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Biomedical subjects

D L Ewert

Publications and source records attributed to D L Ewert.

At least 73 records · Page 4Linked to original sources
PubMed1982

B cell expression of endogenous retroviral envelope antigen: biochemical and immunofluorescence characterization.

Plasma cells of line 15I5 chickens have been shown to express antigen that is cross-reactive with endogenous retroviral envelope glycoprotein. In the present study, we isolated this antigen and showed that it is structurally homologous to envelope glycoprotein. As assayed by immunofluorescence, most, if not all, of the plasma cell-associated envelope glycoprotein is present on the cell surface although it is not bound to surface Ig or Ia antigen. Although envelope antigen was not detectable by immunofluorescence on the surface of 15I5 bursal cells or peripheral B lymphocytes, immunochemical assays established that retroviral envelope glycoprotein is present on the surface of the bursal cells but at much lower levels than on the surface of the plasma cells. Both bursal and plasma cells synthesize envelope glycoprotein. These findings indicate that an increased level of expression of endogenous retroviral envelope glycoprotein is a concomitant of the differentiation of B lymphocytes to plasma cells in 15I5 chickens.

Animals↗
PubMed1981

Expression of endogenous retroviral envelope antigen in Ig(+) B cells of immunized 15I5 X 71 chickens.

In a previous study (1), we observed that antigen cross-reactive with structural protein of the endogenous retrovirus RAV-O is expressed in splenic Ig(+) B lymphocytes of immunized 15I5 X 71 chickens. The present experiments were undertaken to determine the relationship of this antigen to viral gag- and env-coded antigenic specificities. As analyzed by immunofluorescence with several antisera, group-specific determinants of the gp85 envelope glycoprotein as well as viral-related type E-specific determinants were detectable in islands of Ig(+) splenocytes; antigenic determinants of viral gag protein were not detected in the splenic islands. These observations indicated that antigen cross-reactive with endogenous retroviral envelope glycoprotein is expressed in Ig(+) B cells.

Absorption↗
PubMed1981

Endogenous retroviral envelope antigen in plasma cells.

Previous observations that endogenous retroviral envelope antigen is expressed in splenic Ig(+) B cells of SRBC-sensitized 15I5 X 71 chickens suggested that expression of this antigen might be a general property of plasma cells in 15I5 and related strains. To investigate this possibility, immunofluorescence assays with antiviral sera were carried out using plasma cells present in Harder glands. Endogenous retroviral envelope antigen was detectable in plasma cells of line 15I5 X 71, 15I5 X 72, and 15I5 chickens but not in plasma cells of line 72, 15B, or 63 chickens. Higher levels of retroviral envelope antigen were detectable in 15I5 X 71 plasma cells as compared to 15I5 X 71 bursal cells. The presence of retroviral envelope antigen in 15I5 plasma cells, coupled with the absence of detectable levels of retroviral p27-related antigen in these cells, suggested that expression of the former is governed by the ev 6 genetic locus.

Animals↗
PubMed1980

Genetics of Ia-like alloantigens in chickens and linkage with B major histocompatibility complex.

Two sets of backcross matings were performed to test for linkage between genes coding for the Ia-like antigens ("Ia") and the B erythrocyte antigens (Ea-B) of the chicken. Evidence is presented which indicates that the "Ia" antigens are determined by a single codominant locus and that the Ea-B and "Ia" loci are on the same chromosome. Failure to detect a single recombinant between the Ea-B and "Ia" loci out of 208 progeny suggests close linkage of the two genes with a map distance of up to about 2 centimorgans. The "Ia" genes are thus included in the B major histocompatibility complex of the chicken.

Animals↗
PubMed1980

Technique for determining total bacterial virus counts in complex aqueous systems.

A direct method is described for measuring bacteriophage concentrations in complex aqueous systems. Conditions for sample clarification, phage recognition, and recovery were optimized. In contrast to the plaque assay, this procedure permits quantitation of total numbers of phages independent of bacterial host. Also, the modifications increase the sensitivity of the sedimentation assay, permitting detection of particles at a minimum concentration of 10(4) per ml. Maximal total phage concentrations in the aqueous phase of sewage and activated sludge mixed liquor were 1.3 x 10(6) and 4.3 x 10(7) per ml, respectively.

Animals↗
PubMed1980

Enumeration of bacteriophages and host bacteria in sewage and the activated-sludge treatment process.

