Molecular mapping of α-thrombin (αT)/β2-glycoprotein I (β2GpI) interaction reveals how β2GpI affects αT functions

2016 ◽  
Vol 473 (24) ◽  
pp. 4629-4650 ◽  
Author(s):  
Laura Acquasaliente ◽  
Daniele Peterle ◽  
Simone Tescari ◽  
Nicola Pozzi ◽  
Vittorio Pengo ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Molecular Mapping ◽  
Anticoagulant Activity ◽  
Physiological Role ◽  
Molecular Probes ◽  
Glycoprotein I ◽  
Docking Model ◽  
Fibrinogen Binding ◽  
Platelet Receptor ◽  
Domain V

β2-Glycoprotein I (β2GpI) is the major autoantigen in the antiphospholipid syndrome, a thrombotic autoimmune disease. Nonetheless, the physiological role of β2GpI is still unclear. In a recent work, we have shown that β2GpI selectively inhibits the procoagulant functions of human α-thrombin (αT; i.e. prolongs fibrin clotting time, tc, and inhibits αT-induced platelet aggregation) without affecting the unique anticoagulant activity of the protease, i.e. the proteolytic generation of the anticoagulant protein C (PC) from the PC zymogen, which interacts with αT exclusively at the protease catalytic site. Here, we used several different biochemical/biophysical techniques and molecular probes for mapping the binding sites in the αT–β2GpI complex. Our results indicate that αT exploits the highly electropositive exosite-II, which is also responsible for anchoring αT on the platelet GpIbα (platelet receptor glycoprotein Ibα) receptor, for binding to a continuous negative region on β2GpI structure, spanning domain IV and (part of) domain V, whereas the protease active site and exosite-I (i.e. the fibrinogen-binding site) remain accessible for substrate/ligand binding. Furthermore, we provided evidence that the apparent increase in tc, previously observed with β2GpI, is more likely caused by alteration in the ensuing fibrin structure rather than by the inhibition of fibrinogen hydrolysis. Finally, we produced a theoretical docking model of αT–β2GpI interaction, which was in agreement with the experimental results. Altogether, these findings help to understand how β2GpI affects αT interactions and suggest that β2GpI may function as a scavenger of αT for binding to the GpIbα receptor, thus impairing platelet aggregation while enabling normal cleavage of fibrinogen and PC.

Fibrinogen Hershey IV: A Novel Dysfibrinogen with a γ V411I Mutation in the Integrin αIibβ3 Binding Site.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2133-2133
Author(s):  
Veronica H. Flood ◽  
Hamid A. Al-Mondhiry ◽  
Antony C. Bakke ◽  
David H. Farrell
Keyword(s):  
Platelet Aggregation ◽  
Novel Mutation ◽  
Terminal Segment ◽  
Normal Donor ◽  
Thrombin Time ◽  
Wild Type ◽  
Mutant Peptide ◽  
Fibrinogen Binding ◽  
Platelet Receptor ◽  
Bleeding History

Abstract The C-terminal segment of the fibrinogen γ chain plays a crucial role in platelet aggregation via its interaction with the platelet receptor αIIbβ3. It is well established that the last four amino acids of the γ chain (408 to 411) are critical for this function, as mutations or deletions of this region abrogate fibrinogen’s ability to bind αIIbβ3. We describe here the first naturally occurring fibrinogen mutation affecting the C-terminal region of the γ chain and investigate its effects on platelet interactions. The proband, a 49-year-old woman, was diagnosed with dysfibrinogenemia based on a prolonged thrombin time and low fibrinogen activity (55 mg/dL). Her bleeding history was significant for menorrhagia and one episode of post-operative hemorrhage. DNA sequencing of the fibrinogen genes demonstrated heterozygosity for two mutations, γ R275C and γ V411I. The latter γ V411I mutation represents a novel mutation affecting the C-terminal amino acid of the γ chain. We hypothesized that this mutation would decrease fibrinogen’s affinity for the platelet receptor αIIbβ3. In order to isolate the effects of this mutation on fibrinogen-platelet binding, γ 400-411 dodecapeptides were synthesized to mimic the C-terminal γ chain sequence. One peptide contained the wild-type sequence ending in valine (γ 400-V411), and the second peptide incorporated the isoleucine mutation (γ 400-I411). Previous studies have demonstrated that the wild type γ 400-V411 dodecapeptide inhibits platelet aggregation by competing for fibrinogen binding to αIIbβ3. We performed platelet aggregation studies comparing inhibition of aggregation with the wild-type γ 400-V411 and the mutant γ 400-I411 peptides. Washed platelets were obtained from a normal donor, and platelet aggregation monitored using the agonist ADP. The IC50 for the initial rate of aggregation with the γ 400-I411 peptide was 214 μM, compared to 133 μM with the wild-type peptide. We then examined the extent of aggregation in the presence of either wild-type or mutant peptide. Consistent with the previous results, total aggregation was lower with the wild-type peptide compared to the mutant peptide. The IC50 for the γ 400-I411 peptide was 450 μM compared to 250 μM with the γ 400-V411 peptide. Overall, these findings suggest that the γ I411 mutation results in a decreased ability to bind platelets. In the heterozygous state, however, the available amount of wild-type fibrinogen may be sufficient to support platelet aggregation. The bleeding diathesis observed for the proband could therefore reflect other factors, especially the γ R275C mutation.

