RESUMO
BACKGROUND AND AIMS: Zinc (Zn) quantification is of particular interest in many clinical condition (e.g. inflammatory disease, critical care). Currently, Zn status is assessed by measuring plasma/serum concentration. This concentration corresponds to the sum of unbound Zn (Zn-Cu) and Zn highly bound to albumin (Zn-Cb). METHODS: Using a pharmacokinetic approach to the interpretation of total Zn concentration (Zn-Ct), taking into account Zn-Cu and the influence of hypoalbuminemia on Zn-Cb, it is possible to improve the individualization of Zn repletion. RESULTS: Therefore, during pregnancy and in certain inflammatory disease situations, repletion may not be necessary. However, as in critical care, it would be more appropriate to perform Zn-Cu assays to improve Zn repletion. CONCLUSION: Coupled total and unbound Zn should be monitored in order to individualize Zn repletion.
Assuntos
Cobre , Zinco , Gravidez , Feminino , Humanos , Zinco/metabolismoRESUMO
Besides adipocytes, specialized in lipid handling and involved in energy balance regulation, white adipose tissue (WAT) is mainly composed of other cell types among which lymphocytes represent a non-negligible proportion. Different types of lymphocytes (B, alphabetaT, gammadeltaT, NK and NKT) have been detected in WAT of rodents or humans, and vary in their relative proportion according to the fat pad anatomical location. The lymphocytes found in intra-abdominal, visceral fat pads seem representative of innate immunity, while those present in subcutaneous fat depots are part of adaptive immunity, at least in mice. Both the number and the activity of the different lymphocyte classes, except B lymphocytes, are modified in obesity. Several of these modifications in the relative proportions of the lymphocyte classes depend on the degree of obesity, or on leptin concentration, or even fat depot anatomical location. Recent studies suggest that alterations of lymphocyte number and composition precede the macrophage increase and the enhanced inflammatory state of WAT found in obesity. Lymphocytes express receptors to adipokines while several proinflammatory chemokines are produced in WAT, rendering intricate crosstalk between fat and immune cells. However, the evidences and controversies available so far are in favour of an involvement of lymphocytes in the control of the number of other cells in WAT, either adipocytes or immune cells and of their secretory and metabolic activities. Therefore, immunotherapy deserves to be considered as a promising approach to treat the endocrino-metabolic disorders associated to excessive fat mass development.
Assuntos
Tecido Adiposo/metabolismo , Linfócitos/metabolismo , Adipocinas/metabolismo , Animais , Diabetes Mellitus/metabolismo , Humanos , Sistema Imunitário , Inflamação , Linfócitos/citologia , Camundongos , Modelos Biológicos , Obesidade/metabolismo , Fatores de TempoRESUMO
It has been suggested that patients with pulmonary surfactant impairment are more susceptible to Pneumocystis infection than healthy controls. Owing the fact that most patients with pulmonary surfactant impairment also suffer from hypoxia, we explored the effect of intermittent hypobaric hypoxia conditions on the ability of non-immunocompromised rats infected by endotracheal route with P. carinii to clear the infection from their lungs. Control rats, inoculated or not with P. carinii, were maintained in normobaric normoxic conditions, and were submitted or not to dexamethasone administration. It was found that even if hypobaric hypoxia weakened host immune mechanisms and impaired significantly the surfactant composition, mainly of surfactant proteins A and D, these changes were not enough to favour the Pneumocystis growth or to inhibit the clearing of Pneumocystis organisms from the lungs of non-immunocompromised rats. The potential influence of surfactant protein changes on Pneumocystis infection is discussed.
