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The present study reports the evolution of the demographic characteristics and the molecular epidemiology of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) in Belgium from 2005 to 2009. Four hundred and ten CA-MRSA isolates were prospectively collected and screened for the presence of Panton-Valentin leucocidin (PVL) and toxic shock syndrome toxin 1 (TSST-1) encoding genes, while clinical information were recorded. PVL- and TSST-1-positive isolates were genotyped by pulsed-field gel electrophoresis (PFGE). Staphylococcal cassette chromosome mec (SCCmec) type, spa type and multilocus sequence type (MLST) were determined on representative isolates. One hundred and fifty-nine (39 %) isolates were PVL-positive. PVL-positive isolates were significantly more frequently isolated from skin or soft tissue than PVL-negative isolates, causing mainly subcutaneous abscesses and furuncles. Patients with PVL-positive CA-MRSA were significantly younger than patients with PVL-negative CA-MRSA. Eighty-seven percent of the PVL-positive isolates belonged to a limited number (n = 7) of PFGE types belonging to sequence types (ST) ST80, ST8, ST30, ST5, ST152, ST338 and a new ST, a single-locus variant of ST1. A temporal evolution of the distribution of these PFGE types was observed, characterised by (1) the dissemination of the ST8-SCCmecIV arcA-positive (USA300) genotype and (2) a genetic diversification. Forty-seven (11 %) strains were TSST-1-positive, of which 65 % clustered into four PFGE types, all belonging to ST5. The epidemiology of CA-MRSA in Belgium is changing, as the rapid diffusion of the USA300 clone seems to occur, together with a clonal diversification.
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Infecciones Comunitarias Adquiridas/epidemiología , Infecciones Comunitarias Adquiridas/microbiología , Staphylococcus aureus Resistente a Meticilina/clasificación , Infecciones Estafilocócicas/epidemiología , Infecciones Estafilocócicas/microbiología , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Antibacterianos/farmacología , Toxinas Bacterianas/genética , Bélgica/epidemiología , Niño , Preescolar , ADN Bacteriano/análisis , ADN Bacteriano/genética , Farmacorresistencia Bacteriana , Enterotoxinas/genética , Exotoxinas/genética , Femenino , Humanos , Lactante , Leucocidinas/genética , Masculino , Staphylococcus aureus Resistente a Meticilina/efectos de los fármacos , Staphylococcus aureus Resistente a Meticilina/genética , Staphylococcus aureus Resistente a Meticilina/aislamiento & purificación , Pruebas de Sensibilidad Microbiana , Persona de Mediana Edad , Tipificación Molecular , Estudios Prospectivos , Superantígenos/genéticaRESUMEN
The increase in the number of methicillin-resistant Staphylococcus aureus (MRSA) infections in children has prompted paediatricians to broaden th empirical treatment of common community-onset (CO) infections in children in several countries. Most European countries have reported low rates of CO-MRSA infection, but limited data on paediatric CO-MRSA infections are available. A prospective study was conducted from January 2002 to December 2004 in Brussels. CO-MRSA was defined as MRSA first detected by culture within 48 h of admission or in outpatients. Clinical and epidemiological data were recorded. CO-MRSA strains were genotyped by pulsed-field gel electrophoresis and multilocus sequence typing. Staphylococcal chromosomal cassette mec, toxin (Panton-Valentin leukocidin (PVL), toxic shock syndrome toxin 1, and Eta/b), enterotoxin and antibiotic resistance genes were detected by PCR. The antibiotic resistance phenotype was determined by disk diffusion. S. aureus was isolated in 1681 children. Among these, 107 harboured MRSA. Fifty-one children were colonized or infected by CO-MRSA, 20% of whom had no healthcare exposure. Twelve infants <3 months old and five cystic fibrosis patients were colonized. None of the 22 infected patients (59% with acute otitis media and 36% with skin and soft tissue infections (SSTIs)) required hospitalization. Two-thirds of them failed to respond to empirical antibiotic therapy. The 37 characterized CO-MRSA strains were genetically diverse. Most of them had healthcare-associated genotypes. Only six strains were PVL-positive, all of which were ciprofloxacin-susceptible and more common in children with SSTIs (p 0.001). CO-MRSA remains uncommon in our paediatric population. So far, there is no need to modify the empirical treatment of common S. aureus infections. Monitoring of MRSA rates in S. aureus CO infections remains mandatory, and further investigation is warranted to establish the source of colonization in young infants.
