RESUMEN
Viral infections can be fatal because of the direct cytopathic effects of the virus or the induction of a strong, uncontrolled inflammatory response. Virus and host intrinsic characteristics strongly modulate the outcome of viral infections. Recently we determined the circumstances under which enhanced replication of virus within the lymphoid tissue is beneficial for the outcome of a disease. This enforced viral replication promotes anti-viral immune activation and, counterintuitively, accelerates virus control. In this review we summarize the mechanisms that contribute to enforced viral replication. Antigen-presenting cells and CD169+ macrophages exhibit enforced viral replication after infection with the model viruses lymphocytic choriomeningitis virus (LCMV) and vesicular stomatitis virus (VSV). Ubiquitin-specific peptidase 18 (Usp18), an endogenous type I interferon blocker in CD169+ macrophages, has been identified as a proviral gene, as are B cell activating factor (BAFF) and carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1). Lymphotoxins (LT) strongly enhance viral replication in the spleen and lymph nodes. All these factors modulate splenic architecture and thereby promote the development of CD169+ macrophages. Tumor necrosis factor alpha (TNF-α) and nuclear factor kappa-light-chain-enhancer of activated B cell signaling (NF-κB) have been found to promote the survival of infected CD169+ macrophages, thereby similarly promoting enforced viral replication. Association of autoimmune disease with infections is evident from (1) autoimmune phenomena described during a chronic virus infection; (2) onset of autoimmune disease simultaneous to viral infections; and (3) experimental evidence. Involvement of virus infection during onset of type I diabetes is strongly evident. Epstein-Bar virus (EBV) infection was discussed to be involved in the pathogenesis of systemic lupus erythematosus. In conclusion, several mechanisms promote viral replication in secondary lymphatic organs. Identifying such factors in humans is a challenge for future studies.
Asunto(s)
Diabetes Mellitus Tipo 1/inmunología , Lupus Eritematoso Sistémico/inmunología , Sistema Linfático/inmunología , Virus de la Coriomeningitis Linfocítica/fisiología , Vesiculovirus/fisiología , Virosis/inmunología , Replicación Viral , Animales , Diabetes Mellitus Tipo 1/virología , Herpesvirus Humano 4 , Interacciones Huésped-Patógeno , Humanos , Lupus Eritematoso Sistémico/virología , Sistema Linfático/virología , Especificidad de Órganos , Virosis/virologíaRESUMEN
The innate immune system limits virus replication during systemic infection by producing type I interferons (IFN-I) but still has to allow viral replication to achieve maximal innate and adaptive immune activation. Some spleen and lymph node resident antigen presenting cells (APCs) show limited response to IFN-I due to expression of the endogenous inhibitor of IFN-I signaling, Usp18. Therefore, virus in this spleen niche replicates despite high levels of IFN-I. This enforced viral replication leads to an exorbitant propagation of viral antigens and viral RNA. Viral antigen leads to massive activation of the adaptive immune system, while viral RNA to activated innate immunity. In contrast to these APCs, liver resident Kupffer cells, take up most of the systemic virus and suppress its replication in response to IFN-I. In addition, virus specific CD8â+ T cells which are primed in the spleen migrate to the liver and kill virus infected cells. In this review we discuss the different mechanisms, which influence immune activation in spleen and antiviral mechanisms in the liver and how they determine the outcome of virus infection.
Asunto(s)
Interferón Tipo I/inmunología , Hígado/virología , Bazo/virología , Virosis/inmunología , Virosis/virología , Replicación Viral/inmunología , Animales , Humanos , Inmunidad Innata/inmunología , Hígado/inmunología , Modelos Inmunológicos , Bazo/inmunologíaRESUMEN
In virtually all cells including hepatocytes cell volume regulation is accomplished during cell swelling by cellular ion release (activation of K (+) channels and/or anion channels, KCl-cotransport, parallel activation of K (+)/H (+) exchange and Cl (-)/HCO (3)(-) exchange) and following cell shrinkage by cellular ion uptake (activation of Na (+), K (+), 2Cl (-) cotransport, Na (+)/H (+) exchange in parallel to Cl (-)/HCO (3)(-) exchange and Na (+)-channels). Moreover, cell shrinkage triggers the cellular accumulation of organic osmolytes (e. g., myoinositol, betaine, phosphorylcholine, taurine). Cell volume is a powerful regulator of hepatic metabolism. Cell shrinkage stimulates and cell swelling inhibits proteolysis and glycogenolysis. Moreover, cell volume influences the generation of and sensitivity to oxidants. Cell volume regulatory mechanisms furthermore do play a role in fibrosing disease. Kinases stimulating cell volume regulatory mechanisms include the serum and glucocorticoid inducible kinase SGK1, which is expressed in the liver, is genomically up-regulated by cell shrinkage, stimulates a wide variety of channels and transporters including Na (+), K (+), 2Cl (-) cotransport and Na (+)/H (+) exchange and is known to participate in the stimulation of fibrosis. Accordingly, excessive SGK1 expression is observed in liver cirrhosis. The case is made that SGK1 participates in the regulation of liver cell volume and thus in the regulation of hepatic metabolism.
