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J D Oosting

Publications and source records attributed to J D Oosting.

12 recordsLinked to original sources
PubMed1998

Factor V inhibitor associated with cold agglutinin disease.

An 81-year-old man known to have a stable cold agglutinin syndrome presented with a progressive cerebral hemorrhage. Coagulation tests revealed prolonged APTT and prothrombin time and severely decreased factor V activity, which could not be normalized by mixing with normal plasma. The patient appeared refractory to substitution with fresh-frozen plasma, suggesting the presence of a circulating inhibitor specific for factor V. To our knowledge, this is the first case of a lymphoproliferative disease leading to a cold agglutinin syndrome and a putative inhibitor of factor V. In patients with paraproteinemia presenting with bleeding diathesis, the presence of a circulating inhibitor of a specific coagulation factor must be considered.

Aged↗
PubMed1997

Evaluation of an automated photometric fibrinogen assay.

A recently-introduced automated method for the determination of plasma fibrinogen is based on the principle of von Clauss, combined with photometric detection: after addition of thrombin, the coagulation time is determined by measuring the change in absorption at 405 nm. This method was evaluated and compared with the original coagulometric Clauss assay and with the prothrombin time (PT)-derived automated method. The inter-assay coefficient of variation of the Clauss-derived assay was lower (14.1, 3.8 and 4.6%) than the PT-derived assay (16.1, 7.5 and 10.5%, respectively) at all three fibrinogen levels tested (1.2, 4.0 and 7.5 g/l). The correlation between the assays was investigated according to the method of Passing and Bablok and could be described as follows: Clauss-derived = 0.79 (PT-derived) + 0.66; Clauss-derived = 1.12 (Clauss) + 0.143. The interference of heparin (< 1.5 U/ml), haemoglobin (< 30 micromol/l), bilirubin (< 200 micromol/l) and triglycerides (< 5.5 mmol/l) in the Clauss-derived assay was negligible. The effects of fibrinogen degradation products on the Clauss-derived assay were comparable with the effects on the Clauss assay, in contrast to the effects on the PT-derived assay. In conclusion, the Clauss-derived assay is a specific and precise automated method to determine fibrinogen concentrations in plasma, which is not liable to interference from different pathophysiological substances.

Autoanalysis↗
PubMed1993

Antiphospholipid antibodies directed against a combination of phospholipids with prothrombin, protein C, or protein S: an explanation for their pathogenic mechanism?

Despite many studies on the pathophysiology of antiphospholipid antibodies (aPL), the mechanism by which aPL causes thrombosis has not been established. We have tried to elucidate the paradox between the prolongation of the clotting time of phospholipid-dependent coagulation tests in vitro and the occurrence of thrombosis in vivo. The effect on endothelial cell-mediated prothrombinase activity of 30 IgG fractions, of which 22 prolong the aPTT of normal plasma, was investigated. Only 4 of 22 fractions (18%) inhibited prothrombinase activity when tested on this more physiologic phospholipid surface, indicating that in most patients with aPL the prolongation of clotting tests is predominantly as in vitro phenomenon. It was recently reported that in detection methods for aPL, two plasma proteins, beta 2-glycoprotein I and prothrombin, enhance the binding of aPL to phospholipids. We have studied the specificity of the 4 IgG fractions that inhibit the prothrombinase activity and found that they were directed against a combination of phospholipids and prothrombin. However, the involvement of prothrombin in binding of aPL leading to impaired thrombin generation could still result in both a bleeding and a thrombotic tendency. Therefore, we proposed a new thrombogenic mechanism for aPL in which aPL bind to complexes of phospholipids and coagulation proteins, thereby interfering in different coagulation reactions. We tested this new hypothesis by investigating the effect of IgG from the same 30 patients on the activated protein C (APC)-mediated factor Va inactivation in the absence and presence of protein S. Three IgGs that inhibited APC-mediated factor Va inactivation independent of protein S and 4 additional IgGs that inhibited in the presence of protein S were found. Furthermore, we could specifically adsorb the inhibitory IgG with cardiolipin vesicles to which APC with or without protein S was bound. In conclusion, these results suggest that subpopulations of aPL exist that are directed to complexes of phospholipids and different plasma proteins. The identity of the plasma proteins involved in the binding of aPL might determine which pathogenic mechanism causes thrombosis.

Adult↗
PubMed1993

Antiphospholipid antibodies: specificity and pathophysiology.