scholarly journals Fibrinogen binding to human blood platelets: effect of gamma chain carboxyterminal structure and length

Blood ◽  
1986 ◽  
Vol 67 (2) ◽  
pp. 385-390 ◽  
Author(s):  
EI Peerschke ◽  
CW Francis ◽  
VJ Marder
Keyword(s):  
Amino Acid ◽  
Platelet Aggregation ◽  
Blood Platelets ◽  
Exchange Chromatography ◽  
Scatchard Analysis ◽  
Amino Acid Residues ◽  
Gamma Chain ◽  
Fibrinogen Binding ◽  
Platelet Receptor ◽  
Sterically Hinder

Abstract Recent evidence suggests that fibrinogen binding to platelets is mediated by the 12 carboxyterminal amino acid residues of the gamma chain. Because human plasma fibrinogen gamma chains differ in mol wt and carboxyterminal amino acid sequence, we examined the effect of such gamma chain heterogeneity on platelet-fibrinogen interactions, using two fibrinogens of distinct composition, separated by ion exchange chromatography. One fibrinogen possessed only gamma chains of mol wt 50,000 (F gamma 50), the predominant gamma chain species found in plasma. The other fibrinogen possessed equal amounts of gamma chains with mol wt 50,000 and 57,500 (F gamma 50,57.5), with the longer gamma chain (gamma 57.5) possessing an amino acid extension at the carboxyterminal end. The latter fibrinogen was 50% less effective than F gamma 50 in supporting ADP-induced platelet aggregation at concentrations of .01 to 2 mg/mL. Scatchard analysis revealed no difference in the binding affinities of the two fibrinogens to ADP- treated platelets, but the amount of F gamma 50,57.5 that was bound to platelets at saturation was only 50% that of F gamma 50. Fibrinogen receptors that remained unoccupied in the presence of saturating concentrations of F gamma 50,57.5, however, could be occupied by fresh F gamma 50. Excess unlabeled F gamma 50 displaced both radiolabeled fibrinogens from activated platelets, and both fibrinogens bound to the same platelet receptor, as judged by the inhibition of binding to stimulated platelets by a monoclonal antibody directed against the glycoprotein (GP) IIb/IIIa complex. Furthermore, an intact GPIIb/IIIa complex was required for these reactions, since platelets incubated with EDTA at 37 degrees C at alkaline pH failed to aggregate and bound neither fibrinogen in response to ADP following recalcification. Approximately 50% of each fibrinogen bound irreversibly to platelets after one hour and failed to dissociate in the presence of 10 mmol/L of EDTA or excess unlabeled F gamma 50. The data demonstrate that heterodimeric F gamma 50,57.5 binds less well to platelets and supports platelet aggregation only half as well as homodimeric F gamma 50. These results support prior conclusions that the carboxyterminal portion of the gamma chain is important in platelet-fibrinogen interactions, and suggest that the 20 amino acid, hydrophobic gamma chain carboxyterminal extension of F gamma 50,57.5 may sterically hinder the interaction of this fibrinogen with platelet receptors.

scholarly journals Fibrinogen binding to human blood platelets: effect of gamma chain carboxyterminal structure and length

