The effects of cryopreservation on red blood cell microvesiculation, phosphatidylserine externalization, and CD47 expression

Exposure of cryopreserved red cell concentrates to real-world transient warming events has a negligible impact on quality

BACKGROUND

Red cell concentrates (RCCs) may be cryopreserved at Canadian Blood Services (CBS) for up to 10 years; however, inadvertent warming of these units over the prescribed storage temperature (≤ -65°C) may occur. These units may be discarded from inventory to avoid potential adverse transfusion outcomes. This study aimed to assess the quality of RCCs that experienced unintentional transient warming events (TWEs) related to freezer failures.

STUDY DESIGN

Thirty cryopreserved RCCs with known TWEs were selected for this study and classified into three different experimental groups (Event 1 (n = 5) TWE > -65°C for 34 min; Event 2 (n = 23) TWE > -65°C for 48 h; and both Event 1 and Event 2 (n = 2) TWE > -65°C for 34 min and 48 h). Ten additional RCCs with no known TWEs, cryopreserved over the same period, were selected as controls. Thawed RCCs were deglycerolized using the Haemonetics ACP 215, and in vitro quality was assessed throughout hypothermic storage.

RESULTS

RCCs from the control and all three experimental groups met the Canadian Standards Association (CSA) guidelines for hematocrit, total hemoglobin, and hemolysis at expiry. RCCs experiencing a singular TWE had similar in vitro quality to control RCCs.

DISCUSSION

This study's findings revealed that single exposures to specific documented TWEs did not significantly impact the quality of RCCs post-deglycerolization. While units should still be assessed on a case-by-case basis upon TWE, our work provides the first-ever evidence that supports a broader policy of unit retention by blood centers.

CD47 interactions with exportin-1 limit the targeting of m7G-modified RNAs to extracellular vesicles

CD47 is a marker of self and a signaling receptor for thrombospondin-1 that is also a component of extracellular vesicles (EVs) released by various cell types. Previous studies identified CD47-dependent functional effects of T cell EVs on target cells, mediated by delivery of their RNA contents, and enrichment of specific subsets of coding and noncoding RNAs in CD47+ EVs. Mass spectrometry was employed here to identify potential mechanisms by which CD47 regulates the trafficking of specific RNAs to EVs. Specific interactions of CD47 and its cytoplasmic adapter ubiquilin-1 with components of the exportin-1/Ran nuclear export complex were identified and confirmed by coimmunoprecipitation. Exportin-1 is known to regulate nuclear to cytoplasmic trafficking of 5'-7-methylguanosine (m7G)-modified microRNAs and mRNAs that interact with its cargo protein EIF4E. Interaction with CD47 was inhibited following alkylation of exportin-1 at Cys528 by its covalent inhibitor leptomycin B. Leptomycin B increased levels of m7G-modified RNAs, and their association with exportin-1 in EVs released from wild type but not CD47-deficient cells. In addition to perturbing nuclear to cytoplasmic transport, transcriptomic analyses of EVs released by wild type and CD47-deficient Jurkat T cells revealed a global CD47-dependent enrichment of m7G-modified microRNAs and mRNAs in EVs released by CD47-deficient cells. Correspondingly, decreasing CD47 expression in wild type cells or treatment with thrombospondin-1 enhanced levels of specific m7G-modified RNAs released in EVs, and re-expressing CD47 in CD47-deficient T cells decreased their levels. Therefore, CD47 signaling limits the trafficking of m7G-modified RNAs to EVs through physical interactions with the exportin-1/Ran transport complex.

Comparison of the programmed freezer method and deep freezer method in the manufacturing of frozen red blood cell products

BACKGROUND AND OBJECTIVES

Frozen-thawed red blood cells (FTRCs) are useful blood components to patients with rare blood phenotypes. However, frozen red blood cells (FRCs) sometimes cause significant haemolysis after thawing due to the freeze/thaw process. In this study, we aimed to focus on the former process and reduce process-related haemolysis.

