Behnaz Bayat

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.

Neutrophil transmigration mediated by the neutrophil-specific antigen CD177 is influenced by the endothelial S536N dimorphism of platelet endothelial cell adhesion molecule-1.

The human neutrophil-specific adhesion molecule CD177 (also known as the NB1 alloantigen) becomes upregulated on the cell surface in a number of inflammatory settings. We recently showed that CD177 functions as a novel heterophilic counterreceptor for the endothelial junctional protein PECAM-1 (CD31), an interaction that is mediated by membrane-proximal PECAM-1 IgD 6, which is known to harbor an S536N single nucleotide polymorphism of two major isoforms V98N536G643 and L98S536R643 and a yet-to-be-determined region on CD177. In vitro transendothelial migration experiments revealed that CD177+ neutrophils migrated significantly faster through HUVECs expressing the LSR, compared with the VNG, allelic variant of PECAM-1 and that this correlated with the decreased ability of anti-PECAM-1 Ab of ITIM tyrosine phosphorylation in HUVECs expressing the LSR allelic variant relative to the VNG allelic variant. Moreover, engagement of PECAM-1 with rCD177-Fc (to mimic heterophilic CD177 binding) suppressed Ab-induced tyrosine phosphorylation to a greater extent in cells expressing the LSR isoform compared with the VNG isoform, with a corresponding increased higher level of β-catenin phosphorylation. These data suggest that heterophilic PECAM-1/CD177 interactions affect the phosphorylation state of PECAM-1 and endothelial cell junctional integrity in such a way as to facilitate neutrophil transmigration in a previously unrecognized allele-specific manner.

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 mNB1pos/PR3high neutrophils, but not in the mNB1neg/PR3low 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 mNB1pos/mPR3high 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.

A Hydrophobic Patch on Proteinase 3, the Target of Autoantibodies in Wegener Granulomatosis, Mediates Membrane Binding via NB1 Receptors

Proteinase 3 (PR3), the target antigen of antineutrophil cytoplasm autoantibodies, which are found in patients with Wegener granulomatosis, is a neutrophil serine protease localized within cytoplasmic granules. Recently, the human neutrophil antigen NB1 was identified as a specific neutrophil cell surface receptor of PR3. We hypothesized that the unique hydrophobic cluster of PR3 that is not present on human neutrophil elastase and cathepsin G and presumably is also missing in other human PR3 homologs accounts for its binding to the NB1 receptor expressed on the cellular surface of NB1 cells. Instead of generating and testing various artificial human PR3 mutants, we cloned and expressed the very closely related gibbon (Hylobates pileatus) PR3 homolog, which did not bind to the human NB1 receptor. Moreover, a human-gibbon hybrid constructed from the N- and C-terminal half of the human and gibbon PR3, respectively, also did not interact with human NB1. The C-terminal half of gibbon PR3 differs only by 9 residues from human PR3, among which four closely spaced hydrophobic residues are substituted in a nonconservative manner (F166L, W218R, G219A, and L223H). The NB1-bound PR3 was active and was cleared from the surface by α-1-protease inhibitor. Conformational distortion of the hydrophobic 217-225 loop by α-1-protease inhibitor most likely triggers rapid solubilization.

Anti–Human Neutrophil Antigen-3a Induced Transfusion-Related Acute Lung Injury in Mice by Direct Disturbance of Lung Endothelial Cells

Objective—Antibodies against human neutrophil antigen-3a (HNA-3a) located on choline transporter-like protein 2 induce severe transfusion-related acute lung injury (TRALI). This study aims to identify the mechanism implicated in anti–HNA-3a-mediated TRALI. Approach and Results—Our analysis shows that anti–HNA-3a recognizes 2 choline transporter-like protein 2 isoforms (P1 and P2) on human microvascular endothelial cells from lung blood vessels but reacts only with the P1 isoform on neutrophils. Direct treatment of HNA-3a–positive endothelial cells with anti–HNA-3a, but not with anti–HNA-3b, leads to reactive oxygen species production, increased albumin influx, and decreased endothelial resistance associated with the formation of actin stress filaments and loosening of junctional vascular endothelium-cadherin. In a novel in vivo mouse model, TRALI was documented by significant increase in lung water content, albumin concentration, and neutrophil numbers in the bronchoalveolar lavage on injection of human anti–HNA-3a in lipopolysaccharides-treated, as well as nontreated mice. Interestingly, although neutrophil depletion alleviated severity of lung injury, it failed to prevent TRALI in this model. Infusion of anti–HNA-3a F(ab′)2 fragments caused moderate TRALI. Finally, mice lacking nicotinamide adenine dinucleotide phosphate oxidase (NOX2y/-) were protected from anti–HNA-3a-mediated TRALI. Conclusions—These data demonstrate the initiation of endothelial barrier dysfunction in vitro and in vivo by direct binding of anti–HNA-3a on endothelial cells. It seems, however, that the presence of neutrophils aggravates barrier dysfunction. This novel mechanism of TRALI primarily mediated by endothelial cell dysfunction via choline transporter-like protein 2 may help to define new treatment strategies to decrease TRALI-related mortality.

