Ulrich J. Sachs

The pathogenesis of transfusion-related acute lung injury (TRALI).

In recent years, transfusion‐related acute lung injury (TRALI) has developed from an almost unknown transfusion reaction to the most common cause of transfusion‐related major morbidities and fatalities. A clinical definition of TRALI was established in 2004, based on acute respiratory distress, non‐cardiogenic lung oedema temporal association with transfusion and hypoxaemia. Histological findings reveal lung oedema, capillary leucostasis and neutrophil extravasation. However, the pathogenesis of TRALI remains controversial. Leucocyte antibodies, present in fresh frozen plasma and platelet concentrates from multiparous donors, and neutrophil priming agents released in stored cellular blood components have been considered to be causative. As neutrophils and endothelial cells are pivotal in the pathogenesis of TRALI, a threshold model was established to try to unify the various reported findings on pathogenesis. This model comprises the priming of neutrophils and/or endothelium by the patients co‐morbidity, neutrophil and/or endothelial cell activation by the transfused blood component, and the severity of the TRALI reaction.

The junctional adhesion molecule-C promotes neutrophil transendothelial migration in vitro and in vivo

The third member of the family of junctional adhesion molecules (JAMs), JAM-3, also called JAM-C, was recently shown to be a novel counter-receptor on platelets for the leukocyte β2-integrin Mac-1 (αMβ2, CD11b/CD18). Here, new functional aspects of the role of endothelial cell JAM-C were investigated. Endothelial cells express JAM-C, which is predominantly localized within junctions at interendothelial contacts, since it codistributes with a tight junction component, zonula occludens-1. Whereas JAM-C does not participate in neutrophil adhesion to endothelial cells, it mediates neutrophil transmigration in a Mac-1-dependent manner. In particular, inhibition of JAM-C significantly reduced neutrophil transendothelial migration, and the combination of JAM-C and platelet/endothelial cell adhesion molecule-1 blockade almost completely abolished neutrophil transendothelial migration in vitro. In vivo, inhibition of JAM-C with soluble mouse JAM-C resulted in a 50% reduction of neutrophil emigration in the mouse model of acute thioglycollate-induced peritonitis. Thus, JAM-C participates in neutrophil transmigration and thereby provides a novel molecular target for antagonizing interactions between vascular cells that promote inflammatory vascular pathologies.

The Neutrophil-specific Antigen CD177 Is a Counter-receptor for Platelet Endothelial Cell Adhesion Molecule-1 (CD31)

Human neutrophil-specific CD177 (NB1 and PRV-1) has been reported to be up-regulated in a number of inflammatory settings, including bacterial infection and granulocyte-colony-stimulating factor application. Little is known about its function. By flow cytometry and immunoprecipitation studies, we identified platelet endothelial cell adhesion molecule-1 (PECAM-1) as a binding partner of CD177. Real-time protein-protein analysis using surface plasmon resonance confirmed a cation-dependent, specific interaction between CD177 and the heterophilic domains of PECAM-1. Monoclonal antibodies against CD177 and against PECAM-1 domain 6 inhibited adhesion of U937 cells stably expressing CD177 to immobilized PECAM-1. Transendothelial migration of human neutrophils was also inhibited by these antibodies. Our findings provide direct evidence that neutrophil-specific CD177 is a heterophilic binding partner of PECAM-1. This interaction may constitute a new pathway that participates in neutrophil transmigration.

Prospective evaluation of PF4/heparin immunoassays for the diagnosis of heparin-induced thrombocytopenia.