Assuntos
Hipóxia/metabolismo , Hospedeiro Imunocomprometido , Pneumonia por Pneumocystis/metabolismo , Proteínas Associadas a Surfactantes Pulmonares/metabolismo , Surfactantes Pulmonares/metabolismo , Animais , Modelos Animais de Doenças , Masculino , Pneumocystis carinii/crescimento & desenvolvimento , Proteína A Associada a Surfactante Pulmonar , Proteína D Associada a Surfactante Pulmonar , Proteínas Associadas a Surfactantes Pulmonares/análise , Surfactantes Pulmonares/análise , Ratos , Ratos WistarRESUMO
TNF-alpha is a pleiotropic cytokine activating several signaling pathways initiated at distinct intracellular domains of the TNF receptors. Although the C-terminal region is believed to be responsible for apoptosis induction, the functions of more membrane-proximal domains, including the domain that couples to neutral sphingomyelinase activation, are not yet fully elucidated. The roles of this region and of the associated adapter protein FAN (factor associated with neutral SMase activation) in the cytotoxic response to TNF have been investigated. We have now shown that stable expression in human fibroblasts of a dominant negative form of FAN abrogates TNF-induced ceramide generation from sphingomyelin hydrolysis and reduces caspase processing, thus markedly inhibiting TNF-triggered apoptosis. However, the cytotoxic responses to daunorubicin and exogenous ceramide remain unaltered, as do the TNF-induced p42/p44 MAPK activation and CD54 expression. Fibroblasts from FAN-knockout mice also proved to be resistant to TNF toxicity. These findings highlight the previously unrecognized role of the adapter protein FAN in signaling cell death induction by TNF.
Assuntos
Apoptose/fisiologia , Proteínas/fisiologia , Fator de Necrose Tumoral alfa/fisiologia , Clorometilcetonas de Aminoácidos/farmacologia , Animais , Antígenos CD/efeitos dos fármacos , Apoptose/efeitos dos fármacos , Caspases/metabolismo , Linhagem Celular Transformada , Células Cultivadas/efeitos dos fármacos , Ceramidas/biossíntese , Ceramidas/farmacologia , Inibidores de Cisteína Proteinase/farmacologia , Daunorrubicina/farmacologia , Ativação Enzimática/efeitos dos fármacos , Fibroblastos/citologia , Fibroblastos/efeitos dos fármacos , Genes Dominantes , Humanos , Hidrólise , Molécula 1 de Adesão Intercelular/biossíntese , Molécula 1 de Adesão Intercelular/genética , Peptídeos e Proteínas de Sinalização Intracelular , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Camundongos , Camundongos Knockout , Proteína Quinase 1 Ativada por Mitógeno/antagonistas & inibidores , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Estrutura Terciária de Proteína , Proteínas/genética , Receptores do Fator de Necrose Tumoral/efeitos dos fármacos , Receptores Tipo I de Fatores de Necrose Tumoral , Proteínas Recombinantes de Fusão/fisiologia , Sistemas do Segundo Mensageiro , Esfingomielina Fosfodiesterase/metabolismo , Esfingomielinas/metabolismo , Fator de Necrose Tumoral alfa/farmacologia , Fator de Necrose Tumoral alfa/toxicidade , Células U937RESUMO
Close relationships have been demonstrated between adipose tissue and the inflammatory/immune system. Furthermore, obesity is increasingly considered as a state of chronic inflammation. Cytofluorometric analysis reveals the presence of significant levels of lymphocytes in the stroma-vascular fraction of white adipose tissues. In epididymal (EPI) fat, lymphocytes display an "ancestral" immune system phenotype (up to 70% of natural killer (NK), gammadelta+ T and NKT cells among all lymphocytes) whereas the inguinal (ING) immune system presents more adaptive characteristics (high levels of alphabeta+ T and B cells). The percentage of NK cells in EPI fat was decreased in obese mice fed with a high-fat diet, whereas gammadelta positive cells were significantly increased in ING fat. These data support the notion that adipose tissue may elaborate immunological mechanisms to regulate its functions which might be altered in obesity.