Asunto(s)
Tamaño de la Célula , Hepatocitos/citología , Hepatocitos/fisiología , Proteínas Inmediatas-Precoces/metabolismo , Hígado/citología , Hígado/metabolismo , Modelos Biológicos , Proteínas Serina-Treonina Quinasas/metabolismo , Equilibrio Hidroelectrolítico/fisiología , Animales , HumanosRESUMEN
Autoimmune disease is characterized by clinical symptoms mediated by adaptive (T cell and B cell) immune reactions towards autoantigen-expressing tissue. Here we discuss that autoimmune disease is often preceded by autoreactivity, meaning the priming of autoantigen-specific immune cells without relevant tissue damage. Recent experimental evidence has demonstrated that both the induction of autoreactivity and the conversion into autoimmune disease is controlled by the activation of the nonspecific innate immune system. Also, the "inflammatory status" of the target organ critically influences the onset of overt autoimmune disease.
Asunto(s)
Enfermedades Autoinmunes/etiología , Inmunidad Innata , Animales , Enfermedades Autoinmunes/inmunología , Autoinmunidad , Humanos , Infecciones/inmunología , Interferones/fisiología , Sistema Nervioso/inmunología , Transducción de Señal , Linfocitos T Reguladores/fisiología , Receptores Toll-Like/fisiologíaRESUMEN
Regulatory T cells (Tregs) are crucial for the maintenance of immunological self-tolerance and their absence or dysfunction can lead to autoimmunity. However, the molecular pathways that govern Treg biology remain obscure. In this study, we show that the nuclear factor-κB signalling mediator mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is an important novel regulator of both Tregs originating in the thymus ('natural' or nTregs) and Tregs induced to differentiate from naive thymocyte helper (Th) cells in the periphery ('induced' or iTregs). Our examination of mice deficient for MALT1 revealed that these mutants have a reduced number of total Tregs. In young Malt1-/- mice, nTregs are totally absent and iTreg are diminished in the periphery. Interestingly, total Treg numbers increase in older Malt1-/- mice as well as in Malt1-/- mice subjected to experimentally induced inflammation. iTregs isolated from WT and Malt1-/- mice were indistinguishable with respect to their ability to suppress the activities of effector T cells, but Malt1-/- iTregs expressed higher levels of Toll-like receptor (TLR) 2. Treatment of WT and Malt1-/- Th cells in vitro with the TLR2 ligand Pam3Cys strongly enhanced the induction and proliferation of Malt1-/- iTregs. Our data suggest that MALT1 supports nTreg development in the thymus but suppresses iTreg induction in the periphery during inflammation. Our data position MALT1 as a key molecule that contributes to immune tolerance at steady-state while facilitating immune reactivity under stress conditions.
Asunto(s)
Proteína 1 de la Translocación del Linfoma del Tejido Linfático Asociado a Mucosas/metabolismo , Linfocitos T Reguladores/metabolismo , Animales , Diferenciación Celular , Proliferación Celular , Encefalomielitis Autoinmune Experimental/inmunología , Encefalomielitis Autoinmune Experimental/patología , Inflamación/patología , Ratones Endogámicos C57BL , Proteína 1 de la Translocación del Linfoma del Tejido Linfático Asociado a Mucosas/deficiencia , Receptor Toll-Like 2/metabolismoRESUMEN
BACKGROUND: Sphingolipids are signaling molecules in a range of biological processes. While sphingosine-1-phosphate (S1P) is thought to be abundantly stored in platelets and released upon stimulation, knowledge about the distribution and function of other sphingolipids in blood is lacking. OBJECTIVES: To analyze the sphingolipid content of blood components with special emphasis on dynamic changes in platelets. METHODS: Blood components from mice and humans were prepared by gradient centrifugation and analyzed by liquid chromatography-mass spectrometry. Additionally, murine platelets were activated in vitro and in vivo. RESULTS: Isolated non-activated platelets of mice were devoid of S1P, but instead contained dihydrosphingosine-1-phosphate (dhS1P), along with a high concentration of ceramide. Activation of platelets in vitro led to a loss of dhS1P and an increase in sphingosine, accompanied by a reduction of ceramide content. Platelet activation in vivo led to an immediate and continuous rise of dhS1P in plasma, while S1P remained stable. The sphingolipid distribution of human blood was markedly different from mice. Human platelets contained dhS1P in addition to S1P. CONCLUSIONS: Mouse platelets contain dhS1P instead of S1P. Platelet activation causes loss of dhS1P and breakdown of ceramide, implying ceramidase activation. Release of dhS1P from activated platelets might be a novel signaling pathway. Finally, the sphingolipid composition of mouse and human blood shows large differences, which must be considered when studying sphingolipid biology.
