Antibody-induced neutrophil activation as a trigger for transfusion-related acute lung injury in an ex vivo rat lung model

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.

Intravenous immunoglobulin prevents murine antibody-mediated acute lung injury at the level of neutrophil reactive oxygen species (ROS) production

Transfusion-related acute lung injury (TRALI) is a leading cause of transfusion-associated mortality that can occur with any type of transfusion and is thought to be primarily due to donor antibodies activating pulmonary neutrophils in recipients. Recently, a large prospective case controlled clinical study of cardiac surgery patients demonstrated that despite implementation of male donors, a high incidence of TRALI still occurred and suggested a need for additional interventions in susceptible patient populations. To examine if intravenous immunoglobulin (IVIg) may be effective, a murine model of antibody-mediated acute lung injury that approximates human TRALI was examined. When BALB/c mice were injected with the anti-major histocompatibility complex class I antibody 34-1-2s, mild shock (reduced rectal temperature) and respiratory distress (dyspnea) were observed and pre-treatment of the mice with 2 g/kg IVIg completely prevented these symptoms. To determine IVIg's usefulness to affect severe lung damage, SCID mice, previously shown to be hypersensitive to 34-1-2s were used. SCID mice treated with 34-1-2s underwent severe shock, lung damage (increased wet/dry ratios) and 40% mortality within 2 hours. Treatment with 2 g/kg IVIg 18 hours before 34-1-2s administration completely protected the mice from all adverse events. Treatment with IVIg after symptoms began also reduced lung damage and mortality. While the prophylactic IVIg administration did not affect 34-1-2s-induced pulmonary neutrophil accumulation, bone marrow-derived neutrophils from the IVIg-treated mice displayed no spontaneous ROS production nor could they be stimulated in vitro with fMLP or 34-1-2s. These results suggest that IVIg prevents murine antibody-mediated acute lung injury at the level of neutrophil ROS production and thus, alleviating tissue damage.

TRALI-new challenges for histocompatibility and immunogenetics in transfusion medicine

Antibodies against human leukocyte antigens (HLAs) have long been associated with transfusion-related acute lung injury (TRALI). In contrast to febrile transfusion reactions and refractoriness to platelet transfusions in immunized patients, the causative antibodies in TRALI are present in the transfused blood component, i.e. they are formed by the blood donor and not by the recipient. Consequently, blood components with high plasma volume are particularly associated with TRALI. In addition to antibodies against HLAs, antibodies directed against human neutrophil antigens (HNAs) present in the plasma of predominantly multiparous female blood donors can induce severe TRALI reactions. Especially, antibodies to HLA class II and HNA-3a antigens can induce severe or even fatal ALI in critically ill patients. Over the last decade, the clinical importance of TRALI as major cause for severe transfusion-related morbidities has led to the establishment of new guidelines aimed at preventing this condition, including routine testing for HLA and -HNA antibodies for plasma donors with a history of allogeneic sensitization. This, in turn, poses new challenges for close collaboration between blood transfusion centers and histocompatibility and immunogenetics laboratories, for sensitive and specific detection of the relevant antibodies.

Experimental models of transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is defined clinically as acute lung injury occurring within six hours of the transfusion of any blood product. It is the leading cause of transfusion-related death in the United States, but under-recognition and diagnostic uncertainty have limited clinical research to smaller case control studies. In this review we discuss the contribution of experimental models to the understanding of TRALI pathophysiology and potential therapeutic approaches. Experimental models suggest that TRALI occurs when a host, with a primed immune system, is exposed to an activating agent such as anti-leukocyte antibody or a biologic response modifier such as lysophosphatidylcholines. Recent work has suggested a critical role for platelets in antibody-based experimental models and identified potential therapeutic strategies for TRALI.

Many, but not all, outcome studies support exclusion of female plasma from the blood supply

Transfusion-related acute lung injury (TRALI) has been identified as the most common cause of transfusion-related death. Although extensive literature supports restrictions on female-donor plasma to reduce antibody-mediated TRALI, only a few outcome studies have assessed for effects of this change, and some, but not all, have endorsed the policy. A recent report even suggests poorer outcomes in cardiac surgery patients with a shift to male-donor-only plasma, raising concerns that TRALI alone, whether catastrophic or more survivable, is insufficient compared with broader measures, such as short-term mortality or long-term survival, as an end point to assess for overall improvements in patient care.

Transfusion-related acute lung injury: emerging importance of host factors and implications for management

Recent insights from models of transfusion-related acute lung injury (TRALI), and from clinical reports, reveal that host factors are important in TRALI pathogenesis. Predisposing factors with lung neutrophil-priming capacity, such as sepsis and mechanical ventilation, increase susceptibility for a TRALI reaction, and can aggravate the course of disease. These findings may explain the higher incidence of TRALI in the critically ill compared with general hospital populations. The emerging importance of host factors may have implications for TRALI management. Suspected TRALI cases in which another acute lung injury risk factor is present (termed 'possible TRALI' in the consensus definition) should be reported to the blood bank, including patients suffering from an underlying condition. In reporting of TRALI cases, use of the international TRALI consensus definition should be used, rather then national TRALI scoring systems, to ensure a uniform approach, which may decrease variance in estimations of incidence. In terms of treatment of TRALI patients, there is a rationale to apply therapeutic strategies, which have proven to be beneficial in acute lung injury.

