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L W Arnold

Publications and source records attributed to L W Arnold.

At least 19 recordsLinked to original sources
PubMed2001

A VH12 transgenic mouse exhibits defects in pre-B cell development and is unable to make IgM+ B cells.

V(H)12 B cells undergo stringent selection at multiple checkpoints to favor development of B-1 cells that bind phosphatidylcholine. Selection begins with the V(H) third complementarity-determining region (CDR3) at the pre-B cell stage, in which most V(H)12 pre-B cells are selectively eliminated, enriching for those with V(H)CDR3s of 10 aa and a fourth position Gly (designated 10/G4). To understand this selection, we compared B cell differentiation in mice of two V(H)12 transgenic lines, one with the favored 10/G4 V(H)CDR3 and one with a non-10/G4 V(H)CDR3 of 8 aa and no Gly (8/G0). Both H chains drive B cell differentiation to the small pre-BII cell stage, and induce allelic exclusion and L chain gene rearrangement. However, unlike 10/G4 pre-B cells, 8/G0 pre-B cells are deficient in cell division and unable to differentiate to B cells. We suggest that this is due to poor 8/G0 pre-B cell receptor expression and to an inability to form an 8/G0 B cell receptor. Our findings also suggest that V(H)12 H chains have evolved such that association with surrogate and conventional L chains is most efficient with a 10/G4 CDR3. Thus, selection for phosphatidylcholine-binding B-1 cells is most likely the underlying evolutionary basis for the loss of non-10/G4 pre-B cells.

Alleles↗
PubMed2001

Disrupted B-lymphocyte development and survival in interleukin-2-deficient mice.

Interleukin-2-deficient (IL-2-/-) mice develop a spontaneous, progressive, CD4+ T-cell-mediated colitis with an age-related decrease in the number of B lymphocytes. The aim of this study was to determine the mechanisms of B-cell loss in IL-2-/- mice. Serum immunoglobulin G1 (IgG1) levels in 8-week-old IL-2-/- mice were above normal but then decreased dramatically with advancing age. Between 8 and 11 weeks of age, the number of B-cell progenitors (B220+ IgM-) in the bone marrow of IL-2-/- mice was less than half of those in IL-2+/+ littermates. By 22 weeks of age, very few progenitor cells remained in the bone marrow of most mice, and spleens were almost devoid of B cells. Likewise, B1 cells were not present in the peritoneal cavity of aged IL-2-/- mice. Flow cytometry analysis of B-cell differentiation in the bone marrow suggested a progressive loss of B cells from the most mature to the least mature stages, which was not dependent on IL-2 receptor-alpha (IL-2Ralpha) expression. B cells transferred from normal animals had similar survival rates in IL-2-/- and wild-type mice. We conclude that conventional B cells in older IL-2-/- mice are lost by attrition owing to a derangement in B-cell development. Because B1 cells are less dependent on the bone marrow, a separate mechanism for their loss is suggested.

Animals↗
PubMed2000

Identification of a precursor to phosphatidyl choline-specific B-1 cells suggesting that B-1 cells differentiate from splenic conventional B cells in vivo: cyclosporin A blocks differentiation to B-1.

The origin of B-1 cells is controversial. The initial paradigm posited that B-1 and B-2 cells derive from separate lineages. More recently it has been argued that B-1 cells derive from conventional B cells as a result of T-independent Ag activation. To understand B-1 cell differentiation, we have generated Ig transgenic (Tg) mice using the H and L chain genes (VH12 and Vkappa4) of anti-phosphatidyl choline (anti-PtC) B cells. In normal mice anti-PtC B cells segregate to B-1. Segregation is intact in VH12 (6-1) and VH12/Vkappa4 (double) Tg mice that develop large numbers of PtC-specific B cells. However, if B-1 cell differentiation is blocked, anti-PtC B cells in these Tg mice are B-2-like in phenotype, suggesting the existence of an Ag-driven differentiative pathway from B-2 to B-1. In this study, we show that double Tg mice have a population of anti-PtC B cells that have the phenotypic characteristics of both B-2 and B-1 cells and that have the potential to differentiate to B-1 (B-1a and B-1b). Cyclosporin A blocks this differentiation and induces a more B-2-like phenotype in these cells. These findings indicate that these cells are intermediate between B-2 and B-1, further evidence of a B-2 to B-1 differentiative pathway.