Blood ◽  
1986 ◽  
Vol 67 (2) ◽  
pp. 385-390
Author(s):  
EI Peerschke ◽  
CW Francis ◽  
VJ Marder
Keyword(s):  
Amino Acid ◽  
Platelet Aggregation ◽  
Blood Platelets ◽  
Exchange Chromatography ◽  
Scatchard Analysis ◽  
Amino Acid Residues ◽  
Gamma Chain ◽  
Fibrinogen Binding ◽  
Platelet Receptor ◽  
Sterically Hinder

Recent evidence suggests that fibrinogen binding to platelets is mediated by the 12 carboxyterminal amino acid residues of the gamma chain. Because human plasma fibrinogen gamma chains differ in mol wt and carboxyterminal amino acid sequence, we examined the effect of such gamma chain heterogeneity on platelet-fibrinogen interactions, using two fibrinogens of distinct composition, separated by ion exchange chromatography. One fibrinogen possessed only gamma chains of mol wt 50,000 (F gamma 50), the predominant gamma chain species found in plasma. The other fibrinogen possessed equal amounts of gamma chains with mol wt 50,000 and 57,500 (F gamma 50,57.5), with the longer gamma chain (gamma 57.5) possessing an amino acid extension at the carboxyterminal end. The latter fibrinogen was 50% less effective than F gamma 50 in supporting ADP-induced platelet aggregation at concentrations of .01 to 2 mg/mL. Scatchard analysis revealed no difference in the binding affinities of the two fibrinogens to ADP- treated platelets, but the amount of F gamma 50,57.5 that was bound to platelets at saturation was only 50% that of F gamma 50. Fibrinogen receptors that remained unoccupied in the presence of saturating concentrations of F gamma 50,57.5, however, could be occupied by fresh F gamma 50. Excess unlabeled F gamma 50 displaced both radiolabeled fibrinogens from activated platelets, and both fibrinogens bound to the same platelet receptor, as judged by the inhibition of binding to stimulated platelets by a monoclonal antibody directed against the glycoprotein (GP) IIb/IIIa complex. Furthermore, an intact GPIIb/IIIa complex was required for these reactions, since platelets incubated with EDTA at 37 degrees C at alkaline pH failed to aggregate and bound neither fibrinogen in response to ADP following recalcification. Approximately 50% of each fibrinogen bound irreversibly to platelets after one hour and failed to dissociate in the presence of 10 mmol/L of EDTA or excess unlabeled F gamma 50. The data demonstrate that heterodimeric F gamma 50,57.5 binds less well to platelets and supports platelet aggregation only half as well as homodimeric F gamma 50. These results support prior conclusions that the carboxyterminal portion of the gamma chain is important in platelet-fibrinogen interactions, and suggest that the 20 amino acid, hydrophobic gamma chain carboxyterminal extension of F gamma 50,57.5 may sterically hinder the interaction of this fibrinogen with platelet receptors.

Difference of [Ca2+]i Movements in Platelets Stimulated by Thrombin and TRAP: the Involvement of αIIbβ3-Mediated TXA2 Synthesis

1998 ◽  
Vol 79 (06) ◽  
pp. 1184-1190 ◽  
Author(s):  
Yoshiaki Tomiyama ◽  
Shigenori Honda ◽  
Kayoko Senzaki ◽  
Akito Tanaka ◽  
Mitsuru Okubo ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Fibrinogen Binding ◽  
Adp Release ◽  
The Difference ◽  
Txa2 Receptor Antagonist ◽  
High Level ◽  
Inhibition Studies ◽  
Peak Increase ◽  
Second Peak ◽  
Assay Conditions

