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Biomedical subjects

C N Chesterman

Publications and source records attributed to C N Chesterman.

At least 19 recordsLinked to original sources
PubMed1999

Microheterogeneity of beta-2 glycoprotein I: implications for binding to anionic phospholipids.

Considerable interest is currently focused on the interactions of beta-2 glycoprotein I (beta2GPI) and anti-phospholipid antibodies with anionic phospholipids in an attempt to understand the association between these antibodies and clinical diseases such as thrombosis. The interactions of beta2GPI and anionic phospholipids have only been characterized partially, and the physiological role of this glycoprotein remains uncertain. In this study we have explored in detail the physical and phospholipid-binding characteristics of a number of beta2GPI preparations. We have found (i) that perchloric acid-purification methods are damaging to beta2GPI during purification, (ii) that the dissociation constants of the various preparations for phosphatidylserine vary between 0. 1-2 microM and are considerably weaker than previously reported, (iii) that considerable differences in affinity of the various beta2GPI preparations for anionic phospholipids are obtained when comparing anionic phospholipids immobilized to a solid-phase versus phospholipid assembled in unilamellar vesicles, (iv) that the integrity of the fifth domain of beta2GPI is important for binding immobilized anionic phospholipid but not especially important in binding vesicular anionic phospholipid, and (v) that beta2GPI preparations with differing isoelectric species content bind anionic phospholipids differently, suggesting that varying glycosylation and/or protein polymorphisms impact upon phospholipid binding. These results highlight the importance of assessing the determinants of the interaction of beta2GPI with anionic phospholipids assembled in unilamellar vesicles.

Anions↗
PubMed1999

Evolutionary conservation of circulating soluble low density lipoprotein receptor-related protein-like ("LRP-like") molecules.

Low density lipoprotein receptor family members characteristically bind 39-kDa receptor associated protein (RAP). Soluble forms of these receptors have been described in humans including the 515/85-kDa dimeric receptor, low density lipoprotein receptor-related protein (LRP/alpha2MR), which is involved in multiple processes including lipoprotein and protease metabolism. Here we demonstrate evolutionary conservation in the generation of these soluble RAP-binding proteins of high molecular weight, by identifying their presence in mammalian, avian, and reptilian sera as well as in the circulating haemolymph of a mollusc. Sera extracted on immobilized RAP, produced bands at approximately 500 kDa in radiolabeled ligand blots by using the LRP/alpha2MR-specific ligand, Pseudomonas exotoxin A (PEA). These findings suggest that circulating RAP-binding proteins with high molecular weight in vertebrates share features of LRP/alpha2MR (LRP-like molecules). RAP-binding molecules in the mammalian serum extracts were further characterized as LRP/alpha2MR homologues in Western blots by using antibodies against the 515-kDa alpha-chain of LRP/alpha2MR. Western blots of mammalian serum extracts using two monoclonal antibodies recognizing the 85-kDa transmembrane beta-chain suggested that a portion of the beta-chain's ectodomain remains associated with the alpha-chain, but the beta-chain's intracellular carboxy terminus is absent. These results are consistent with evolutionary conservation in the generation, composition, and ligand-binding ability of soluble LRP-like receptors and suggest that their presence is a necessary aspect of the receptor's function.

Animal Population Groups↗
PubMed1999

Early growth response factor-1 induction by injury is triggered by release and paracrine activation by fibroblast growth factor-2.

