Accumulation of bioactive lipids during storage of blood products is not cell but plasma derived and temperature dependent

Investigation into temporal changes in the human bloodstain lipidome

Bloodstains are crucial pieces of physical evidences found at violent crime scenes, providing valuable information for reconstructing forensic cases. However, there is limited data on how bloodstain lipidomes change over time after deposition. Hence, we deployed a high-throughput high-performance liquid chromatography-mass spectrometry (HPLC-MS) approach to construct lipidomic atlases of bloodstains, whole blood, plasma, and blood cells from 15 healthy adults. A time-course analysis was also performed on bloodstains deposited for up to 6 months at room temperature (~ 25°C). The molecular levels of 60 out of 400 detected lipid species differed dramatically between bloodstain and whole blood samples, with major disturbances observed in membrane glycerophospholipids. More than half of these lipids were prevalent in the cellular and plasmic fractions; approximately 27% and 10% of the identified lipids were uniquely derived from blood cells and plasma, respectively. Furthermore, a subset of 65 temporally dynamic lipid species arose across the 6-month room-temperature deposition period, with decreased triacylglycerols (TAGs) and increased lysophosphatidylcholines (LPCs) as representatives, accounting for approximately 8% of the total investigated lipids. The instability of lipids increased linearly with time, with the most variability observed in the first 10 days. This study sheds light on the impact of air-drying bloodstains on blood components at room temperature and provides a list of potential bloodstain lipid markers for determining the age of bloodstains.

The Effect of the Donor's and Recipient's Sex on Red Blood Cells Evaluated Using Transfusion Simulations

The hypothesis of the potential impact of the sex of red blood cell (RBC) concentrate (RCC) donors, as well as the sex of the recipients, on the clinical outcome, is still under evaluation. Here, we have evaluated the sex impact on RBC properties using in vitro transfusion models. Using a "flask model", RBCs from RCCs (representing the donor)-at different storage lengths-were incubated in a sex-matched and sex-mismatched manner with fresh frozen plasma pools (representing the recipient) at 37 °C, with 5% of CO2 up to 48 h. Standard blood parameters, hemolysis, intracellular ATP, extracellular glucose and lactate were quantified during incubation. Additionally, a "plate model", coupling hemolysis analysis and morphological study, was carried out in similar conditions in 96-well plates. In both models, RBCs from both sexes hemolyzed significantly less in female-derived plasma. No metabolic or morphological differences were observed between sex-matched and -mismatched conditions, even though ATP was higher in female-derived RBCs during incubations. Female plasma reduced hemolysis of female- as well as male-derived RBCs, which may be related to a sex-dependent plasma composition and/or sex-related intrinsic RBC properties.

Intermittent scavenging of storage lesion from stored red blood cells by electrospun nanofibrous sheets enhances their quality and shelf-life

Transfusion of healthy red blood cells (RBCs) is a lifesaving process. However, upon storing RBCs, a wide range of damage-associate molecular patterns (DAMPs), such as cell-free DNA, nucleosomes, free-hemoglobin, and poly-unsaturated-fatty-acids are generated. DAMPs can further damage RBCs; thus, the quality of stored RBCs declines during the storage and limits their shelf-life. Since these DAMPs consist of either positive or negative charged species, we developed taurine and acridine containing electrospun-nanofibrous-sheets (Tau-AcrNFS), featuring anionic, cationic charges and an DNA intercalating group on their surfaces. We show that Tau-AcrNFS are efficient in scavenging DAMPs from stored human and mice RBCs ex vivo. We find that intermittent scavenging of DAMPs by Tau-AcrNFS during the storage reduces the loss of RBC membrane integrity and reduces discocytes-to-spheroechinocytes transformation in stored-old-RBCs. We perform RBC-transfusion studies in mice to reveal that intermittent removal of DAMPs enhances the quality of stored-old-RBCs equivalent to freshly collected RBCs, and increases their shelf-life by ~22%. Such prophylactic technology may lead to the development of novel blood bags or medical device, and may therefore impact healthcare by reducing transfusion-related adverse effects.