MATERIALS AND METHODS

Five-day-old red blood cells (RBCs) (5D) or 9-week-old RBCs (9 W) were glycerolized, pooled and split into two aliquots. RBCs were frozen using either the programmed freezer (PF) method or the deep freezer (DF) method. After 4-8 weeks, the FRCs were thawed and washed. In vitro characteristics were compared between the PF and DF methods. Nine week were used as a starting material for FTRCs with the assumption that they can mimic disqualified FTRCs with respect to Hb recovery.

RESULTS

The PF method resulted in a significantly higher Hb recovery rate than the DF method (5D: 85.9 ± 2.1 vs. 81.1% ± 3.5%, p < 0.001) (9 W: 56.8 ± 4.0 vs. 52.4% ± 3.5%, p < 0.001). Both 5D and 9W-derived FTRCs immediately after preparation prepared by the PF method were more resistible to haemolysis than those prepared by the DF method. On the other hand, there were no significant differences between PF and DF methods in Adenosine 5'-triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG).

CONCLUSION

The PF method was more suitable for RBC freezing than the DF method in terms of Hb recovery in FTRCs. Although it was only 4%-5%, the improvement in the Hb recovery rate will contribute to a more stable supply.

Red blood cell phenotype fidelity following glycerol cryopreservation optimized for research purposes

Intact red blood cells (RBCs) are required for phenotypic analyses. In order to allow separation (time and location) between subject encounter and sample analysis, we developed a research-specific RBC cryopreservation protocol and assessed its impact on data fidelity for key biochemical and physiological assays. RBCs drawn from healthy volunteers were aliquotted for immediate analysis or following glycerol-based cryopreservation, thawing, and deglycerolization. RBC phenotype was assessed by (1) scanning electron microscopy (SEM) imaging and standard morphometric RBC indices, (2) osmotic fragility, (3) deformability, (4) endothelial adhesion, (5) oxygen (O2) affinity, (6) ability to regulate hypoxic vasodilation, (7) nitric oxide (NO) content, (8) metabolomic phenotyping (at steady state, tracing with [1,2,3-13C3]glucose ± oxidative challenge with superoxide thermal source; SOTS-1), as well as in vivo quantification (following human to mouse RBC xenotransfusion) of (9) blood oxygenation content mapping and flow dynamics (velocity and adhesion). Our revised glycerolization protocol (40% v/v final) resulted in >98.5% RBC recovery following freezing (-80°C) and thawing (37°C), with no difference compared to the standard reported method (40% w/v final). Full deglycerolization (>99.9% glycerol removal) of 40% v/v final samples resulted in total cumulative lysis of ~8%, compared to ~12-15% with the standard method. The post cryopreservation/deglycerolization RBC phenotype was indistinguishable from that for fresh RBCs with regard to physical RBC parameters (morphology, volume, and density), osmotic fragility, deformability, endothelial adhesivity, O2 affinity, vasoregulation, metabolomics, and flow dynamics. These results indicate that RBC cryopreservation/deglycerolization in 40% v/v glycerol final does not significantly impact RBC phenotype (compared to fresh cells).

Characteristics of Extracellular Vesicles in Red Blood Concentrates Change with Storage Time and Blood Manufacturing Method

Background

Extracellular vesicles (EVs) in blood products are potential effectors of inflammation and coagulation after transfusion. The aim of this study was to assess the impact of different blood manufacturing methods and duration of hypothermic storage on the EV subpopulations in relation to other in vitro quality parameters of red blood cell concentrate (RCC) products.

Methods

RCCs were produced using whole blood filtration (WBF) or red cell filtration (RCF) (n = 12/method), refrigerated for 43 days, and evaluated for EV size profile and concentration, red cell deformability, ATP and 2,3-DPG, hemolysis, and hematological indices.

Results

The total number of EVs increased significantly with storage in both methods, and WBF-RCCs contained the higher numbers of EVs compared to RCF-RCCs. The concentration of small EVs was greater in WBF-RCCs versus RCF-RCCs, with difference between the two methods observed on day 43 of storage (p = 0.001). Throughout storage, significant decreases were identified in ATP, 2,3-DPG, and EI_max, while an increase in hemolysis was observed in both RCC products.