[The immunological conflict in the transfusion-related acute lung injury or TRALI]

Despite its underrated incidence, transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related morbidity and mortality worldwide. The pulmonary edema in TRALI occurs in the course of the transfusion of apheresis products or erythrocyte concentrates. Its pathogenesis is attributed to the infusion of donor antibodies that recognize leucocyte antigens in the transfused host, with subsequent sequestration of leucocytes in the pulmonary vessels. It is also associated with the passive transfer of lipids and other biological response modifiers that accumulate during the storage or processing of blood components. The innate immunity and inflammatory kinins are key components. The knowledge of its etiopathogenesis must come into play for improving prevention and diagnosis and for application of adapted care of the patient.

Complement receptor Mac-1 is an adaptor for NB1 (CD177)-mediated PR3-ANCA neutrophil activation

The glycosylphosphatidylinositol (GPI)-anchored neutrophil-specific receptor NB1 (CD177) presents the autoantigen proteinase 3 (PR3) on the membrane of a neutrophil subset. PR3-ANCA-activated neutrophils participate in small-vessel vasculitis. Since NB1 lacks an intracellular domain, we characterized components of the NB1 signaling complex that are pivotal for neutrophil activation. PR3-ANCA resulted in degranulation and superoxide production in the mNB1(pos)/PR3(high) neutrophils, but not in the mNB1(neg)/PR3(low) subset, whereas MPO-ANCA and fMLP caused similar responses. The NB1 signaling complex that was precipitated from plasma membranes contained the transmembrane receptor Mac-1 (CD11b/CD18) as shown by MS/MS analysis and immunoblotting. NB1 co-precipitation was less for CD11a and not detectable for CD11c. NB1 showed direct protein-protein interactions with both CD11b and CD11a by surface plasmon resonance analysis (SPR). However, when these integrins were presented as heterodimeric transmembrane proteins on transfected cells, only CD11b/CD18 (Mac-1)-transfected cells adhered to immobilized NB1 protein. This adhesion was inhibited by mAb against NB1, CD11b, and CD18. NB1, PR3, and Mac-1 were located within lipid rafts. In addition, confocal microscopy showed the strongest NB1 co-localization with CD11b and CD18 on the neutrophil. Stimulation with NB1-activating mAb triggered degranulation and superoxide production in mNB1(pos)/mPR3(high) neutrophils, and this effect was reduced using blocking antibodies to CD11b. CD11b blockade also inhibited PR3-ANCA-induced neutrophil activation, even when β2-integrin ligand-dependent signals were omitted. We establish the pivotal role of the NB1-Mac-1 receptor interaction for PR3-ANCA-mediated neutrophil activation.

Mechanism of transfusion-related acute lung injury induced by HLA class II antibodies

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-associated mortality in the United States and other countries. In most TRALI cases, human leukocyte antigen (HLA) class II antibodies are detected in implicated donors. However, the corresponding antigens are not present on the cellular key players in TRALI: neutrophils and endothelium. In this study, we identify monocytes as a primary target in HLA class II–induced TRALI. Monocytes become activated when incubated with matched HLA class II antibodies and are capable of activating neutrophils, which, in turn, can induce disturbance of an endothelial barrier. In an ex vivo rodent model, HLA class II antibody–dependent monocyte activation leads to severe pulmonary edema in a relevant period of time, whenever neutrophils are present and the endothelium is preactivated. Our data suggest that in most TRALI cases, monocytes are cellular key players, because HLA class II antibodies induce TRALI by a reaction cascade initiated by monocyte activation. Furthermore, our data support the previous assumption that TRALI pathogenesis follows a threshold model. Having identified the biologic mechanism of HLA class II antibody–induced TRALI, strategies to avoid plasma from immunized donors, such as women with a history of pregnancy, appear to be justified preventive measures.

The paradox of the neutrophil's role in tissue injury

The neutrophil is an essential component of the innate immune system, and its function is vital to human life. Its production increases in response to virtually all forms of inflammation, and subsequently, it can accumulate in blood and tissue to varying degrees. Although its participation in the inflammatory response is often salutary by nature of its normal interaction with vascular endothelium and its capability to enter tissues and respond to chemotactic gradients and to phagocytize and kill microrganisms, it can contribute to processes that impair vascular integrity and blood flow. The mechanisms that the neutrophil uses to kill microorganisms also have the potential to injure normal tissue under special circumstances. Its paradoxical role in the pathophysiology of disease is particularly, but not exclusively, notable in seven circumstances: 1) diabetic retinopathy, 2) sickle cell disease, 3) TRALI, 4) ARDS, 5) renal microvasculopathy, 6) stroke, and 7) acute coronary artery syndrome. The activated neutrophil's capability to become adhesive to endothelium, to generate highly ROS, and to secrete proteases gives it the potential to induce local vascular and tissue injury. In this review, we summarize the evidence for its role as a mediator of tissue injury in these seven conditions, making it or its products potential therapeutic targets.