Cell migration and proliferation that follows injury to the artery wall is preceded by signaling and transcriptional events that converge at the promoters of multiple genes whose products can influence formation of the neointima. Transcription factors, such as early growth response factor-1 (Egr-1), with nucleotide recognition elements in the promoters of many pathophysiologically relevant genes, are expressed at the endothelial wound edge within minutes of injury. The mechanisms underlying the inducible expression of Egr-1 in this setting are not clear. Understanding this process would provide important mechanistic insights into the earliest events in the response to injury. In this report, we demonstrate that fibroblast growth factor-2 (FGF-2) is released by injury and that antibodies to FGF-2 almost completely abrogate the activation and nuclear accumulation of Egr-1. FGF-2-inducible egr-1-promoter-dependent expression is blocked by PD98059, a specific inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK)-1/2 (MEK-1/2), as well as by dominant negative mutants of ERK-1/2. Inducible ERK phosphorylation after injury is dependent on release and stimulation by endogenous FGF-2. Antisense oligonucleotides directed at egr-1 mRNA suggest that Egr-1 plays a necessary role in endothelial repair after denudation of the monolayer. These findings demonstrate that inducible Egr-1 expression after injury is contingent on the release and paracrine action of FGF-2.

Animals↗
PubMed1998

Quinine-dependent antibodies bind a restricted set of epitopes on the glycoprotein Ib-IX complex: characterization of the epitopes.

Severe immune thrombocytopenia is an idiosyncratic complication of quinine therapy. Although in most cases the responsible antibody is directed against platelet membrane glycoprotein (GP) Ib-IX, specificity for GPIIb-IIIa or both epitopes has also been reported. The objective of this study was to characterize the binding site of GPIb-IX-specific quinine-dependent antibodies. Antibody binding to Chinese hamster ovary cells or mouse L cells stably transfected with various combinations of the three genes (Ibalpha, Ibbeta, or IX) that encode this complex was detected using flow cytometry, monoclonal antibody-specific immobilization of platelet antigens assay, and differential adsorption studies. IgG in sera from 15 patients with quinine-induced thrombocytopenia binding to the cells, in the presence of quinine, showed three distinct patterns. Group 1 sera contained at least two antibody populations, one which binds to GPIbalpha and another which recognizes GPIX. Group 2 sera contained an antibody which binds drug dependently to GPIX, and Group 3 sera contained an antibody which recognizes a quinine-dependent epitope on GPIbalpha. Thus, the quinine-dependent antibodies fall into two distinct populations that bind to GPIbalpha and GPIX independently. Using proteases which cleave GPIbalpha at specific sites, we have shown that the GPIbalpha-specific antibody binds to an 11-amino acid (283 to 293) region. Peptide inhibition studies provide confirmatory evidence that this region contains the epitope for the GPIbalpha-specific quinine-dependent antibody.

Amino Acid Sequence↗
PubMed1998

The effects of alcohol on coagulation and fibrinolytic factors: a controlled trial.

Light-to-moderate alcohol intake is associated with a reduced incidence of ischaemic cardiovascular events, whilst heavy alcohol intake can predispose individuals to stroke. Alcohol-induced changes in coagulation and fibrinolysis may be relevant and are the subject of this controlled trial of varying alcohol intake in 55 predominantly beer-drinking men. Following 4 weeks stabilization maintaining usual drinking habits, participants were randomized to either continue usual alcohol intake or to restrict alcohol by changing to low alcohol beer for 4 weeks. In a final 4 week period, they crossed over to low or usual alcohol intake, respectively. Comparing combined low and usual alcohol periods, an increase in mean weekly alcohol intake from 92 to 410 ml (mean daily intake from 13 to 58 ml) was associated with a decrease in plasma fibrinogen (by 11%, P < 0.001) and platelet count (3%, P < 0.05), but increases in factor VII (7%, P = 0.001), tissue plasminogen activator (tPA; 16%, P = 0.01) and plasminogen activator inhibitor-1 (PAI-1; 21%, P < 0.001). The ratio, tPA/PAI-1, fell from 0.50 to 0.44 (P = 0.02) confirming the relatively greater increase in PAI-1 with alcohol consumption. Two lipid-associated natural anticoagulants, tissue factor pathway inhibitor and beta 2-glycoprotein-I, did not change. The substantial reduction in plasma fibrinogen with alcohol intake may well contribute to the apparent protection alcohol confers against ischaemic coronary and cerebral events. The increase in factor VII and relatively greater increase in PAI-1 than tPA with alcohol intake may attenuate this benefit and indeed may sufficiently predispose individuals to thrombosis to contribute to the increased incidence of ischaemic stroke seen in heavier drinkers. The balance of anticoagulant and procoagulant and fibrinolytic effects in any individual may vary depending on quantity and type of alcoholic beverage ingested, as well as on genetic and other variables, all of which merit further study.

