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1.  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.
PMCID: PMC4154536  PMID: 20194726
2.  Blockade of maternal anti-HPA-1a-mediated platelet clearance by an HPA-1a epitope-specific F(ab′)2 in an in vivo mouse model of alloimmune thrombocytopenia 
Transfusion  2008;49(2):265-270.
Neonatal alloimmune thrombocytopenia (NAIT) is most commonly caused by transplacental passage of maternal human platelet-specific alloantigen (HPA)-1a antibodies that bind to fetal platelets (PLTs) and mediate their clearance. SZ21, a monoclonal antibody (MoAb) directed against PLT glycoprotein IIIa, competitively inhibits the binding of anti-HPA-1a alloantibodies to PLTs in vitro. The purpose of this investigation was to determine whether SZ21 F(ab′)2 fragments might be therapeutically effective in inhibiting or displacing maternal HPA-1a antibodies from the fetal PLT surface and preventing their clearance from circulation.
Study Design and Methods
Resting human PLTs from HPA-1ab heterozygous donors were injected into nonobese diabetic/severe combined immunodefi-cient (NOD/SCID) mice. Purified F(ab′)2 fragments of SZ21 or control immunoglobulin G (IgG) were injected intraperitoneally 30 minutes before introduction of HPA-1a antibodies. Blood samples were taken periodically and analyzed by flow cytometry to determine the percentage of circulating human PLTs.
Anti-HPA-1a IgG from NAIT cases were able to efficiently clear HPA-1a–positive PLTs from murine circulation. Administration of SZ21 F(ab′)2 fragments not only inhibited binding of HPA-1a antibodies to circulating human PLTs, preventing their clearance, but also displaced bound HPA-1a antibodies from the PLT surface.
F(ab′)2 fragments of HPA-1a–selective MoAb SZ21 effectively inhibit anti-HPA-1a–mediated clearance of human PLT circulating in an in vivo NOD/SCID mouse model. These results suggest that agents that inhibit binding of anti-HPA-1a to PLTs may have therapeutic potential in the treatment of NAIT.
PMCID: PMC4154534  PMID: 19000229
3.  Proteinase 3 contributes to transendothelial migration of NB1-positive neutrophils 
Neutrophil transmigration requires the localization of neutrophils to endothelial cell junctions, where receptor-ligand interactions and the action of serine proteases promote leukocyte diapedesis. NB1 (CD177) is a neutrophil-expressed surface molecule that has been reported to bind proteinase 3 (PR3), a serine protease released from activated neutrophils. PR3 has demonstrated proteolytic activity on a number of substrates, including extracellular matrix proteins, although its role in neutrophil transmigration is unknown. Recently, NB1 has been shown to be a heterophilic binding partner for the endothelial cell junctional protein, PECAM-1. Disrupting the interaction between NB1 and PECAM-1 significantly inhibits neutrophil transendothelial cell migration on endothelial cell monolayers. Because NB1 interacts with endothelial cell PECAM-1 at cell junctions where transmigration occurs, we considered that NB1-PR3 interactions may play a role in aiding neutrophil diapedesis. Blocking antibodies targeting the heterophilic binding domain of PECAM-1 significantly inhibited transmigration of NB1-positive neutrophils through IL-1β-stimulated endothelial cell monolayers. PR3 expression and activity were significantly increased on NB1-positive neutrophils following transmigration, while neutrophils lacking NB1 demonstrated no increase in PR3. Finally, using selective serine protease inhibitors, we determined that PR3 activity facilitated transmigration of NB1-positive neutrophils under both static and flow conditions. These data demonstrate that PR3 contributes in the selective recruitment of the NB1-positive neutrophil population.
PMCID: PMC3288489  PMID: 22266279
PECAM-1; CD31; transmigration; serine protease; endothelial cells
4.  A point mutation in the EGF-4 domain of β3 integrin is responsible for the formation of the Seca platelet alloantigen and affects receptor function 
Thrombosis and haemostasis  2011;107(1):80-87.
Neonatal alloimmune thrombocytopenia (NAIT) is caused by fetomaternal platelet incompatibility with maternal antibodies crossing the placenta and destroying fetal platelets. Antibodies against human platelet antigen-1a (HPA-1a) and HPA-5b are responsible for the majority of NAIT cases. We observed a suspected NAIT in a newborn with a platelet count of 25 G/l and petechial haemorrhages. Serological analysis of maternal serum revealed an immunisation against αIIbβ3 on paternal platelets only, indicating the presence of an antibody against a new rare alloantigen (Seca) residing on αIIbβ3. The location of Seca on αIIbβ3 was confirmed by immunoprecipitation. Nucleotide sequence analysis of paternal β3 revealed a single nucleotide exchange (G1818T) in exon 11 of the β3 gene (ITGB3), changing Lys580 (wild-type) to Asn580 (Seca). Two additional members of the family Sec were typed Seca positive, but none of 300 blood donors. Chinese hamster ovary cells expressing Asn580, but not Lys580 αIIbβ3, bound anti-Seca, which was corroborated by immunoprecipitation. Adhesion of transfected cells onto immobilised fibrinogen showed reduced binding of the Asn580 variant compared to wild-type αIIbβ3. Analysis of transfected cells with anti-LIBS and PAC-1 antibody showed reduced binding when compared to the wild-type. No such effects were observed with Seca positive platelets, which, however, are heterozygous for the Lys580Asn mutation. In this study, we describe a NAIT case caused by maternal alloimmunisation against a new antigen on αIIbβ3. Analysis with mutant transfected cells showed that the Lys580Asn mutation responsible for the formation of the Seca antigenic determinant affects αIIbβ3 receptor function.