Animals↗
PubMed1999

Selection at multiple checkpoints focuses V(H)12 B cell differentiation toward a single B-1 cell specificity.

Phosphatidyl choline (PtC)-specific B cells segregate to the B-1 subset, where they comprise up to 10% of the B-1 repertoire. About half express V(H)12 and Vkappa4/5H and are restricted in V(H)CDR3. We have previously reported that anti-PtC V(H)CDR3 is enriched among V(H)12-expressing cells by selective elimination of pre-B cells. We report here a bias for Vkappa4/5H expression among V(H)12-expressing B cells, even among those that do not bind PtC and are not B-1. This is due in part to an inability of V(H)12 to associate with many light (L) chains but must also be due to a selective advantage in survival or clonal expansion in the periphery for Vkappa4/5H-expressing cells. Thus, the bias for Vkappa4/5H expression is independent of PtC binding, and, as segregation to B-1 occurs after Ig gene expression, it precedes segregation to the B-1 subset. In 6-1 mice, splenic B-1 cells reside in follicles but segregate to follicles distinct from those that contain B-2 cells. These data indicate that selection at multiple developmental checkpoints ensures the co-expression of an anti-PtC V(H)CDR3 and L chain in a high frequency of V(H)12 B cells. This focus toward specificity for PtC facilitates the development of a large anti-PtC B-1 repertoire.

Amino Acid Sequence↗
PubMed1999

Effects of chronic heparin administration on coronary vascular adaptation to hypertension and ventricular hypertrophy in sheep.

BACKGROUND: Hypertension decreases myocardial perfusion capacity in adults for several reasons, including insufficient coronary angiogenesis with left ventricular (LV) hypertrophy, arteriolar hypertrophy, and altered vasomotion. Heparin influences growth factors that promote angiogenesis and vasodilation and inhibit arteriolar wall thickening. METHODS AND RESULTS: Adult sheep were given heparin 200 U/kg body wt SC twice daily throughout 6 weeks of LV and coronary hypertension from a progressively constricted ascending aortic band (n=14). They were compared with untreated sheep with (n=13) and without (n=13) aortic stenosis. After 6 weeks, maximum myocardial perfusion was measured during adenosine infusion in the conscious state by the microsphere method. Sheep with aortic stenosis had less maximum coronary flow per gram, less conductance reserve, and thicker arteriolar walls in the LV and nonhypertrophied right ventricle. Capillary density decreased in the LV endomyocardium and remained unchanged in the right ventricle. Heparin-treated sheep had significant partial normalization of coronary conductance reserve and maximum perfusion in both ventricles and capillary density in the LV endomyocardium. Arteriolar wall thickness was unchanged. Compared with untreated sheep with aortic stenosis, in heparin-treated sheep LV FGF-2 protein increased 2-fold, whereas FGF-2 mRNA remained unchanged. VEGF mRNA and protein increased 3-fold and 1.4-fold, respectively, whereas TGF-beta(1) mRNA declined 3-fold. CONCLUSIONS: Heparin administration during LV hypertension increases heparin-binding angiogenic factors FGF-2 and VEGF in the LV and ameliorates decreases in LV perfusion capacity and capillary density.

Adaptation, Physiological↗
PubMed1998

B-1 cell development: evidence for an uncommitted immunoglobulin (Ig)M+ B cell precursor in B-1 cell differentiation.