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Infecciones Comunitarias Adquiridas/epidemiología , Infecciones Comunitarias Adquiridas/microbiología , Variación Genética , Staphylococcus aureus Resistente a Meticilina/clasificación , Staphylococcus aureus Resistente a Meticilina/aislamiento & purificación , Infecciones Estafilocócicas/epidemiología , Infecciones Estafilocócicas/microbiología , Adolescente , Antibacterianos/uso terapéutico , Bélgica/epidemiología , Niño , Preescolar , Análisis por Conglomerados , Estudios de Cohortes , Infecciones Comunitarias Adquiridas/patología , Electroforesis en Gel de Campo Pulsado , Femenino , Genotipo , Hospitales , Humanos , Lactante , Recién Nacido , Masculino , Tipificación de Secuencias Multilocus , Reacción en Cadena de la Polimerasa , Estudios Prospectivos , Infecciones Estafilocócicas/patología , Resultado del Tratamiento , Factores de Virulencia/genética , Adulto JovenRESUMEN
INTRODUCTION: Tetanus is still a significant health hazard in developing countries, with high associated mortality. OBJECTIVE: Describe the management of patients with severe tetanus in intensive care units (ICUs), in two different periods. SETTING: ICUs of two general hospitals. DESIGN: Concurrent cohort study. METHODS: Follow-up of all patients hospitalized with the diagnosis of severe tetanus in the ICUs from October 1981 to March 2001. We collected data prospectively, regarding the site of injury, clinical features, frequent clinical and infectious complications, concomitant illnesses, and mortality. The patients were divided into two groups according to the treatment protocol used; before 1993 and after 1993. RESULTS: There were 126 patients in group 1 (93 males) with a mean age of 39.0 +/- 18.8 years. There were 110 patients in group 2 (95 males) with a mean age of 48.4+/-17.8 years. Incubation period, onset period, and symptomatic period were higher in group 2 ( P < or = 0.02). The duration of neuromuscular junction blockade, benzodiazepine administration, mechanical ventilation, and ICU stay were longer in group 2, P < 0.001. Infectious complications were more frequent in group 2 ( P < 0.001). The mortality rate in group 1 was 36.5% and in group 2, 18.0% ( P = 0.002). Mortality was directly associated with symptomatic period, acute renal failure cardiac arrest and hypotension, and inversely associated with onset period in the multivariate analyses. CONCLUSIONS: The reduced mortality in severe accidental tetanus patients in group 2 is probably related to advances in ICU management, despite the higher incidence of infectious complications, which are probably related to the longer ICU stay.
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Mortalidad Hospitalaria , Unidades de Cuidados Intensivos/estadística & datos numéricos , Tétanos/mortalidad , Accidentes , Adulto , Brasil/epidemiología , Estudios de Cohortes , Femenino , Hospitales Generales , Humanos , Masculino , Persona de Mediana Edad , Medición de Riesgo , Tétanos/complicaciones , Tétanos/diagnóstico , Tétanos/fisiopatología , Heridas y Lesiones/complicacionesRESUMEN
A three-dimensional solute transport model with biological reactions is presented for simulating the natural attenuation study (NATS) at the Columbus Air Force Base in eastern Mississippi. NATS consisted of the release of a petroleum-based nonaqueous phase liquid (NAPL) and subsequent monitoring of BTEX (benzene, toluene, ethylbenzene, p-xylene), naphthalene, decane, and bromide in a shallow, unconfined aquifer. Conceptual and mathematical models were developed for NAPL source release, sequential aerobic/anaerobic biodegradation, and sorption during NATS. A multiple species, solute transport code (SEAM3D) was used to simulate fully three-dimensional transport and aerobic, nitrate-reducing, ferrogenic, and methanogenic hydrocarbon biodegradation. Simulation results matched individual BTEX concentration distributions collected five- and nine-months following NAPL release. SEAM3D mass-balance calculations at t = nine months indicated that 49% of the hydrocarbon mass that dissolved into the aqueous phase was consumed by biodegradation, 13% of this mass was sorbed, and the remaining 38% was present in the aqueous phase. Mass calculations at t = nine months further indicated that aerobic biodegradation accounted for the majority of hydrocarbon biodegradation (46% of the biodegraded mass), followed by ferrogenesis (28%), nitrate-reduction (21%), and methanogenesis (5%). Model results were particularly sensitive to the NAPL release rate, the initial ferric iron (Fe[III]) concentration, hydrocarbon utilization rates, initial condition for the anaerobic microbial populations, and dispersivity.