Assuntos
Tecido Adiposo/imunologia , Linfócitos/citologia , Obesidade/imunologia , Tecido Adiposo/citologia , Animais , Gorduras na Dieta/farmacologia , Epididimo/citologia , Masculino , Camundongos , Camundongos ObesosRESUMO
The properties of coenzymes Q (CoQ9 and CoQ10) are closely linked to their redox state (CoQox/total CoQ) x 100. In this work, CoQ redox state was biologically validated by high performance liquid chromatography-electrochemical measurement after modulation of mitochondrial electron flow of cultured cells by molecules increasing (rotenone, carbonyl cyanide chlorophenylhydrazone) or decreasing (antimycin) CoQ oxidation. The tissue specificity of CoQ redox state and content were investigated in control and hypoxic rats. In control rats, there was a strong negative linear regression between tissular CoQ redox state and CoQ content. Hypoxia increased CoQ9 redox state and decreased CoQ9 content in a negative linear relationship in the different tissues, except the heart and lung. This result demonstrates that, under conditions of mitochondrial impairment, CoQ redox control is tissue-specific.
Assuntos
Mitocôndrias/metabolismo , Ubiquinona/metabolismo , Células 3T3 , Animais , Cromatografia Líquida de Alta Pressão , Transporte de Elétrons/fisiologia , Hipóxia/metabolismo , Masculino , Camundongos , Oxirredução , Estresse Oxidativo , Ratos , Ratos Wistar , Análise de Regressão , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Distribuição Tecidual , Ubiquinona/químicaAssuntos
Neovascularização de Coroide/etiologia , Comportamento Alimentar , Degeneração Macular/etiologia , Estresse Oxidativo/fisiologia , Vitaminas/sangue , Idoso , Idoso de 80 Anos ou mais , Antioxidantes/metabolismo , Estudos de Casos e Controles , Neovascularização de Coroide/sangue , Neovascularização de Coroide/epidemiologia , Feminino , França , Humanos , Estilo de Vida , Degeneração Macular/sangue , Degeneração Macular/epidemiologia , Masculino , Pessoa de Meia-Idade , Projetos Piloto , Fatores de Risco , Fumar/epidemiologia , Zinco/sangue , beta Caroteno/sangueRESUMO
BACKGROUND: Fatty acids (FAs) and adipokines such as adiponectin or interleukin-6 (IL-6) are known to modulate inflammation and the development of metabolic syndrome. Whether FA composition assessed in plasma triacylglycerols (TAGs), phospholipids (PLs) and non-esterified fatty acids (NEFAs) and adipose tissue (AT) PLs differed between dysmetabolic and non-dysmetabolic severely obese women remains to be established. Whether the plasma and/or AT arachidonic acid (AA)/eicosapentaenoic acid (EPA) ratio in the PL sub-fraction may be associated with adipokine AT gene expression needs to be examined. METHODS: FA composition was measured in plasma lipid classes and in the TAG and PL sub-fractions of subcutaneous abdominal and omental ATs of severely obese women paired for age and adiposity but showing a dysmetabolic profile (n = 13) or not (n = 14). FA profile was assessed by gas chromatography. Plasma and AT mRNA concentrations of adiponectin and IL-6 were measured by ELISA and real-time polymerase chain reaction, respectively. RESULTS: Plasma adiponectin and FA concentrations in the NEFA sub-fraction were, respectively, lower and higher in dysmetabolic than in non-dysmetabolic women (p < 0.05). Despite similar FA levels in the PL sub-fraction, the AA/EPA ratio was higher in plasma and ATs (p < 0.005), because of an EPA decrease in plasma and subcutaneous abdominal fat vs. an AA increase in the omental depot. The AA/EPA ratio was negatively associated with adiponectin concentrations in plasma and subcutaneous abdominal AT (0.01 < p < 0.05). CONCLUSIONS: Metabolic dysfunction is associated with a pro-inflammatory phospholipid AA/EPA ratio in plasma and ATs, and an altered adiponectin secretion that could contribute to developing metabolic syndrome.