Murine phosphatidyl choline (PtC)-specific B cells in normal mice belong exclusively to the B-1 subset. Analysis of anti-PtC (VH12 and VH12/Vkappa4) transgenic (Tg) mice indicates that exclusion from B-0 (also known as B-2) occurs after immunoglobulin gene rearrangement. This predicts that PtC-specific B-0 cells are generated, but subsequently eliminated by either apoptosis or differentiation to B-1. To investigate the mechanism of exclusion, PtC-specific B cell differentiation was examined in mice expressing the X-linked immunodeficiency (xid) mutation. xid mice lack functional Bruton's tyrosine kinase (Btk), a component of the B cell receptor signal transduction pathway, and are deficient in B-1 cell development. We find in C57BL/ 6.xid mice that VH12 pre-BII cell selection is normal and that PtC-specific B cells undergo modest clonal expansion. However, the majority of splenic PtC-specific B cells in anti-PtC Tg/xid mice are B-0, rather than B-1 as in their non-xid counterparts. These data indicate that PtC-specific B-0 cell generation precedes segregation as predicted, and that Btk function is required for efficient segregation to B-1. Since xid mice exhibit defective B cell differentiation, not programmed cell death, these data are most consistent with an inability of PtC-specific B-0 cells to convert to B-1 and a single B cell lineage.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1997

Noninvasive determination of cardiac output in a model of acute lung injury.

OBJECTIVE: To examine the utility of single breath CO2 analysis as a noninvasive measure of cardiac output in a model of acute lung injury. SETTING: An animal laboratory in a university-affiliated medical center. DESIGN: A prospective, animal cohort study comparing 21 parameters derived from single breath CO2 analysis with cardiac output determined by an ultrasonic flow probe. SUBJECTS: Six adult sheep with saline lavage-induced acute lung injury. INTERVENTIONS: Animals were treated with repetitive saline lavage to achieve a uniform degree of acute lung injury (PaO2 of < 100 torr [< 13.32 kPa] on an FIO2 of 1.0). Cardiac output was manipulated by successive injections of an hydraulic constrictor placed around the inferior vena cava and measured using an ultrasonic flow probe. Twenty-one derived components of the CO2 expirogram were evaluated as predictors of cardiac output. MEASUREMENTS AND MAIN RESULTS: Thirty-eight measurements of cardiac output were available for comparison with derived variables from the CO2 expirogam. Stepwise linear regression identified four variables for the equation predicting cardiac output: a) PaO2/FIO2 ratio; b) the angle between the slope lines for phases II and III divided by the tidal volume; c) mixed expired CO2 tension; and d) physiologic deadspace to tidal volume ratio. The multivariate equation was highly statistically significant and explained 80% of the variance (adjusted R2 = .80, p < .0001). The blas and precision of the calculated cardiac output were .00 and .38, respectively. The mean percent difference for the cardiac output estimates derived from the single breath CO2 analysis station was -0.01%. CONCLUSIONS: Our results indicate that changes in cardiac output can be determined using components of the CO2 expirogram with a high degree of reliability in animals with induced acute lung injury. Specifically, the use of four parameters derived from a plot of expired CO2 concentration vs. expired volume predict changes in cardiac output in adult sheep with induced lung injury with an adjusted coefficient of determination of .80. Prospective application of this technology in the clinical setting with the rapidly changing physiology that is characteristic of the acutely ill patient will be essential in determining the clinical usefulness of single breath CO2 analysis as a noninvasive measure of cardiac output.

Acute Disease↗
PubMed1996

Phenotype of B cells responding to the thymus-independent type-2 antigen polyvinyl pyrrolidinone.

We have determined the origin and cell surface phenotype of B cells producing antibody in response to immunization with the non-self TI-2 antigen polyvinyl pyrrolidinone (PVP). We report that the responding cells are derived from precursors in adult bone marrow and display the phenotype characteristic of B-1 cells. By use of allotype marked chimeric mice, constructed by reconstituting lethally irradiated recipients with adult bone marrow and peritoneal B-1 lymphocytes of recognizably different Ig allotypes, immunized with 1 microgram PVP, we found that although a substantial part of the total IgM produced in these chimeras bore the allotype of the transferred peritoneal B-1 cells, essentially all of the anti-PVP IgM expressed the allotype of the adult bone marrow. Fifteen of 16 hybridomas derived from a normal PVP-immune adult mouse bore N nucleotides at the V-D and D-J junctions of their heavy chain CDR3 regions, indicating their origin from precursors in the adult bone marrow. By use of ELISA spot analysis, we found the cells responding to PVP to be localized in the spleens of normal immunized mice. We then used multiparameter flow cytometric sorting to determine the cell surface phenotype of these cells. We found that the cells producing anti-PVP were greatly enriched in a small subpopulation with the phenotypic characteristics of B-1 cells; they were B220intermediate, CD5low, IgMhigh, IgDlow, CD43+ and CD23-. This subpopulation was also enriched for all cells producing IgM, regardless of specificity (the so-called 'spontaneous' antibody). We conclude that the B-1 phenotype is more likely a marker for a state of differentiation than for a discrete lineage of B cells.