Conclusion

The dynamic shift in the size and concentration of the EV subpopulations is dependent on the blood manufacturing method and length of storage. Better understanding of the potential clinical implications of these heterogeneous populations of EVs are needed.

Previous Cryopreservation Alters the Natural History of the Red Blood Cell Storage Lesion

BACKGROUND

During storage, packed red blood cells (pRBCs) undergo a number of biochemical, metabolic, and morphologic changes, collectively known as the "storage lesion." We aimed to determine the effect of cryopreservation on the red blood cell storage lesion compared with traditional 4°C storage.

METHODS

Previously cryopreserved human pRBCs were compared with age-matched never-frozen pRBCs obtained from the local blood bank. The development of the red cell storage lesion was evaluated after 7, 14, 21, 28, and 42 days of storage at 4°C in AS-3 storage medium. We measured physiological parameters including cell counts, lactic acid, and potassium concentrations as well as signs of eryptosis including loss of phosphatidylserine (PS) asymmetry, microparticle production, and osmotic fragility in hypotonic saline.

RESULTS

Compared with controls, previously cryopreserved pRBC at 7 days of storage in AS-3 showed lower red cell counts (3.7 vs. 5.3 × 10 cells/μL, P < 0.01), hemoglobin (Hgb) (12.0 vs. 16.5 g/dL, P < 0.01), hematocrit (33.0% vs. 46.5%, P < 0.01), and pH (6.27 vs. 6.72, P < 0.01). Over 28 days of storage, storage cryopreserved pRBC developed increased cell-free Hgb (0.7 vs. 0.3 g/dL, P < 0.01), greater PS exposure (10.1% vs. 3.3%, P < 0.01), and microparticle production (30,836 vs. 1,802 MP/μL, P < 0.01). Previously cryopreserved cells were also less resistant to osmotic stress.

CONCLUSION

The red blood cell storage lesion is accelerated in previously cryopreserved pRBC after thawing. Biochemical deterioration of thawed and deglycerolized red cells suggests that storage time before transfusion should be limited to achieve similar risk profiles as never-frozen standard liquid storage pRBC units.

Red blood cell storage time and transfusion: current practice, concerns and future perspectives

Red blood cells (RBCs) units are the most requested transfusion product worldwide. Indications for transfusion include symptomatic anaemia, acute sickle cell crisis, and acute blood loss of more than 30% of the blood volume, with the aim of restoring tissue oxygen delivery. However, stored RBCs from donors are not a qualitative equal product, and, in many ways, this is a matter of concern in the transfusion practice. Besides donor-to-donor variation, the storage time influences the RBC unit at the qualitative level, as RBCs age in the storage bag and are exposed to the so-called storage lesion. Several studies have shown that the storage lesion leads to post-transfusion enhanced clearance, plasma transferrin saturation, nitric oxide scavenging and/or immunomodulation with potential unwanted transfusion-related clinical outcomes, such as acute lung injury or higher mortality rate. While, to date, several studies have claimed the risk or deleterious effects of "old" vs "young" RBC transfusion regimes, it is still a matter of debate, and consideration should be taken of the clinical context. Transfusion-dependent patients may benefit from transfusion with "young" RBC units, as it assures longer inter-transfusion periods, while transfusion with "old" RBC units is not itself harmful. Unbiased Omics approaches are being applied to the characterisation of RBC through storage, to better understand the (patho)physiological role of microparticles (MPs) that are found naturally, and also on stored RBC units. Perhaps RBC storage time is not an accurate surrogate for RBC quality and there is a need to establish which parameters do indeed reflect optimal efficacy and safety. A better Omics characterisation of components of "young" and "old" RBC units, including MPs, donor and recipient, might lead to the development of new therapies, including the use of engineered RBCs or MPs as cell-based drug delivering tools, or cost-effective personalised transfusion strategies.