The frequencies of human neutrophil alloantigens in the Chinese Han population of Guangzhou.

BACKGROUND: Antibodies against polymorphic structures on human neutrophil antigens (HNAs) play a role in alloimmune‐mediated neutropenia and are the leading cause of antibody‐mediated transfusion‐related acute lung injury (TRALI). This study aimed to determine the frequencies of HNAs in the major Han ethnic group living in Guangdong Province, Southern China.

Implication of transfected cell lines for the detection of alloantibodies against human neutrophil antigen‐3

BACKGROUND: Alloantibodies against human neutrophil antigen‐3 (HNA‐3) are responsible for the fatalities reported in transfusion‐related acute lung injury. Consequently, reliable detection of these alloantibodies is mandatory to improve blood transfusion safety. In this study, we developed stable cell lines for the detection of HNA‐3 antibodies.

Antiendothelial αvβ3 Antibodies Are a Major Cause of Intracranial Bleeding in Fetal/Neonatal Alloimmune Thrombocytopenia

Objective—Fetal/neonatal alloimmune thrombocytopenia is a severe bleeding disorder, which can result in intracranial hemorrhage (ICH), leading to death or neurological sequelae. In whites, maternal anti–human platelet antigen-1a (HPA-1a) antibodies are responsible for the majority of cases. No predictive factors for ICH are available to guide prophylactic treatment during pregnancy. In this study, we investigated antibodies from mothers with ICH-positive fetal/neonatal alloimmune thrombocytopenia and with ICH-negative fetal/neonatal alloimmune thrombocytopenia to identify serological and functional differences between the groups. Approach and Results—In an antigen capture assay, we observed a stronger binding of +ICH antibodies to endothelial cell (EC)–derived &agr;v&bgr;3. By absorption experiments, we subsequently identified anti–HPA-1a antibodies of anti-&agr;v&bgr;3 specificity in the +ICH but not in the −ICH cohort. Only the anti–&agr;v&bgr;3 subtype, but not the anti–&bgr;3 subtype, induced EC apoptosis of HPA-1a–positive ECs by caspase-3/7 activation, and mediated by reactive oxygen species. In addition, only the anti–&agr;v&bgr;3 subtype, but not the anti-&bgr;3 subtype, interfered with EC adhesion to vitronectin and with EC tube formation. Conclusions—We conclude that the composition of the anti–HPA-1a antibody subtype(s) of the mother may determine whether ICH occurs. Analysis of anti–HPA-1a antibodies of the anti–&agr;v&bgr;3 subtype in maternal serum has potential in the diagnostic prediction of ICH development and may allow for modification of prophylactic treatment in fetal/neonatal alloimmune thrombocytopenia.

Rapid enzyme-linked immunosorbent assay for the detection of antibodies against human neutrophil antigens -1a, -1b, and -1c.

BACKGROUND: Several methods exist for the detection of neutrophil antibodies; most of them, however, require fresh neutrophils. In this study, an enzyme‐linked immunosorbent assay (ELISA) using recombinant HNA‐1 antigens (rHNAs) was developed to detect HNA‐1a, ‐1b, and ‐1c alloantibodies in serum samples.

A new platelet alloantigen, Swia, located on glycoprotein Ia identified in a family with fetal and neonatal alloimmune thrombocytopenia

BACKGROUND: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a bleeding disorder caused by transplacental passage of maternal antibodies to fetuses whose platelets (PLTs) express the corresponding human PLT antigen (HPA).