Animals↗
PubMed1996

Single breath CO2 analysis: description and validation of a method.

OBJECTIVES: To evaluate the performance of a newly developed single breath CO2 analysis station in measuring the airway deadspace in a lung model (study 1), and then to quantify the bias and precision of the physiologic deadspace measurement in a surfactant-depleted animal model (study 2). DESIGN: A prospective bench validation of a new technique of airway deadspace measurement using a criterion standard (study 1); a prospective, animal cohort study comparing a new technique of physiologic deadspace measurement with a reference method (Bohr-Enghoff method) (study 2). SETTING: A bench laboratory and animal laboratory in a university-affiliated medical center. SUBJECTS: A lung model (study 1), and adult sheep with induced surfactant deficiency (saline lavage) (study 2). METHODS: The single breath CO2 analysis station consists of a mainstream capnometer, a variable orifice pneumotachometer, a signal processor, and computer software with capability for both on- and off-line data analysis. Study 1: We evaluated the accuracy of the airway deadspace calculation using a plexiglass lung model. The capnometer and pneumotachometer were placed at the ventilator Y-piece with polyvinyl chloride tubing added to simulate increased airway deadspace. Segments of tubing were sequentially removed during each testing session to simulate decreasing deadspace. The calculated airway deadspace was derived from the single breath CO2 plot and compared with the actual tubing volume using least-squares linear regression and paired t-tests. Study 2: The accuracy of the physiologic deadspace measurement was examined in a saline-lavaged animal model by comparing the physiologic deadspace calculated from the single breath CO2 analysis station with values obtained using the Enghoff modification of the Bohr equation: deadspace/tidal volume ratio = (PaCO2-mixed expired PCO2)/PaCO2. MEASUREMENTS AND MAIN RESULTS: Study 1: Thirty-six measurements of calculated airway deadspace were made and compared with actual circuit deadspace during four different testing conditions. Measured airway deadspace correlated significantly with actual circuit deadspace (r2 = .99). The proportional error of the method was -0.8% with a 95% confidence interval from -3.6% to 1.9%. Study 2: A total of 27 pairs of measurements in four different animals were available for analysis. The derived physiologic deadspace/tidal volume ratio significantly correlated with the value obtained using the Bohr-Enghoff method (r2 = .84). The bias and precision of our physiologic deadspace calculation were .02 and .02, respectively, and the mean percent difference for the physiologic deadspace calculated from the single breath CO2 analysis station was 2.4%. CONCLUSIONS: Our initial experience with the single breath CO2 analysis station indicates that this device can reliably provide on-line evaluation of the single-breath CO2 waveform. In particular, estimation of the airway and physiologic deadspace under a variety of testing conditions was consistently within 5% of actual values. We feel that with further application and refinement of the technique, single breath CO2 analysis may provide a noninvasive, on-line monitor of changes in pulmonary blood flow.

Animals↗
PubMed1996

Noninvasive determination of cardiac output using single breath CO2 analysis.