The effect of prefreeze rejuvenation on postthaw storage of red blood cells in AS-3 and SAGM

BACKGROUND

We investigated whether improving the metabolic status of red blood cell concentrates before freezing could extend the postthaw shelf life beyond 14 days while still meeting the requirements for hemolysis (0.8%) and total adenylate (>82% of original values).

STUDY DESIGN AND METHODS

At Day 8 after collection, four leukoreduced red blood cell concentrates in saline-adenine-glucose-mannitol (SAGM) were pooled, mixed, and split (n = 4). Of these concentrates, two were rejuvenated in Rejuvesol. In addition, two leukoreduced red blood cell concentrates in phosphate-adenine-glucose-guanosine-gluconate-mannitol (PAGGGM) were pooled, mixed, and split at Day 8 after collection (n = 4). All concentrates were glycerolized, frozen, and stored for at least 2 weeks at -80°C. After thawing and deglycerolization, from each pair, one red blood cell concentrate was resuspended in SAGM, and one was suspended in AS-3. During postthaw storage at 2 to 6°C for 35 days, all concentrates were sampled weekly and analyzed for hematologic, metabolic, and morphologic parameters.

RESULTS

Both Rejuvesol and PAGGGM treatment produced increased adenosine triphosphate and total adenylate and 2,3-diphosphoglycerate levels compared with untreated red blood cell concentrates. Regardless of prefreeze Rejuvesol or PAGGGM treatment, postthaw hemolysis remained below 0.8% during 7 days in SAGM and during 35 days in AS-3. At Day 35 of postthaw storage in AS-3, total adenylate in nonrejuvenated red blood cell concentrates had decreased to 72% of the original values; whereas, in prefreeze Rejuvesol-treated and PAGGGM-treated concentrates, adenylate values were still were at 101% and 98%, respectively.

CONCLUSION

Based on maximum allowable hemolysis of 0.8% and total adenylate content greater than 82% of the original value, thawed, prefreeze Rejuvesol-treated or PAGGGM-treated red blood cell concentrates can be stored for 35 days at 2 to 6ºC in AS-3.

The effects of freezing on long-term storage of canine erythrocytes

Human medicine studies have so far demonstrated that erythrocytes may be preserved and stored at low temperatures for decades retaining their metabolic and biochemical properties. However, detailed studies regarding this problem are not yet available in veterinary medicine. Therefore, the objective of the current study was to investigate time-dependent effects of long-term frozen storage of canine red blood cells.

Twelve healthy adult dogs meeting the criteria for blood transfusion were used in the study. Whole blood samples (450 ± 45 ml) collected from each dog were centrifuged by a cryogenic microcentrifuge and packed RBC suspensions were obtained. The samples were prewashed three times in 0.9% NaCl solution and were allocated into three groups to be evaluated at three different time points (day 0 and month 4 and 6). The samples to be frozen were subjected to glycerolization and then stored at −80°C for 4 and 6-month periods. At the end of this period the packed RBC samples were thawed, centrifuged and then washed in a consecutive series of dextrose solutions. 2,3-Diphosphoglycerate (2,3-DPG), Adenosin triphosphate (ATP), supernatant hemoglobin (SupHb), sodium (Na+) and potassium (K+) levels, residual glycerol concentrations and hemograms were evaluated and compared. Sterility tests were performed on all samples for bacterial contamination. A statistically significant decrease was noted in potassium levels, which was the natural outcome of deglycerolization process. No significant change was observed in terms of other parameters due based on different time points. In conclusion, long-term frozen storage had no negative effect on the quality parameters of canine erythrocytes.