Antiphospholipid antibodies are autoantibodies that can be detected in plasma or serum with phospholipid-dependent coagulation tests or solid-phase immunoassays. The presence of these autoantibodies is strongly associated with an increased risk for arterial and venous thrombosis, recurrent fetal loss and thrombocytopenia. This paradoxical association of the in vitro prolongation of clotting assays and in vivo thrombosis has stimulated the search for the real antigen to which the autoantibodies are directed. A large number of potential pathological mechanisms have been proposed, and although disturbance of a certain metabolic pathway by the antibodies can explain a thrombotic tendency in one patient, no general pathological mechanism explaining thrombosis in the whole patient population has been found. This suggests that the antiphospholipid antibodies are a heterogeneous group of autoantibodies and is supported by the recent observations that antiphospholipid antibodies are not directed against phospholipids alone but against a combination of phospholipids and phospholipid-binding proteins. Both the phospholipid and the protein are part of the antigen. For the detection of antiphospholipids in an ELISA set-up, beta 2-glycoprotein I is the protein cofactor. In the coagulation tests, beta 2-glycoprotein, as well as prothrombin, can act as cofactor. However, the presence of these two proteins as a part of the epitope of the antiphospholipid antibodies does not explain the thrombotic tendency in the patient group. We have found that more physiologically relevant cofactors such as protein C and protein S, for which it is known that a partial deficiency is correlated with a thrombotic tendency, can also act as cofactors for the binding of antiphospholipid antibodies. It is concluded that antiphospholipid antibodies are a heterogeneous group of autoantibodies with varying affinity for different protein-phospholipid complexes and that inhibition of the biological activity of the protein part of the complex determines the pathological capacity of the antibodies.

Abortion, Habitual↗
PubMed1993

Autoantibodies directed against the epidermal growth factor-like domains of thrombomodulin inhibit protein C activation in vitro.

No consensus has been obtained about the question whether autoantibodies, in particular antiphospholipid antibodies (aPL), may cause thrombosis by inhibiting thrombomodulin (TM) mediated protein C activation. In order to clarify the mechanism by which autoantibodies inhibit TM-mediated protein C activation, we have screened 12 patients with autoimmune diseases for the presence of circulating autoantibodies inhibiting TM function. In a cross-sectional study we found that IgG fractions from two patients (who were aPL negative) inhibited TM mediated protein C activation in an assay system using purified components. A longitudinal study of six patients with a history of thrombosis of which two were aPL positive showed that all had at some time circulating antibodies inhibiting TM function, suggesting that the presence of these antibodies is transient. Three different TMs were used to identify the epitope of the antithrombomodulin antibodies (aTM): rabbit TM, which contains the entire TM molecule; Solulin, which contains the extracellular part of TM, and rEGF-TM, which contains the six epidermal growth factor (EGF) domains of TM. We showed that the aTM inhibited protein C activation mediated by all three TMs, indicating that the aTM are directed against the region containing the EGF domains. When TM was incorporated in phospholipid vesicles, no inhibition by these aTM could be demonstrated. In addition, protein C activation mediated by cultured endothelial cells (EC) could not be inhibited by aTM. The lack of inhibition of TM in phospholipid vesicles and EC-TM by a TM suggests that aTM only inhibit soluble TM. In conclusion, we demonstrated the transient presence of circulating autoantibodies directed against the region of TM containing the EGF domains in SLE patients with a history of thrombotic complications. We postulate that the presence of antibodies to soluble TM may be, in addition to aPL, a risk factor for the occurrence of thrombosis in patients with autoimmune diseases.

Adult↗
PubMed1992

Antiphospholipid antibody positive sera enhance endothelial cell procoagulant activity--studies in a thrombosis model.