Plasma characteristic metabolites of pediatric community-acquired pneumonia in traditional Chinese medicine syndrome differentiation

Community-acquired pneumonia (CAP) is the leading cause of lower respiratory tract infections in children. Heat syndrome (HS) and cold syndrome (CS) are two main syndrome types of pediatric CAP in traditional Chinese medicine (TCM). This study aimed to identify plasma metabolic profiles in pediatric CAP and to further select potential biomarkers to distinguish between HS and CS. An ultra-performance liquid chromatography coupled with linear ion trap quadrupole-orbitrap mass spectrometry method was applied to plasma samples of 296 patients and 55 healthy controls (HC). The samples were divided into the discovery group (n = 213, HS = 160, CS = 23, HC = 30) and the validation group (n = 138, HS = 93, CS = 20, HC = 25). The orthogonal partial least-squares discriminant analysis, the value of fold change, and Kruskal-Wallis test with false discovery rate correction (q-value <0.05) were applied to identify differential plasma metabolites. The area under the ROC curve (AUC) was used to evaluate the diagnostic performance of the screened metabolites. The results showed that the plasma levels of aspartic acid, phenylalanine, arginine, lysoPC20:1, lysoPE16:0, lysoPE18:0, and PE (16:0_22:6) were increased in CS compared with HC. The plasma levels of PC (18:1_18:1), PC (20:4_20:4), PE (16:0_18:2), lysoPE20:4, lysoPE18:2, and lysoPE22:6 were decreased, whereas, the plasma level of ceramide (d18:1_24:1) was increased in HS compared with HC. There were 13 differential metabolites in CS (AUC = 0.995) and 15 differential metabolites in HS (AUC = 0.954), compared with HC. A panel of seven biomarkers, including LysoPC20:1, lysoPE16:0, lysoPE18:2, lysoPE20:4, lysoPE22:6, PC (18:1_18:1), and PC (20:4_20:4) showed good discrimination between HS and CS with an AUC of 0.982. Altered plasma amino acids and lipids may provide an objective basis for TCM syndrome differentiation in pediatric CAP.

The Blood Bag Plasticizer Di-2-Ethylhexylphthalate Causes Red Blood Cells to Form Stomatocytes, Possibly by Inducing Lipid Flip-Flop

Background

During storage of red blood cell (RBC) concentrates, the plasticizer di-2-ethylhexylphthalate (DEHP) that keeps the blood bags soft leaches out and can be taken up by the RBCs. DEHP is known to be beneficial for the RBC storage quality, but the molecular mechanisms of the action are unknown.

Methods

Aqueous suspensions of DEHP were added to RBCs in buffer. The morphological effects were observed on RBCs from 5 donors. Flow cytometry with annexin A5 binding was used to measure the exposed phosphatidylserine.

Results

DEHP induced the formation of stomatocytes at concentrations as low as ng/ml, provided that the cell suspension was also sufficiently dilute. Some spherocytes, which were susceptible to lysis, were also formed; after lysis, RBC ghosts were seen to continue the transition to the cup-shaped stomatocyte form. Incubation with DEHP increased the exposed phosphatidylserine, an effect that was also observed in the presence of vanadate, which inhibits the ATP-dependent translocases that maintain the membrane's lipid asymmetry.

Conclusions

DEHP can have an active effect on RBC shape, instead of just preventing the storage-related shape changes. The effect appears to be mediated by increased flip-flop of lipids between the leaflets of the RBC membrane.

Mechanisms of red blood cell transfusion-related immunomodulation

Red blood cell (RBC) transfusion is common in critically ill, postsurgical, and posttrauma patients in whom both systemic inflammation and immune suppression are associated with adverse outcomes. RBC products contain a multitude of immunomodulatory mediators that interact with and alter immune cell function. These interactions can lead to both proinflammatory and immunosuppressive effects. Defining clinical outcomes related to immunomodulatory effects of RBCs in transfused patients remains a challenge, likely due to complex interactions between individual blood product characteristics and patient-specific risk factors. Unpacking these complexities requires an in-depth understanding of the mechanisms of immunomodulatory effects of RBC products. In this review, we outline and classify potential mediators of RBC transfusion-related immunomodulation and provide suggestions for future research directions.

Platelet proteins cause basophil histamine release through an immunoglobulin-dependent mechanism

BACKGROUND

A general understanding of allergic transfusion reaction mechanisms remains elusive. Multiple mechanisms have been proposed, but none have been compared experimentally.

STUDY DESIGN AND METHODS

We used histamine release (HR) from healthy human donor basophils to model allergic transfusion reactions. Platelet component supernatant (plasma), platelet lysate, and manipulated platelet lysates (dialyzed, delipidated, trypsinized, mild heat-inactivated, and ultracentrifuged) were used to characterize allergic stimuli. Immunoglobulin-dependent mechanisms were investigated through cell surface immunoglobulin depletion and ibrutinib signaling inhibition. HR induced by platelet mitochondria was compared with HR by platelet lysate with or without DNase treatment.