Recipient T lymphocytes modulate the severity of antibody-mediated transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is a serious complication of transfusion and has been ranked as one of the leading causes of transfusion-related fatalities. Nonetheless, many details of the immunopathogenesis of TRALI, particularly with respect to recipient factors are unknown. We used a murine model of antibody-mediated TRALI in an attempt to understand the role that recipient lymphocytes might play in TRALI reactions. Intravenous injection of an IgG2a antimurine major histocompatibility complex class I antibody (34-1-2s) into BALB/c mice induced moderate hypothermia and pulmonary granulocyte accumulation but no pulmonary edema nor mortality. In contrast, 34-1-2s injections into mice with severe combined immunodeficiency caused severe hypothermia, severe pulmonary edema, and approximately 40% mortality indicating a critical role for T and B lymphocytes in suppressing TRALI reactions. Adoptive transfer of purified CD8+ T lymphocytes or CD4+ T cells but not CD19+ B cells into the severe combined immunodeficiency mice alleviated the antibody-induced hypothermia, lung damage, and mortality, suggesting that T lymphocytes were responsible for the protective effect. Taken together, these results suggest that recipient T lymphocytes play a significant role in suppressing antibody-mediated TRALI reactions. They identify a potentially new recipient mechanism that controls the severity of TRALI reactions.

Transfusion-related acute lung injury: from bedside to bench and back

Over the past 60 years, the transfusion medicine community has attained significant knowledge regarding transfusion-related acute lung injury (TRALI) through the bedside to bench and back to the bedside model. First, at the bedside, TRALI causes hypoxia and noncardiogenic pulmonary edema, typically within 6 hours of transfusion. Second, bedside studies showed a higher incidence in plasma and platelet products than in red blood cell products (the fatal TRALI incidence for plasma is 1:2-300 000 products; platelet, 1:3-400 000; red blood cells, 1:25 002 000), as well as an association with donor leukocyte antibodies (∼ 80% of cases). Third, at the bench, antibody-dependent and antibody-independent mechanisms have been described, requiring neutrophil and pulmonary endothelial cell activation. Antibodies, as well as alternate substances in blood products, result in neutrophil activation, which, in a susceptible patient, result in TRALI (2-hit hypothesis). Fourth, back to the bedside, policy changes based on results of these studies, such as minimizing use of plasma and platelet products from donors with leukocyte antibodies, have decreased the incidence of TRALI. Thus, steps to mitigate TRALI are in place, but a complete mechanistic understanding of the pathogenesis of TRALI and of which patients are at highest risk remains to be elucidated.

Transfusion-related acute lung injury (TRALI): A Canadian blood services research and development symposium

Since the first description of transfusion-related acute lung injury (TRALI) more than 2 decades ago, we have only recently begun to learn how this disorder may occur and how to prevent it. Scientists from around the world have made great strides in identifying the possible causes of this condition. Blood banks and transfusion services have risen to the challenges of prevention. Recent introduction of restricting most plasma products to those obtained from male donors only has greatly reduced the incidence of TRALI worldwide. Scientists have recently identified the gene and protein for the human neutrophil antigen-3a associated with most mortality due to TRALI, and this presents an opportunity for a screening assay to prevent future TRALI-associated deaths. Finally, animal models of TRALI have provided insight into the possible mechanisms of this disorder and can be used to explore potential treatment modalities.

Transfusion therapy and acute lung injury

Transfusion-related acute lung injury (TRALI) remains the deadliest complication of transfusion. Consensus definitions of TRALI have been developed but remain controversial. Recent evidence supports a strong relationship between blood transfusion and the development of acute lung injury in the critically ill and trauma population. Plasma and platelet transfusions have been the most commonly implicated blood products. The 'two hit' model may best explain the immune and nonimmune pathogenesis of TRALI. Current treatment remains largely supportive; effective measures for decreasing the incidence of TRALI include the use of predominantly male plasma and apheresis platelets. Greater understanding of the blood component and patient risk factors for TRALI will hopefully lead to novel treatment and preventive strategies for reducing the risk of this life-threatening syndrome.

The role of neutrophils in the pathogenesis of transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is the major cause of transfusion related morbidity and mortality, world wide. Efforts to reduce or eliminate this serious complication of blood transfusion are hampered by an incomplete understanding of its pathogenesis. Currently, TRALI is thought to be mediated by donor alloantibodies directed against host leukocytes or the result of 2 distinct clinical events. For both proposed mechanisms, the neutrophil is the key effector cell. This article reviews TRALI pathophysiology, explores the role of the neutrophil, details practical information for appropriate diagnosis and promotes further studies into the pathogenesis of TRALI.