PMCID: PMC3564509  PMID: 22116617
NAIT; HPA; thrombocytopenia; GP IIb/IIIa
5.  A novel function of Junctional Adhesion Molecule-C in mediating melanoma cell metastasis 
Cancer research  2011;71(12):4096-4105.
Hematogenous dissemination of melanoma is a life-threatening complication of this malignant tumor. Here, we identified Junctional Adhesion Molecule-C (JAM-C) as a novel player in melanoma metastasis to the lung. JAM-C expression was identified in human and murine melanoma cell lines, in human malignant melanoma, as well as in metastatic melanoma including melanoma lung metastasis. JAM-C expressed on both murine B16 melanoma cells as well as on endothelial cells, promoted the transendothelial migration of the melanoma cells. We generated mice with inactivation of JAM-C. JAM-C−/− mice as well as endothelial-specific JAM-C-deficient mice displayed significantly decreased B16 melanoma cell metastasis to the lung, whereas treatment of mice with soluble JAM-C prevented melanoma lung metastasis. Together, JAM-C represents a novel therapeutic target for melanoma metastasis.
PMCID: PMC3117056  PMID: 21593193
6.  Mechanisms of neutrophil transendothelial migration 
Neutrophil recruitment is an integral part of the immune response to infection as well as of inflammatory disorders. The process of neutrophil extravasation comprises a complex multistep cascade that is orchestrated by a tightly coordinated sequence of adhesive interactions with vessel wall endothelial cells. Adhesion receptors as well as signaling molecules in both neutrophils and endothelial cells regulate the recruitment of neutrophils into the site of inflammation or infection. The present review will focus on novel aspects with regards to the last step of neutrophil recruitment, namely the transmigration of neutrophils through endothelial cells.
PMCID: PMC2672407  PMID: 19273149
7.  Junctional adhesion molecule-C regulates vascular endothelial permeability by modulating VE-cadherin–mediated cell–cell contacts 
The Journal of Experimental Medicine  2006;203(12):2703-2714.
We recently reported that junctional adhesion molecule (JAM)-C plays a role in leukocyte transendothelial migration. Here, the role of JAM-C in vascular permeability was investigated in vitro and in vivo. As opposed to macrovascular endothelial cells that constitutively expressed JAM-C in cell–cell contacts, in quiescent microvascular endothelial cells, JAM-C localized mainly intracellularly, and was recruited to junctions upon short-term stimulation with vascular endothelial growth factor (VEGF) or histamine. Strikingly, disruption of JAM-C function decreased basal permeability and prevented the VEGF- and histamine-induced increases in human dermal microvascular endothelial cell permeability in vitro and skin permeability in mice. Permeability increases are essential in angiogenesis, and JAM-C blockade reduced hyperpermeability and neovascularization in hypoxia-induced retinal angiogenesis in mice. The underlying mechanisms of the JAM-C–mediated increase in endothelial permeability were studied. JAM-C was essential for the regulation of endothelial actomyosin, as revealed by decreased F-actin, reduced myosin light chain phosphorylation, and actin stress fiber formation due to JAM-C knockdown. Moreover, the loss of JAM-C expression resulted in stabilization of VE-cadherin–mediated interendothelial adhesion in a manner dependent on the small GTPase Rap1. Together, through modulation of endothelial contractility and VE-cadherin–mediated adhesion, JAM-C helps to regulate vascular permeability and pathologic angiogenesis.
PMCID: PMC2118160  PMID: 17116731
8.  The Junctional Adhesion Molecule 3 (JAM-3) on Human Platelets is a Counterreceptor for the Leukocyte Integrin Mac-1 
The recently described junctional adhesion molecules (JAMs) in man and mice are involved in homotypic and heterotypic intercellular interactions. Here, a third member of this family, human JAM-3, was identified and described as a novel counterreceptor on platelets for the leukocyte β2-integrin Mac-1 (αMβ2, CD11b/CD18). With the help of two monoclonal antibodies, Gi11 and Gi13, against a 43-kD surface glycoprotein on human platelets, a full-length cDNA encoding JAM-3 was identified. JAM-3 is a type I transmembrane glycoprotein containing two Ig-like domains. Although JAM-3 did not undergo homophilic interactions, myelo-monocytic cells adhered to immobilized JAM-3 or to JAM-3–transfected cells. This heterophilic interaction was specifically attributed to a direct interaction of JAM-3 with the β2-integrin Mac-1 and to a lower extent with p150.95 (αXβ2, CD11c/CD18) but not with LFA-1 (αLβ2, CD11a/CD18) or with β1-integrins. These results were corroborated by analysis of K562 erythroleukemic cells transfected with different heterodimeric β2-integrins and by using purified proteins. Moreover, purified JAM-3 or antibodies against JAM-3 blocked the platelet-neutrophil interaction, indicating that platelet JAM-3 serves as a counterreceptor for Mac-1 mediating leukocyte–platelet interactions. JAM-3 thereby provides a novel molecular target for antagonizing interactions between vascular cells that promote inflammatory vascular pathologies such as in atherothrombosis.
PMCID: PMC2194005  PMID: 12208882
monoclonal antibody; adhesion molecule; integrins; neutrophils; athero- thrombosis

Results 1-8 (8)