RESULTS

Robust, dose-responsive HR to platelet lysate was observed in two of eight nulliparous, never-transfused, healthy donors. No HR was observed with plasma. Among manipulated platelet lysates, only trypsin treatment significantly reduced HR (39% reduction; p = 0.008). HR in response to platelet lysate significantly decreased with either cell surface immunoglobulin depletion or ibrutinib pretreatment. Platelet mitochondria induced minimal basophil HR, and DNase treatment did not inhibit platelet lysate-induced HR.

CONCLUSION

Type I immediate hypersensitivity to platelet proteins may be an allergic transfusion reaction mechanism. Prior sensitization to human proteins is not required for basophil responses to platelet proteins. Further study into the relative contributions of hypersensitivity to platelet versus plasma proteins in transfusion is warranted.

Acid sphingomyelinase mediates murine acute lung injury following transfusion of aged platelets

Pulmonary complications from stored blood products are the leading cause of mortality related to transfusion. Transfusion-related acute lung injury is mediated by antibodies or bioactive mediators, yet underlying mechanisms are incompletely understood. Sphingolipids such as ceramide regulate lung injury, and their composition changes as a function of time in stored blood. Here, we tested the hypothesis that aged platelets may induce lung injury via a sphingolipid-mediated mechanism. To assess this hypothesis, a two-hit mouse model was devised. Recipient mice were treated with 2 mg/kg intraperitoneal lipopolysaccharide (priming) 2 h before transfusion of 10 ml/kg stored (1–5 days) platelets treated with or without addition of acid sphingomyelinase inhibitor ARC39 or platelets from acid sphingomyelinase-deficient mice, which both reduce ceramide formation. Transfused mice were examined for signs of pulmonary neutrophil accumulation, endothelial barrier dysfunction, and histological evidence of lung injury. Sphingolipid profiles in stored platelets were analyzed by mass spectrophotometry. Transfusion of aged platelets into primed mice induced characteristic features of lung injury, which increased in severity as a function of storage time. Ceramide accumulated in platelets during storage, but this was attenuated by ARC39 or in acid sphingomyelinase-deficient platelets. Compared with wild-type platelets, transfusion of ARC39-treated or acid sphingomyelinase-deficient aged platelets alleviated lung injury. Aged platelets elicit lung injury in primed recipient mice, which can be alleviated by pharmacological inhibition or genetic deletion of acid sphingomyelinase. Interventions targeting sphingolipid formation represent a promising strategy to increase the safety and longevity of stored blood products.

The accumulation of lipids and proteins during red blood cell storage: the roles of leucoreduction and experimental filtration

Pre-storage leucoreduction has been universally adopted in most developed countries in Asia, Europe and the Americas. It decreases febrile transfusion reactions, alloimmunisation to HLA antigens, cytomegalovirus exposure, the accumulation of a number of pro-inflammatory mediators in the supernatant, including the accumulation of platelet-and leucocyte-derived proteins and metabolites during routine storage. This review will highlight the lipids and proteins, biological response modifiers (BRMs) that accumulate, their clinical effects in transfused hosts, and methods of mitigation.

Transfusion-related acute lung injury: transfusion, platelets and biological response modifiers

Transfusion-related acute lung injury (TRALI) may be induced by plasma, platelet concentrates and red blood cell concentrates. The mechanism leading to TRALI is thought to involve two steps. The priming step consists of previous inflammatory pathological conditions or external factors attracting leukocytes to lung vessels and creating conditions favorable for the second step, in which anti-HLA or anti-HNA antibodies or biologically active lipids, usually in transfused blood products, stress leukocytes and inflame lung epithelia. Platelets may be involved in the pathogenesis of TRALI because of their secretory potential and capacity to interact with other immune cells. There is no drug based-prophylaxis, but transfusion strategies are used to mitigate the risk of TRALI.