Human neutrophil alloantigen-1a, -1b, -2, -3a and -4a frequencies in Brazilians

Human neutrophil reactive antibodies may cause clinical disorders such as transfusion-related acute lung injury, febrile transfusion reactions, alloimmune neonatal neutropenia, immune neutropenia after stem cell transplantation, refractoriness to granulocyte transfusion, drug-induced neutropenia and autoimmune neutropenia. Using the granulocyte immunofluorescence test by flow cytometry, the phenotypic frequencies of the human neutrophil alloantigens (HNA)-1a, -1b, -2, -3a and -4a were determined in 100 healthy Brazilian persons. Neutrophils were separated from blood samples by sedimentation, centrifugated and incubated with HNA-specific alloantibody plus fluorescein isothiocyanate-labeled F(ab')(2) fragments of anti-human IgG. The results showed that the phenotype frequencies of HNA-1a, -1b, -2a, -3a and -4a were 65%, 83%, 97%, 95% and 94%, respectively. We detected that neutrophils from 17% of Brazilians typed positive only with anti-HNA-1a (HNA-1a/a), 35% only with anti-HNA-1b (HNA-1b/b) and 48% reacted with both antibodies (HNA-1a/b). The frequencies found for HNA-1a and -1b were quite similar to that reported among Africans and American-Africans, but different from those found in Japanese and Chinese. In addition, our data showed that the frequencies of HNA-2, -3a and -4a in Brazilians were comparable with those observed in Caucasians. The determination of HNAs frequencies among populations with distinct racial backgrounds is important not only for anthropological reasons, but also for neonatal typing in suspected cases of alloimmune neutropenia or when patients are severely neutropenic.

The effect of previous pregnancy and transfusion on HLA alloimmunization in blood donors: implications for a transfusion-related acute lung injury risk reduction strategy

BACKGROUND

Antibodies to human leukocyte antigens (HLA) in donated blood have been implicated as a cause of transfusion-related acute lung injury (TRALI). A potential measure to reduce the risk of TRALI includes screening plateletpheresis donors for HLA antibodies. The prevalence of HLA antibodies and their relationship to previous transfusion or pregnancy in blood donors was determined.

STUDY DESIGN AND METHODS

A total of 8171 volunteer blood donors were prospectively recruited by six US blood centers from December 2006 to May 2007. Donors provided a detailed history of pregnancy and transfusion and a sample for HLA Class I and II antibody testing by multiantigen bead flow analysis.

RESULTS

A total of 8171 donors were enrolled; 7920 (96.9%) had valid HLA antibody test results and 7841 (99%) of those had complete pregnancy and transfusion information. The prevalence of any HLA antibody was similar in nontransfused (n = 1138) and transfused (n = 895) men, 1.0% versus 1.7% (p = 0.16). HLA antibodies were detected in 17.3% of all female donors (n = 5834) and in 24.4% of those with a history of previous pregnancy (n = 3992). The prevalence of HLA antibodies increased in women with greater numbers of pregnancy: 1.7% (zero), 11.2% (one), 22.5% (two), 27.5% (three), and 32.2% (four or more pregnancies; p < 0.0001).

CONCLUSION

HLA Class I and Class II antibodies are detectable at low prevalence in male donors regardless of transfusion and in female donors without known immunizing events. The prevalence of HLA antibodies increases significantly with more pregnancies. These data will allow blood centers to estimate the impact of HLA antibody testing as a potential TRALI risk reduction measure.

Transfusion-related acute lung injury (TRALI): current concepts and misconceptions

Transfusion-related acute lung injury (TRALI) is the most common cause of serious morbidity and mortality due to hemotherapy. Although the pathogenesis has been related to the infusion of donor antibodies into the recipient, antibody negative TRALI has been reported. Changes in transfusion practices, especially the use of male-only plasma, have decreased the number of antibody-mediated cases and deaths; however, TRALI still occurs. The neutrophil appears to be the effector cell in TRALI and the pathophysiology is centered on neutrophil-mediated endothelial cell cytotoxicity resulting in capillary leak and ALI. This review will detail the pathophysiology of TRALI including recent pre-clinical data, provide insight into newer areas of research, and critically assess current practices to decrease it prevalence and to make transfusion safer.

Parabolic flight primes cytotoxic capabilities of polymorphonuclear leucocytes in humans

BACKGROUND

Previously performed in vitro studies suggested that gravitational stress may alter functions of immune cells. This study investigated the in vivo effects of parabolic flight manoeuvres as a short-term model of micro- and hypergravity on the cytotoxic and microbicidal polymorphonuclear leucocyte (PMN) functions as the key element of innate immunity.

MATERIAL AND METHODS

Twenty-one healthy male volunteers underwent 30 subsequent parabolic flight manoeuvres. Each manoeuvre produced 22-s periods of nearly weightlessness close to <<0g>>, with each parabola starting with a pull-up and ending with a pull-out (hypergravity) at 1.8 g for about 20 s each. Blood samples were drawn 24 h prior to take off (T0), after 25-30 parabolas (T1), and 24 h (T2) and 48 h (T3) after flight for determination of (i) leucocyte number and subpopulations, (ii) PMNs' capabilities to produce hydrogen peroxide (H(2)O(2)) and to adhere and phagocytose particles and (iii) plasma cytokines known to prime PMN functions [interleukin-8 (IL-8), tumour necrosis factor-alpha (TNF-alpha), granulocyte-colony stimulating factor (G-CSF) and granulocyte-macrophage colony stimulating factor (GM-CSF)].