Assuntos
Ácidos Araquidônicos/sangue , Ácido Eicosapentaenoico/sangue , Síndrome Metabólica/sangue , Obesidade Mórbida/sangue , Gordura Subcutânea Abdominal/metabolismo , Adulto , Cromatografia Gasosa , Ensaio de Imunoadsorção Enzimática , Feminino , Humanos , Interleucina-6/sangue , Síndrome Metabólica/etiologia , Obesidade Mórbida/complicações , Reação em Cadeia da Polimerase em Tempo RealAssuntos
Divisão Celular/fisiologia , Regulação da Expressão Gênica , Linfócitos/citologia , Músculo Liso Vascular/citologia , Músculo Liso Vascular/fisiologia , Animais , Bovinos , Células Cultivadas , Meios de Cultivo Condicionados , Citocinas/análise , Citocinas/biossíntese , Teste de Histocompatibilidade , Humanos , Teste de Cultura Mista de Linfócitos , Linfócitos/imunologia , Transplante HomólogoAssuntos
Cromatografia Líquida de Alta Pressão/métodos , Leucina/sangue , Doença da Urina de Xarope de Bordo/sangue , Doença da Urina de Xarope de Bordo/diagnóstico , Estudos de Casos e Controles , Cromatografia Líquida de Alta Pressão/economia , Cromatografia Líquida de Alta Pressão/normas , Progressão da Doença , Nutrição Enteral , Hemodiafiltração , Humanos , Lactente , Recém-Nascido , Doença da Urina de Xarope de Bordo/classificação , Doença da Urina de Xarope de Bordo/terapia , Fatores de Tempo , Resultado do TratamentoRESUMO
Ancestral lymphoid cells reside in adipose tissues, and their numbers are highly altered in obesity. Leptin, production of which is correlated to fat mass, is strongly involved in the relationships between adipose tissues and immune system. We investigated in epididymal (EPI) and inguinal (ING) fat pads to determine whether 1) lymphocyte phenotypes were correlated to the tissue weight and 2) leptin was involved in such relationships. Immunohistological analyses revealed a tight relationship between the T and NK lymphocytes of the stromal vascular fraction and adipocytes. We identified a significant negative and positive correlation between EPI weight and the percentage of NK and total T cells respectively by cytofluorometric analyses. The NK and ancestral gammadelta T cell contents were directly dependent of leptin since they increased significantly in high-fat (HF) diet mice but not in leptin-deficient (ob/ob) mice as compared to control. By contrast, the alphabeta T cell content seemed independent of leptin because their percentages increased significantly with the EPI weight whatever the type of mice (control, HF, ob/ob). The present study suggests that adipose tissues present, according to their localization, different immunological mechanisms that might be involved in the regulation of adipose cells functions and proliferations.
Assuntos
Tecido Adiposo/imunologia , Adiposidade/imunologia , Leptina/fisiologia , Tecido Adiposo/citologia , Animais , Complexo CD3/análise , Epididimo/química , Epididimo/citologia , Citometria de Fluxo , Imuno-Histoquímica , Integrina alfa2/análise , Células Matadoras Naturais/química , Células Matadoras Naturais/citologia , Leptina/genética , Linfócitos/química , Linfócitos/citologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Receptores para Leptina , Subpopulações de Linfócitos T/química , Subpopulações de Linfócitos T/citologia , Linfócitos T/química , Linfócitos T/citologiaRESUMO
T cell antigen receptor (TcR) heterodimers of both the Ti-alpha beta and Ti-gamma delta types are expressed at the surface of T cells noncovalently associated with the CD3 complex composed of the monomorphic chains gamma, delta, epsilon and zeta. The structural relationship and assembly of the various components of this multimeric protein complex is still not fully understood. In this report, the human leukemic T cell line Lyon which expresses a Ti-gamma delta/CD3 complex, was characterized and compared to another human leukemic T cell line Jurkat (Ti-alpha beta/CD3). Membrane TCR-/CD3- variants of the T cell Lyon were induced and found to produce all of the Ti/CD3 components, with the exception of Ti-delta. Biochemical analysis indicated that: (1) Ti-gamma/CD3 gamma, delta, epsilon complexes were formed in the endoplasmic reticulum in the absence of Ti-delta; (2) the CD3-zeta chain did not associate with the Ti-gamma/CD3 gamma delta epsilon complex and (3) the Ti-delta chain was required for cell surface expression of the Ti-gamma delta/CD3 complex. Introduction of Jurkat wild-type Ti-alpha cDNA into Lyon T cells resulted in Ti-alpha beta/CD3 expression and abrogated Ti-gamma delta/CD3 expression. In contrast, the expression of the Ti-gamma delta/CD3 complex was not affected by transfection of a mutated Ti-alpha cDNA into Lyon cells. The mutated Ti-alpha chain formed complexes with Ti-beta and CD3 gamma delta epsilon, but the CD3-zeta chain did not associate with these complexes. Taken together analysis of Lyon cells transfected with either wild-type or mutated Ti-alpha suggested that the CD3-zeta chain may have higher affinity for Ti-alpha beta/CD3 complexes than for Ti-gamma delta/CD3 complexes.