OBJECTIVE: To examine the utility of single breath CO2 analysis as a noninvasive measure of cardiac output. SETTING: An animal laboratory in a university-affiliated medical center. DESIGN: A prospective, animal cohort study comparing 21 parameters derived from single breath CO2 analysis with cardiac output determined by an ultrasonic flow probe. SUBJECTS: Six healthy adult sheep. METHODS: The single breath CO2 analysis station consists of a mainstream capnometer, a variable orifice pneumotachometer, a signal processor, and computer software with capability for both on- and off-line data analysis. Twenty-one derived components of the CO2 expirogram were evaluated as predictors of cardiac output. Cardiac output was manipulated by successive injections of a hydraulic constrictor placed around the inferior vena cava. MEASUREMENTS AND MAIN RESULTS: Thirty-four measurements of cardiac output were available for comparison with derived variables from the CO2 expirogram. Stepwise linear regression identified two variables that were most predictive of cardiac output: a) the angle between the slope lines for phase II and III of the CO2 expirogram divided by the volume of CO2 per breath (angle/mL CO2); and b) the slope of phase II. The multivariate equation was highly statistically significant and explained 94% of the variance (adjusted r2 = .94, p < .0001). The bias and precision of the calculated cardiac output were .00 and .23, respectively. The mean percent difference for the cardiac output estimate derived from the single breath CO2 analysis station was 0.36%. CONCLUSIONS: Our data indicate that analysis of the CO2 expirogram can yield accurate information about the cardiovascular system. Specifically, two variables derived from a plot of expired CO2 concentration vs. expired volume predict changes in cardiac output in healthy adult sheep with an adjusted coefficient of determination of .94. Prospective application of this technology in the setting of lung injury and rapidly changing physiology will be essential in determining the clinical usefulness of the technique.

Animals↗
PubMed1996

Antiphencyclidine monoclonal Fab fragments reverse phencyclidine-induced behavioral effects and ataxia in rats.

Antiphencyclidine monoclonal antibody binding fragments (anti-PCP Fab) were studied in rats as a possible treatment for phencyclidine (PCP) overdose. Each male Sprague-Dawley rat (n = 4 per group) received an i.v. dose of 1 mg/kg of PCP followed 5 min later (as toxicity maximized) by one of three treatments in a random cross-over design. The treatments were 1 ml of saline, a nonspecific polyclonal human Fab, or a high affinity (Kd = 1.8 nM) anti-PCP monoclonal Fab. The doses of the nonspecific and anti-PCP Fab were 0.3, 1.0 and 3.0 times the mole equivalent (mol-eq) dose of PCP. Changes in locomotor activity and ataxia were the best indicators of PCP-induced behaviors among several time-dependent behavioral changes that were evaluated. PCP administration followed by saline treatment resulted in increases in locomotor activity and ataxia that declined to base line after 35 to 40 min. Anti-PCP Fab at 1.0 and 3.0 times the mol-eq dose of PCP significantly (P < .05) and rapidly reversed PCP-induced behaviors to base-line values. Although the 0.3 mol-eq dose of Fab appeared to slightly decrease the behavioral toxicity, the effects were not statistically different from controls in most cases. No significant effects on PCP-induced behaviors were observed after any dose of the nonspecific Fab. In addition, pharmacological and immunological specificity were tested further by treatment of MK-801 {(+)-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine-}-induced behavioral effects. MK-801 is a PCP-like, noncompetitive N-methyl-D-aspartate receptor antagonist which is structurally unrelated to PCP. The anti-PCP Fab treatment had no effect on MK-801-induced locomotor activity. These data clearly show that anti-PCP Fab is a specific PCP antagonist that can rapidly reverse PCP-induced behavioral toxicity in the rat.

Animals↗
PubMed1994

Development of B-1 cells: segregation of phosphatidyl choline-specific B cells to the B-1 population occurs after immunoglobulin gene expression.

