142,228 research outputs found
Characterization of a Putative Hemolysin Expressed by Sneathia amnii, a Preterm Birth-associated Pathogen
The gram-negative bacteria Sneathia amnii is a poorly-characterized commensal of the female urogenital tract frequently associated with adverse clinical outcomes such as bacterial vaginosis (BV), amnionitis, and preterm labor. To investigate its potential role in virulence, we sought to identify and characterize virulence determinants produced by S. amnii in an effort to better understand the pathogenesis of infectious preterm birth. Through sequencing of the Sn35 genome (type strain of S. amnii), we identified two genes with amino acid sequence similarity and structural similarity to the filamentous hemagglutinin (FHA) protein of Bordetella pertussis and its Type Vb transporter. Because S. amnii requires human blood components for growth and lyses human red blood cells, we hypothesized that this two-partner system was involved in hemolysis. To characterize the function of the FHA-like protein, a purified, recombinant peptide was used to induce an antibody response. The polyclonal rabbit serum against the antigenic peptide was incubated with S. amnii to block the FHA-like protein prior to the addition of red blood cells. Pre-treatment with the antiserum inhibited hemolytic activity against human erythrocytes suggesting that the FHA-like protein is somehow involved in hemolysis. Additionally, we found that the hemolytic activity of S. amnii was highly specific against human red blood cells; it did not lyse horse or rabbit red blood cells and only minimally lysed sheep red blood cells. Further research efforts will focus on purifying functional FHA-like protein for further characterization and to determine whether it is sufficient to induce hemolysis.https://scholarscompass.vcu.edu/uresposters/1249/thumbnail.jp
Viscoelastic transient of confined Red Blood Cells
The unique ability of a red blood cell to flow through extremely small
microcapillaries depends on the viscoelastic properties of its membrane. Here,
we study in vitro the response time upon flow startup exhibited by red blood
cells confined into microchannels. We show that the characteristic transient
time depends on the imposed flow strength, and that such a dependence gives
access to both the effective viscosity and the elastic modulus controlling the
temporal response of red cells. A simple theoretical analysis of our
experimental data, validated by numerical simulations, further allows us to
compute an estimate for the two-dimensional membrane viscosity of red blood
cells, Nsm. By comparing our
results with those from previous studies, we discuss and clarify the origin of
the discrepancies found in the literature regarding the determination of
, and reconcile seemingly conflicting conclusions from
previous works
Following red blood cells in a pulmonary capillary
The red blood cells or erythrocytes are biconcave shaped cells and consist
mostly in a membrane delimiting a cytosol with a high concentration in
hemoglobin. This membrane is highly deformable and allows the cells to go
through narrow passages like the capillaries which diameters can be much
smaller than red blood cells one. They carry oxygen thanks to hemoglobin, a
complex molecule that have very high affinity for oxygen. The capacity of
erythrocytes to load and unload oxygen is thus a determinant factor in their
efficacy. In this paper, we will focus on the pulmonary capillary where red
blood cells capture oxygen. We propose a camera method in order to numerically
study the behavior of the red blood cell along a whole capillary. Our goal is
to understand how erythrocytes geometrical changes along the capillary can
affect its capacity to capture oxygen. The first part of this document presents
the model chosen for the red blood cells along with the numerical method used
to determine and follow their shapes along the capillary. The membrane of the
red blood cell is complex and has been modelled by an hyper-elastic approach
coming from Mills et al (2004). This camera method is then validated and
confronted with a standard ALE method. Some geometrical properties of the red
blood cells observed in our simulations are then studied and discussed. The
second part of this paper deals with the modeling of oxygen and hemoglobin
chemistry in the geometries obtained in the first part. We have implemented a
full complex hemoglobin behavior with allosteric states inspired from
Czerlinski et al (1999).Comment: 17 page
Tratamento Endovascular de Aneurismas da Aorta e Transfusão de Sangue. O que Precisamos?
INTRODUCTION:
Comparatively to open repair, endovascular aneurysm repair has reduced transfusion rates but thereâs no recommendation about number of red blood cells units to be crossmatched preoperatively. Our aim is contribute to the analysis of red blood cells units needs in endovascular and hybrid aortic aneurysm repair and developing a protocol for maximum surgical blood orders schedule.