Adult↗
PubMed1997

Low density lipoprotein receptor-related protein (LRP) expression varies among Hep G2 cell lines.

The multiligand receptor, low density lipoprotein receptor-related protein (LRP), is implicated in processes such as atherosclerosis and fibrinolysis through its mediation of the catabolism of lipoproteins, proteases, and protease inhibitor complexes. The hepatoma cell line Hep G2 expresses LRP and has been used widely to investigate the catabolism of LRP ligands including tissue-type plasminogen activator (tPA). However, the mechanism and degree by which tPA interacts with Hep G2 has been reported with some inconsistencies which may reflect variation in their level of LRP expression. To address this possibility we characterized, antigenically and functionally, LRP expression in high and low passage Hep G2 cells both from the parental line (ATCC sourced) and a cloned subline, a16. The LRP contribution to 125I-tPA binding varied from 65% for high passage a16 cells, to 20% for low passage parent cells as quantified by inhibition in the presence of 39-kD receptor associated protein (RAP) which prevents binding of all known LRP ligands. The same trend in LRP expression among Hep G2 sublines was further evident in their ability to degrade 125I-tPA and survive Pseudomonas exotoxin A challenge. These results imply wide variability in basal LRP expression among Hep G2 lines dependent on cell lineage and long-term culture conditions.

ADP Ribose Transferases↗
PubMed1997

Soluble low density lipoprotein receptor-related protein (LRP) circulates in human plasma.

Our studies have identified a soluble molecule in normal human plasma and serum with the characteristics of the alpha-chain of the low density lipoprotein receptor-related protein (LRP). LRP is a large multifunctional receptor mediating the clearance of diverse ligands, including selected lipoproteins, various protease inhibitor complexes, and thrombospondin. A soluble molecule (sLRP) has been isolated from plasma using an affinity matrix coupled with methylamine-activated alpha2-macroglobulin, the ligand uniquely recognized by LRP, and eluted with EDTA. This eluate contains a protein that co-migrates on SDS-polyacrylamide gel electrophoresis with authentic human placental LRP alpha-chain, is recognized by anti-LRP alpha-chain monoclonal antibodies, and binds the 39-kDa receptor-associated protein (RAP) and tissue plasminogen activator-inhibitor complexes. A similar RAP-binding molecule was detected in medium conditioned for 24 h by primary cultures of rat hepatocytes, suggesting that the liver may be the in vivo source of sLRP. In contrast, immunoprecipitation experiments failed to detect the production of sLRP by cultured HepG2 hepatoma and primary human fibroblast cells. Addition of a soluble form of LRP to cultured HepG2 cells resulted in a significant inhibition of capacity of these cells to degrade tPA, a process that has been demonstrated to be mediated by cell surface LRP. Preliminary data indicate that the concentration of sLRP is altered in the plasma of patients with liver disease. Increased levels of sLRP may antagonize the clearance of ligands by cell bound LRP perturbing diverse processes including lipid metabolism, cell migration and extracellular proteinase activity.

Animals↗
PubMed1997

Interaction of platelet-derived growth factor with thrombospondin 1.