Bacteriophage populations in an activated-sludge sewage treatment plant were enumerated. A newly developed assay for quantitation of total phages, employing direct electron microscopic counts, was used in conjunction with the plaque assay. The total concentration of phages was significantly higher in reactor mixed liquor and effluent than in influent sewage, indicating a net production of phages within the reactor. Maximum total phage concentrations in the fluid phase of sewage, activated-sludge mixed liquor, and reactor effluent were 2.2 x 10(7), 9.5 x 10(7), and 8.4 x 10(7)/ml, respectively. Conditions were optimized for isolation of predominant heterotrophic aerobic bacteria from sewage and mixed liquor. Blending at ice water temperatures was superior to ultrasound or enzyme treatments for maximum release of viable bacteria from microbial floc. A solidified extract of mixed liquor was superior to standard media for cultivating maximum numbers of heterotrophic bacteria. The highest culture counts for sewage and mixed liquor were 1.4 x 10(7) and 1.3 x 10(9)/ml, respectively, which represented only 3 and 6.8% of the total microscopic cell counts. Only 3 out of 48 dominant bacterial isolates from either mixed liquor or sewage were hosts for phages present in the system. The sum of phage populations infecting these three hosts accounted for, at best, 3.8% (sewage) and 0.2% (mixed liquor) of the total number of phages present. Generally, specific phage titers were lower in mixed liquor than in sewage, indicating that these hosts were not responsible for the net production of phages in the reactor. This study emphasizes the limitations of the plaque assay for ecological studies of phages, and it suggests that bacteria responsible for phage production in activated-sludge mixed liquor are either minor components of the heterotrophic population, floc-producing strains, or members of other physiological groups.

Bacteria↗
PubMed1979

Local antibody response in chickens: analysis of antibody synthesis to Newcastle disease virus by solid-phase radioimmunoassay and immunofluorescence with class-specific antibody for chicken immunoglobulins.

The antibody response to Newcastle disease virus was monitored in the sera and salivas of adult chickens immunized by two methods: (i) combined intratracheal-intranasal vaccination followed by intratracheal revaccination or (ii) intramuscular vaccination followed by intratracheal revaccination. By solid-phase radioimmunoassay, only immunoglobulin G (IgG) and IgA antibodies to Newcastle disease virus were detected in the salivas, whereas IgA and IgM antibodies were present in egg whites. The first method produced the highest antibody levels in both serum and saliva and, in addition, prevented detectable virus multiplication in the respiratory tracts upon revaccination 4 weeks later. Plasma cells of all three classes were distributed throughout the tissues lining the oral cavities. The highest densities of plasma cells were in the Harderian glands; IgG was the predominant class, whereas IgA and IgM plasma cells were present in almost equal but lower numbers. The Harderian plasma cells were the most likely source of the antibody found in saliva.

Animals↗
PubMed1978

Effect of aflatoxin on the humoral and cell-mediated immune systems of the chicken.

Chickens fed 2.5 microgram of aflatoxin/g of diet from 2 to 4 weeks of age or from hatching to 4 weeks were deficient in cell-mediated immunity, as measured at 4 weeks of age by the graft-versus-host reaction. Delayed-type hypersensitive skin reactions to tuberculin were also reduced in chickens given dietary aflatoxin from hatching to 7 weeks of age. Humoral immunity, as measured by the ability of 4-week-old chicks to produce natural agglutinins to rabbit red blood cells, was not significantly altered by dietary aflatoxin. A significant decrease in concentrations of serum immunoglobulins (Ig) IgG and IgA, but no IgM, however, did occur in chicks given dietary aflatoxin from hatching to 4 weeks or between 2 and 4 weeks of age. Aflatoxin consumption from 0 to 2 weeks of age produced no marked effect on either cell-mediated or humoral immunity in 4-week-old chicks.

Aflatoxins↗
PubMed1977

Factors influencing the appearance of antibody in tracheal washes and serum of young chickens after exposure to Newcastle disease virus.

The development of plaque-neutralizing antibody in tracheal washes and hemagglutination inhibition antibody in serum was followed after intratracheal and intranasal or intramuscular inoculation of 1-, 14-, or 28-day-old chicks with a lentogenic strain of Newcastle disease virus (NDV). Serum antibody could be detected between 7 and 10 days after intratracheal and intranasal vaccination in birds either with or without maternal antibody to NDV. However, among the 1-day-old group only birds without maternal antibody showed an antibody response after intramuscular inoculation. All birds possessing either actively or passively acquired serum antibody showed a sharp rise and subsequent decline of anti-NDV activity in tracheal washes between 4 and 10 days after intratracheal or intranasal vaccination. Using radiolabeled chicken immunoglobulin injected intravenously as a tracer, it was shown that this initial peak of anti-NDV activity in tracheal washes could be accounted for by enhanced transudation of serum antibody. The transudation of serum antibody coincided with the course of viral pathology observed in the tracheae of infected birds. Neutralizing antibody in tracheal washes beyond 10 to 14 days postvaccination was, most likely, porduced locally, in the respiratory tract.