Asunto(s)
Plaquetas/metabolismo , Activación Plaquetaria , Esfingolípidos/sangre , Animales , Anticuerpos , Plaquetas/efectos de los fármacos , Plaquetas/inmunología , Separación Celular , Ceramidas/sangre , Cromatografía Liquida , Eritrocitos/química , Citometría de Flujo , Humanos , Técnicas In Vitro , Leucocitos/química , Lisofosfolípidos/sangre , Ratones , Ratones Endogámicos BALB C , Activación Plaquetaria/efectos de los fármacos , Activación Plaquetaria/inmunología , Glicoproteína IIb de Membrana Plaquetaria/inmunología , Especificidad de la Especie , Espectrometría de Masa por Ionización de Electrospray , Esfingolípidos/metabolismo , Esfingosina/análogos & derivados , Esfingosina/sangre , Trombina/farmacologíaRESUMEN
Inflammatory bowel disease (IBD) is characterized by chronic, uncontrolled inflammation in the intestinal mucosa. Although the etiology is poorly understood, it is widely accepted that loss of tolerance is involved in the development of IBD. Therefore, re-establishing tolerance or gut homeostasis is one of the key features in the development of new therapeutic strategies. Here we show that antigen targeting to DEC-205 on dendritic cells leads to an interleukin (IL)-10-dependent downregulation of C-X-C chemokine receptor 3 (CXCR3) expression on differentiated antigen-specific T helper type 1 (Th1) cells in vivo. This downregulation interferes with the migration of Th1 cells into the gut and protects mice against severe acute and relapsing intestinal inflammation. Moreover, CD4(+)CXCR3(+) T cells are highly enriched in the inflamed mucosa of IBD patients. Interference with this pathway may therefore be a promising approach for the treatment of IBD. In conclusion, we propose a hitherto undescribed mechanism by which IL-10 can act on effector T cells and orchestrate intestinal immune responses.
Asunto(s)
Antígenos CD/inmunología , Colitis Ulcerosa/inmunología , Enfermedad de Crohn/inmunología , Interleucina-10/inmunología , Lectinas Tipo C/inmunología , Antígenos de Histocompatibilidad Menor/inmunología , Receptores CXCR3/inmunología , Receptores de Superficie Celular/inmunología , Células TH1/inmunología , Animales , Antígenos CD/genética , Antígenos CD4/genética , Antígenos CD4/inmunología , Movimiento Celular , Colitis Ulcerosa/genética , Colitis Ulcerosa/patología , Enfermedad de Crohn/genética , Enfermedad de Crohn/patología , Células Dendríticas/inmunología , Células Dendríticas/patología , Regulación de la Expresión Génica , Humanos , Tolerancia Inmunológica , Interleucina-10/genética , Mucosa Intestinal/inmunología , Mucosa Intestinal/patología , Lectinas Tipo C/genética , Ratones , Ratones Endogámicos BALB C , Ratones Transgénicos , Antígenos de Histocompatibilidad Menor/genética , Receptores CXCR3/genética , Receptores de Superficie Celular/genética , Transducción de Señal , Células TH1/patologíaRESUMEN
Erythrocytes are devoid of mitochondria and nuclei and were considered unable to undergo apoptosis. As shown recently, however, the Ca(2+)-ionophore ionomycin triggers breakdown of phosphatidylserine asymmetry (leading to annexin binding), membrane blebbing and shrinkage of erythrocytes, features typical for apoptosis in nucleated cells. In the present study, the effects of osmotic shrinkage and oxidative stress, well-known triggers of apoptosis in nucleated cells, were studied. Exposure to 850 mOsm for 24 h, to tert-butyl-hydroperoxide (1 mM) for 15 min, or to glucose-free medium for 48 h, all elicit erythrocyte shrinkage and annexin binding, both sequelae being blunted by removal of extracellular Ca(2+) and mimicked by ionomycin (1 microM). Osmotic shrinkage and oxidative stress activate Ca(2+)-permeable cation channels and increase cytosolic Ca(2+) concentration. The channels are inhibited by amiloride (1 mM), which further blunts annexin binding following osmotic shock, oxidative stress and glucose depletion. In conclusion, osmotic and oxidative stress open Ca(2+)-permeable cation channels in erythrocytes, thus increasing cytosolic Ca(2+) activity and triggering erythrocyte apoptosis.