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Hidrocarburos , Modelos Teóricos , Petróleo , Microbiología del Suelo , Contaminantes del Suelo/análisis , Contaminantes Químicos del Agua/análisis , Absorción , Bacterias Aerobias , Bacterias Anaerobias , Biodegradación Ambiental , Monitoreo del Ambiente , Hierro/química , Contaminantes del Suelo/metabolismoRESUMEN
Several brain regions associated with analogical mapping were identified using (15)O-positron emission tomography with 12 normal, high intelligence adults. Each trial presented during scanning consisted of a source picture of colored geometric shapes, a brief delay, and a target picture of colored geometric shapes. Analogous pictures did not share similar geometric shapes but did share the same system of abstract visuospatial relations. Participants judged whether each source-target pairing was analogous (analogy condition) or identical (literal condition). The results of the analogy-literal comparison showed activation in the dorsomedial frontal cortex and in the left hemisphere; the inferior, middle, and medial frontal cortices; the parietal cortex; and the superior occipital cortex. Based on these results as well as evidence from relevant cognitive neuroscience studies of reasoning and of executive working memory, we hypothesize that analogical mapping is mediated by the left prefrontal and inferior parietal cortices.
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Mapeo Encefálico , Encéfalo/anatomía & histología , Encéfalo/metabolismo , Tomografía Computarizada de Emisión , Adulto , Encéfalo/diagnóstico por imagen , Toma de Decisiones/fisiología , Femenino , Lóbulo Frontal/diagnóstico por imagen , Lóbulo Frontal/metabolismo , Lateralidad Funcional/fisiología , Humanos , Masculino , Lóbulo Parietal/diagnóstico por imagen , Lóbulo Parietal/metabolismoRESUMEN
OBJECTIVES: To determine the predictive value of early determination of tumor necrosis factor (TNF)-alpha, TNF-alpha 1 and 2 soluble receptors (sTNFR1 and sTNFR2) and endothelin-1 (ET-1) for mortality in patients with septic shock. DESIGN: Prospective study. SETTING: Intensive care unit of a university hospital. PATIENTS: Twenty-one patients with septic shock. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: Patients with septic shock had a pulmonary artery catheter inserted and blood samples drawn at time zero, 6, 12 and 24 h, simultaneously with hemodynamic assessments. Plasma levels of all markers were measured by ELISA. All patients were followed up to hospital discharge or death. Age and APACHE II scores were significantly higher in nonsurvivors (n = 11) than in survivors (n = 10). Hemodynamic assessments did not aid in the discrimination between the two groups of patients (P > 0.05). Levels of TNF-alpha were higher in nonsurvivors than in survivors at all time-points. sTNFR1 and sTNFR2 were also significantly elevated in nonsurvivors, but not in all measurements. Endothelin-1, however, was significantly higher in nonsurvivors than in survivors only at 6 h (P = 0.02). When both TNF-alpha and ET-1 were increased at early time-points, the best predictive values for mortality were obtained [positive and negative predictive values of 72 and 100% at 6 h, odds ratio 3.0, 95% CI (1.2-7.6)]. CONCLUSIONS: Increased levels of TNF-alpha were consistently higher at all time-points in nonsurvivors with septic shock. ET-1 levels, however, appeared also to be an early and sensitive predictor of mortality. Very early determination of TNF-alpha and ET-1 in septic shock may help to identify patients at higher risk for adverse outcome.
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Endotelina-1/sangre , Choque Séptico/sangre , Choque Séptico/mortalidad , Factor de Necrosis Tumoral alfa/metabolismo , APACHE , Adulto , Anciano , Anciano de 80 o más Años , Antígenos CD/sangre , Enfermedad Crítica , Ensayo de Inmunoadsorción Enzimática , Femenino , Hemodinámica , Humanos , Masculino , Persona de Mediana Edad , Valor Predictivo de las Pruebas , Pronóstico , Estudios Prospectivos , Receptores del Factor de Necrosis Tumoral/sangre , Receptores Tipo I de Factores de Necrosis Tumoral , Receptores Tipo II del Factor de Necrosis TumoralRESUMEN
When people interpret language, they can reduce the ambiguity of linguistic expressions by using information about perspective: the speaker's, their own, or a shared perspective. In order to investigate the mental processes that underlie such perspective taking, we tracked people's eye movements while they were following instructions to manipulate objects. The eye fixation data in two experiments demonstrate that people do not restrict the search for referents to mutually known objects. Eye movements indicated that addressees considered objects as potential referents even when the speaker could not see those objects, requiring addressees to use mutual knowledge to correct their interpretation. Thus, people occasionally use an egocentric heuristic when they comprehend. We argue that this egocentric heuristic is successful in reducing ambiguity, though it could lead to a systematic error.
