment: a decrease in mitochondrial trans-membrane potential, cleavage of Bid, release of cytochrome c, and activation of caspase-8 and -3. An increase in the intracellular Ca2+ concentration ([Ca2+]i), externalization of Fas, and decrease in Hsp70 and phosphorylated HSF1 were observed following the combined treatment. Furthermore, scavengers of NO an d ONOO- significantly inhibited the enhancement of apoptosis, the externalization of Fas and the increase in [Ca2+]i. These results suggest that, (1) NO is released from PBN by hyperthermia, and subsequently reacts with O2- to form ONOO-, (2) NO and ONOO- are involved in the enhancement of apoptosis through Fas-mitochondria-caspase and [Ca2+]i-dependent pathways, and (3) a decrease in Hsp70 and phosphorylated HSF1 also contributed to the enhancement of apoptosis.

Retinal oxidative stress induced by high intraocular pressure

Glaucoma is an optic neuropathy in which retinal ganglion cells die probably through an apoptotic process. Apoptosis is known to involve free radicals in several systems including the retina. In this context, the aim of the present work was to analyze retinal oxidative damage in rats with glaucoma induced by the chronic injection of hyaluronic acid in the eye anterior chamber. The results showed a significant decrease in total retinal superoxide dismutase and catalase activities after 6 and 3 weeks of treatment with hyaluronic acid, respectively. Also, although GPX activity increased after 10 weeks of ocular hypertension, GSH levels significantly decreased at 6 weeks of treatment with hyaluronic acid. Moreover, retinal lipid peroxidation significantly increased in a time-of-hypertension-dependent manner. On the other hand, a significant decrease in both diurnal and nocturnal retinal melatonin content was detected at 3, 6, or 10 weeks of treatment with hyaluronic acid. The present results suggest that retinal oxidative stress may be involved in glaucomatous cell death. Thus, manipulation of intracellular redox status using antioxidants may be a new therapeutic tool to prevent glaucomatous neurodegeneration.

Signal transduction events in lung injury induced by 2-chloroethyl ethyl sulfide, a mustard analog

Sulfur mustard has been used as a vesicant chemical warfare agent. To understand the mechanism by which mustard gas exposure causes respiratory damage, we have used 2-chloroethyl ethyl sulfide (CEES) as a mustard analog. Our initial studies have shown that guinea pigs exposed to CEES intratracheally accumulate high levels of TNF-alpha. Accumulation of TNF-alpha leads to activation of both acid and neutral sphingomyelinases, resulting in high accumulation of ceramides, a second messenger involved in cell apoptosis. In addition, NF-kappa B was activated for a short period (1-2 h after exposure) as determined by mobility shift assay. Supershift assays indicated that both p50 and p65 of NF-kappa B were activated due to CEES exposure. However, NF-kappa B rapidly disappeared after 2 h. It is possible that the initial activation of NF-kappa B was an adaptive response to protect the cells from damage since NF-kappa B is known to inhibit TNF-alpha/ceramide-induced cell apoptosis. Since NF-kappa B disappeared after 2 h, the cells continued being damaged owing to accumulation of ceramides and activation of several caspases, leading to apoptosis.

Control of myeloid activity during retinal inflammation

Combating myeloid cell-mediated destruction of the retina during inflammation or neurodegeneration is dependent on the integrity of homeostatic mechanisms within the tissue that may suppress T cell activation and their subsequent cytokine responses, modulate infiltrating macrophage activation, and facilitate healthy tissue repair. Success is dependent on response of the resident myeloid-cell populations [microglia (MG)] to activation signals, commonly cytokines, and the control of infiltrating macrophage activation during inflammation, both of which appear highly programmed in normal and inflamed retina. The evidence that tissue CD200 constitutively provides down-regulatory signals to myeloid-derived cells via cognate CD200-CD200 receptor (R) interaction supports inherent tissue control of myeloid cell activation. In the retina, there is extensive neuronal and endothelial expression of CD200. Retinal MG in CD200 knockout mice display normal morphology but unlike the wild-type mice, are present in increased numbers and express nitric oxide synthase 2, a macrophage activation marker, inferring that loss of CD200 or absent CD200R ligation results in "classical" activation of myeloid cells. Thus, when mice lack CD200, they show increased susceptibility to and accelerated onset of tissue-specific autoimmunity.

Cutting edge: MHC class II-restricted peptides containing the inflammation-associated marker 3-nitrotyrosine evade central tolerance and elicit a robust cell-mediated immune response

Nitrotyrosine is widely recognized as a surrogate marker of up-regulated inducible NO synthase expression at sites of inflammation. However, the potential immunogenicity of autologous proteins containing nitrotyrosine has not previously been investigated. Herein, we used the I-E(K)-restricted T cell epitope of pigeon/moth cytochrome c (PCC/MCC(88-103)) to assess the ability of T cells to recognize ligands containing nitrotyrosine. Substitution of the single tyrosine (Y97) in PCC/MCC(88-103) with nitrotyrosine abrogates recognition by the MCC(88-103)-specific T cell hybridoma 2B4. CBA (H2(K)) mice immunized with MCC(88-103) or nitrated MCC(88-103) peptides produce T cell responses that are mutually exclusive. Transgenic mice that constitutively express PCC under the control of an MHC class I promoter are tolerant toward immunization with MCC(88-103), but exhibited a robust immune response against nitrated MCC(88-103). Analysis of T cell hybridomas specific for nitrated-MCC(88-103) indicated that subtle differences in TCR VDJ gene usage are sufficient to allow nitrotyrosine-specific T cells to escape the processes of central tolerance.