CHANGES IN ERYTHROCYTE SURFACE MARKER CD44 DURING HYPOTHERMIC AND LOW TEMPERATURE STORAGE

We studied the changes in surface marker CD44 in erythrocytes, cryopreserved under the protection of glycerol and PEG–1500, or stored in hypothermic conditions. It was shown that during hypothermic storage the CD44 characteristics in erythrocyte suspension were unchanged within 10 days. In cryopreserved erythrocytes a reduction in CD44–positive cells and in the level of expression of the surface marker were marked. Using PEG–1500 resulted in more pronounced change in erythrocyte CD44 characteristics after freeze–thawing in comparison with glycerol. Removal of cryoprotectants and the loss of a part of cells during the washing process led to the restoration of the CD44 characteristics in freeze–thawed erythrocytes suspension which successfully survived after the stresses. The results indicate that revealed changes in cryopreserved erythrocytes cover only a part of the cells, and they are associated with the instability of the population of erythrocytes with altered CD44 characteristics wherethrough after the removal of cryoprotectants with concomitant hemolysis of unstable cells the CD44 parameters in erythrocyte suspensions recovered. The mechanisms underlying the changes in the parameters of the surface marker CD44 in freeze–thawed erythrocyte may be related to the disruption of intermolecular interactions in the membrane under the influence of physical and chemical environmental factors, followed by the membrane vesiculation with the inclusion of the CD44 into the vesicles.

Gamma-irradiation of deglycerolized red cells does not significantly affect in vitro quality

BACKGROUND AND OBJECTIVES

Red cells frozen with glycerol may require gamma-irradiation after thawing and deglycerolization for transfusion to at-risk patients. Both freezing and irradiation are known to cause red cell damage. However, the effect of irradiation on the quality of deglycerolized red cells and the optimal shelf life of such a component is currently unknown.

MATERIALS AND METHODS

Red cells (<7 days) were pooled, split and glycerolized using an ACP-215 automated cell washer (n = 12 pairs) and frozen at -80°C. Red cells were thawed, deglycerolized and resuspended in SAG-M. One of each pair was gamma-irradiated, while the other served as a control. Products were stored at 2-6°C and sampled for in vitro testing immediately after irradiation, and at 24 and 48 h postirradiation.

RESULTS

Irradiation of deglycerolized red cells led to a >1·5-fold increase in extracellular potassium, compared to control units at 24 and 48 h postirradiation. Other parameters, including haemolysis, were not significantly affected by irradiation postdeglycerolization.

CONCLUSION

Deglycerolized, irradiated red cells had increased supernatant potassium, but remained of acceptable quality for 24 h postirradiation.

Functional capacity of reconstituted blood in 1:1:1 versus 3:1:1 ratios: a thrombelastometry study

INTRODUCTION

Different transfusion ratio concepts of packed red blood cells (pRBCs), fresh frozen plasma (FFP) and platelets (PLTs) have been implemented in trauma care, but the optimal ratios are still discussed. In this study the hemostatic potential of two predefined ratios was assessed by using an in vitro thrombelastometric approach. Furthermore, age effects of reconstituted blood were analyzed.

METHODS

Whole blood (WB) of voluntary donors was separated into pRBCs, FFP and PLTs and reconstituted into the ratios 1:1:1 and 3:1:1 at day 1, 4, 14, and 24. Standard blood count, electrolytes and coagulation proteins were quantified. The functional coagulation in ratio- and age-specific groups was evaluated using rotational thromboelastometry (ROTEM).

RESULTS

Several coagulation factors reduced significantly in the 3:1:1 ratio and were consistent with increased INR, decelerated clot formation times and A10 (amplitude 10 minutes after clotting time (CT)), flattened α-angle during the EXTEM and diminished MCF for distinct time points during the INTEM, FIBTEM and APTEM assays. With rising age of pRBCs the pH, sodium and potassium reached non-physiological levels.

CONCLUSION

Under standardized in vitro conditions the higher amount of pRBCs in the 3:1:1 ratio diluted coagulation factors significantly on the expense of its functional coagulation capacity as revealed by ROTEM results. Thus, the coagulation functionality of the 1:1:1 ratio predominated.

