Reactivity of Fibrinogen Derivatives with Antisera to Human Fibrin D-Dimer and Its γ-γ Chain Remnant

Ero1alpha is expressed on blood platelets in association with protein-disulfide isomerase and contributes to redox-controlled remodeling of alphaIIbbeta3

Recent evidence supports a role of protein-disulfide isomerase (PDI) in redox-controlled remodeling of the exofacial domains of α(IIb)β(3) in blood platelets. The aim of this study was to explain whether Ero1α can be responsible for extracellular reoxidation of the PDI active site. We showed that Ero1α can be found on platelets and is rapidly recruited to the cell surface in response to platelet agonists. It is physically associated with PDI and α(IIb)β(3), as suggested by colocalization analysis in confocal microscopy and confirmed by immunoprecipitation experiments. Apart from monomeric oxidized Ero1α, anti-α(IIb)β(3) immunoprecipitates showed the presence of several Ero1α-positive bands that corresponded to the complexes α(IIb)β(3)-PDI-Ero1α, PDI-Ero1α, and Ero1α-Ero1α dimers. It binds more efficiently to the activated α(IIb)β(3) conformer, and its interaction is inhibited by RGD peptides. Ero1α appears to be involved in the regulation of α(IIb)β(3) receptor activity because of the following: (a) blocking the cell surface Ero1α by antibodies leads to a decrease in platelet aggregation in response to agonists and a decrease in fibrinogen and PAC-1 binding, and (b) transfection of MEG01 with Ero1α increases α(IIb)β(3) receptor activity, as indicated by increased binding of fibrinogen.

Anti-(Arg-Gly-Asp-Ser) antibody and its interaction with fibronectin, fibrinogen and platelets

An antibody population recognizing the sequence Arg-Gly-Asp-Ser (RGDS) in fibronectin, anti-(RGDS)N, was isolated by immunoadsorption. Between 2.5% and 4.9% of antibodies were obtained from two different anti-fibronectin sera indicating that this region represents an antigenic epitope in native fibronectin. Complete inhibition of binding of 125I-fibronectin to anti-(RGDS)N was produced only by nonreduced and reduced fibronectin. Fibrinogen and synthetic RGDS tetrapeptide, each at concentration of 10 microM, showed only a slight inhibition of 22% and 17%, respectively. Measurements of the conformational constant, the equilibrium constant for the interconversion of the non-native and native conformations of this epitope, showed that less than 0.0001% of the RGDS molecules adopt the native conformation in aqueous solutions. It indicates that long-range interactions in fibronectin and fibrinogen result in different conformations of the RGDS sequence in both proteins. Anti-(RGDS)N antibodies purified from anti-fibronectin serum had a strong inhibitory effect on thrombin-stimulated platelet aggregation. They also inhibited binding of fibronectin and fibrinogen to thrombin-stimulated platelets, supporting the primary role of the RGDS sequence in the direct interaction of these proteins with platelet membrane receptors.

Monoclonal antibodies to crosslinked fibrin degradation products (XL-FDP). II. Evaluation in a variety of clinical conditions

Plasmas from patients with a wide variety of thrombotic and presumed prethrombotic conditions were examined for high molecular weight crosslinked fibrin degradation products (known as X-oligomers) using a two-site enzyme-linked immunospecific assay (ELISA). This assay employed a catcher-tag principle using two monoclonal antibodies (mabs) directed towards different epitopes on the complex X-oligomer fraction. In general, thrombotic events (pulmonary embolism, PE, myocardial infarction, MI, peripheral vascular disease, PVD, and disseminated intravascular coagulation, DIC) were accompanied by elevated levels of X-oligomers in the plasma. During pregnancy the value of X-oligomer assays was demonstrated to be a clear-cut marker for pre-eclampsia. Patients following a variety of forms of surgery present with heterogeneous plasma levels of X-oligomers and this may merely reflect the formation and lysis of the fibrin formed during and after surgery. The possible value of this ELISA procedure in monitoring thrombolytic therapy is discussed with a critical analysis of the data presented herein. While the assay of X-oligomer was demonstrated to be a valuable marker of fibrinolysis in plasma, more extensive data are required in order to assess whether such an assay is of diagnostic value in thrombosis-related conditions.