Macrophages induce apoptosis in proximal tubule cells

Macrophages play important roles during renal inflammation. Infiltrating macrophages produce proinflammatory mediators and induce apoptosis in a variety of target cells. Because proximal tubules are frequently damaged in inflammatory processes, we investigated murine macrophages (J774) in the induction of apoptosis in murine PKSV-PR proximal tubule cells. PKSV-PR cells were co-cultured with activated or non-activated macrophages. Apoptosis was assessed by Annexin-V-FITC/propidium iodide staining and analyzed by fluorescence-activated cell sorting. Macrophages were separated from tubule cells with transwell membranes to distinguish soluble factor-mediated from direct cell-to-cell contact-mediated apoptosis. Cell supernatants from activated and non-activated macrophages were analyzed for induction of apoptosis. Activated (but not non-activated) macrophages induced tubule cell apoptosis in co-culture. Soluble factors were mainly responsible for induction of apoptosis; membrane separation and transfer of cell supernatant from activated macrophages showed similar levels of apoptosis induction. Although tumor necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta(1), measured by ELISA, increased significantly in supernatants from activated macrophages, blocking TNF-alpha and TGF-beta did not decrease apoptosis in PKSV-PR cells co-cultured with macrophages. Moreover, exogenous addition of TNF-alpha, TGF-beta, anti-Fas antibody, or TRAIL failed to induce apoptosis in tubule cells. We conclude that inflammatory macrophages mediate proximal tubule cell death, directing apoptosis mainly via release of unidentified soluble factors.

Ethanol promotes T cell apoptosis through the mitochondrial pathway

Clinical reports suggest that acute ethanol intoxication is often associated with lymphopenia. Previously, ethanol was reported to invoke thymocyte apoptosis. We studied the effect of ethanol on T cell apoptosis. In addition, we evaluated the molecular mechanism of ethanol-induced T cell apoptosis. Human T cells harvested from healthy subjects after an alcohol drinking binge showed enhanced T cell apoptosis (before, 0.4 +/- 0.2% versus after, 19.6 +/- 2.5% apoptotic lymphocytes/field; P < 0.001). In in vitro studies, ethanol in a concentration of 50 mm and higher enhanced the apoptosis of Jurkat cells. DNA isolated from ethanol-treated Jurkat cells displayed integer multiples of 180 base pairs. Ethanol decreased Jurkat cell expression of Bcl-2, whereas ethanol increased Jurkat cell expression of Bax. Jurkat cells treated with ethanol also showed translocation of cytochrome C into cytosol. Moreover, a caspase-9 inhibitor partially inhibited ethanol-induced Jurkat cell apoptosis. In in vivo studies, after binge drinking, T cell expression of Bcl-2 also decreased. In addition, binge drinking induced the cleavage of caspase-3, suggesting activation of caspase-3 in T cells. These results suggest that ethanol promotes T cell apoptosis through the activation of intrinsic or mitochondrial pathway.

Constitutive retinal CD200 expression regulates resident microglia and activation state of inflammatory cells during experimental autoimmune uveoretinitis

Recent evidence supports the notion that tissue OX2 (CD200) constitutively provides down-regulatory signals to myeloid-lineage cells via CD200-receptor (CD200R). Thus, mice lacking CD200 (CD200(-/-)) show increased susceptibility to and accelerated onset of tissue-specific autoimmunity. In the retina there is extensive expression of CD200 on neurons and retinal vascular endothelium. We show here that retinal microglia in CD200(-/-) mice display normal morphology, but unlike microglia from wild-type CD200(+/+) mice are present in increased numbers and most significantly, express inducible nitric oxide synthase (NOS2), a macrophage activation marker. Onset and severity of uveitogenic peptide (1-20) of interphotoreceptor retinoid-binding protein-induced experimental autoimmune uveoretinitis is accelerated in CD200(-/-) mice and although tissue destruction appears no greater than seen in CD200(+/+) mice, there is continued increased ganglion and photoreceptor cell apoptosis. Myeloid cell infiltrate was increased in CD200(-/-) mice during experimental autoimmune uveoretinitis, although NOS2 expression was not heightened. The results indicate that the CD200:CD200R axis regulates retinal microglial activation. In CD200(-/-) mice the release of suppression of tonic macrophage activation, supported by increased NOS2 expression in the CD200(-/-) steady state accelerates disease onset but without any demonstration of increased target organ/tissue destruction.

Role of changes in tissular nucleotides on the development of apoptosis during ischemia/reperfusion in rat small bowel

The aim of this study was to evaluate whether xanthine and adenosine, substances modified proportionally to the duration of ischemia, can determine cell demise (apoptosis/necrosis) during intestinal ischemia/reperfusion (I/R) and to determine the role of nitric oxide (NO) during this process. The following experimental groups were studied: I, cold ischemia; I+X, effect of xanthine; I+T, effect of adenosine (blocking its receptor by theophylline); I+A, effect of excess adenosine; I+T+X, effect of xanthine alone, and I+T+ spermine NONOate (NONOs), I+A+NONOs, I+X+NONOs, role of NO. DNA fragmentation, xanthine/adenosine levels, caspase-3 activity, NO generation, and histological analysis were measured in tissue samples. The rats treated with xanthine or adenosine showed increased levels of caspase-3 activity and DNA fragmentation. In contrast, theophylline-treated rats showed decreased levels of DNA fragmentation and tended to show lower mean values of caspase-3 activity. Administration of xanthine or NONOs to theophylline-treated rats reversed these effects. The results of histological evaluation were in agreement with these previous results. In conclusion, the present study indicates that xanthine and adenosine induced an apoptotic response during cold ischemic preservation of rat small intestine. In particular, the action of adenosine on apoptotic events was mediated by NO. We consider that identification of the role of these factors may help to define the best conditions of tissue preservation before intestinal transplantation.