Key factors that mediate vascular smooth muscle cell proliferation and migration are platelet-derived growth factor (PDGF) and thrombospondin 1 (TSP1). We now report that PDGFBB bound tightly and specifically to TSP1, that this interaction was markedly dependent on the disulphide bond arrangement in TSP1, and that binding of PDGFBB to TSP1 did not preclude PDGFBB from binding to its receptor on rat aortic vascular smooth-muscle cells. At physiologic ionic strength and pH, PDGFBB bound to Ca2+-depleted TSP1 with a dissociation constant of 11 +/- 2 nM and to Ca2+-replete TSP1 with a dissociation constant of 32 +/- 5 nM. Binding was specific, as both soluble TSP1 and unlabelled PDGFBB competed for binding of iodinated PDGFBB to immobilized TSP1, whereas other platelet alpha-granule proteins did not compete. The tertiary structure of TSP1 is regulated by intramolecular disulphide interchange; we found that catalysis of disulphide interchange in TSP1 by protein disulphide isomerase ablated the binding of PDGFBB. The interaction of PDGFBB with TSP1 was weakened by increasing salt concentration and essentially ablated at 0.65 ionic strength; it was inhibited by heparin with a half-maximal effect at 20 i.u./ml, implying that the binding was mediated largely by ionic interactions. An anti TSP1 monoclonal antibody decreased the binding of iodinated PDGFBB to PDGF receptor on rat aortic vascular smooth-muscle cells by 37 +/- 2%, whereas platelet TSP1 non-competitively inhibited binding of iodinated PDGFBB. Uncomplexed PDGFBB bound to PDGF receptor with an affinity 5 +/- 2 times that of PDGFBB-TSP1 complexes. These results suggest that TSP1 might assist in the targeting of PDGF to its receptor on vascular smooth-muscle cells.

Animals↗
PubMed1997

Generation of angiostatin by reduction and proteolysis of plasmin. Catalysis by a plasmin reductase secreted by cultured cells.

Extracellular manipulation of protein disulfide bonds has been implied in diverse biological processes, including penetration of viruses and endotoxin into cells and activation of certain cytokine receptors. We now demonstrate reduction of one or more disulfide bonds in the serine proteinase, plasmin, by a reductase secreted by Chinese hamster ovary or HT1080 cells. Reduction of plasmin disulfide bond(s) triggered proteolysis of the enzyme, generating fragments with the domain structure of the angiogenesis inhibitor, angiostatin. Two of the known reductases secreted by cultured cells are protein disulfide isomerase and thioredoxin, and incubation of plasmin with these purified reductases resulted in angiostatin fragments comparable with those generated from plasmin in cell culture. Thioredoxin-derived angiostatin inhibited proliferation of human dermal microvascular endothelial cells with half-maximal effect at approximately 0.2 microg/ml. Angiostatin made by cells and by purified reductases contained free sulfhydryl group(s), and S-carbamidomethylation of these thiol group(s) ablated biological activity. Neither protein disulfide isomerase nor thioredoxin were the reductases used by cultured cells, because immunodepletion of conditioned medium of these proteins did not affect angiostatin generating activity. The plasmin reductase secreted by HT1080 cells required a small cofactor for activity, and physiologically relevant concentrations of reduced glutathione fulfilled this role. These results have consequences for plasmin activity and angiogenesis, particularly in the context of tumor growth and metastasis. Moreover, this is the first demonstration of extracellular reduction of a protein disulfide bond, which has general implications for cell biology.

Angiostatins↗
PubMed1997

Identification of PDGF receptors on human megakaryocytes and megakaryocytic cell lines.

Platelet-derived growth factor (PDGF) is a potent chemotactic and mitogenic factor implicated to play important roles in a variety of normal and pathophysiologic settings. We investigated PDGF receptor expression on human megakaryocytes and several megakaryocytic cell lines (CHRF, DAMI, Meg-01, M-07e) using enzyme-linked immunosorbent assay (ELISA), flow cytometry and immunocytochemical staining. Both PDGF receptor subtypes were identified on CHRF, DAMI, and Meg-01 cells by ELISA; PDGF beta-receptor levels exceeded alpha-receptor levels. Flow cytometry revealed that beta-receptor levels on CHRF and DAMI cells exceeded those on Meg-01 cells, and that M-07e expressed neither receptor. Immunocytochemical staining confirmed these findings and determined that bone marrow megakaryocytes also expressed PDGF receptors. Exposure of megakaryocytes to PDGF-BB dramatically induced the expression of the immediate-early gene, c-fos, within 30 min. Moreover, PDGF-BB significantly stimulated CHRF proliferation and colony formation. The present study demonstrates the presence of functional PDGF receptors on human megakaryocytes and their ability to mediate a mitogenic response.