SummaryThis study investigated the difference of [Ca2+]i movement in platelets in response to thrombin and TRAP. The involvement of αIIbβ3 in this signaling was also studied. Stimulation of platelets with thrombin at 0.03 U/ml caused platelet aggregation and a two-peak increase in [Ca2+]i. The second peak of [Ca2+]i, but not the first peak was abolished by the inhibition of platelet aggregation with αIIbβ3 antagonists or by scavenging endogenous ADP with apyrase. A cyclooxygenase inhibitor, aspirin, and a TXA2 receptor antagonist, BM13505, also abolished the second peak of [Ca2+]i but not the first peak, although these regents did not inhibit aggregation. Under the same assay conditions, measurement of TXB2 demonstrated that αIIbβ3 antagonists and aspirin almost completely inhibited the production of TXB2. In contrast to thrombin-stimulation, TRAP caused only a single peak of [Ca2+]i even in the presence of platelet aggregation, and a high level of [Ca2+]i increase was needed for the induction of platelet aggregation. The inhibition of aggregation with αIIbβ3 antagonists had no effect on [Ca2+]i change and TXB2 production induced by TRAP. Inhibition studies using anti-GPIb antibodies suggested that GPIb may be involved in the thrombin response, but not in the TRAP. Our findings suggest that low dose thrombin causes a different [Ca2+]i response and TXA2 producing signal from TRAP. Endogenous ADP release and fibrinogen binding to αIIbβ3 are responsible for the synthesis of TXA2 which results in the induction of the second peak of [Ca2+]i in low thrombin- but not TRAP-stimulated platelets.

Effects of a Monoclonal Antibody to Glycoprotein IIb/IIIa (P256) and of Enzymically Derived Fragments of P256 on Human Platelets

1991 ◽  
Vol 65 (04) ◽  
pp. 432-437 ◽  
Author(s):  
A W J Stuttle ◽  
M J Powling ◽  
J M Ritter ◽  
R M Hardisty
Keyword(s):  
Monoclonal Antibody ◽  
Flow Cytometry ◽  
Platelet Aggregation ◽  
Calcium Ions ◽  
Human Platelet ◽  
Human Platelets ◽  
In Vivo Detection ◽  
Fibrinogen Binding ◽  
Specific Antagonist

SummaryThe anti-platelet monoclonal antibody P256 is currently undergoing development for in vivo detection of thrombus. We have examined the actions of P256 and two fragments on human platelet function. P256, and its divalent fragment, caused aggregation at concentrations of 10−9−3 × 10−8 M. A monovalent fragment of P256 did not cause aggregation at concentrations up to 10−7 M. P256–induced platelet aggregation was dependent upon extracellular calcium ions as assessed by quin2 fluorescence. Indomethacin partially inhibited platelet aggregation and completely inhibited intracellular calcium mobilisation. Apyrase caused partial inhibition of aggregation. Aggregation induced by the divalent fragment was dependent upon fibrinogen and was inhibited by prostacyclin. Aggregation induced by the whole antibody was only partially dependent upon fibrinogen, but was also inhibited by prostacyclin. P256 whole antibody was shown, by flow cytometry, to induce fibrinogen binding to indomethacin treated platelets. Monovalent P256 was shown to be a specific antagonist for aggregation induced by the divalent forms. In–111–labelled monovalent fragment bound to gel-filtered platelets in a saturable and displaceable manner. Monovalent P256 represents a safer form for in vivo applications

Partial Inhibition of Platelet Aggregation and Fibrinogen Binding by a Murine Monoclonal Antibody to GPIIIa: Requirement for Antibody Bivalency

1994 ◽  
Vol 72 (06) ◽  
pp. 964-972 ◽  
Author(s):  
Jeffery L Kutok ◽  
Barry S Coller
Keyword(s):  
Monoclonal Antibody ◽  
Platelet Aggregation ◽  
Murine Monoclonal Antibody ◽  
Platelet Glycoprotein ◽  
Igg Antibody ◽  
Surface Receptors ◽  
Partial Inhibition ◽  
Fibrinogen Binding ◽  
Igg Binding ◽  
Agonist Concentration

SummaryWe produced a murine monoclonal antibody, 7H2, and localized its epitope to one or more small regions on platelet glycoprotein (GP) Ilia. 7H2-IgG and 7H2-F(ab’)2 completely inhibit platelet aggregation and fibrinogen binding at low agonist concentrations, but only partially inhibit aggregation and fibrinogen binding at high agonist concentrations; 7H2-Fab has no effect on aggregation or fibrinogen binding at any agonist concentration. 7H2-IgG binds to the entire platelet population as judged by flow cytometry. At near saturating concentrations, ∼40,000 7H2-IgG antibody molecules bind per platelet. In contrast, ∼80,000 7H2 Fab molecules bind per platelet, suggesting that 7H2-IgG binding is bivalent. 7H2 was unable to inhibit fibrinogen binding to purified, immobilized GPIIb/IIIa. These data indicate that the bivalent binding of 7H2 to GPIIIa is required for its partial inhibition of fibrinogen binding to platelets, perhaps through dimerization of GPIIb/IIIa surface receptors (or more complex GPIIb/IIIa redistribution triggered by 7H2 binding) resulting in limited accessibility of fibrinogen to its binding site(s).