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Conocimiento , Lingüística , Procesos Mentales , Adulto , Movimientos Oculares , Humanos , Pruebas del Lenguaje , MasculinoRESUMEN
Mathematical development and model application is provided for a multiple substrate, sequential electron acceptor model, accounting for hydrodynamic transport, adsorption, and sequential oxygen/iron(III)-based biodegradation. Equations for iron(III)-based biodegradation of petroleum hydrocarbons are developed based on oxygen-inhibited Monod kinetics. The iron(III)-based biodegradation expressions were combined with earlier work by Widdowson and Aelion, to develop the two-dimensional, multiple substrate, oxygen/iron(III) sequential electron acceptor biodegradation model presented here. In addition to mathematical model development, simulations demonstrating the advantages of sequential electron acceptor and multiple substrate biodegradation models are provided. These simulations show that commonly-used single electron acceptor models may underpredict natural, in situ biodegradation potential at sites where indigenous microorganisms are capable of using multiple electron acceptors. Additional simulations show that, for contaminant plumes composed of constituents which biodegrade at different rates and under varying electron acceptor conditions, a multiple substrate model may allow more accurate prediction of both individual contaminant concentrations and the total amount of biodegraded contaminant. Considering that typical contaminant plumes are composed of multiple constituents with varying biodegradation properties and health risks, multiple substrate sequential electron acceptor models have the potential to provide more accurate tracking of individual constituent migration. The model was applied to a leaking UST site in Laurel Bay, South Carolina. Laboratory and monitoring well data presented in Landmeyer et al. have established that the petroleum hydrocarbon contaminants are present in the groundwater and are undergoing sequential oxygen-iron(III)-based biodegradation. Model simulations proved capable of reproducing the trends observed at the Laurel Bay site in that BTX contaminants were removed by sequential biodegradation, occurring first aerobically and subsequently anaerobically, and that iron(III)-reducing organisms biodegrade contaminants only in the absence of oxygen. The BTX compounds were individually but simultaneously modeled, allowing explicit modeling of specific contaminant biodegradation properties (e.g., toluene and xylene are assumed to degrade sequentially and benzene is assumed to degrade aerobically only). Although simulations presented here can reproduce trends observed at the Laurel Bay site, inclusion of additional electron acceptors and additional model calibration to data from this and other sites is necessary to improve and verify the model's capability to predict the efficacy of intrinsic biodegradation of petroleum hydrocarbon contaminants in groundwater.
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Biodegradación Ambiental , Transporte de Electrón/fisiología , Petróleo/metabolismo , Contaminantes Químicos del Agua/metabolismo , Bacterias/crecimiento & desarrollo , Biomasa , Hierro/metabolismo , Cinética , Modelos Teóricos , Oxígeno/metabolismoRESUMEN
The theory and practice of external infrared reflection absorption spectrometry (IRRAS) as applied to monomolecular films at the air-water interface are reviewed. The observed IR frequencies for films of amphiphilic species provide information about the conformational states of the hydrocarbon chains and the hydrogen bonding and ionization states of the polar head groups, under conditions of controlled surface pressure. Determination of molecular orientation is also feasible and requires detailed consideration of the reflection-absorption properties of the three- phase (air-monolayer-water) system. Current theoretical approaches are described. Applications of IRRAS to the study of single- and double-chain amphiphiles and proteins are reviewed, and initial excursions into biochemistry (interfacial enzyme catalysis) and physiology (pulmonary surfactant function) are reported.