Assuntos
Receptores de Antígenos de Linfócitos T gama-delta/metabolismo , Receptores de Antígenos de Linfócitos T/metabolismo , Linfócitos T/metabolismo , Transporte Biológico , Northern Blotting , Southern Blotting , Linhagem Celular , Retículo Endoplasmático/metabolismo , Citometria de Fluxo , Humanos , Complexo Receptor-CD3 de Antígeno de Linfócitos T/metabolismo , Receptores de Antígenos de Linfócitos T/genética , Receptores de Antígenos de Linfócitos T alfa-beta/genética , Receptores de Antígenos de Linfócitos T alfa-beta/metabolismo , Transfecção , Células Tumorais CultivadasRESUMO
T lymphocytes express membrane antigen receptor TcR/CD3 complexes only when all subunits are correctly assembled. Studies on TcR/CD3 membrane negative T cell variants containing all necessary subunits intracellularly, may allow to identify amino acids important for different subunit interactions. In this review, we summarize our recent work on TcR/CD3 negative variants of the human T cell line Jurkat. We found two critical amino acids in the TcR-alpha and TcR-beta extracellular constant regions (phenylalanine n. 216 and intrachain disulfide cysteine n. 212) involved in TcR-alpha beta/CD3- gamma epsilon, delta epsilon intermediary complex/zeta 2 homodimer interactions: (1) amino acid exchanges of phenylalanine demonstrated the importance of an aromatic amino acid residue at this position; (2) the intrachain disulfide bond assures a tertiary structure of the constant domain that is necessary for association with zeta 2 homodimers.
Assuntos
Complexo Receptor-CD3 de Antígeno de Linfócitos T/biossíntese , Sequência de Aminoácidos , Animais , Cisteína/metabolismo , Humanos , Proteínas de Membrana/química , Proteínas de Membrana/metabolismo , Dados de Sequência Molecular , Mutação , Fenilalanina/metabolismo , Estrutura Terciária de Proteína , Complexo Receptor-CD3 de Antígeno de Linfócitos T/genética , Alinhamento de SequênciaRESUMO
A spontaneous TCR cell surface variant (3P11) of the Jurkat T cell line is described and characterized. 3P11 was selected by incubation of Jurkat cells with anti-TCR mAb followed by passage through Ig anti-Ig columns and cloning. 3P11 contained mRNA for both Ti alpha and Ti beta and CD3 gamma, delta, epsilon and zeta. Biochemical analyses demonstrated that all of the TCR components were produced in 3P11 cells. The Ti alpha beta/CD3 gamma delta epsilon zeta complex was assembled in the endoplasmic reticulum but the zeta did not associate with this complex. Epitopes recognized by the Ti beta chain specific mAb beta F1 and JOVI as well as anti-V beta 8 were affected in the 3P11 Ti beta chain indicating that the 3P11 Ti beta chain was mutated. Transfection of a wild-type Ti beta cDNA into 3P11 cells reconstituted TCR expression. Sequence analyses of the 3P11 Ti beta chain demonstrated a guanine to adenine change in the second nucleotide of the triplet coding for cysteine191 resulting in a cysteine to tyrosine exchange. Cysteine191 is the C-terminal cysteine involved in the intrachain disulfide bond in the C domain of the Ti beta chain; thus, the 3P11 Ti beta chain did not contain this disulfide bond. Transfection of a site-directed Ti beta chain containing the 3P11 mutation into a Ti beta negative variant of the Jurkat cell line resulted in a TCR phenotype identical with 3P11 demonstrating that the mutation identified in the 3P11 Ti beta chain was the sole cause for the 3P11 defect.