Activation of blood platelets and increased plasma fibrinogen and fibronectin in men exposed to infrasounds, acoustic noise and airborne dust in electric steelworks

Concentration of platelet factor 4 (PF4), beta-thromboglobulin (beta TG), fibrinogen (Fg), and fibronectin (Fn) was determined in samples of blood plasma taken from healthy men employed in two electric steelworks in Poland. They had been working at electric arc furnaces and thus particularly exposed to intense infrasounds, acoustic noise and airborne dust during 2 to 15 years for 6-8 hours per day. We found a significant increase in levels of beta TG, Fn, and Fg, but not of PF4, in blood plasma of men exposed to these agents. The beta TG/PF4 ratio, significantly higher in studied groups (p less than 0.001) when compared to control ones, was considerably correlated (r = 0.47, p less than 0.02) with their duration of work. We also found weak correlations between plasma beta TG levels (r = 0.33, p less than 0.05) or concentration of plasma Fn (r = 0.38, p less than 0.02) and time of work under such hazardous conditions.

Kinetics of the beta-thromboglobulin release from alpha-granules of blood platelets activated by ADP

Mathematical model of the beta-thromboglobulin (BTG) release from alpha-granules stimulated with ADP is compared with experimental data. Secretion of BTG was analysed using platelets washed by different procedures in the presence or absence of inhibitors of platelet activation. The release of BTG was monitored in response to 5-100 microM ADP. The rate constant of the release of BTG (K = 1.83 X 10(3) M-1 min-1) and efficient amount of ADP molecules secreted by a single platelet (W = 5.2 X 10(-18) mole) were estimated. The model precisely describes the release of BTG associated with the isolation of platelets (blood collection, washing procedure) and allows to estimate the extent of activation of blood platelets in the suspension.

Quantitation and characterization of human platelet glycoprotein IIIa by radioimmunoassay

Glycoprotein IIIa was quantitated in human platelets by radioimmunoassay using antisera specific to platelet membranes and purified glycoprotein IIIa. Glycoprotein IIIa and glycoprotein IIb were isolated from washed platelets by Triton X-114 extraction followed by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Radioiodinated glycoprotein IIIa was further purified by affinity chromatography on Lentil lectin-Sepharose 4B. Purified glycoprotein IIb showed little crossreactivity with 125I-labeled glycoprotein IIIa using the anti-platelet membrane or anti-glycoprotein IIIa antisera on a competition inhibition radioimmunoassay. The expression of glycoprotein IIIa epitopes were the same for the purified glycoprotein IIIa and glycoprotein IIIa in Triton X-100 solubilized platelets. A 66 kDa protein derived from glycoprotein IIIa by limited proteolysis of platelet membranes also expressed the same epitopes as intact glycoprotein IIIa. Solubilized platelets contained approximately 16 micrograms of total glycoprotein IIIa antigen per 10(9) cells. The level of glycoprotein IIIa determined by radioimmunoassay in one patient with Glanzmann's thrombasthenia amounted to 6.7% of normal and it was close to the values obtained by other methods.

A latex immunoassay of fibrin/fibrinogen degradation products in plasma using a monoclonal antibody

We have developed a latex immunoassay using an anti D neo monoclonal antibody (F2C5) which recognizes an epitope present in fragment D but which is hidden in intact fibrinogen and in early fibrinogen degradation products. This technique was applied directly to plasma of both healthy donors and patients, and was shown to be very convenient for clinical investigation, especially in emergency cases for diagnosis of intravascular coagulation. The use of plasma samples instead of serum offers several advantages: it is not time consuming since blood clotting is not required; it avoids overestimation when fibrinogen cannot be totally clotted, and underestimation due to the binding of nonclottable fibrin degradation products to the clot during clotting in vitro. This monoclonal antibody, which reacts more with FbDP (expressed in fragment D) than with fragment D, does not allow fibrin and fibrinogen degradation products to be differentiated. However, this discrimination does not seem critical for its clinical use since the level of fragment D neo antigen remained within the normal range in 12 cases of spontaneous or venous occlusion-induced hyperfibrinolysis.