Specific Cross-reaction of IgG Anti-phospholipid Antibody with Platelet Glycoprotein IIIa

1996 ◽  
Vol 75 (01) ◽  
pp. 168-174 ◽  
Author(s):  
Shigeru Tokita ◽  
Morio Arai ◽  
Naomasa Yamamoto ◽  
Yasuhiro Katagiri ◽  
Kenjiro Tanoue ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Heparan Sulfate ◽  
Disulfide Bonds ◽  
Dextran Sulfate ◽  
Human Platelets ◽  
Platelet Glycoprotein ◽  
Activated Platelets ◽  
Fibrinogen Binding ◽  
Dose Dependent Fashion ◽  
Glycoprotein Iiia

SummaryTo study the pathological functions of anti-phospholipid (anti-PL) antibodies, we have analyzed their effect on platelet function. We identified an IgG anti-PL mAb, designated PSG3, which cross-reacted specifically with glycoprotein (GP) IIIa in human platelets and inhibited platelet aggregation. PSG3 bound also to certain polyanionic substances, such as double-stranded DNA, heparan sulfate, dextran sulfate and acetylated-LDL, but not to other polyanionic substances. The binding of PSG3 to GPIIIa was completely inhibited by heparan sulfate and dextran sulfate, indicating that PSG3 recognizes a particular array of negative charges expressed on both GPIIIa and the specified polyanionic substances. Since neither neuraminidase- nor endoglycopeptidase F-treatment of GPIIIa had any significant effect on the binding of PSG3, this array must be located within the amino acid sequence of GPIIIa but not in the carbohydrate moiety. Reduction of the disulfide bonds in GPIIIa greatly reduced its reactivity, suggesting that the negative charges in the epitope are arranged in a particular conformation. PSG3 inhibited platelet aggregation induced by either ADP or collagen, it also inhibited fibrinogen binding to activated platelets in a dose-dependent fashion. PSG3, however, did not inhibit the binding of GRGDSP peptide to activated platelets. These results suggest that the PSG3 epitope on GPIIIa contains a particular array of negative charges, and possibly affects the fibrinogen binding to GPIIb/IIIa complex necessary for platelet aggregation.

Modulation of Platelet Activation by Native DNA – Initial Description of Platelet Receptor Type, Number and Discrimination for Native DNA

1981 ◽  
Vol 45 (03) ◽  
pp. 263-266 ◽  
Author(s):  
B A Fiedel ◽  
M E Frenzke
Keyword(s):  
Platelet Aggregation ◽  
Human Platelets ◽  
Scatchard Analysis ◽  
Type Number ◽  
Single Class ◽  
Receptor Ligand ◽  
Platelet Receptor ◽  
Platelet Binding ◽  
Ligand Interactions ◽  
Initial Description

SummaryNative DNA (dsDNA) induces the aggregation of isolated human platelets. Using isotopically labeled dsDNA (125I-dsDNA) and Scatchard analysis, a single class of platelet receptor was detected with a KD = 190 pM and numbering ~275/platelet. This receptor was discriminatory in that heat denatured dsDNA, poly A, poly C, poly C · I and poly C · poly I failed to substantially inhibit either the platelet binding of, or platelet aggregation induced by, dsDNA; by themselves, these polynucleotides were ineffective as platelet agonists. However, poly G, poly I and poly G · I effectively and competitively inhibited platelet binding of the radioligand, independently activated the platelet and when used at a sub-activating concentration decreased the extent of dsDNA stimulated platelet aggregation. These data depict a receptor on human platelets for dsDNA and perhaps certain additional polynucleotides and relate receptor-ligand interactions to a physiologic platelet function.