RESUMEN
A Fourier transform infrared spectrometer has been interfaced with a surface balance and a new external reflection infrared sampling accessory, which permits the acquisition of spectra from protein monolayers in situ at the air/water interface. The accessory, a sample shuttle that permits the collection of spectra in alternating fashion from sample and background troughs, reduces interference from water vapor rotation-vibration bands in the amide I and amide II regions of protein spectra (1520-1690 cm-1) by nearly an order of magnitude. Residual interference from water vapor absorbance ranges from 50 to 200 microabsorbance units. The performance of the device is demonstrated through spectra of synthetic peptides designed to adopt alpha-helical, antiparallel beta-sheet, mixed beta-sheet/beta-turn, and unordered conformations at the air/water interface. The extent of exchange on the surface can be monitored from the relative intensities of the amide II and amide I modes. Hydrogen-deuterium exchange may lower the amide I frequency by as much as 11-12 cm-1 for helical secondary structures. This shifts the vibrational mode into a region normally associated with unordered structures and leads to uncertainties in the application of algorithms commonly used for determination of secondary structure from amide I contours of proteins in D2O solution.
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Péptidos/química , Conformación Proteica , Estructura Secundaria de Proteína , Aire , Secuencia de Aminoácidos , Dicroismo Circular , Deuterio , Hidrógeno , Cinética , Matemática , Modelos Teóricos , Datos de Secuencia Molecular , Oligopéptidos/química , Espectroscopía Infrarroja por Transformada de Fourier/métodos , Relación Estructura-Actividad , AguaRESUMEN
The current theory of pulmonary surfactant function requires that very low surface tension be achieved and maintained in the alveolar surface film during compression (expiration). To effect this condition, it has been hypothesized that the unsaturated and/or fluid components of surfactant are selectively excluded or "squeezed out" from mixed monolayers containing both saturated and unsaturated phospholipids, leaving a surface film of essentially pure 1,2-dipalmitoylphosphatidylcholine (DPPC). External reflection Fourier transform infrared (FT-IR) spectroscopy has been employed to quantitatively test this hypothesis. Mixed monolayer films of acyl chain-perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC-d62) with 1,2-dioleoylphosphatidylglycerol (DOPG), 1-palmitoyl, 2-oleoylPG (POPG), 1,2-dipalmitoylPG (DPPG) were examined in situ at the air/water interface as a function of surface pressure. The relative intensities of CD2 (CH2) stretching vibrations of the deuterated (proteated) components permitted quantitative determination of the relative concentrations of each in the film. For 7:1 (mol:mol) mixtures of DPPC-d62/DOPG, progressive, selective squeeze out of up to about 90% of the PG component is observed over a range of surface pressures from about 51 to 68 mN/m. The extent of maximal PG squeeze out was reduced to 61% for a 7:1 (mol:mol) mixture of DPPC-d62/POPG. This phenomenon, which is at least partially reversible, appears to require relatively high rates of film compression. Squeeze out was reduced (< 20%) for 7:1 (mol:mol) mixtures of DPPC-d62/DPPG or for 7:3 mixtures of DPPC-d62/POPG. Squeeze out requires that the lipid mixture achieve surface pressures greater than about 50-60 mN/m along with unsaturation (or at least conformational disorder) in the acyl chains of the non-DPPC component.(ABSTRACT TRUNCATED AT 250 WORDS)
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1,2-Dipalmitoilfosfatidilcolina/química , Membrana Dobles de Lípidos , Fosfatidilgliceroles/química , Surfactantes Pulmonares/química , Surfactantes Pulmonares/fisiología , Aire , Animales , Pulmón/fisiología , Modelos Biológicos , Conformación Molecular , Espectroscopía Infrarroja por Transformada de Fourier/métodos , AguaRESUMEN
External reflection Fourier transform infrared (FT-IR) experiments are reported for insoluble monomolecular films of an equimolar mixture of 1,2-dipalmitoylphosphatidylcholine (DPPC) and 1,2-dipalmitoylphosphatidylserine (DPPS) at the A/W interface as a function of surface pressure and Ca2+ ion presence. The separate components showed a surface pressure-induced conformational ordering of the acyl chains. The conformational ordering occurred more cooperatively for the DPPS. Acyl chain perdeuteration of the DPPC permitted the observation of the response of the individual components in the binary mixture to changes in surface tension and to the presence of Ca2+. Plots of surface pressure versus CH2 or CD2 stretching frequencies were analyzed with a two-state model. At each surface pressure within the two-state region, the fraction of disordered form was the same for each lipid component, suggesting that they are well mixed on the surface. Calcium ion (5 mM in the subphase) produces almost no effect on the pressure-induced acyl chain ordering of the DPPC in a single component film, whereas the same levels of Ca2+ induce acyl chain ordering at all surface pressures in both components of the binary mixture. Thus, unlike the bulk phase mixture of DPPC/DPPS, the binary lipids in this mixed monolayer film appear to retain their miscibility in the presence of Ca2+. Finally, Ca(2+)-induced dehydration of the phosphate group was observed through characteristic frequency shifts in the asymmetric PO2- stretching mode.