Administration, Intranasal↗
PubMed1977

Effect of bursectomy and depletion of immunoglobulin A on antibody production and resistance to respiratory challenge after local or systemic vaccination of chickens with Newcastle disease virus.

Surgical removal of the bursa of Fabricius from newly hatched chicks resulted in a depletion of immunoglobulin A (IgA) from serum and bile of 55 and 67% of the birds, respectively, up to 11 weeks of age. The occurrence of IgG and IgM in serum and IgG in bile was not affected by neonatal bursectomy (Bx). A slight compensatory increase in the occurrence of IgM in bile was noted in Bx birds. When exposed to a lentogenic strain of Newcastle disease virus by either intramuscular or intratracheal routes, the Bx group produced a level of serum hemagglutinating antibody and tracheal wash neutralizing antibody indistinguishable from that reached in the sham-Bx group. All of the vaccinated Bx birds challenged by intratracheal exposure to a velogenic strain of Newcastle disease virus remained healthy. These results suggest that IgA is not essential for the development of immunity in the chicken and that other locally produced immunoglobulins or transuded serum antibody may protect the tracheal mucosa in the absence of IgA.

Aerosols↗
PubMed1977

Effect of infectious bursal disease virus on the immunological responsiveness of the chicken.

The immunological response of chickens infected at 28 days of age with infectious bursal disease virus (IBDV) was examined. Cellular immunity was studied by the graft-versus-host reaction and delayed type hypersensitivity skin reactions to tuberculin. Antibody responses to sheep red blood cells (S-RBC's) were tested by a direct hemagglutination test. Circulating levels of immunoglobulins (Ig's) IgM, IgG and IgA were monitored by the radial immunodiffusion test. The results of the graft-versus-host reaction and delayed type hypersensitivity reactions were similar for both the infected and control chicks. IBDV significantly reduced the primary antibody response to S-RBC's, but had no marked effect on the secondary antibody response. Chicks infected with IBDV had normal levels of serum IgM and IgG, but significantly lower levels of IgA when compared to uninfected control birds.

Animals↗
PubMedDate not supplied

Effects of 12 days exposure to simulated microgravity on central circulatory hemodynamics in the rhesus monkey.

Central circulatory hemodynamic responses were measured before and during the initial 9 days of a 12-day 10 degrees head-down tilt (HDT) in 4 flight-sized juvenile rhesus monkeys who were surgically instrumented with a variety of intrathoracic catheters and blood flow sensors to assess the effects of simulated microgravity on central circulatory hemodynamics. Each subject underwent measurements of aortic and left ventricular pressures, and aortic flow before and during HDT as well as during a passive head-up postural test before and after HDT. Heart rate, stroke volume, cardiac output, and left ventricular end-diastolic pressure were measured, and dP/dt and left ventricular elastance was calculated from hemodynamic measurements. The postural test consisted of 5 min of supine baseline control followed by 5 minutes of 90 degrees upright tilt (HUT). Heart rate, stroke volume, cardiac output, and left ventricular end-diastolic pressure showed no consistent alterations during HDT. Left ventricular elastance was reduced in all animals throughout HDT, indicating that cardiac compliance was increased. HDT did not consistently alter left ventricular +dP/dt, indicating no change in cardiac contractility. Heart rate during the post-HDT HUT postural test was elevated compared to pre-HDT while post-HDT cardiac output was decreased by 52% as a result of a 54% reduction in stroke volume throughout HUT. Results from this study using an instrumented rhesus monkey suggest that exposure to microgravity may increase ventricular compliance without alternating cardiac contractility. Our project supported the notion that an invasively-instrumented animal model should be viable for use in spaceflight cardiovascular experiments to assess potential changes in myocardial function and cardiac compliance.

Aerospace Medicine↗
PubMedDate not supplied

A technique for sequential segmental neuromuscular stimulation with closed loop feedback control.

In dynamic myoplasty, dysfunctional muscle is assisted or replaced with skeletal muscle from a donor site. Electrical stimulation is commonly used to train and animate the skeletal muscle to perform its new task. Due to simultaneous tetanic contractions of the entire myoplasty, muscles are deprived of perfusion and fatigue rapidly, causing long-term problems such as excessive scarring and muscle ischemia. Sequential stimulation contracts part of the muscle while other parts rest, thus significantly improving blood perfusion. However, the muscle still fatigues. In this article, we report a test of the feasibility of using closed-loop control to economize the contractions of the sequentially stimulated myoplasty. A simple stimulation algorithm was developed and tested on a sequentially stimulated neo-sphincter designed from a canine gracilis muscle. Pressure generated in the lumen of the myoplasty neo-sphincter was used as feedback to regulate the stimulation signal via three control parameters, thereby optimizing the performance of the myoplasty. Additionally, we investigated and compared the efficiency of amplitude and frequency modulation techniques. Closed-loop feedback enabled us to maintain target pressures within 10% deviation using amplitude modulation and optimized control parameters (correction frequency = 4 Hz, correction threshold = 4%, and transition time = 0.3 s). The large-scale stimulation/feedback setup was unfit for chronic experimentation, but can be used as a blueprint for a small-scale version to unveil the theoretical benefits of closed-loop control in chronic experimentation.