Cell Line↗
PubMed1996

Catalysis of disulfide isomerization in thrombospondin 1 by protein disulfide isomerase.

Thrombospondin 1 is a multidomain glycoprotein from platelets and most cells that participates in diverse biological processes. The structure and some functional properties of thrombospondin 1 are regulated by disulfide interchange in the Ca(2+)-binding repeats and C-globular domain. The recent identification of the enzyme, protein disulfide isomerase, on the platelet surface suggested that protein disulfide isomerase may catalyze disulfide isomerization in platelet thrombospondin 1. Protein disulfide isomerase was found to form disulfide-linked complexes with thrombospondin 1, which is consistent with protein disulfide isomerase-mediated rearrangement of disulfide bonds in thrombospondin 1. To quantitate disulfide interchange in thrombospondin 1, perturbation of the enzyme inhibitory properties of platelet thrombospondin 1 were measured, specifically changes in the apparent dissociation constant for inhibition of neutrophil cathepsin G by thrombospondin 1. The inhibition constant increased > or = 10-14-fold following incubation of either Ca(2+)-replete or Ca(2+)-depleted thrombospondin 1 with protein disulfide isomerase and reduced glutathione. The rate of protein disulfide isomerase-catalyzed disulfide interchange in thrombospondin 1 increased linearly with protein disulfide isomerase concentration and the K(m) for reduced glutathione was 0.4 +/- 0.2 mM. Disulfide isomerization in both platelet and fibroblast thrombospondin 1 was probed by measuring perturbation in epitopes for two anti-thrombospondin 1 monoclonal antibodies. Antibody D4.6 binds to the C-terminal Ca(2+)-binding domains which are involved in disulfide interchange, whereas antibody HB8432 binds toward the N-terminus of the thrombospondin 1 subunit. In accordance with the location of these epitopes, incubation of platelet thrombospondin 1 or fibroblast thrombospondin 1 with protein disulfide isomerase and reduced glutathione resulted in 2-fold enhancement of binding of D4.6, whereas binding of HB8432 did not significantly change. In summary, protein disulfide isomerase catalyzes disulfide interchange in thrombospondin 1 which alters binding of neutrophil cathepsin G and antibody D4.6 to thrombospondin 1.

Blood Platelets↗
PubMed1996

Prospective evaluation of the clinical usefulness of an antigen-specific assay (MAIPA) in idiopathic thrombocytopenic purpura and other immune thrombocytopenias.

The diagnosis of idiopathic immune thrombocytopenia remains a clinical diagnosis based on the exclusion of other causes of immune and nonimmune thrombocytopenia. Measurement of platelet-associated Ig (PAIg), while sensitive, is nonspecific for the diagnosis of immune thrombocytopenia. Published experience of antigen capture assays (including monoclonal antibody immobilization of platelet antigens or MAIPA) suggest a high sensitivity and specificity (70% to 80%) in selected groups of patients. In a prospective evaluation of 158 patients with thrombocytopenia from all causes, we report a sensitivity of 51% and specificity of 80% for direct MAIPA assays. MAIPA was considerably better in discriminating immune from nonimmune thrombocytopenia than two assays of PAIgG. Antiplatelet antibodies detected by MAIPA were more frequently directed against the glycoprotein (GP) IIb/IIIa than the GP Ib/IX complex. Our experience suggests that MAIPA assays are useful in the laboratory assessment of thrombocytopenia, should be performed before therapy, and that some patients with 'nonimmune' thrombocytopenia may have genuine antiplatelet antibodies.

Antibodies, Monoclonal↗
PubMed1996

Fibroblast growth factor and heparin protect endothelial cells from the effects of interleukin 1.