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1,2-Dipalmitoilfosfatidilcolina/química , Calcio/química , Membranas Artificiales , Fosfatidilserinas/química , Aire , Fenómenos Biofísicos , Biofisica , Deuterio , Modelos Químicos , Estructura Molecular , Presión , Solubilidad , Espectroscopía Infrarroja por Transformada de Fourier , Agua/químicaRESUMEN
The structure and dynamics of synthetic melittin (MLT) and MLT analogues bound to monomyristoylphosphatidylcholine micelles, dimyristoylphosphatidylcholine vesicles, and diacylphosphatidylcholine films have been investigated by fluorescence, CD, attenuated total reflectance (ATR) FTIR, and 13C NMR spectroscopy. All of these methods provide information about peptide secondary structure and/or about the environment of the single tryptophan side chain in these lipid environments. ATR-FTIR data provide additional information about the orientation of helical peptide segments with respect to the bilayer plane. Steady-state fluorescence anisotropy, fluorescence lifetime, and 13C NMR relaxation data are used in concert to provide quantitative information about the dynamics of a single 13C-labeled tryptophan side chain at position 19 in lipid-bound MLT, and at positions 17, 11, and 9, respectively, in lipid-bound MLT analogues. Peptide chain dynamics are probed by NMR relaxation studies of 13C alpha-labeled glycine incorporated into each of the MLT peptides at position 12. The cumulative structural and dynamic data are consistent with a model wherein the N-terminal alpha-helical segment of these peptides is oriented perpendicular to the bilayer plane. Correlation times for the lysolipid-peptide complexes provide evidence for binding of a single peptide monomer per micelle. A model for the membranolytic action of MLT and MLT-like peptides is proposed.
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Membrana Dobles de Lípidos/química , Meliteno/química , Péptidos/química , Dicroismo Circular , Polarización de Fluorescencia , Análisis de Fourier , Espectroscopía de Resonancia Magnética , Meliteno/análogos & derivados , Meliteno/síntesis química , Micelas , Unión Proteica , Conformación Proteica , Espectrometría de Fluorescencia , Espectrofotometría Infrarroja , Relación Estructura-Actividad , Triptófano/químicaRESUMEN
There are conflicting reports in the literature regarding the role of the Ah locus in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) immunotoxicity. The present studies have utilized two congenic strains of C57Bl/6 mice that differ only at this locus to assess its influence on TCDD-induced suppression of antibody responses. Mice were given a single oral dose of TCDD 2 days prior to challenge with sheep red blood cells (SRBC) or trinitrophenyl-lipopolysaccharide (TNP-LPS). The subsequent dose-dependent effects of TCDD on the amount of antibody produced by splenic plasma cells were measured using the hemolytic antibody isotope release assay. In addition, the relative importance of the Ah genotype of lymphoid versus nonlymphoid tissue was examined in adoptive transfer experiments. Aryl hydrocarbon hydroxylase (AHH) activity was significantly induced in Ahbb mice by a dose of 0.5 micrograms/kg TCDD and maximally induced by a dose of 2 micrograms/kg. Ahdd mice required 10-fold higher doses of TCDD to induce comparable levels of AHH. The degree of thymic involution and liver hypertrophy induced by TCDD was also influenced by the Ah genotype of the animals. Both Ahbb and Ahdd mice exhibited dose-dependent suppression of the anti-TNP response following TCDD exposure. The ID50 was 7.0 micrograms/kg in Ahbb mice and 30.8 micrograms/kg in Ahdd mice. Suppression of the antibody response to SRBC was also dependent on the Ah locus. The ID50 in Ahbb mice was 0.6 micrograms/kg TCDD. However, an apparent biphasic dose response for suppression of the anti-SRBC response in Ahdd mice suggested the involvement of an Ah-independent component of suppression as well. In adoptive transfer studies, lymphocytes were identified as an Ah-dependent component of the response. The Ah-independent component of the response was not identified, and could be either lymphoid or nonlymphoid in nature. The possibility that T helper cells represent the Ah-independent component is discussed.