Adult mice have two easily recognizable subsets of B cells: the predominant resting population of the spleen, called B-2, and those called B-1, which predominate in coelomic cavities and can express CD5. Some antibody specificities appear to be unique to the B-1 population. Cells expressing antibody specific for phosphatidyl choline (PtC) are the most frequent, comprising 2-10% of peritoneal B cells in normal mice. To understand the basis for the segregation of the anti-PtC specificity to this population, we have produced transgenic (Tg) mice expressing the rearranged VH12 and V kappa 4 genes of a PtC-specific B-1 cell lymphoma. We find that VH12-Tg and VH12/V kappa 4 double-Tg mice develop very high numbers of PtC-specific peritoneal and splenic B cells. These cells have the characteristics of B-1 cells; most are CD5+, and are all IgMhi, B220lo, and CD23-. In the peritoneum these cells are also CD11b+. In addition, adult mice have many splenic B cells (up to one third of Tg+ cells) that express the VH12 Tg but do not bind PtC, presumably because they express a V kappa gene other than V kappa 4. These cells appear to be B-2 cells; they are CD23+, CD11b-, IgMlo, B220hi, and CD5-. Thus, mice given either the VH12 Tg alone or together with the V kappa 4 Tg develop a large population of PtC-specific B cells which belong exclusively to the B-1 population. Since B-2 cells can express the VH12 and V kappa 4 gene separately, we interpret these data to indicate that the events leading to the segregation of PtC-specific B cells to the B-1 population in normal mice are initiated after Ig gene rearrangement and expression. These data are discussed with regard to hypotheses of the origin of B-1 cells. We also find that VH12-Tg mice have a marked decrease in the generation of Tg-expressing B cells in adult bone marrow, but not newborn liver. We speculate that this may be related to positive selection of VH12-expressing B cells during differentiation.

Animals↗
PubMed1994

Anti-phencyclidine monoclonal Fab fragments markedly alter phencyclidine pharmacokinetics in rats.

The purpose of these studies was to explore the use of phencyclidine (PCP)-specific high affinity antibodies as a possible treatment for phencyclidine toxicity. High affinity (Kd = 1.8 nM) anti-PCP monoclonal Fab fragments were purified from papain digested anti-PCP immunoglobulin produced in mouse ascites. Control animals (n = 5) received an i.v. bolus dose of 1 mg/kg of PCP, along with a tracer dose of 250 microCi of [3H]PCP. Fab-treated rats (n = 5) also received this PCP dose, but at 2 hr after dosing (when PCP distribution was complete) they received an equimolar dose of anti-PCP Fab (50 mg). Within 5 min after the anti-PCP Fab administration, serum [3H]PCP concentrations increased approximately 60- to 100-fold. Fab treatment caused the [3H]PCP volume of distribution at steady state to decrease from 12.6 +/- 3.0 liters/kg (mean +/- S.D.) in control animals to 0.6 +/- 0.2 liters/kg in the Fab-treated animals (about 5% of control values). Systemic clearance changed from 66.3 +/- 16.9 to 6.8 +/- 2.8 ml/min/kg (about 10% of control values). Because both volume of distribution and systemic clearance decreased to a similar degree, the terminal elimination half-life did not change significantly (3.9 hr in controls vs. 4.9 hr in treated animals, harmonic means). Renal clearance decreased from 1.8 +/- 0.6 to 0.62 +/- 0.17 ml/min/kg after Fab treatment. The anti-PCP Fab caused the percentage of PCP recovered in urine to increase from 2.5 +/- 0.5 to 10.3 +/- 4.7%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Mechanisms that limit the diversity of antibody: three sequentially acting mechanisms that favor the spontaneous production of germline encoded anti-phosphatidyl choline.

Antibody to phosphatidyl choline (PtC) is produced spontaneously in mice, by approximately 2-10% of naturally occurring CD5+ (B1) B cells in the peritoneum. Much of this antibody is encoded by the VH11 gene associated with a specific V kappa 9 gene. Constraints on the size and structure of the H chain CDR3 have been defined from nucleotide sequences of genes expressed by hybridomas and lymphomas derived from adult mice. All employ JH1 and all encode tyrosine as the first amino acid in CDR3, which is either nine or 10 amino acids long; the last six are always the same, start with tyrosine, and are rich in aromatic amino acids. Those with nine amino acids in CDR3 have glycine or serine in the second position and asparagine, serine or proline in the third; those with 10 have an additional aspartate or glycine inserted after the first tyrosine. DSP2 genes are used by 80% and DFL16 by 20%. Productively rearranged VH11 genes in neonates and in 18 day fetal liver display a greater, but still limited degree of diversity. All four JH genes are used and the length of CDR3 varies from three to 12 amino acids, but the first is tyrosine in 58 of 61 and DSP2 genes are used by 80% of these productive VDJ assemblies. Non-productive rearrangements of VH11 in fetal liver show a different pattern; 41% use DFL16 genes and only 40% have a TAx codon in the first position of CDR3. All rearrangements show evidence of a bias in favor of joining the VH11 gene to D genes at positions of matching nucleotide overlap.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Transition from compensated hypertrophy to intrinsic myocardial dysfunction during development of left ventricular pressure-overload hypertrophy in conscious sheep. Systolic dysfunction precedes diastolic dysfunction.