Vascular endothelium is involved in both active and passive processes in haemostasis, but inflammatory cytokines such as interleukin 1 (IL-1) and tumour necrosis factor (TNF) have been reported to convert the comparatively inert endothelial cell to an inflammatory state. Acidic fibroblast growth factor (aFGF) in the presence of heparin has effects opposite to IL-1 on cultured human umbilical vein endothelial cells (HUVEC); therefore, we have investigated the modulation of IL-1-induced effects by the c combination of aFGF and heparin (aFGF/heparin). First passage HUVEC were cultured for 6 days in the presence of 20% human serum with and without the addition of 625 pM human recombinant aFGF (hr aFGF) and 7 microM heparin. On day 5, recombinant IL-1 beta was included for 24 h. The following day the cells were washed and measurements made of the release of prostacyclin, von Willebrand factor, plasminogen activator inhibitor type 1, and thrombospondin, both in the resting state and following stimulation for 60 min with 1 U/ml thrombin. Tissue-type plasminogen activator was assayed in HUVEC lysates. Similar experiments were performed to assess effects on the expression of vascular adhesion molecule, intracellular adhesion molecule, and E-selectin using an ELISA on cells in situ. This study indicates that aFGF/heparin in the culture medium of HUVEC abrogates the measured responses to IL-1. These data imply that routine endothelial cell culture with aFGF/heparin may cause artefacts, the effects of FGF and Il-1 may involve common pathways, and FGF/heparin may offer an approach to design therapeutics to counter the adverse effects of IL-1.

Cell Adhesion Molecules↗
PubMed1996

Extracellular matrix is a source of mitogenically active platelet-derived growth factor.

Platelet-derived growth factor (PDGF) is a chemotactic and mitogenic agent for fibroblasts and smooth muscle cells and plays a key role in the development of atherosclerotic lesions. PDGF is produced by a number of normal and transformed cell types and occurs as homo- or heterodimers of A and B polypeptide chains. Using Chinese hamster ovary (CHO) cells transfected with various forms of PDGF, we have previously shown that PDGF A(s) (short splice version) is secreted, PDGF A(l) (long splice version) predominantly extracellular matrix-associated, and PDGF B divided between medium, cells, and matrix. In the present study we have demonstrated the mitogenic activity of matrix-localized PDGF in artificial and more physiologically relevant models by culturing Balb/c-3T3 cells (3T3), human foreskin fibroblasts (HFF), and rabbit aortic smooth muscle cells (SMC) on extracellular matrix (ECM) laid down by PDGF-expressing CHO cells and human umbilical vein endothelial cells (HUVEC). These cells responded to the local growth stimulus of PDGF-containing CHO ECM and HUVEC ECM. We showed that 3T3 cells required proteolytic activity to utilize matrix-localized PDGF, as aprotinin and epsilon-ACA inhibited growth and 3T3 cells were shown to possess plasminogen activator activity. HFF and SMC did not appear to require proteolytic activity (including metalloproteinase and serine protease activity) as a prerequisite for mitogenesis but were able to access immobilized PDGF by contact with the matrix. An understanding of the mechanisms whereby the utilization of stored PDGF is controlled in situations of excessive cellular proliferation will aid in the development of therapy for these conditions.

3T3 Cells↗
PubMed1996

Characterization of IgG Fc receptors on CD34 antigen-expressing cell lines (KG-1 and KG-1a).