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Dioxinas/toxicidad , Tolerancia Inmunológica/efectos de los fármacos , Dibenzodioxinas Policloradas/toxicidad , Receptores de Droga/genética , Animales , Formación de Anticuerpos/efectos de los fármacos , Antígenos T-Independientes/inmunología , Hidrocarburo de Aril Hidroxilasas/biosíntesis , Peso Corporal/efectos de los fármacos , Eritrocitos/inmunología , Femenino , Inmunización Pasiva , Lipopolisacáridos/inmunología , Hígado/efectos de los fármacos , Masculino , Ratones , Ratones Endogámicos C57BL , Tamaño de los Órganos/efectos de los fármacos , Receptores de Hidrocarburo de Aril , Ovinos/inmunología , Linfocitos T/inmunologíaRESUMEN
The objective of the present studies was to determine if acute exposure to an immunotoxic dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces alterations in the expression of lymphocyte surface markers as measured by multiparameter flow cytometry. The immunotoxicity of a single oral dose of TCDD was assessed by the anti-SRBC PFC response; an ED50 of 0.74 micrograms/kg was determined. Subpopulations in the spleen and thymus of C57B1/6 mice were analyzed 2 days following exposure to 2 micrograms/kg TCDD. In addition, splenic lymphocyte subsets were examined on Days 1-4 following SRBC challenge of mice treated with 0, 2, or 5 micrograms/kg TCDD. T and B cells were identified by single parameter analysis of Thy 1.2 and Ig expression. T cell subsets were defined by dual parameter analysis of CD4 and CD8 expression. In TCDD-treated mice, the percentage and the total number of double-positive CD4+ CD8+ thymocytes were significantly decreased while the percentage but not the total number of double-negative CD4- CD8- thymocytes was significantly increased. No changes in the percentage or total number of single positive (CD4+ CD8- or CD4- CD8+) thymocyte subsets were observed. In contrast to the thymus, lymphocyte subsets in the spleen were not significantly altered in percentage or total number 2 days following acute TCDD exposure. When splenic lymphocytes were analyzed daily following SRBC challenge, Ig+, Thy 1.2+, and CD4+ CD8- subpopulations remained relatively unchanged in both control and TCDD-treated animals. A small but significant decrease in the percentage of CD4- CD8+ T cells was observed on Day 3 in mice treated with 2 or 5 micrograms/kg TCDD when compared to that of vehicle-treated mice. The total number of CD4- CD8+ splenocytes was also significantly lower in the 5-micrograms/kg group on Day 3. However, this effect appeared to result from an elevation of the CD4- CD8+ subset in the controls rather than from a reduction in the TCDD-treated groups. Double-positive (CD4+ CD8+) lymphocytes were not detected in either control or TCDD-treated spleens. These results indicate that an acute dose of TCDD which reduced the splenic anti-SRBC response by 65-80% did not cause detectable changes in major splenic lymphocyte subpopulations. This is an important finding from the standpoint of utilizing lymphocyte subset analysis to screen for potential immunotoxic effects of TCDD. Specifically, the absence of subset changes does not preclude the presence of functional immunosuppression.