BACKGROUND: Patients with aortic stenosis have a period of compensated left ventricular hypertrophy but may eventually develop congestive heart failure. Previous experimental studies showed either normal myocardial contractility in mild short-term pressure overload or myocardial dysfunction with severe pressure overload. Transition from compensated left ventricular hypertrophy to myocardial dysfunction has not been experimentally demonstrated in an adult large animal. Controversial issues in pressure-overload hypertrophy include whether the left ventricular dysfunction is due to insufficient hypertrophy (afterload mismatch) or to intrinsic myocardial dysfunction and whether diastolic dysfunction precedes systolic dysfunction. METHODS AND RESULTS: We induced left ventricular hypertrophy (41% increase in left ventricular to body weight ratio) by gradually tightening a hydraulic constrictor around the ascending aorta in 9 chronically instrumented conscious sheep. Afterload (end-systolic stress) elevation remained constant (approximately 33% greater than baseline) by adjustment of the aortic constrictor over 6 weeks, gradually increasing left ventricular pressure (from 117 +/- 6 to 163 +/- 5 mm Hg) as hypertrophy developed. Four sets (baseline, 2 weeks, 4 weeks, and 6 weeks) of serial hemodynamic studies were performed in each animal with beta-blockade, first with and then without aortic constriction to mechanically match loading conditions. Stepwise methoxamine infusion was performed to obtain load-independent assessment of myocardial contractility. Midwall shortening (P < .05) and shortening rate (P < .05) at mechanically matched loading conditions showed that myocardial dysfunction developed between the fourth and the sixth week. Shortening-preload-afterload (P < .05) and shortening rate-preload-afterload (P < .05) relations, load-independent contractility indices based on the systolic myocardial stiffness concept, also revealed depressed myocardial contractility at the sixth week. Time constant of left ventricular isovolumic relaxation and diastolic myocardial stiffness constant did not change over the 6 weeks. CONCLUSIONS: Transition from normal myocardial contractility to myocardial dysfunction was demonstrated. This transition occurred even when the elevation of afterload remained constant as hypertrophy incompletely adapted to increasing left ventricular pressure. Systolic dysfunction preceded diastolic dysfunction in this model.

Adaptation, Physiological↗
PubMed1992

Autoantibodies to phosphatidylcholine. The murine antibromelain RBC response.

The observation that murine B-cell populations can contain relatively large numbers of cells that produce IgM with the ability to lyse bromelain-treated mouse erythrocytes (BrMRBC), but not normal untreated MRBC, was made nearly 20 years ago. The major observations regarding the antigen specificity, the cells that produce this IgM, and the immunoglobulin V genes that encode them are summarized in this report. The epitope on BrMRBC that is recognized has been identified as the head group of phosphatidylcholine (PtC); B cells whose IgM has this specificity can be easily identified by their ability to bind fluorescent synthetic liposomes whose membrane contains PtC. The cells producing IgM specific for PtC all derive from the Ly-1 B-cell subset, and they use primarily two VH/VL gene pairs to encode the anti-PtC antibodies. The VH genes used describe two new VH gene families, VH11 and VH12. The genes encoding anti-PtC are unmutated and have characteristics and restricted VDJ constructions. The cells with this specificity, within individual mice, are polyclonal. These criteria are consistent with a primary antigen-driven clonal selection mechanism as the basis for the development of this immune specificity.

Animals↗