Utilization and quality of cryopreserved red blood cells in transfusion medicine

Cryopreserved (frozen) red blood cells have been used in transfusion medicine since the Vietnam war. The main method to freeze the red blood cells is by usage of glycerol. Although the usage of cryopreserved red blood cells was promising due to the prolonged storage time and the limited cellular deterioration at subzero temperatures, its usage have been hampered due to the more complex and labour intensive procedure and the limited shelf life of thawed products. Since the FDA approval of a closed (de) glycerolization procedure in 2002, allowing a prolonged postthaw storage of red blood cells up to 21 days at 2-6°C, cryopreserved red blood cells have become a more utilized blood product. Currently, cryopreserved red blood cells are mainly used in military operations and to stock red blood cells with rare phenotypes. Yet, cryopreserved red blood cells could also be useful to replenish temporary blood shortages, to prolong storage time before autologous transfusion and for IgA-deficient patients. This review describes the main methods to cryopreserve red blood cells, explores the quality of this blood product and highlights clinical settings in which cryopreserved red blood cells are or could be utilized.

Bio-inspired cryo-ink preserves red blood cell phenotype and function during nanoliter vitrification

Current red-blood-cell cryopreservation methods utilize bulk volumes, causing cryo-injury of cells, which results in irreversible disruption of cell morphology, mechanics, and function. An innovative approach to preserve human red-blood-cell morphology, mechanics, and function following vitrification in nanoliter volumes is developed using a novel cryo-ink integrated with a bioprinting approach.

CD47: A Cell Surface Glycoprotein Which Regulates Multiple Functions of Hematopoietic Cells in Health and Disease

Interactions between cells and their surroundings are important for proper function and homeostasis in a multicellular organism. These interactions can either be established between the cells and molecules in their extracellular milieu, but also involve interactions between cells. In all these situations, proteins in the plasma membranes are critically involved to relay information obtained from the exterior of the cell. The cell surface glycoprotein CD47 (integrin-associated protein (IAP)) was first identified as an important regulator of integrin function, but later also was shown to function in ways that do not necessarily involve integrins. Ligation of CD47 can induce intracellular signaling resulting in cell activation or cell death depending on the exact context. By binding to another cell surface glycoprotein, signal regulatory protein alpha (SIRPα), CD47 can regulate the function of cells in the monocyte/macrophage lineage. In this spotlight paper, several functions of CD47 will be reviewed, although some functions may be more briefly mentioned. Focus will be on the ways CD47 regulates hematopoietic cells and functions such as CD47 signaling, induction of apoptosis, and regulation of phagocytosis or cell-cell fusion.

Storage of red blood cells affects membrane composition, microvesiculation, and in vitro quality

BACKGROUND

During storage detrimental biochemical and biomechanical changes occur within a red blood cell (RBC). RBC microparticles (RMPs) produced during storage have been identified as biomarkers of RBC quality, being potentially immunogenic and inhibitory to nitric oxide regulation.

STUDY DESIGN AND METHODS

In this study, microvesiculation and changes in the composition of the RBC membrane were investigated throughout 49 days of storage and were correlated with in vitro assays examining membrane quality. Leukoreduced RBC units produced using the buffy coat method were collected and stored at 1 to 6°C and were tested weekly for hemolysis, osmotic fragility, deformability, ATP, hematologic indices, and morphology. Microvesiculation was assessed using multicolor flow cytometry. High-performance liquid chromatography and mass spectrometry were used to determine the composition and quantity of phospholipids (PLs) and cholesterol (C) on Days 2 and 43.

RESULTS

The assessment of RBCs throughout storage revealed significant increases in percent hemolysis, while significant decreases in ATP concentrations, and the mean corpuscular hemoglobin concentration were observed. Flow cytometry analysis revealed a significant increase in the mean number of microparticles per microliter during storage. Throughout storage, significant decreases were identified in the amount of PLs and total lipids within the RBC membrane. No significant change in the amount of C in the RBC membrane was identified.

CONCLUSION

Significant changes to the RBC membrane occur during storage. The length of storage will influence RMP generation, osmotic fragility, hemolysis, and changes in deformability. These changes in RBC in vitro quality may contribute to transfusion reactions and negative posttransfusion outcomes.