Assuntos
Receptores de Antígenos de Linfócitos T alfa-beta/análise , Linfócitos T/química , Sequência de Aminoácidos , Animais , Anticorpos Monoclonais/imunologia , Sequência de Bases , DNA Complementar/química , Epitopos/análise , Humanos , Camundongos , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Receptores de Antígenos de Linfócitos T alfa-beta/biossíntese , Receptores de Antígenos de Linfócitos T alfa-beta/química , Relação Estrutura-Atividade , TransfecçãoRESUMO
Activated T-lymphocytes are present in early atherosclerotic lesions where they may interact with oxidized low-density lipoproteins (oxLDLs). In this study the non-specific effect of oxLDLs on the activation of T-cells in vitro was investigated. LDLs were oxidized by UV irradiation and characterized by a low level of lipid peroxidation and only slight apolipoprotein B modification. Peripheral blood lymphocytes from normal individuals were stimulated in vitro with the polyclonal activator phytohaemagglutinin in the presence of various doses of LDLs and oxLDLs. LDLs enhanced the proliferation of peripheral blood lymphocytes at doses up to 100 microg/ml but were inhibitory at 200 microg/ml, whereas low doses of oxLDLs (over 10 microg/ml) inhibited the proliferation. OxLDLs also inhibited the proliferative responses of an alloreactive CD4+ T-cell line immortalized by Herpes virus saimiri and an influenza haemagglutinin-specific CD4+ T-cell clone. Viability tests using Trypan Blue exclusion or expression of Apo2.7, an apoptosis marker, did not indicate any significant cell death at doses up to 100 microg/ml oxLDL. At this concentration, cell-cycle analysis showed an accumulation of cells at the G1/S interface in the CD4+ cell clone, without significant DNA fragmentation. The expression of the activation antigen CD25 on T-lymphocytes (on phytohaemagglutinin-activated T-cells and on CD4+ T-cell clone), requisite to the commitment of activated T-cells from G1 phase to S phase, was also inhibited by oxLDLs whereas expression of other activation antigens such as CD69 and HLA-DR was unchanged. In conclusion, these data show that mildly oxidized LDLs inhibit the proliferation and CD25 expression of activated T-lymphocytes and suggest that oxLDLs may slow down the T-cell response in atherosclerotic lesions.
Assuntos
Linfócitos T CD4-Positivos/citologia , Lipoproteínas LDL/metabolismo , Receptores de Interleucina-2/metabolismo , Linfócitos T CD4-Positivos/efeitos dos fármacos , Linfócitos T CD4-Positivos/metabolismo , Divisão Celular , Células Cultivadas , Humanos , Ativação Linfocitária/efeitos dos fármacos , Oxirredução , Fito-Hemaglutininas/farmacologia , Timidina/metabolismoRESUMO
Oxidized low density lipoproteins (oxLDLs) and activated T lymphocytes are present in early atherosclerotic plaques. It has been shown that oxLDLs are cytotoxic to cultured vascular cells but their possible toxic action on T lymphocytes has not been described. Peripheral blood lymphocytes from healthy individuals were stimulated in vitro with the polyclonal activator phytohemagglutinin and treated with various doses of native and mildly oxidized LDLs. Low doses of oxLDLs inhibited cell growth and DNA synthesis after 48 h culture and at 200 microg apoB/ml we observed a loss of cell viability. Dead cells did not exhibit significant increase of alteration of membrane integrity (i.e., necrosis) but showed chromatin fragmentation evaluated by DNA staining with 4', 6-diamidino-2-phenylindole and propidium iodide. This fragmentation increased with TBARS and hydroperoxide levels. The expression of early apoptosis marker Apo2.7 rose among the CD3(+) T-cell population. In addition, morphological analysis showed apoptotic features (cell shrinking, nucleus condensation, and fragmentation). Study of phosphatidylserine expression using Annexin V confirmed that oxLDLs induced apoptosis in activated lymphocytes. In the Jurkat T-cell line cultured with oxLDLs, apoptotic morphological changes (condensation and nucleus fragmentation) were observed and they were accompanied by DNA fragmentation visualized by propidium iodide staining and electrophoresis showing apoptotic ladder. These results demonstrate that mildly oxidized LDLs induce apoptosis in a part of activated and proliferating T cells. T-lymphocyte apoptosis induction in atherosclerotic lesions might contribute to the development of an inappropriate local T cell response.