MATERIAL AND METHODS:
We retrospectively analyzed our prospective database of elective endovascular aneurysm repair from 2001 to 2012. We analyzed patients' age, gender, ASA classification, maximum surgical blood orders schedule, red blood cells units transfused and timings, types of endoprosthesis, red blood cells units consumption/endoprosthesis' type ratio, crossmatch to transfusion ratio, conversion to open repair, hemoglobin concentrations before surgery and discharge.
RESULTS:
We selected 187 patients, 90% men, mean age 73.1, ASA mode III. The endoprosthesis were aorto-bi-iliac in 71%, aorto-uni-iliac in 23% and thoracic in 6%. Of these, 72,6% of the patients did not require blood transfusion. We transfused 171 red blood cells units. Crossmatch to transfusion ratio was 10.1 until 2010 and 7.3 after. The ratio of red blood cells units consumption/endoprosthesis in the first 24 hours was 0.21 red blood cells units/aorto-bi-iliac, 0.46 red blood cells units/aorto-uni-iliac, 0.8 red blood cells units/thoracic, 1.3 red blood cells units/hybrid-thoracic and 2 red blood cells units/hybrid-aorto-bi-iliac. A statistical correlation was observed between red blood cells units transfused postoperatively and type of endoprosthesis (p < 0.001) and between ASA classification and red blood cells units transfused after 24 hours (p < 0.01).
DISCUSSION:
Guidelines from the British Society of Haematology are based on a crossmatch to transfusion ratio of 2:1. Our crossmatch to transfusion ratio was 10.1 until 2010 and 7.3 from 2011 to 2012.
CONCLUSION:
These results changed our policy of maximum surgical blood orders schedule for endovascular aneurysm repair. We now type and screen aorto-bi-iliac and aorto-uni-iliac. We crossmatch two red blood cells units for thoracic, three red blood cells units for hybrid thoracic and four red blood cells units for hybrid abdominal procedures. This may lead to financial savings, improved efficiency and reduce workload in hematology department.info:eu-repo/semantics/publishedVersio
Swinging of red blood cells under shear flow
We reveal that under moderate shear stress (of the order of 0.1 Pa) red blood
cells present an oscillation of their inclination (swinging) superimposed to
the long-observed steady tanktreading (TT) motion. A model based on a fluid
ellipsoid surrounded by a visco-elastic membrane initially unstrained (shape
memory) predicts all observed features of the motion: an increase of both
swinging amplitude and period (1/2 the TT period) upon decreasing the shear
stress, a shear stress-triggered transition towards a narrow shear stress-range
intermittent regime of successive swinging and tumbling, and a pure tumbling
motion at lower shear stress-values.Comment: 4 pages 5 figures submitted to Physical Review Letter
The buckling instability of aggregating red blood cells
Plasma proteins such as fibrinogen induce the aggregation of red blood cells
(RBC) into rouleaux, which are responsible for the pronounced shear thinning
behavior of blood, control the erythro- cyte sedimentation rate (ESR) a common
hematological test and are involved in many situations of physiological
relevance such as structuration of blood in the microcirculation or clot
formation in pathological situations. Confocal microscopy is used to
characterize the shape of RBCs within rouleaux at equilibrium as a function of
macromolecular concentration, revealing the diversity of contact zone
morphology. Three different configurations that have only been partly predicted
before are identified, namely parachute, male-female and sigmoid shapes, and
quantitatively recovered by numerical simulations. A detailed experimental and
theoretical analysis of clusters of two cells shows that the deformation
increases nonlinearly with the interaction energy. Models indicate a forward
bifurcation in which the contacting membrane undergoes a buckling instability
from a flat to a de- formed contact zone at a critical value of the interaction
energy. These results are not only relevant for the understanding of the
morphology and stability of RBC aggregates, but also for a whole class of
interacting soft deformable objects such as vesicles, capsules or cells in
tissues.Comment: 22 pages, 12 figure
Recommended from our members
Blood Flow in silico: From Single Cells to Blood Rheology
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Mesoscale hydrodynamics simulations of red blood cells under flow have provided much new
insight into their shapes and dynamics in microchannel flow. The presented results range from the behavior
of single cells in confinement and the shape changes in sedimentation, to the clustering and arrangement of
many cells in microchannels and the viscosity of red blood cell suspensions under shear flow. The interaction