RESULTS

Parabolic flight induced an increase in leucocyte number with a significant elevation of the PMN fraction. The spontaneous H(2)O(2) production by PMNs did not change; however, the capability of PMNs to produce H(2)O(2) in response to soluble stimuli [N-formyl-methionyl-leucyl-phenylalanine (fMLP), fMLP and TNF-alpha, calcium ionophore (A23187), phorbol myristate acetate (PMA)] was increased. Adhesive and phagocytic properties of PMNs were not altered. Regarding priming cytokines, IL-8 and G-CSF were significantly elevated.

CONCLUSIONS

Our data indicate that parabolic flight induces priming of the cytotoxic capabilities of PMNs without affecting microbicidal functions.

Animal models of transfusion-related acute lung injury

Currently, more than 50 years after its apparent early recognition in case reports, and more than 20 years after its name was coined to denote a distinct entity of pulmonary transfusion reactions, transfusion-related acute lung injury (TRALI) has emerged as a serious cause of transfusion-associated morbidity and the subject of an exponentially growing scientific literature. However, review articles, clinical case reports, and case series continue to dominate the published literature on the topic and experimental studies aimed at modeling and elucidating TRALI mechanisms are less frequent. This article reviews the current status of the known experimental models of TRALI, with particular emphasis on efforts to establish in vivo animal models of this important pulmonary transfusion reaction.

Transfusion-related lung injury

This paper describes the history and pathogenesis of TRALI and illustrates this with personal experience of the condition over 15 years at a single hospital. It discusses the contribution of transfusion to ALI seen in critically ill patients, and the effect of preventative measures taken in the UK.

Specificities of leucocyte alloantibodies in transfusion-related acute lung injury and results of leucocyte antibody screening of blood donors

BACKGROUND

Antibody-mediated transfusion-related acute lung injury (TRALI) is an important cause of transfusion-associated morbidity and death. Preventive strategies are currently a matter of debate.

METHODS

Specificities of leucocyte antibodies implicated in previous severe TRALI reactions were determined using standard techniques. Based on these results, a leucocyte antibody screening strategy for the testing of parous female donors was introduced.

RESULTS

Of 36 TRALI cases, 17, 12, four and three were due to human leucocyte antigen (HLA) class II, human neutrophil alloantigen (HNA), HLA class I, and mixtures of HLA class I and II antibodies, respectively. HNA-3a antibodies accounted for 10 of 12 HNA antibody-mediated reactions and 6 of 10 fatalities including one after transfusion of red blood cells. Investigation 5332 parous female donors showed leucocyte antibodies in 473 samples, resulting in an alloimmunization rate of 8.9%. Sixty-one per cent of these donors presented HLA class I, 19% class II, 12% HLA class I and II antibodies and 5% HNA antibodies. Additional HLA class I antibodies were found in 39% of HLA class II and in 17% of HNA antibodies containing sera. Our restrictive plasma strategy did not result in a shortage of plasma or platelets. No antibody-mediated TRALI case was observed since introduction of the policy of plasma from male, nulliparous or tested multiparous donors.

CONCLUSION

Compared to HLA class I antibodies, those directed against HLA class II and HNA-3a were of greater clinical relevance. Isolated HLA class I antibody screening was found to be insufficient for leucocyte antibody screening.

Transfusion-related acute lung injury: current concepts for the clinician

The leading cause of transfusion-related morbidity and mortality in the United States is transfusion-related acute lung injury (TRALI). Diagnostic criteria for TRALI have recently been developed and primarily consist of hypoxia and bilateral pulmonary edema occurring during or within 6 h of a transfusion in the absence of cardiac failure or intravascular volume overload. The primary differential diagnosis is transfusion-associated circulatory overload and differentiation can be difficult. Treatment is supportive with oxygen and mechanical ventilation. Diuresis is not indicated and the role of steroids is unproven. Patients typically recover within a few days. All types of blood products have been associated with TRALI, however, the plasma-rich components, such as fresh frozen plasma and apheresis platelets, have been most frequently implicated. The pathogenesis of TRALI is not completely understood. Leukocyte antibodies in donor plasma have been implicated in most cases with antibodies directed at human leukocyte antigen (HLA) class I, HLA class II or neutrophil-specific antigens, particularly HNA-3a. Activation of pulmonary endothelium is important in the development of TRALI and may account for most cases being observed in surgical or intensive care unit patients. Transfused leukoagglutinating antibodies bind to recipients' neutrophils localized to pulmonary endothelium resulting in activation and release of oxidases and other damaging biologic response modifiers that cause capillary leak. In a minority of TRALI cases, no antibodies are identified and it is postulated that neutrophil priming factors in the transfused component can mediate TRALI in a patient with pulmonary endothelial activation, the so called "two hit" mechanism. Recognition of the role of anti-leukocyte antibodies has led to new strategies to reduce the risk of TRALI. Female blood donors with a previous pregnancy frequently have HLA antibodies with an overall prevalence of 24% and increasing prevalence related to the number of previous pregnancies. Since HLA antibodies have been implicated in TRALI, blood centers have adopted policies to produce plasma components primarily from male donors. Strategies to reduce the risk from apheresis platelets are problematic and are likely to involve testing female apheresis platelet donors for HLA antibodies. Much more research is needed to understand the blood component and patient risk factors for TRALI so that novel strategies for treatment and additional measures to reduce the risk of TRALI can be developed.