Although Fc gamma receptors (Fc gamma R) on mature blood cells have been extensively studied, there are only limited data on Fc gamma R expression in the early haematopoietic progenitor cells. In this study, we used the stem cell antigen (CD34)-expressing cell line (KG-1) and its less differentiated subline (KG-1a) as a model for the study of Fc gamma R in the early haematopoietic progenitors. Flow cytometry and immunoprecipitation studies on KG-1 and KG-1a cells with anti-Fc gamma R mAb showed that Fc gamma RII is the only Fc gamma R expressed on the cell surface. Analysis of the steady-state levels of Fc gamma R mRNA in KG-1 and KG-1a cells using a quantitative in situ hybridization assay revealed the presence of only Fc gamma RII mRNA. On further analysis Fc gamma RIIA mRNA but no Fc gamma RIIB or Fc gamma RIIC transcripts were found in these cells; Fc gamma RIIA transcripts with and without the transmembrane exon were present in approximately equal amounts. These findings are surprisingly similar to those observed previously with Fc gamma R in platelets and megakaryocytic cells but different from those found with Fc gamma R in cells of other lineages. These data suggest that the Fc gamma R transcript distribution pattern observed in the early haematopoietic progenitors (KG-1 cells) is retained in later stages of haematopoietic differentiation only in cells of megakaryocytic lineage.

Antigens, CD34↗
PubMed1996

Beta 2-glycoprotein I in thrombosis: evidence for a role as a natural anticoagulant.

Although the physiological role of beta2-glycoprotein (B2GPI) is unknown, in vitro evidence indicates that B2GPI may be a natural anticoagulant. In this study we have examined whether fluctuations of plasma B2GPI occur in in vivo coagulation. Serial measurements of B2GPI and other anticoagulant proteins were performed in 51 patients with thrombotic (group 1: six patients with disseminated intravascular coagulation (DIC), group 2: venous (n = 4) or arterial (n = 170 thrombosis) and non-thrombotic disease (group 3: 24 patients undergoing elective surgery). Reductions in plasma B2GPI levels were seen in most patients which were roughly proportional to the severity of their illness. Particularly striking reductions of B2GPI, protein C (PC) and antithrombin III (AT-III) (mean +/- 95% CI: 42.7 +/- 8.6%, 42.1 +/- 14.8%, 39.1 +/- 28.4% respectively) were seen in group 1. The reductions in plasma B2GPI were significantly greater in group 1 than in the other groups. Dilutional factors explain most of the reductions in B2GPI, PC and AT-III in groups 2 and 3, but contribute little to group 1. In conclusion, although B2GPI behaves as a 'negative acute phase reactant', the magnitude of reduction of plasma B2GPI levels, accompanied by reductions in other anticoagulant proteins in patients with DIC, suggests specific consumption of B2GPI in in vivo coagulation. This study provides further evidence that B2GPI is an anticoagulant of physiological importance.

Acute Disease↗
PubMed1996

Characterization of Fc gamma receptors on human megakaryocytes.

Megakaryocyte and platelet Fc gamma receptors (FcR) are of importance in the pathophysiology of immune complex-mediated thrombocytopenias such as heparin-induced thrombocytopenia. In this study, Fc gamma R proteins and mRNAs in normal human megakaryocytes were examined. Fc gamma R proteins were studied with immunocytochemical staining, dual colour flow cytometry and immunoprecipitation using monoclonal antibodies against Fc gamma R I, Fc gamma R II and Fc gamma R III. Fc gamma R mRNAs were measured with biotinylated cDNA of oligonucleotide probes using a novel quantitative in situ hybridization technique. Using these techniques, Fc gamma R II protein and mRNA, but not Fc gamma R I and Fc gamma R III proteins and transcripts were detected in megakaryocytes. Further, transcript analysis showed that megakaryocytes contain only the transcript of Fc gamma R IIA gene but no transcripts of Fc gamma R IIB nor Fc gamma R IIC genes; Fc gamma R IIA transcripts with and without the transmembrane (TM) exon are present in approximately equal proportions. In contrast, neutrophils and macrophages also contain Fc gamma R IIA transcript but Fc gamma R IIA transcript with the TM exon predominates suggesting cell lineage-specific Fc gamma R IIA expression. Fc gamma R IIA transcript lacking the TM exon predicts the presence of a potential soluble form of Fc gamma R in platelets and megakaryocytes which may have a physiological role as it can compete with the membrane-bound Fc gamma R IIA for binding of IgG-containing immune complexes and thus protect these cells from excessive binding and injurious effects of immune complexes.

Base Sequence↗