of red blood cells with other particles and cells, such as white blood cells, platelets, and drug carriers, shows
an essential role of red blood cells in the margination of other blood components
Red blood cells: the immune system’s hidden regulator, investigation into the role of red blood cells in inflammatory cytokine signalling
Red blood cells are the most abundant cell type in mammals, although, they are mostly described as inert carriers of haemoglobin that function only in gas exchange and transport. Evidence is now mounting that these enucleate cells are more complex than previously understood. Studies have reported that red blood cells from healthy individuals regulate immune cell activity and maturation, but red blood cells from inflammatory disease cohorts are dysfunctional. Red blood cells are known to bind a small number of chemokines and have been described as a sink for these molecules, and the loss of this activity is correlated with disease progression. This results of this thesis support a broader role for red blood cells in regulating inflammation by acting as a cytokine buffer and modulating cell activity. The aims and hypotheses of this thesis were founded on the discovery that red blood cells are a major reservoir for the pro-inflammatory cytokine, macrophage migration inhibitory factor (MIF); in fact, they contribute 1000-fold more per millilitre than plasma. Red blood cells were also identified to be a major reservoir of 30 additional cytokines, chemokines, and growth factors. Further investigation showed that red blood cells bind and release significant quantities of these proteins, a function that can be modulated by other cells and by enzyme inhibitors. Incubating red blood cells with a cancer cell line (A549 cells) resulted in the significant increase of eight pro-tumorigenic cytokines in the red blood cell lysates. These primed red blood cells altered the activity of lymphocytes by stimulating the proliferation of T cells compared to controls, and promoted the expression of cell activation markers. This study supports the hypothesis that red blood cells act as a buffer for cytokines through binding and release, and that alterations in red blood cells from cell-to-cell interactions affects the activity of T cells. This thesis proposes that red blood cells have multiple functions and the results have implications for the study of inflammation, the role of red blood cells in diagnostics, and on the development of red blood cell derived therapeutics
Red blood cells and other non-spherical capsules in shear flow: oscillatory dynamics and the tank-treading-to-tumbling transition
We consider the motion of red blood cells and other non-spherical
microcapsules dilutely suspended in a simple shear flow. Our analysis indicates
that depending on the viscosity, membrane elasticity, geometry and shear rate,
the particle exhibits either tumbling, tank-treading of the membrane about the
viscous interior with periodic oscillations of the orientation angle, or
intermittent behavior in which the two modes occur alternately. For red blood
cells, we compute the complete phase diagram and identify a novel
tank-treading-to-tumbling transition at low shear rates. Observations of such
motions coupled with our theoretical framework may provide a sensitive means of
assessing capsule properties.Comment: 11 pages, 4 figure
Blood-feeding in the young adult filarial worms litomosoides sigmodontis
In this study with the filarial model Litomosoides sigmodontis, we demonstrate that the worms ingest host red blood cells at a precise moment of their life-cycle, immediately after the fourth moult. The red blood cells (RBC) were identified microscopically in live worms immobilized in PBS at 4 degrees C, and their density assessed. Two hosts were used: Mongolian gerbils, where microfilaraemia is high, and susceptible BALB/c mice with lower microfilaraemia. Gerbils were studied at 12 time-points, between day 9 post-inoculation (the worms were young 4th stage larvae) and day 330 p.i. (worms were old adults). Only the very young adult filarial worms had red blood cells in their gut. Haematophagy was observed between days 25 and 56 p.i. and peaked between day 28 and day 30 p.i. in female worms. In males, haematophagy was less frequent and intense. Similar kinetics of haematophagy were found in BALB/c mice, but frequency and intensity tended to be lower. Haematophagy seems useful to optimize adult maturation. These observations suggest that haematophagy is an important step in the life-cycle of L. sigmodontis. This hitherto undescribed phenomenon might be characteristic of other filarial species including human parasites
- …