Asunto(s)
Apoptosis/efectos de los fármacos , Cationes/metabolismo , Eritrocitos/fisiología , Canales Iónicos/fisiología , Estrés Oxidativo/fisiología , Amilorida/farmacología , Anexinas/metabolismo , Apoptosis/fisiología , Calcio/farmacocinética , Recuento de Células , Tamaño de la Célula/efectos de los fármacos , Citosol/química , Citosol/efectos de los fármacos , Eritrocitos/citología , Eritrocitos/efectos de los fármacos , Eritrocitos/metabolismo , Glucosa/metabolismo , Humanos , Canales Iónicos/antagonistas & inhibidores , Ionomicina/farmacología , Ionóforos/farmacología , Presión Osmótica/efectos de los fármacos , Técnicas de Placa-Clamp , terc-Butilhidroperóxido/farmacologíaRESUMEN
Erythrocytes lack nuclei and mitochondria, the organelles important for apoptosis of nucleated cells. However, following increase of cytosolic Ca(2+) activity, erythrocytes undergo cell shrinkage, cell membrane blebbing and breakdown of phosphatidylserine asymmetry, all features typical for apoptosis in nucleated cells. The same events are observed following osmotic shock, an effect mediated in part by activation of Ca(2+)-permeable cation channels. However, erythrocyte death following osmotic shock is blunted but not prevented in the absence of extracellular Ca(2+) pointing to additional mechanisms. As shown in this study, osmotic shock (950 mOsm) triggers sphingomyelin breakdown and formation of ceramide. The stimulation of annexin binding following osmotic shock is mimicked by addition of ceramide or purified sphingomyelinase and significantly blunted by genetic (aSM-deficient mice) or pharmacologic (50 microM 3,4-dichloroisocoumarin) knockout of sphingomyelinase. The effect of ceramide is blunted but not abolished in the absence of Ca(2+). Conversely, osmotic shock-induced annexin binding is potentiated in the presence of sublethal concentrations of ceramide. In conclusion, ceramide and Ca(2+) entry through cation channels concert to trigger erythrocyte death during osmotic shock.
Asunto(s)
Ceramidas/metabolismo , Eritrocitos/citología , Eritrocitos/metabolismo , Animales , Anexinas/metabolismo , Calcio/metabolismo , Caspasas/metabolismo , Muerte Celular/efectos de los fármacos , Tamaño de la Célula/efectos de los fármacos , Ceramidas/biosíntesis , Ceramidas/farmacología , Cumarinas/farmacología , Eritrocitos/efectos de los fármacos , Fumonisinas/farmacología , Humanos , Ionomicina/farmacología , Isocumarinas , Ratones , Ratones Noqueados , Presión Osmótica/efectos de los fármacos , Unión Proteica/efectos de los fármacos , Esfingomielina Fosfodiesterasa/antagonistas & inhibidores , Esfingomielina Fosfodiesterasa/genética , Esfingomielina Fosfodiesterasa/metabolismo , Esfingomielinas/metabolismoRESUMEN
During virus infection and autoimmune disease, inflammatory dendritic cells (iDCs) differentiate from blood monocytes and infiltrate infected tissue. Following acute infection with hepatotropic viruses, iDCs are essential for re-stimulating virus-specific CD8(+) T cells and therefore contribute to virus control. Here we used the lymphocytic choriomeningitis virus (LCMV) model system to identify novel signals, which influence the recruitment and activation of iDCs in the liver. We observed that intrinsic expression of Toso (Faim3, FcµR) influenced the differentiation and activation of iDCs in vivo and DCs in vitro. Lack of iDCs in Toso-deficient (Toso(-/-)) mice reduced CD8(+) T-cell function in the liver and resulted in virus persistence. Furthermore, Toso(-/-) DCs failed to induce autoimmune diabetes in the rat insulin promoter-glycoprotein (RIP-GP) autoimmune diabetes model. In conclusion, we found that Toso has an essential role in the differentiation and maturation of iDCs, a process that is required for the control of persistence-prone virus infection.