Plasma from stored packed red blood cells and MHC class I antibodies causes acute lung injury in a 2-event in vivo rat model

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion death. We hypothesize that TRALI requires 2 events: (1) the clinical condition of the patient and (2) the infusion of antibodies against MHC class I antigens or the plasma from stored blood. A 2-event rat model was developed with saline (NS) or endotoxin (LPS) as the first event and the infusion of plasma from packed red blood cells (PRBCs) or antibodies (OX18 and OX27) against MHC class I antigens as the second event. ALI was determined by Evans blue dye leak from the plasma to the bronchoalveolar lavage fluid (BALF), protein and CINC-1 concentrations in the BALF, and the lung histology. NS-treated rats did not evidence ALI with any second events, and LPS did not cause ALI. LPS-treated animals demonstrated ALI in response to plasma from stored PRBCs, both prestorage leukoreduced and unmodified, and to OX18 and OX27, all in a concentration-dependent fashion. ALI was neutrophil (PMN) dependent, and OX18/OX27 localized to the PMN surface in vivo and primed the oxidase of rat PMNs. We conclude that TRALI is the result of 2 events with the second events consisting of the plasma from stored blood and antibodies that prime PMNs.

Pulmonary transfusion reactions

BACKGROUND

In recent years, pulmonary transfusion reactions have gained increasing importance as serious adverse transfusion events.

METHODS

Review of the literature.

RESULTS

Pulmonary transfusion reactions are not extremely rare and, according to hemovigilance data, important causes of transfusion-induced major morbidity and death. They can be classified as primary with predominant pulmonary injury and secondary as part of another transfusion reaction. Primary reactions include transfusion-related acute lung injury (TRALI), transfusion-associated circulatory overload (TACO) and transfusion-associated dyspnea (TAD). Secondary pulmonary reactions are often observed in the wake of hemolytic transfusion reactions, hypotensive/anaphylactic reactions, and transfusion-transmitted bacterial infections.

CONCLUSION

Knowledge and careful management of cases of pulmonary transfusion reactions are essential for correct reporting to blood services and hemovigilance systems. Careful differentiation between TRALI and TACO is important for taking adequate preventive measures.

Postinjury life threatening coagulopathy: is 1:1 fresh frozen plasma:packed red blood cells the answer?

BACKGROUND

Recent military experience suggests that immediate 1:1 fresh frozen plasma (FFP); red blood cells (RBC) for casualties requiring >10 units packed red blood cells (RBC) per 24 hours reduces mortality, but no clinical trials exist to address this issue. Consequently, we reviewed our massive transfusion practices during a 5-year period to test the hypothesis that 1:1 FFP:RBC within the first 6 hours reduces life threatening coagulopathy.

METHODS

We queried our level I trauma center's prospective registry from 2001 to 2006 for patients undergoing massive transfusion. Logistic regression was used to evaluate the independent effect of FFP:RBC in 133 patients who received >10 units RBC in 6 hours on (1) Coagulopathy (international normalized ratio [INR] >1.5 at 6 hours), controlling for our previously described risk factors predictive of coagulopathy, as well as RBC, FFP, and platelet administration (2) Death (controlling for all variables plus age, crystalloids per 24 hours, INR >1.5 at 6 hours).

RESULTS

Overall mortality was 56%; 50% died from acute blood loss in the operating room. Over 80% of the RBC transfusions were completed in the first 6 hours: (Median RBC: 18 units) Median FFP:RBC survivors, 1:2, nonsurvivors: 1:4. (p < 0.001) INR >1.5 at 6 hours occurred in 30 (23%); 81% died. Regarding mortality, logistic regression showed significant variables (p < 0.05) included: RBC per 6 hours (OR = 1.248, 95%CI: 1.957-53.255), INR at 6 hours >1.5 (OR = 10.208, 95% CI: 1.957-53.255), ED temperature <34 degrees C (OR = 15.491, 95% CI 1.376-174.396), and age >55 years (OR = 40.531, CI 5.315-309.077). The adjusted OR for FFP:RBC ratio including the quadratic term was found to follow a U-shaped association (quadratic term estimate 0.6737 +/- 0.0345, p = 0.0189).

CONCLUSION

Although our data suggest that 1:1 FFP:RBC reduced coagulopathy, this did not translate into a survival benefit. Our findings indicate that the relationship between coagulopathy and mortality is more complex, and further clinical investigation is necessary before recommending routine 1:1 in the exsanguinating trauma patient.

Endothelial permeability is increased by the supernatant of peripheral blood mononuclear cells stimulated with HLA Class II antibody

BACKGROUND

The generation of inflammatory mediators from monocytes activated by HLA Class II antibodies is thought to play important roles in the etiology of nonhemolytic transfusion reactions. Increased permeability of endothelial cells contributes to the pathogenesis of rash, urticaria, angioedema, and pulmonary edema, which are symptoms of transfusion reactions.