The Effect of the Phospholipase Inhibitor Mepacrine on Platelet Aggregation, the Platelet Release Reaction and Fibrinogen Binding to the Platelet Surface

1981 ◽  
Vol 45 (03) ◽  
pp. 257-262 ◽  
Author(s):  
P D Winocour ◽  
R L Kinlough-Rathbone ◽  
J F Mustard
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Surface ◽  
Release Reaction ◽  
Fibrinogen Binding ◽  
Platelet Release

SummaryWe have examined whether inhibition by mepacrine of freeing of arachidonic acid from platelet phospholipids inhibits platelet aggregation to collagen, thrombin or ADP, and the release reaction induced by thrombin or collagen. Loss of arachidonic acid was monitored by measuring the amount of 14 C freed from platelets prelabelled with 14 C-arachidonic acid. Mepacrine inhibited 14 C loss by more than 80% but did not inhibit thrombin-induced platelet aggregation and had a small effect on release. ADP-induced platelet aggregation did not cause 14 C loss. Mepacrine inhibited ADP-induced platelet aggregation by inhibiting the association of fibrinogen with platelets during aggregation. The effect of mepacrine on fibrinogen binding could be considerably decreased by washing the platelets but the inhibition of 14 C loss persisted. Platelets pretreated with mepacrine and then washed show restoration of aggregation to collagen. Thus, mepacrine has two effects; 1. it inhibits phospholipases, 2. it inhibits fibrinogen binding. Freeing of arachidonic acid is not necessary for platelet aggregation or the release reaction.

Anticoagulant Activity of β2-Glycoprotein I Is Potentiated by a Distinct Subgroup of Anticardiolipin Antibodies

1992 ◽  
Vol 68 (03) ◽  
pp. 297-300 ◽  
Author(s):  
Monica Galli ◽  
Paul Comfurius ◽  
Tiziano Barbui ◽  
Robert F A Zwaal ◽  
Edouard M Bevers
Keyword(s):  
Human Plasma ◽  
Anticoagulant Activity ◽  
Factor Xa ◽  
Type A ◽  
Lipid Vesicles ◽  
Dependent Manner ◽  
Type B ◽  
Distinct Subgroup ◽  
Glycoprotein I ◽  
Thrombin Formation

SummaryPlasmas of 16 patients positive for both IgG anticardiolipin (aCL) antibodies and lupus anticoagulant (LA) antibodies were subjected to adsorption with liposomes containing cardiolipin. In 5 of these plasmas both the anticardiolipin and the anticoagulant activities were co-sedimented with the liposomes in a dose-dependent manner, whereas in the remaining cases only the anticardiolipin activity could be removed by the liposomes, leaving the anticoagulant activity (LA) in the supernatant plasma. aCL antibodies purified from the first 5 plasmas were defined as aCL-type A, while the term aCL-type B was used for antibodies in the other 11 plasmas, from which 2 were selected for this study.Prolongation of the dRVVT was produced by affinity-purified aCL-type A antibodies in plasma of human as well as animal (bovine, rat and goat) origin. aCL-type B antibodies were found to be devoid of anticoagulant activity, while the corresponding supernatants containing LA IgG produced prolongation of the dRVVT only in human plasma.These anticoagulant activities of aCL-type A and of LA IgG's were subsequently evaluated in human plasma depleted of β2-glycoprotein I (β2-GPI), a protein which was previously shown to be essential in the binding of aCL antibodies to anionic phospholipids. Prolongation of the dRVVT by aCL-type A antibodies was abolished using β2-GPI deficient plasma, but could be restored upon addition of β2-GPI. In contrast, LA IgG caused prolongation of the dRVVT irrespective of the presence or absence of β2-GPI.Since β2-GPI binds to negatively-charged phospholipids and impedes the conversion of prothrombin by the factor Xa/Va enzyme complex (Nimpf et al., Biochim Biophys Acta 1986; 884: 142–9), comparison was made of the effect of aCL-type A and aCL-type B antibodies on the rate of thrombin formation in the presence and absence of β2-GPI. This was measured in a system containing highly purified coagulation factors Xa, Va and prothrombin and lipid vesicles composed of 20 mole% phosphatidylserine and 80 mole% phosphatidylcholine. No inhibition on the rate of thrombin formation was observed with both types of aCL antibodies when either β2-GPI or the lipid vesicles were omitted. Addition of β2-GPI to the prothrombinase assay in the presence of lipid vesicles causes a time-dependent inhibition which was not affected by the presence of aCL-type B or non-specific IgG. In contrast, the presence of aCL-type A antibodies dramatically increased the anticoagulant effect of β2-GPI. These data indicate that the anticoagulant activity of aCL-type A antibodies in plasma is mediated by β2-GPI.

Sign in / Sign up

Export Citation Format

Share Document