Asunto(s)
Proteínas Portadoras/inmunología , Diferenciación Celular/inmunología , Células Dendríticas/inmunología , Coriomeningitis Linfocítica/inmunología , Virus de la Coriomeningitis Linfocítica/inmunología , Proteínas de la Membrana/inmunología , Animales , Linfocitos T CD8-positivos/inmunología , Proteínas Portadoras/genética , Diferenciación Celular/genética , Células Dendríticas/patología , Diabetes Mellitus Experimental/genética , Diabetes Mellitus Experimental/inmunología , Diabetes Mellitus Experimental/patología , Inmunidad Celular , Inflamación/genética , Inflamación/inmunología , Inflamación/patología , Hígado/inmunología , Hígado/patología , Coriomeningitis Linfocítica/genética , Coriomeningitis Linfocítica/patología , Proteínas de la Membrana/genética , Ratones , Ratones Noqueados , RatasRESUMEN
Vitiligo is a skin and hair disorder characterized by circumscribed depigmented lesions due to lack of melanocytes in the respective areas. It has been suggested that vitiligo is caused by an autoimmune-mediated destruction of melanocytes. Recently, the presence of a high frequency of skin-homing melanocyte-specific cytotoxic T lymphocytes in the peripheral blood of patients with vitiligo was reported. Our study examines the frequency of melanocyte-specific cytotoxic T lymphocytes in vitiligo patients and its relationship to disease activity. Thirty-two patients with moderate to active vitiligo and 17 control subjects were included. Melanocyte specific reactive CD8(+) T cells were identified by enzyme-linked immunospot assay after stimulation with five peptides from gp100, four peptides from MelanA/MART1, and two peptides from tyrosinase. In selected patients, intracellular interferon-gamma staining for the detection of specific reactive CD8(+) T cells was additionally performed. In seven of 10 patients (70%) with actively progressive disease CD8(+) T cells directed against melanocyte epitopes were detected, whereas only in four of 22 patients (18%) with moderate disease activity such specific reactivity was found. MelanA/MART1 peptides were immunodominant in nine patients reacting against EAAGIGILTV and three patients reacting against ILTVILGVL. Intracellular interferon-gamma staining confirmed the findings obtained by the enzyme-linked immunospot technique. The present study supports the hypothesis that vitiligo is a cytotoxic T lymphocyte-mediated autoimmune disease. The presence of melanocyte-specific reactive CD8(+) T cells seems to be closely related to disease activity.
Asunto(s)
Linfocitos T CD8-positivos/inmunología , Antígeno HLA-A2/inmunología , Melanocitos/inmunología , Vitíligo/inmunología , Adulto , Anciano , Antígenos de Diferenciación de Linfocitos T , Antígenos de Neoplasias , Femenino , Humanos , Interferón gamma/biosíntesis , Antígeno MART-1 , Masculino , Glicoproteínas de Membrana/análisis , Persona de Mediana Edad , Proteínas de NeoplasiasRESUMEN
Even though lacking mitochondria and nuclei erythrocytes do undergo apoptotic cell death which is characterized by breakdown of phosphatidylserine asymmetry (leading to annexin binding), membrane blebbing and cell shrinkage. Previously, we have shown that erythrocyte apoptosis is triggered by osmotic shrinkage at least in part through activation of cell volume-sensitive cation channels and subsequent Ca2+ entry. The channels could not only be activated by cell shrinkage but as well by replacement of Cl- with gluconate. Both, channel activity and annexin binding were sensitive to high concentrations of amiloride (1 mM). The present study has been performed to search for more effective blockers. To this end channel activity has been evaluated utilizing whole-cell patch-clamp and annexin binding determined by FACS analysis as an indicator of erythrocyte apoptosis. It is shown that either, increase of osmolarity or replacement of Cl- by gluconate triggers the activation of the cation channel which is inhibited by amiloride at 1 mM but not at 100 microM. Surprisingly, the cation channel was significantly more sensitive to the amiloride analogue ethylisopropylamiloride (EIPA, IC(50)=0.6+/-0.1 microM, n=5). Exposure of the cells to osmotic shock by addition of sucrose (850 mOsm) led to stimulation of annexin binding which was inhibited similarly by EIPA (IC(50)=0.2+/-0.2 microM, n=4). Moreover, annexin binding was inhibited by higher concentrations of HOE 642 (IC(50)=10+/-5 microM, n=5) and HOE 694 (IC(50)=12+/-6 microM, n=4). It is concluded that osmotic shock stimulates a cation channel which participates in the triggering of erythrocyte apoptosis. EIPA is an effective inhibitor of this cation channel and of channel mediated triggering of erythrocyte apoptosis.