The stability of blood fatty acids during storage and potential mechanisms of degradation: A review

Fatty acids in blood samples, particularly polyunsaturated fatty acids (PUFAs), are susceptible to degradation through peroxidation reactions during long-term storage. Storage of blood samples is necessary in almost all studies and is crucial for larger clinical studies and in field research settings where it is not plausible for analytical infrastructure. Despite this, PUFA stability during blood storage is often overlooked. This review introduces and discusses lipid peroxidation and popular strategies employed to prevent or minimize peroxidation reactions during fatty acid analysis. Further, an in-depth examination of fatty acid stability during storage of blood is discussed in detail for all blood fractions including plasma/serum, erythrocytes and whole blood stored both in cryovials and on chromatography paper before discussing the associated mechanisms of degradation during storage. To our knowledge this is the first review of its kind and will provide researchers with the necessary information to confidently store blood samples for fatty acid analysis.

Analysis of leucocyte antibodies, cytokines, lysophospholipids and cell microparticles in blood components implicated in post-transfusion reactions with dyspnoea

BACKGROUND AND OBJECTIVES

Post-transfusion reactions with dyspnoea (PTR) are major causes of morbidity and death after blood transfusion. Transfusion-related acute lung injury (TRALI) and transfusion-associated circulatory overload (TACO) are most dangerous, while transfusion-associated dyspnoea (TAD) is a milder respiratory distress. We investigated blood components for immune and non-immune factors implicated in PTR.

MATERIAL AND METHODS

We analysed 464 blood components (RBCs, PLTs, L-PLTs, FFP) transfused to 271 patients with PTR. Blood components were evaluated for 1/antileucocyte antibodies, 2/cytokines: IL-1β, IL-6, IL-8, TNF-α, sCD40L, 3/lysophosphatidylcholines (LysoPCs), 4/microparticles (MPs) shed from plateletes (PMPs), erythrocytes (EMPs) and leucocytes (LMPs).

RESULTS

Anti-HLA class I/II antibodies or granulocyte-reactive anti-HLA antibodies were detected in 18.2% of blood components (RBC and FFP) transfused to TRALI and in 0.5% of FFP transfused to TAD cases. Cytokines and LysoPCs concentrations in blood components transfused to PTR patients did not exceed those in blood components transfused to patients with no PTR. Only EMPs percentage in RBCs transfused to patients with TRALI was significantly higher (P < 0.05) than in RBCs transfused to patients with no PTR.

CONCLUSION

Immune character of PTR was confirmed mainly in 1/5 TRALI cases. Among non-immune factors, only MPs released from stored RBCs are suggested as potential mediators of TRALI. Our results require further observations in a more numerous and better defined group of patients.

Experimental prestorage filtration removes antibodies and decreases lipids in RBC supernatants mitigating TRALI in vivo

Transfusion-related acute lung injury (TRALI) remains a significant cause of transfusion-related mortality with red cell transfusion. We hypothesize that prestorage filtration may reduce proinflammatory activity in the red blood cell (RBC) supernatant and prevent TRALI. Filters were manufactured for both small volumes and RBC units. Plasma containing antibodies to human lymphocyte antigen (HLA)-A2 or human neutrophil antigen (HNA)-3a was filtered, and immunoglobulins and specific HNA-3a and HLA-2a neutrophil (PMN) priming activity were measured. Antibodies to OX27 were added to plasma, and filtration was evaluated in a 2-event animal model of TRALI. RBC units from 31 donors known to have antibodies against HLA antigens and from 16 antibody-negative controls were filtered. Furthermore, 4 RBC units were drawn and underwent standard leukoreduction. Immunoglobulins, HLA antibodies, PMN priming activity, and the ability to induce TRALI in an animal model were measured. Small-volume filtration of plasma removed >96% of IgG, antibodies to HLA-A2 and HNA-3a, and their respective priming activity, as well as mitigating antibody-mediated in vivo TRALI. In RBC units, experimental filtration removed antibodies to HLA antigens and inhibited the accumulation of lipid priming activity and lipid-mediated TRALI. We conclude that filtration removes proinflammatory activity and the ability to induce TRALI from RBCs and may represent a TRALI mitigation step.

Transfusion-related acute lung injury: advances in understanding the role of proinflammatory mediators in its genesis

Transfusion-related acute lung injury (TRALI) is the most common cause of serious morbidity and mortality due to hemotherapy. The pathogenesis is the result of two events: the first related to the recipient's clinical condition, predisposing to acute lung injury (ALI) through neutrophil or polymorphonuclear leukocyte sequestration, and the second being the infusion of antibodies or mediators that activate these adherent polymorphonuclear neutrophils, resulting in endothelial damage, capillary leak and ALI. TRALI is most prevalent in the critically ill, although many of these cases are termed ALI. Although mitigation strategies, such as the use of male-only plasma, have decreased the number of TRALI cases and deaths, TRALI still occurs. This review will detail the pathophysiology of TRALI, provide insight into newer areas of research and critically assess current practices to mitigate TRALI and improve transfusion safety.