Algorithms↗
PubMedDate not supplied

Electric analog model of the aortic valve for calculation of continuous beat-to-beat aortic flow using a pressure gradient.

The objective was to develop a technique for calculating continuous, beat-to-beat aortic flow (AoF) using only left ventricular pressure (LVP) and aortic pressure (AoP). An electric analog model of the aortic valve was developed that includes resistance (R), inertance (L), and compliance (C) parameters, and resulting second order differential equations were derived. Aortic flow, AoP, and LVP recorded in eight subjects during a 5 day period and during lower body negative pressure (LBNP) were used to validate the model. Resistance, L, and C were estimated using a least-squares fit to the measured AoF on day 0 and during 0 mm Hg LBNP. For days 1-4, AoF was calculated using measured values of AoP and LVP and the R, L, and C values from day 0. Similarly, for LBNP, AoF was calculated using measured values of AoP and LVP, and the R, L, and C values from 0 mm Hg LBNP. The calculated and measured AoF were compared. Differences in cardiac output between the calculated and measured flows were less than 13.1+/-17% across days and under minor altered physiologic conditions (LBNP). Waveform morphology for the calculated AoF also agreed well with the measured AoF. Spectral analysis showed differences in magnitude and phase between measured and calculated aortic flow for the first five harmonics across days, less than 20+/-6% and 25+/-14 degrees, respectively. Preliminary evaluation indicates that our model works well for calculating flow through a biologic valve using LVP and AoP. We speculate that it may perform better for a mechanical valve, and if so it may be possible to develop an instrumented mechanical valve capable of continuous LVP, AOP, and AoF measurements.

Animals↗
PubMedDate not supplied

Development of a flow feedback pulse duplicator system with rhesus monkey arterial input impedance characteristics.

An in vitro pulsatile pump flow system that is capable of producing physiologic pressures and flows in a mock circulatory system tuned to reproduce the first nine harmonics of the input impedance of a rhesus monkey was developed and tested. The system was created as a research tool for evaluating cardiovascular function and for the design, testing, and evaluation of electrical-mechanical cardiovascular models and chronically implanted sensors. The system possesses a computerized user interface for controlling a linear displacement pulsatile pump in a controlled flow loop format to emulate in vivo cardiovascular characteristics. Evaluation of the pump system consisted of comparing its aortic pressure and flow profiles with in vivo rhesus hemodynamic waveforms in the time and frequency domains. Comparison of aortic pressure and flow data between the pump system and in vivo data showed good agreement in the time and frequency domains, however, the pump system produced a larger pulse pressure. The pump system can be used for comparing cardiovascular parameters with predicted cardiovascular model values and for evaluating such items as vascular grafts, heart valves, biomaterials, and sensors. This article describes the development and evaluation of this feedback controlled cardiovascular dynamics simulation modeling system.

Animals↗
PubMedDate not supplied

Can a linear electrical analog model of a mechanical valve predict flow by using a pressure gradient?

The objective was to determine whether a previously developed technique for biological aortic valves could predict flow through a mechanical valve. An electrical analog model of the aortic valve that includes compliance, resistance, and inertance parameters, and corresponding second order differential equations was used to predict flow given a pressure gradient, as previously reported. Simulated pressures and flow were recorded by using a pulse duplicator system. The heart rate was varied from 60 to 180 bpm, and the stroke volume was varied from 22 to 67 cc. Resistance, inertance, and compliance parameters of the governing differential equation were estimated by using a least-squares fit to the measured flow at 120 bpm and 50 cc stroke volume. By using these parameter estimates, flow was calculated for other heart rates and stroke volumes. To achieve a better flow prediction, a nonlinear filter (third order polynomial range calibration equation) was applied to the output of the linear model (flow). The mean error, full-scale error, and spectral error in magnitude and phase between measured and predicted flow were compared. Error in mean flow ranged from 3% at medium flow rates to 90% at low flow rates. The maximum and minimum full scale errors were 12% and 5%, respectively. Error in the harmonics of measured and calculated flow ranged from 0% to 55%. Larger errors were usually present at the higher harmonics. The agreement between measured and calculated flow was better at normal and high flows but rather poor at low flows. The nonlinear filter (range calibration equation) was unable to account for the discrepancies between the measured and calculated flow over all flow ranges. It seems that this linear model and nonlinear filter have limited application, and an alternate nonlinear approach may produce better results.

Aortic Valve↗