Asunto(s)
Amilorida/análogos & derivados , Amilorida/farmacología , Apoptosis/efectos de los fármacos , Eritrocitos/fisiología , Canales Iónicos/antagonistas & inhibidores , Amilorida/administración & dosificación , Anexinas/metabolismo , Apoptosis/fisiología , Cationes/metabolismo , Tamaño de la Célula/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Eritrocitos/citología , Eritrocitos/metabolismo , Guanidinas/farmacología , Humanos , Técnicas In Vitro , Canales Iónicos/metabolismo , Canales Iónicos/fisiología , Presión Osmótica/efectos de los fármacos , Técnicas de Placa-Clamp , Sulfonas/farmacologíaRESUMEN
The efficacy of immune surveillance and antigen-specific cancer immunotherapy equally depends on the activation of a sustained immune response targeting cancer antigens and the susceptibility of cancer cells to immune effector mechanisms. Using functional expression cloning and T-cell receptor (TCR) transgenic mice, we have identified cyclooxygenase 2/prostaglandin-endoperoxide synthase 2 (COX-2) as resistance factor against the cytotoxicity induced by activated, antigen-specific T cells. Expressing COX-2, but not a catalytically inactive COX-2 mutant, increased the clonogenic survival of E1A-transformed murine cancer cells when cocultured with lymphocytes from St42Rag2(-/-) mice harboring a transgenic TCR directed against an E1A epitope. COX-2 expressing tumors established in immune-deficient mice were less susceptible to adoptive immunotherapy with TCR transgenic lymphocytes in vivo. Also, immune surveillance of COX-2-positive tumor cells in TCR transgenic mice was less efficient. The growth of murine MC-GP tumors, which show high endogenous COX-2 expression, in immunocompetent mice was effectively suppressed by treatment with a selective COX-2 inhibitor, celecoxib. Mechanistically, COX-2 expression blunted the interferon-gamma release of antigen-specific T cells exposed to their respective cellular targets, and increased the expression of interleukin-4 and indoleamine 2,3-dioxygenase by tumor cells. Addition of interferon-gamma sensitized COX-2 expressing cancer cells to tumor suppression by antigen-specific T cells. In conclusion, COX-2, which is frequently induced in colorectal cancer, contributes to immune evasion and resistance to antigen-specific cancer immunotherapy by local suppression of T-cell effector functions.
Asunto(s)
Linfocitos T CD8-positivos/inmunología , Ciclooxigenasa 2/inmunología , Neoplasias/enzimología , Neoplasias/inmunología , Animales , Ciclooxigenasa 2/genética , Citotoxicidad Inmunológica , Humanos , Inmunoterapia Adoptiva , Indolamina-Pirrol 2,3,-Dioxigenasa/inmunología , Interferón gamma/inmunología , Interleucina-4/inmunología , Ratones , Ratones Endogámicos C57BL , Ratones SCID , Ratones Transgénicos , Neoplasias/genética , Neoplasias/terapia , Receptores de Antígenos de Linfocitos T/genética , Receptores de Antígenos de Linfocitos T/inmunología , Especificidad de la EspecieRESUMEN
CD8(+) T-cell functions are critical for preventing chronic viral infections by eliminating infected cells. For healthy immune responses, beneficial destruction of infected cells must be balanced against immunopathology resulting from collateral damage to tissues. These processes are regulated by factors controlling CD8(+) T-cell function, which are still incompletely understood. Here, we show that the interferon regulatory factor 4 (IRF4) and its cooperating binding partner B-cell-activating transcription factor (BATF) are necessary for sustained CD8(+) T-cell effector function. Although Irf4(-/-) CD8(+) T cells were initially capable of proliferation, IRF4 deficiency resulted in limited CD8(+) T-cell responses after infection with the lymphocytic choriomeningitis virus. Consequently, Irf4(-/-) mice established chronic infections, but were protected from fatal immunopathology. Absence of BATF also resulted in reduced CD8(+) T-cell function, limited immunopathology, and promotion of viral persistence. These data identify the transcription factors IRF4 and BATF as major regulators of antiviral cytotoxic T-cell immunity.