Transfusion-related acute lung injury: a clinical review

Three decades ago, transfusion-related acute lung injury (TRALI) was considered a rare complication of transfusion medicine. Nowadays, the US Food and Drug Administration acknowledge the syndrome as the leading cause of transfusion-related mortality. Understanding of the pathogenesis of TRALI has resulted in the design of preventive strategies from a blood-bank perspective. A major breakthrough in efforts to reduce the incidence of TRALI has been to exclude female donors of products with high plasma volume, resulting in a decrease of roughly two-thirds in incidence. However, this strategy has not completely eradicated the complication. In the past few years, research has identified patient-related risk factors for the onset of TRALI, which have empowered physicians to take an individualised approach to patients who need transfusion.

Translational research in pediatrics II: blood collection, processing, shipping, and storage

Translational research often involves tissue sampling and analysis. Blood is by far the most common tissue collected. Due to the many difficulties encountered with blood procurement from children, it is imperative to maximize the quality and stability of the collected samples to optimize research results. Collected blood can remain whole or be fractionated into serum, plasma, or cell concentrates such as red blood cells, leukocytes, or platelets. Serum and plasma can be used for analyte studies, including proteins, lipids, and small molecules, and as a source of cell-free nucleic acids. Cell concentrates are used in functional studies, flow cytometry, culture experiments, or as a source for cellular nucleic acids. Before initiating studies on blood, a thorough evaluation of practices that may influence analyte and/or cellular integrity is required. Thus, it is imperative that child health researchers working with human blood are aware of how experimental results can be altered by blood sampling methods, times to processing, container tubes, presence or absence of additives, shipping and storage variables, and freeze-thaw cycles. The authors of this review, in an effort to encourage and optimize translational research using blood from pediatric patients, outline best practices for blood collection, processing, shipment, and storage.

Inhibition of lysophosphatidic acid increase by prestorage whole blood leukoreduction in autologous CPDA-1 whole blood

BACKGROUND

Lysophosphatidylcholine (LPC) has been implicated in the onset of transfusion-related acute lung injury (TRALI). In plasma, LPC is converted to lysophosphatidic acid (LPA) by autotaxin (ATX). The effect of leukoreduction in the accumulation of these bioactive lipids and ATX in human autologous blood has not been fully investigated.

STUDY DESIGN AND METHODS

The accumulation of choline-containing phospholipids (LPC, sphingomyelin [SM], and phosphatidylcholine [PC]), LPA, and ATX during the storage of autologous blood and the changes caused by leukoreduction were investigated. A total of 26 orthopedic patients were enrolled. Autologous blood was collected as whole blood and, after leukoreduction, preserved refrigerated until use. Prestorage leukoreduced (LR) and non-LR autologous blood samples were analyzed. The time-dependent changes and the effect of the filtration were compared.

RESULTS

A time-dependent and significant increase in the levels of LPA was observed in both non-LR and LR samples. The concentration of LPA was significantly reduced in LR compared to non-LR samples. The concentration of LPC was higher in LR compared to non-LR samples. The levels of PC, SM, and ATX were not affected by either the storage period or the leukoreduction.

CONCLUSIONS

Leukoreduction of autologous whole blood effectively reduced the accumulation of LPA. On the other hand, prestorage leukoreduction resulted in an increased concentration of LPC, without significantly affecting ATX. Further studies are necessary to confirm the role of LPA in the pathogenesis of adverse effects of blood transfusion, especially TRALI.

Liquid chromatography-tandem mass spectrometry-based plasma metabonomics delineate the effect of metabolites' stability on reliability of potential biomarkers

Metabonomics is an important platform for investigating the metabolites of integrated living systems and their dynamic responses to changes caused by both endogenous and exogenous factors. A metabonomics strategy based on liquid chromatography-mass spectrometry/mass spectrometry in both positive and negative ion modes was applied to investigate the short-term and long-term stability of metabolites in plasma. Principal components analysis and ten types of identified metabolites were used to summarize the time-dependent change rules in metabolites systematically at different temperatures. The long-term stability of metabolites in plasma specimens stored at -80 °C for five years was also studied. Analysis of these subjects identified 36 metabolites with statistically significant changes in expression (p < 0.05) and found a kind of metabolite with a hundred-fold change. The stability of metabolites in blood at 4 °C for 24 h was also investigated. These studies show that a thorough understanding of the effects of metabolite stability are necessary for improving the reliability of potential biomarkers.