Phospholipidomics reveals differences in glycerophosphoserine profiles of hypothermically stored red blood cells and microvesicles

During their normal in vivo life cycle erythrocytes (red blood cells, RBCs) undergo biochemical changes leading to membrane microvesiculation and shedding. RBC microvesiculation also occurs in vitro under conditions of blood bank storage, so microvesicles (MVs) accumulate in the storage (preservation) medium over storage time. Considerable effort has been put into gaining a mechanistic understanding of the RBC microvesiculation process, as this is crucial to better understand RBC biology in disease and in health. Additionally, MVs accumulated in stored RBCs have been implicated in transfusion adverse inflammatory reactions, with chloroform extractable compounds, thus lipophilic, known to trigger the effect. However, because thin layer chromatography resolution of RBC and MV lipids has always enabled one to conclude high compositional similarities, in depth analysis of MV lipids has not been extensively pursued. Here we present an orbitrap mass spectrometry (MS) approach to compare the phospholipid composition of RBCs and MVs from leukoreduced, hypothermically (2-6°C) stored RBC units. We used shotgun MS analysis and electrospray ionization (ESI) intra-source separation, and demonstrated high similarity of compositional profiles, except for glycerophosphoserines (PS). Contrasting abundances of PS 38:4 and PS 38:1 characterized MV and RBC profiles and suggested that storage-associated microvesiculation possibly involves shedding of specific membrane rafts. This finding indicates that phospholipidomics could likely contribute to a better understanding of the RBC microvesiculation process.

CD47 in Erythrocyte Ageing and Clearance - the Dutch Point of View

Recently, an important role for CD47, a well-known 'don't eat me' signal, in the clearance of aged erythrocytes was revealed. Experimental data support the conversion of CD47 from a 'don't eat me' to an 'eat me' signal through a conformational change in CD47. Intriguingly, erythrocyte phagocytosis after this switch seems to be mediated by the same receptor that normally signals inhibition of phagocytosis, SIRPα. In this review, the possible molecular mechanisms leading to this conformational change in CD47 as well as the possible signal transduction events leading to phagocytosis after this switch are discussed. Lastly, the consequences of this newly identified mode of erythrocyte phagocytosis for the clearance of aged erythrocytes during normal turnover and after erythrocyte transfusion are addressed.

Quality of red blood cells isolated from umbilical cord blood stored at room temperature

Red blood cells (RBCs) from cord blood contain fetal hemoglobin that is predominant in newborns and, therefore, may be more appropriate for neonatal transfusions than currently transfused adult RBCs. Post-collection, cord blood can be stored at room temperature for several days before it is processed for stem cells isolation, with little known about how these conditions affect currently discarded RBCs. The present study examined the effect of the duration cord blood spent at room temperature and other cord blood characteristics on cord RBC quality. RBCs were tested immediately after their isolation from cord blood using a broad panel of quality assays. No significant decrease in cord RBC quality was observed during the first 65 hours of storage at room temperature. The ratio of cord blood to anticoagulant was associated with RBC quality and needs to be optimized in future. This knowledge will assist in future development of cord RBC transfusion product.

Relationship between clotting activity and phosphatidylserine expression on erythrocyte membranes in polycythemia vera patients with the JAK2 V617F mutation

INTRODUCTION

Polycythemia vera (PV) accompanies the clinical course of thrombosis. Phosphatidylserine (PS) expression on the plasma membrane has been known to be one of place where the coagulation system activates. We studied the relationship between clotting factor activity and PS expression on the erythrocyte membrane in patients with erythrocytosis.

METHODS

The coagulation test and PS expression in 23 patients with erythrocytosis were measured. PS expression was determined indirectly by measuring annexin V binding to erythrocytes using fluorescence activated cell sorter analysis (FACS).

RESULTS

The activity of clotting factors (II, V, VII, VIII, von Willebrand factor, IX, X) was significantly lower in PV than in the mutation-negative erythrocytosis. There was a significant correlation between reduced activity of clotting factors such as V, X, and IX and increased PS expression of the erythrocyte membrane.

CONCLUSION

Increased expression of PS on the erythrocyte membrane may reduce the activities of clotting factors in PV patients with JAK2 V617F mutation.