Assuntos
Apoptose , Lipoproteínas LDL/fisiologia , Fito-Hemaglutininas/farmacologia , Linfócitos T/fisiologia , Divisão Celular , Sobrevivência Celular , Humanos , Células Jurkat , Microscopia de Fluorescência , Oxirredução , Linfócitos T/efeitos dos fármacosRESUMO
In the present study, we have investigated the importance of a phenylalanine (phe195) in the Tcr-C alpha region on Tcr-alpha,beta/CD3 membrane expression. An exchange of phe195 with a tyrosine residue does not affect Tcr/CD3 membrane expression; however, exchange with aspartic acid, histidine or valine prohibit completely Tcr/CD3 membrane expression. This seems to be due to a lack of interaction between mutated Tcr-alpha,beta/CD3-gamma epsilon,delta epsilon complexes and zeta 2 homodimers. The Tcr-C alpha region around phe195 seems together with the same region in the Tcr-C beta region to constitute an interaction site for zeta 2 homodimers. The presence of phe195 on both Tcr-C alpha and Tcr-C beta causes high avidity interaction with zeta 2 homodimers, whereas his195 in both Tcr-C gamma and Tcr-C delta results in an apparently lower avidity interaction with zeta 2 homodimers. It is suggested that the phe195 region (on beta-strand F) and eventually adjacent aromatic amino acid residues on beta-strand B region may play an important role in Tcr-alpha,beta/CD3 membrane expression, in Tcr-alpha,beta/CD3 competition with Tcr-gamma,delta/CD3 complexes for zeta 2 homodimers and in the control of formation of 'mixed' Tcr heterodimers.
Assuntos
Complexo CD3/biossíntese , Fenilalanina/fisiologia , Receptores de Antígenos de Linfócitos T alfa-beta/biossíntese , Sequência de Aminoácidos , Animais , Sequência de Bases , Evolução Biológica , Linhagem Celular , Membrana Celular/metabolismo , Sequência Conservada , DNA Complementar , Humanos , Dados de Sequência Molecular , Mutação Puntual , Conformação Proteica , Receptores de Antígenos de Linfócitos T alfa-beta/genética , Receptores de Antígenos de Linfócitos T gama-delta/metabolismo , Homologia de Sequência de Aminoácidos , Ovinos , Linfócitos T/metabolismo , Transfecção , Células Tumorais CultivadasRESUMO
Recently, it was demonstrated that CD8(+) T cells are important for the response against Chlamydia pneumoniae. By use of the human monocytic cell line U937 and human monocytes taken from peripheral blood, we investigated the effect of infection on various molecules critical for CD8(+) T cell function. A strong secretion of interleukin (IL)-10 by infected cells was observed, together with an inhibited expression of major histocompatibility complex (MHC) class I antigens, but without significant alteration of tumor growth factor-beta secretion or MHC class II expression. Recombinant IL-10 added to uninfected U937 cells decreased the expression of MHC class I, whereas blocking antibodies to IL-10 and its receptor abolished the C. pneumoniae-induced inhibition of MHC class I expression. Analysis of our data provides evidence that IL-10 secretion induced by C. pneumoniae infection of monocytic cells down-regulates the expression of MHC class I molecules and thereby might reduce the presentation of bacterial epitopes by MHC. This would decrease the ability of CD8(+) T cells to eliminate infected cells.