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.

Therapeutic options for transfusion related acute lung injury; the potential of the G2A receptor

Priming of polymorphonuclear leukocytes (PMNs) enhances their adhesion to endothelium, the release of their granule content and their production of reactive oxygen species. These effects are etiological in transfusion related acute lung injury (TRALI) and many clinically important mediators of TRALI prime PMNs. A priming activity that develops over time in stored blood products has been shown to be due to the accumulation of lysophospatidylcholines (lyso-PCs) and has been found to be related clinically to TRALI. Lyso- PCs prime PMNs activating the G2A receptor and several inhibitors of this receptor, which could potentially be therapeutic in TRALI, have been identified. Recent work has described early steps in the signaling from the G2A receptor which has revealed potential targets for novel antagonists of lyso-PC mediated priming via G2A. Additionally, characterization of the process by which lyso-PCs are generated in stored blood products could allow development of inhibitors and additive solutions to block their formation in the first place.

Transfusion-related acute lung injury: a preventable syndrome?

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related morbidity and mortality. Recent insights into the pathophysiology of TRALI have led to various preventive strategies. Strategies in donor management range from antibody testing of sensitized donors to the deferral of female plasma donors altogether. However, knowledge on the efficacy of measures to reduce TRALI is limited. In addition, the various measures may lead to a substantial loss of donors, hampering steady blood supply. Thereby, consensus among countries and blood-collecting facilities regarding the optimal strategy to prevent TRALI is lacking. In this review, the advantages and disadvantages of various preventive measures to prevent TRALI are discussed, related to both patient factors as well as blood component-processing strategies, including transfusion policy, donor management and practices of preparation and storage conditions of blood components.

Transfusion-related acute lung injury: Current understanding and preventive strategies

Transfusion-related acute lung injury (TRALI) is the most serious complication of transfusion medicine. TRALI is defined as the onset of acute hypoxia within 6 hours of a blood transfusion in the absence of hydrostatic pulmonary oedema. The past decades have resulted in a better understanding of the pathogenesis of this potentially life-threating syndrome. The present notion is that the onset of TRALI follows a threshold model in which both patient and transfusion factors are essential. The transfusion factors can be divided into immune and non-immune mediated TRALI. Immune-mediated TRALI is caused by the passive transfer of human neutrophil antibodies (HNA) or human leukocyte antibodies (HLA) present in the blood product reacting with a matching antigen in the recipient. Non-immune mediated TRALI is caused by the transfusion of stored cell-containing blood products. Although the mechanisms behind immune-mediated TRALI are reasonably well understood, this is not the case for non-immune mediated TRALI. The increased understanding of pathways involved in the onset of immune-mediated TRALI has led to the design of preventive strategies. Preventive strategies are aimed at reducing the risk to exposure of HLA and HNA to the recipient of the transfusion. These strategies include exclusion of "at risk" donors and pooling of high plasma volume products and have shown to reduce the TRALI incidence effectively. This review discusses the current understanding of TRALI and preventive strategies available.

A threshold model for the susceptibility to transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is a serious, often life-threatening pulmonary transfusion reaction characterized by non-cardiogenic lung oedema, hypoxemia and respiratory distress in temporal association with blood transfusion. The critical mechanism in TRALI is the sudden increase in permeability of the pulmonary endothelium and the subsequent, often extensive shift of fluid into the alveolae. The rapid clinical recovery seen in most patients makes it likely that this is a temporary phenomenon. Reactive oxygen species released by neutrophils or other cells are attractive candidate mediators of this process. There is experimental and clinical evidence that several pathways can induce barrier breakdown in TRALI, a concept known as the threshold model of TRALI. Surprisingly, neutrophils may not always be required. Other cells may play a role as multipliers or attenuators of TRALI, depending on recipient-related and transfusion-related factors involved. This review will summarize recent findings on pathophysiology, with a focus on newly discovered or disenchanted recipient-related and transfusion-related risk factors for TRALI and will present the threshold model of TRALI as a unifying concept on how TRALI develops.