Asunto(s)
Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/fisiología , Linfocitos T CD8-positivos/fisiología , Factores Reguladores del Interferón/fisiología , Virus de la Coriomeningitis Linfocítica/inmunología , Animales , Apoptosis , Linfocitos T CD8-positivos/virología , Células Cultivadas , Citotoxicidad Inmunológica , Memoria Inmunológica , Activación de Linfocitos , Ratones Endogámicos C57BL , Ratones NoqueadosRESUMEN
Cluster of differentiation (CD)8(+) T cells are like a double edged sword during chronic viral infections because they not only promote virus elimination but also induce virus-mediated immunopathology. Elevated levels of reactive oxygen species (ROS) have been reported during virus infections. However, the role of ROS in T-cell-mediated immunopathology remains unclear. Here we used the murine lymphocytic choriomeningitis virus to explore the role of ROS during the processes of virus elimination and induction of immunopathology. We found that virus infection led to elevated levels of ROS producing granulocytes and macrophages in virus-infected liver and spleen tissues that were triggered by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Lack of the regulatory subunit p47phox of the NADPH oxidase diminished ROS production in these cells. While CD8(+) T cells exhibited ROS production that was independent of NADPH oxidase expression, survival and T-cell function was elevated in p47phox-deficient (Ncf1(-/-)) mice. In the absence of p47phox, enhanced T-cell immunity promoted virus elimination and blunted corresponding immunopathology. In conclusion, we find that NADPH-mediated production of ROS critically impairs the immune response, impacting elimination of virus and outcome of liver cell damage.
Asunto(s)
Virus de la Coriomeningitis Linfocítica/fisiología , Especies Reactivas de Oxígeno/metabolismo , Animales , Butionina Sulfoximina/farmacología , Linfocitos T CD8-positivos/citología , Linfocitos T CD8-positivos/efectos de los fármacos , Linfocitos T CD8-positivos/inmunología , Supervivencia Celular , Células Cultivadas , Modelos Animales de Enfermedad , Glutatión/metabolismo , Hígado/metabolismo , Coriomeningitis Linfocítica/patología , Coriomeningitis Linfocítica/prevención & control , Coriomeningitis Linfocítica/virología , Virus de la Coriomeningitis Linfocítica/efectos de los fármacos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , NADPH Oxidasas/deficiencia , NADPH Oxidasas/genética , NADPH Oxidasas/metabolismo , Bazo/metabolismoRESUMEN
BACKGROUND AND HYPOTHESIS: Cholestasis is associated with high morbidity and mortality in patients undergoing major liver surgery, but the mechanisms responsible remain elusive. Increased ischaemic liver injury and inflammation may contribute to the poor outcome. METHODS: Common bile duct ligation (biliary obstruction with hyperbilirubinaemia) or selective ligation of the left hepatic duct (biliary obstruction without hyperbilirubinaemia) was performed in C57BL/6 mice before 1 h of hepatic ischaemia and 1, 4 or 24 h of reperfusion. Infection with the intracellular hepatic pathogen Listeria monocytogenes for 12 and 48 h was used to study ischaemia-independent hepatic inflammation. RESULTS: Cholestatic mice showed considerable protection from ischaemic liver injury as determined by transaminase release, histological liver injury and neutrophil infiltration. In cholestatic mice, reduced injury correlated with a failure to activate nuclear factor kappaB (NFkappaB) and tumour necrosis factor alpha (TNFalpha) mRNA synthesis, two key mediators of post-ischaemic liver inflammation. After selective bile duct ligation, both the ligated and the non-ligated lobes showed blocked activation of NFkappaB as well as reduced induction of TNFalpha mRNA synthesis and neutrophil infiltration. By contrast, infection with L monocytogenes showed comparable activation of NFkappaB and hepatic recruitment of neutrophils 12 h after infection. CONCLUSION: Cholestasis does not increase but rather dramatically protects the liver from ischaemic injury and inflammation. This effect is mediated by a systemic factor, but not bilirubin, and is associated with a preserved capacity to trigger an inflammatory response to other stimuli such as a bacterial pathogen.
Asunto(s)
Colestasis/fisiopatología , Isquemia/fisiopatología , Hígado/irrigación sanguínea , Animales , Aspartato Aminotransferasas/sangre , Bilirrubina/análisis , Colestasis/inmunología , Colestasis/patología , Modelos Animales de Enfermedad , Inflamación/inmunología , Inflamación/fisiopatología , Isquemia/inmunología , Isquemia/patología , Listeriosis/inmunología , Hígado/patología , Ratones , Ratones Endogámicos C57BL , FN-kappa B/inmunología , Neutrófilos/inmunología , ARN Mensajero/análisis , Factor de Necrosis Tumoral alfa/inmunología , Regulación hacia Arriba/inmunologíaRESUMEN
Osmotic shock triggers eryptosis, a suicidal death of erythrocytes characterized by cell shrinkage, cell membrane blebbing and phosphatidylserine exposure at the cell surface. Phosphatidylserine-exposing erythrocytes are recognized by macrophages, engulfed, degraded and thus cleared from circulating blood. Eryptosis following osmotic shock is mediated by two distinct signalling pathways. On the one hand, osmotic shock stimulates a cyclooxygenase leading to formation of prostaglandin E2 and subsequent activation of Ca2+-permeable cation channels. On the other hand, osmotic shock activates a phospholipase A2 leading to release of platelet activating factor, which in turn activates a sphingomyelinase and thus stimulates the formation of ceramide. The increased cytosolic Ca2+ concentrations on the one hand and ceramide on the other trigger phospholipid scrambling of the cell membrane with the subsequent shift of phosphatidylserine from the inner to the outer cell membrane leaflet. Ca2+ further activates Ca2+-sensitive K+ channels leading to cellular KCl loss and further cell shrinkage. The cation channels are inhibited by Cl- anions, erythropoietin and dopamine. The sphingomyelinase is inhibited by high concentrations of urea. Thus, the high Cl- and urea concentrations in renal medulla presumably prevent the triggering of eryptosis despite hyperosmolarity. The mechanisms involved in eryptosis may not only affect the survival of erythrocytes but may be similarly operative in nucleated cells exposed to osmotic shock.