STUDY DESIGN AND METHODS

We investigated whether inflammatory mediators released from monocytes upon stimulation by HLA Class II antibodies could increase endothelial permeability. Human endothelial cell monolayers were incubated with cell-free supernatants of peripheral blood mononuclear cells (PBMNCs) stimulated with HLA Class II antibody-containing plasma (anti-HLA-DR plasma), which has been implicated in severe nonhemolytic transfusion reactions. The permeability of endothelial cells to dextran was measured.

RESULTS

The supernatants of PBMNCs stimulated with the anti-HLA-DR plasma in corresponding antigen-antibody combinations were able to increase endothelial permeability. At least 3 hours of exposure of PBMNCs to anti-HLA-DR plasma was required to produce a supernatant that could induce a significant increase in permeability. Simultaneous addition of tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) neutralizing antibodies to the activated PBMNC supernatant significantly reduced the increase in permeability. Treatment of the endothelial cells with an inhibitor of nuclear factor kappaB (NF-kappaB), but not inhibitors of apoptosis, significantly prevented the increase in permeability.

CONCLUSION

Both TNF-alpha and IL-1 beta, generated from PBMNCs by anti-HLA-DR plasma in a corresponding antigen-antibody-dependent manner, led to an increase in endothelial permeability. The activation of monocytes by the HLA-DR antibodies and the resultant inflammatory mediators could contribute to the pathogenesis of rash, urticaria, angioedema, and pulmonary edema after transfusion.

Neutrophil-specific antigen HNA-2a, NB1 glycoprotein, and CD177

PURPOSE OF REVIEW

Several advances have been made in characterization of the molecule that carries human neutrophil antigen (HNA)-2a, NB1 glycoprotein, the gene that encodes NB1 glycoprotein, CD177, and the role of antibodies to HNA-2a in transfusion reactions.

RECENT FINDINGS

NB1 glycoprotein binds to the endothelial cell adhesion molecule, platelet endothelial cell adhesion molecule-1 (PECAM-1), and participates in neutrophil transmigration. The overexpression of neutrophil CD177 mRNA has become a useful, but nonspecific biomarker of myeloproliferative diseases, especially polycythemia vera. CD177 mRNA overexpression is also a biomarker of a subset of patients with essential thrombocythemia who are at increased risk of thromboembolic complications. In patients with myeloproliferative disorders CD177 mRNA overexpression is secondary to a gain-of-function mutation in JAK2, JAK2 V617F. NB1 glycoprotein is co-localized on neutrophil plasma membranes with proteinase 3 and a complex of NB1 glycoprotein and proteinase 3 may initiate the activation of neutrophils by antineutrophil cytoplasmic antibodies in patients with Wegener's granulomatosis. The inadvertent transfusion of antibodies to HNA-2a with blood components frequently causes pulmonary transfusion reactions.

SUMMARY

The expression of CD177 is an important biomarker of myeloproliferative diseases, NB1 glycoprotein is a ligand for PECAM-1 and it may have a role in Wegener's granulomatosis, and antibodies to HNA-2a frequently cause pulmonary transfusion reactions.

Human neutrophil alloantigens

OBJECTIVE

This review describes alloantigens currently listed in the human neutrophil alloantigen (HNA) system.

MATERIAL AND METHODS

Review of the literature.

RESULTS

Neutrophil antigens are implicated in a variety of clinical conditions including neonatal immune neutropenia, transfusion-related acute lung injury, refractoriness to granulocyte transfusions, febrile transfusion reactions, immune neutropenia after bone marrow transplantation, autoimmune neutropenia and drug-induced immune neutropenia. Seven antigens have been listed in the HNA system that are assigned to five antigen groups. Six antigens have been characterized biochemically and molecularly so that their primary structure is now known. As shown by regularly performed international granulocyte immunology workshops, a combination of granulocyte agglutination and immunofluorescence tests together with a panel of typed cells is currently the best means of detection.

CONCLUSIONS

Most of the HNA antigens have been well-characterized so that HNA typing as well as the detection of the corresponding antibodies are now reliably possible. This will improve diagnostics of neutrophil antibody-mediated clinical conditions as well as the prevention of transfusion-related acute lung injury.

Interference with TRALI-causing anti-HLA DR alloantibody induction of human pulmonary microvascular endothelial cell injury by purified soluble HLA DR

BACKGROUND AND OBJECTIVE

Antibodies to human leucocyte antigens (HLA) and human polymorphonuclear neutrophil (PMN) antigens are considered etiologic agents of transfusion-related acute lung injury (TRALI). The aim of this study was to clarify the role of anti-HLA DR antibodies in the pathophysiology of TRALI and the ability of purified soluble HLA DR (psHLA DR) to inhibit the release of cytokines in an in vitro model.

MATERIALS AND METHODS

A coculture of human pulmonary microvascular endothelial cells (HMVEC) and monocytes in the presence of serum containing anti-HLA DR alloantibodies previously associated with cases of TRALI was used as an in vitro TRALI model. The release of leukotriene B(4) (LTB(4)) and tumour necrosis factor-alpha (TNF-alpha), the apoptosis of HMVECs were measured.