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Antígenos de Superficie/análisis , Dioxinas/toxicidad , Recuento de Leucocitos/efectos de los fármacos , Linfocitos/efectos de los fármacos , Dibenzodioxinas Policloradas/toxicidad , Bazo/efectos de los fármacos , Timo/efectos de los fármacos , Animales , Antígenos de Diferenciación de Linfocitos T/análisis , Antígenos CD4/análisis , Antígenos CD8 , Relación Dosis-Respuesta a Droga , Femenino , Citometría de Flujo , Tolerancia Inmunológica , Linfocitos/inmunología , Ratones , Ratones Endogámicos C57BL , Fenotipo , Bazo/inmunología , Timo/inmunologíaRESUMEN
A method originally proposed by Snyder and Poore [(1973) Macromolecules 6, 708-715] as a specific probe of trans-gauche isomerization in hydrocarbon chains and recently applied [Mendelsohn et al. (1989) Biochemistry 28, 8934-8939] to the quantitative determination of phospholipid acyl chain conformational order is utilized to monitor the effects of cholesterol at various depths in dipalmitoylphosphatidylcholine (DPPC) bilayers. The method is based on the observation that the CD2 rocking modes from the acyl chains of specifically deuterated phospholipids occur at frequencies in the Fourier transform infrared spectrum which depend upon the local geometry (trans or gauche) of the C-C-C skeleton surrounding a central CD2 group. Three specifically deuterated derivatives of DPPC, namely, 4,4,4',4'-d4 DPPC (4-d4 DPPC), 6,6,6',6'-d4 DPPC (6-d4 DPPC), and 12,12,12',12'-d4 DPPC (12-d4 DPPC), have been synthesized, and the effects of cholesterol addition at 2:1 DPPC/cholesterol (mol:mol) on acyl chain order at various temperatures have been determined. At 48 degrees C, cholesterol inhibits gauche rotamer formation by factors of approximately 9 and approximately 6 at positions 6 and 4, respectively, of the acyl chains, thus demonstrating a strong ordering effect in regions of the bilayer where the sterol rings are presumed to insert parallel to the DPPC acyl chains. In contrast, the ability of the sterol to order the acyl chains is much reduced at the 12-position. The sterol demonstrates only a slight disordering of phospholipid gel phases. Finally, the contributions of different classes of gauche conformers to the spectra have been determined.(ABSTRACT TRUNCATED AT 250 WORDS)
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Dimiristoilfosfatidilcolina , Membrana Dobles de Lípidos , Colesterol , Deuterio , Modelos Teóricos , Conformación Molecular , Espectrofotometría InfrarrojaRESUMEN
A quantitative infrared characterization of phospholipid acyl chain disordering in 6,6,6'6'-d4 dipalmitoylphosphatidylcholine/ Gramicidin D bilayers has been made. Three CD2 rocking modes, at 622 cm-1, 646-649 cm-1, and 651-653 cm-1, assigned to particular conformers, were used to determine disorder in the presence of peptide, as well as percentages of particular classes of conformer within the total gauche population. At 44C, the gauche percentages in 10:1 and 30:1 lipid/peptide mixtures were 15% and 17%, respectively. At 34C, the corresponding values were 9.8% and 2.6%. The percentage of (single gauche bend + kink) conformers, relative to multiple gauche forms, decreases dramatically from 78% in the 30:1 mixture to 15% in the 10:1 mixture at 44C. These data provide the first quantitative measure of the extent to which a membrane-spanning peptide disorders phospholipid gel phases and orders liquid crystal phases.
Asunto(s)
1,2-Dipalmitoilfosfatidilcolina , Gramicidina , Lípidos de la Membrana , Colesterol , Modelos Biológicos , Conformación Molecular , Espectrofotometría InfrarrojaRESUMEN
A method is proposed and demonstrated for the direct determination of conformational disorder (trans-gauche isomerization) as a function of acyl-chain position in phospholipid bilayer membranes. Three specifically deuterated derivatives of dipalmitoylphosphatidylcholine (DPPC), namely 4,4,4',4'-d4-DPPC (4-d4-DPPC), 6,6,6',6'-d4-DPPC (6-d4-DPPC), and 10,10,10',10'-d4-DPPC (10-d4-DPPC), have been synthesized. The CD2 rocking modes in the Fourier transform infrared (FT-IR) spectrum have been monitored as a function of temperature for each derivative. A method originally applied by Snyder and Poore [(1973) Macromolecules 6, 708-715] as a specific probe of hydrocarbon chain conformation in alkanes has been used to analyze the data. The rocking modes appear at 622 cm-1 for a CD2 segment surrounded by a trans C-C-C skeleton and between 645 and 655 cm-1 for segments surrounded by particular gauche conformers. The integrated band intensities of these modes have been used to monitor trans-gauche isomerization in the acyl chains at particular depths in the bilayer. At 48 degrees C, above the gel-liquid-crystal phase transition, the percentage of gauche rotamers present is 20.7 +/- 4.2, 32.3 +/- 2.3, and 19.7 +/- 0.8 for 4-d4-DPPC, 6-d4-DPPC, and 10-d4-DPPC, respectively. The gel phase of the latter two molecules is highly ordered. In contrast, a substantial population of gauche rotamers was observed for the 4-d4-DPPC. The conformational analysis yields a range of 3.6-4.2 gauche rotamers/acyl chain of DPPC above the phase transition. This range is in excellent accord with the dilatometric data of Nagle and Wilkinson [(1978) Biophys. J. 23, 159-175]. The significant advantages of the FT-IR approach are discussed.