The peptide beta 43-47 which increases microvascular permeability is released by plasmin during cleavage of fragment Y of fibrinogen

A synthetic pentapeptide corresponding to sequence 43-47 of human fibrinogen B beta chain elicited, in rabbits, antibodies that during immunoblotting recognized intact fibrinogen, fragments X and Y as well as the B beta chain. Since fragment Y is the last peptide product which reacts with anti-beta 43-47 antibodies, splitting of fragment Y into fragment D and fragment E must be accompanied by plasmin cleavage of the peptide bond beta Lys-47-Ala-48.

Structural basis for the species selectivity of a fibrin-specific monoclonal antibody

The structural determinant underlying the species specificity of a monoclonal anti-fibrin antibody (59D8) is the leucyl residue at position 5 in beta-chains of human fibrin. Anti-fibrin antibody 59D8 which had been elicited by immunization with human beta(1-7) peptide, Gly-His-Arg-Pro-Leu-Asp-Lys, binds to human and canine fibrins but not to bovine, ovine, or porcine fibrins. A comparison of the available amino acid sequence data suggested that the ability of anti-fibrin antibody 59D8 to discriminate among various fibrin beta-chains might be due to the amino acid at position 5. This was confirmed by competitive inhibition studies using synthetic fibrin-like peptides and determination of the amino acid sequences of the N-termini of ovine and porcine fibrin beta-chains. Edman degradation employing o-phthalaldehyde blocking permitted use of fibrin monomer rather than its separated constituent polypeptide chains. The same sequencing strategy was used to obtain partial sequence data for the alpha-chains of bovine, ovine, and porcine fibrin.

Specificity of antisera obtained to substance P and its C-terminal hexapeptide

Synthetic fragments and analogs were used to characterize specificity of antisera to SP and SP6-11. [Tyr8] SP and [Lys6] SP6-11 were both used as radioiodinated ligands. The latter was conjugated with Bolton-Hunter reagents before labelling. In both systems, the C-terminal pentapeptide SP7-11 was the shortest fragment showing antigenic identity with Substance P molecule. Substitution of different amino acid residues in SP6-11 by His or Gly showed that all but Glu6 take part in the structure of the antigenic determinant.

Measurement of cross linked fibrin derivatives in plasma: an immunoassay using monoclonal antibodies

Fibrinogen degradation, fibrin polymerisation, and the insertion of cross links into fibrin by fibrin stabilising factor lead to the appearance of new antigenic determinants. Antibodies against these antigenic sites may react specifically with the derivatives but not with the parent molecules. We have utilised a monoclonal antibody, which interacts with the cross linked fragment D dimer and related high molecular weight fibrin derivatives, to develop an enzyme immunoassay which measures cross linked fibrin derivatives in plasma and serum using D dimer as standard. Mean concentration in plasma from normal subjects was 75 ng/ml with an upper limit of about 144 ng/ml. Concentrations in patients with pulmonary embolism, deep venous thrombosis, arterial thromboembolism, and disseminated intravascular coagulation were raised in all cases. Confirmation of the specific increase of cross linked fibrin derivatives in patients with disseminated intravascular coagulation was obtained by parallel monitoring of their fibrin degradation products in serum using affinity chromatography and sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. In many patients the plasma concentrations greatly exceeded the serum values of cross linked fibrin degradation products, suggesting that the procedure can measure fibrin derivatives in plasma which are absent from serum.

An immunoassay for human D dimer using monoclonal antibodies

Monoclonal antibodies (MAb) were raised against human D dimer. The hybridomas were screened with a solid phase enzyme immunoassay against D dimer and fibrinogen degradation products. Among the panel of MAb identified, two distinct patterns emerged; the majority belonging to a panspecific class reacting against epitopes present on both D dimer and fibrinogen degradation product Dcate and a monospecific class reacting with determinants apparently present only on D dimer. A number of MAb were further characterised for their ability to specifically capture antigen in a solid phase enzyme immunoassay and assays were developed which have a sensitivity of 10 ng/ml for D dimer or crosslinked fibrin derivatives and may be suitable for detection of crosslinked derivatives in serum and plasma samples in a clinical situation.

Alteration of the antigenic structure of human fibronectin caused by complexing with collagen

The complex formation between fibronectin and denatured collagen is associated with a significant decrease of antigenic expression of the fibronectin epitopes. This conclusion is evidenced by critical changes in the value of competitive inhibition parameters such as CImax. Generally, an alteration of the fibronectin antigenic structure is similar to that observed after thermic denaturation of the molecule.