RESULTS

The release of LTB(4) and TNF-alpha and apoptosis of HMVECs were observed in the model. The addition of psHLA DR markedly reduced the release of LTB(4) and TNF-alpha and inhibited apoptosis of HMVECs.

CONCLUSION

These results support the critical role of anti-HLA DR alloantibodies in the pathogenesis of TRALI and suggest that the soluble HLA DR could inhibit TRALI development caused by anti-HLA DR alloantibodies.

Leukocyte antigen and antibody detection assays: tools for assessing and preventing pulmonary transfusion reactions

Antibodies to neutrophil and HLA antigens can cause pulmonary transfusion reactions, and in some cases acute lung injury. When evaluating cases of pulmonary transfusion reactions, it is often necessary to test donors for neutrophil and HLA antibodies and also type the recipient for neutrophil and HLA antigens. A variety of enzyme-linked immunosorbent assay (ELISA) and flow cytometry-based solid phase assays are available to test for HLA class I and class II antibodies, but not neutrophil antibodies. Screening for neutrophil antibodies requires the preparation of panels of fresh neutrophils and testing in agglutination, immunofluorescence, or flow cytometry assays. Genotyping of HLA class I and II antigens is performed with a variety of sequence-specific primers, sequenced-specific oligonucleotide probe, and sequence-based typing assays. Neutrophil-specific antigens HNA-1a, -1b, -1c, -4a, and -5a can be genotyped, but not HNA-2a or -3a. Phenotyping of HNA-2a can be performed with CD177 monoclonal antibodies, but the gene encoding HNA-3a has not been identified, and the genomic basis for the HNA-2a-negative phenotype is not known. In conclusion, patients and donors involved with pulmonary transfusion reactions can be quickly typed for HLA antigens and tested for HLA antibodies, but testing for neutrophil antibodies and antigens requires the use of a reference laboratory.

The pathogenesis of transfusion-related acute lung injury and how to avoid this serious adverse reaction of transfusion

Transfusion-related acute lung injury (TRALI) is a serious, life-threatening complication of blood transfusion. Available evidence strongly suggests that leukocyte antibodies present in donor plasma are the predominant mechanism in TRALI. These antibodies lead to recipient neutrophil activation, with activated neutrophils inducing endothelial and alveolar damage in the lungs. These mechanisms are discussed in detail as are the alternative mechanisms that have been proposed. Preventive strategies that may help to reduce TRALI are presented.

Transfusion-related acute lung injury in the critically ill: prospective nested case-control study

RATIONALE

Acute lung injury (ALI) that develops 6 hours after transfusion (TRALI) is the leading cause of transfusion-related mortality. Several transfusion characteristics have been postulated as risk factors for TRALI, but the evidence is limited to retrospective studies.

OBJECTIVES

To compare patient and transfusion risk factors between patients who do and do not develop ALI.

METHODS

In this prospective cohort study, consecutive transfused critically ill patients were closely observed for development of ALI. Donor samples were collected from the transfusion bags. Risk factors were compared between patients who developed ALI after transfusion and transfused control patients, matched by age, sex, and admission diagnosis.

MEASUREMENTS AND MAIN RESULTS

Seventy-four of 901 transfused patients developed ALI within 6 hours of transfusion (8%). Compared with transfused control subjects, patients with ALI were more likely to have sepsis (37 vs. 22%, P = 0.016) and a history of chronic alcohol abuse (37 vs. 18%, P = 0.006). When adjusted for patient characteristics, transfusion of plasma from female donors (odds ratio [OR], 5.09; 95% confidence interval [95% CI], 1.37-18.85) rather than male donors (OR, 1.60; 95% CI, 0.76 to 3.37), number of pregnancies among the donors (OR, 1.19; 95% CI, 1.05 to 1.34), number of donor units positive for anti-granulocyte antibodies (OR, 4.85; 95% CI, 1.32-17.86) and anti-HLA class II antibodies (OR, 3.08; 95% CI, 1.15-8.25), and concentration of lysophosphatidylcholine in the donor product (OR, 1.69; 95% CI, 1.10 to 2.59) were associated with the development of ALI.

CONCLUSIONS

Both patient and transfusion risk factors determine the probability of ALI after transfusion. Transfusion factors represent attractive targets for the prevention of ALI.

TRALI--definition, mechanisms, incidence and clinical relevance

Transfusion-related acute lung injury (TRALI) is defined as new acute lung injury (ALI) that occurs during or within six hours of transfusion, not explained by another ALl risk factor. Transfusion of part of one unit of any blood product can cause TRALI. The mechanism may include factors in unit(s) of blood, such as antibody and biologic response modifiers. In addition, yet to be described factors in a patient's illness may predispose to the condition. The current incidence is estimated to be 1 in 5000 units. Patients present with acute dyspnea, or froth in the endotracheal tube in intubated patients. Hypertension, hypotension, acute leukopenia have been described. Management is similar to that for ALI and is predominantly supportive. When TRALI is suspected, Blood banks should be notified to quarantine other components from the same donation. No special blood product is required for subsequent transfusion of a patient who has developed TRALI.