Summary.  Background: Heparin‐induced thrombocytopenia (HIT) is an adverse complication of heparin caused by HIT antibodies that recognize platelet factor 4‐heparin (PF4/hep) complexes leading to platelet activation. Several methods are available for the identification of HIT antibodies. Objectives: To evaluate the clinical usefulness of different antigen‐binding assays for detection of antibodies against PF4/hep complexes in a prospective study. Patients/methods: A prospective cohort of 500 surgical and medical patients suspected of having HIT was evaluated. The laboratory assessment included particle gel immunoassay (PaGIA), polyspecific ELISA recognizing IgG, IgM and IgA antibodies (Poly‐ELISA), IgG‐specific ELISA (IgG‐ELISA) and the HIPA test. The pretest probability of HIT was determined using the 4T’s model. Positive and negative predictive values (PPV, NPV) of each immunoassay were determined depending upon the heparin‐induced platelet activation (HIPA) results and the clinical scoring. The operating characteristics of each immunoassay were determined using the receiver‐operation characteristic (ROC) curve. Results: Platelet‐activating antibodies were identified in 35/500 patients, all of whom had intermediate to high clinical probability. PF4/hep antibodies were detected in 124, 86 and 90 sera using Poly‐ELISA (PPV = 28), IgG‐ELISA (PPV = 40.6) and PaGIA (PPV = 36.6). NPV was 100% for Poly‐ and IgG‐ELISA, but only 99.5% for PaGIA. ROC analysis revealed that PaGIA is less informative than ELISA. The IgG‐ELISA provides better diagnostic information than the other assays. In addition, there is a clear correlation between optical density (OD) value and the probability of having HIT. Conclusions: Our observation indicates that an IgG‐ELISA provides the best diagnostic information of all antigen‐binding assays.

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.

Recommendations of the ISBT Working Party on Granulocyte Immunobiology for leucocyte antibody screening in the investigation and prevention of antibody-mediated transfusion-related acute lung injury.

Background  Transfusion‐related acute lung injury (TRALI) is currently one of the most common causes of transfusion‐related major morbidity and death. Among the many TRALI mediators, leucocyte antibodies have been identified as important triggers of severe TRALI.

White blood cell-reactive antibodies are undetectable in solvent/detergent plasma.

BACKGROUND: Transfusion‐related acute lung injury (TRALI) is a life‐threatening complication of transfusion. Although all types of blood products have been associated with TRALI, fresh‐frozen plasma (FFP) is the most commonly implicated component. It has been postulated that TRALI is an immune‐mediated event, because white blood cell (WBC)‐reactive antibodies in the donors plasma are frequently associated with the syndrome. In contrast to single donor–derived FFP, solvent/detergent (S/D) plasma is produced from multiple donations, leading to an at least 500‐fold dilution of a single plasma unit. It was hypothesized that WBC‐reactive antibodies are undetectable in S/D FFP.

Transfusion-associated graft-versus-host disease.

Transfusion-associated graft-versus-host disease (TA-GvHD) is a rare complication of blood transfusion that has a fatal outcome in most patients. It is caused by the transfusion of viable T cells present in blood products that are not rejected by the transfusion recipient, either because of recipient immunodeficiency or because of a common HLA haplotype between the blood donor and recipient. Because effective treatment is not available, risk identification and prevention are of central importance. Among the potential risk factors that have been discussed to date, a definite hazard for developing TA-GvHD has been recognized for HLA-matched transfusions or transfusions from blood relatives, intrauterine and exchange transfusions, patients with congenital immunodeficiency syndromes, bone marrow transplantation, stem cell transplantation, or lymphomas. Patients at possible TA-GvHD risk who will require further evaluation include patients with hematologic malignancies, solid tumors, or solid organ transplantation. Although postulated, an increased risk for term or preterm newborns and patients with HIV/AIDS has not thus far been demonstrated.

TRALI after the transfusion of cross‐match‐positive granulocytes

BACKGROUND: TRALI is a serious complication of transfusion. WBC antibodies have been associated with TRALI. The importance of such antibodies for the transfusion of granulocytes is unknown.

Safety and efficacy of therapeutic early onset granulocyte transfusions in pediatric patients with neutropenia and severe infections

BACKGROUND: Bacterial and fungal infections in profound neutropenia after chemotherapy are associated with high mortality despite appropriate antibacterial and antifungal treatment. Granulocyte transfusions are used as a therapeutic addendum, but concern regarding pulmonary reactions often results in delayed use in clinical practice. Accordingly, many patients are already at advanced stages of their infectious disease once granulocytes are transfused. Thus, a prospective Phase II trial was conducted to test the safety and efficacy of therapeutic early‐onset granulocyte transfusions in immunocompromised children with neutropenia and severe infections.