Asunto(s)
Eritrocitos/metabolismo , Eritrocitos/patología , Canales Iónicos , Transducción de Señal/fisiología , Animales , Apoptosis , Calcio/metabolismo , Cationes , Membrana Celular/metabolismo , Tamaño de la Célula , Ceramidas/metabolismo , Citosol/metabolismo , Humanos , Presión Osmótica , Fosfatidilserinas/metabolismo , Factor de Activación Plaquetaria/metabolismoRESUMEN
Cell proliferation and apoptosis are paralleled by altered regulation of ion channels that play an active part in the signaling of those fundamental cellular mechanisms. Cell proliferation must--at some time point--increase cell volume and apoptosis is typically paralleled by cell shrinkage. Cell volume changes require the participation of ion transport across the cell membrane, including appropriate activity of Cl- and K+ channels. Besides regulating cytosolic Cl- activity, osmolyte flux and, thus, cell volume, most Cl- channels allow HCO3- exit and cytosolic acidification, which inhibits cell proliferation and favors apoptosis. K+ exit through K+ channels may decrease intracellular K+ concentration, which in turn favors apoptotic cell death. K+ channel activity further maintains the cell membrane potential, a critical determinant of Ca2+ entry through Ca2+ channels. Cytosolic Ca2+ may trigger mechanisms required for cell proliferation and stimulate enzymes executing apoptosis. The switch between cell proliferation and apoptosis apparently depends on the magnitude and temporal organization of Ca2+ entry and on the functional state of the cell. Due to complex interaction with other signaling pathways, a given ion channel may play a dual role in both cell proliferation and apoptosis. Thus, specific ion channel blockers may abrogate both fundamental cellular mechanisms, depending on cell type, regulatory environment and condition of the cell. Clearly, considerable further experimental effort is required to fully understand the complex interplay between ion channels, cell proliferation and apoptosis.
Asunto(s)
Apoptosis/fisiología , Proliferación Celular , Canales Iónicos/fisiología , Canales de Potasio/fisiología , Animales , Canales de Calcio/fisiología , Tamaño de la Célula , Genes ras/fisiología , Humanos , Concentración de Iones de Hidrógeno , Canales Aniónicos Dependientes del Voltaje/fisiología , Receptor fas/fisiologíaRESUMEN
Hyperosmotic stress is known to induce apoptotic cell death, an effect previously attributed to seemingly ligand-independent clustering of tumour necrosis factor alpha (TNF alpha) receptors. An alternative explanation for the clustering of TNF alpha receptors may be stimulation of TNF alpha production, with subsequent autocrine or paracrine stimulation of the receptors. The present study was performed to test for an effect of exposure to hyperosmotic extracellular fluid on cellular TNF alpha production. In both the macrophage cell line U937 and the B lymphocyte cell line LCL721, an increase of extracellular osmolarity to 500 mosmol/l indeed increased TNF alpha expression, an effect reversed by the p38 kinase inhibitor SB203580. In both cell types hyperosmotic stress triggered apoptosis, which in U937 cells was significantly inhibited by neutralizing antibodies against TNF alpha and by SB203580 and was similarly elicited by exogenous addition of TNF alpha. In contrast, osmotically induced apoptosis of LCL721 cells was only slightly blunted by anti-TNF alpha antibodies and rather increased by SB203580. In conclusion, through activation of p38 kinase hyperosmotic stress stimulates the expression of TNF alpha which at least in U937 macrophages may participate in the triggering of subsequent apoptotic cell death. However, the observations in LCL721 cells point to other, TNF alpha-independent, mechanisms mediating apoptotic cell death following an excessive increase of extracellular osmolarity.