The effect of sera and IgG from 12 patients with systemic lupus erythematosus (SLE) on the endothelial cell (EC) procoagulant activity (PCA) was investigated in an in vitro thrombosis model. Six of the 12 SLE sera contained antiphospholipid antibodies (aPL). EC were stimulated for 8 h at 37 degrees C with or without 50 pM tumor necrosis factor (TNF) in culture medium containing 20% patient or control serum. Then the endothelial cell matrix (ECM) was isolated and subsequently exposed in a perfusion chamber to circulating normal whole blood, anticoagulated with low molecular weight heparin (LMWH). The PCA of the ECM was determined as the amount of generated fibrinopeptide A (FPA) in samples taken before and after perfusion. Furthermore, cross sections were made of the perfused matrix and analyzed for platelet adhesion and aggregate formation. All six aPL containing sera induced a small, but significant increase of ECM procoagulant activity. When added in combination with a low dose of TNF (50 pM), a synergistic enhancement of ECM procoagulant activity was found. The FPA generation was increased to 150-614% from the values obtained after stimulation with TNF and control serum. Also a shift towards the formation of larger platelet thrombi was observed. After stimulation with TNF and patient serum the surface of ECM covered with large aggregates (greater than 5 microns) was increased by 124-329% compared to the results obtained after stimulation with control serum and TNF. When patient sera were depleted from IgG the effects were strongly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies↗
PubMed1992

Lupus anticoagulant activity is frequently dependent on the presence of beta 2-glycoprotein I.

Antiphospholipid antibodies (aPL) are defined by anticardiolipin antibody (aCL) ELISA and prolongation of phospholipid dependent coagulation assays (lupus anticoagulant; LAC). For the binding of aCL to cardiolipin a cofactor, beta 2-glycoprotein I (beta 2-GPI), is necessary. We have investigated whether the same cofactor is essential for LAC activity. Plasma from 6 LAC positive patients and 3 controls was depleted from beta 2-GPI by means of affinity chromatography. From the 6 LAC positive plasmas, 4 became LAC negative (tested with dRVVT) when beta 2-GPI was depleted and became positive again when purified beta 2-GPI (200 micrograms/ml) was added. A dose response curve showed that addition of 50 micrograms/ml beta 2-GPI to beta 2-GPI deficient patient plasma, led to a positive dRVVT. Depletion of, and addition of beta 2-GPI to plasma from controls had no effect on the dRVVT. Measurement of beta 2-GPI plasma levels in 19 LAC positive patients, 40 LAC negative patients and 15 controls showed no difference in beta 2-GPI levels. These results show that a combination of aPL and beta 2-GPI is essential not only for binding to cardiolipin, but also for LAC activity and imply that low beta 2-GPI levels (less than 50 micrograms/ml) can lead to false negative LAC tests. These observations may lead to new insights in the pathophysiological complications associated with aPL.

Adult↗
PubMed1991

In vitro studies of antiphospholipid antibodies and its cofactor, beta 2-glycoprotein I, show negligible effects on endothelial cell mediated protein C activation.

The effect of sera and purified IgG isolated from plasma of 46 patients with systemic lupus erythematosus (SLE) and 9 healthy donors on the endothelial cell (EC) mediated protein C activation was investigated. Out of the 46 SLE sera used, 19 were antiphospholipid antibodies (aPL) positive. From 12 patients IgG was isolated, of which 6 contained aPL. EC were first incubated with IgG (7 mg/ml) or serum (1:1 diluted) for 1 h and then tested for their ability to promote protein C activation by thrombin, with the cells either in a monolayer or in a suspension. The normal range (mean of control values +/- 2 SD) of protein C activation was 80-120%. In contrast to others, we could not detect an inhibition of protein C activation by any of the patient IgG's or sera. The recently described cofactor for binding of antiphospholipid antibodies to phospholipids, beta 2-glycoprotein I, was purified and added to the purified IgG's. A combination of these two components did not inhibit the EC mediated protein C activation by thrombin. This study suggests that the inhibition of the protein C activation, mediated by EC, is not a general mechanism by which aPL related thrombosis can be explained.

Adolescent↗
PubMed1991

Identification of linear epitopes on Semliki Forest virus E2 membrane protein and their effectiveness as a synthetic peptide vaccine.

Semliki Forest virus (SFV) infection of mice was used as a model to study the applicability of synthetic peptides containing only linear epitopes as viral vaccines. The identification of linear epitopes with vaccine potential on the E2 membrane protein of SFV was based on the binding of SFV-specific antibodies to a set of overlapping synthetic hexapeptides (Pepscan) representing the whole E2 amino acid sequence. The 14 available E2-specific monoclonal antibodies which were protective in vivo proved to be unsuitable for the identification of linear epitopes because they recognized only conformational epitopes, as indicated by their lack of reactivity with unfolded, reduced E2 protein on immunoblots. Three epitopes were detected with polyclonal anti-SFV serum at amino acid positions 135 to 141, 177 to 185 and 240 to 246 of the E2 protein. Synthetic peptides containing these epitopes were coupled to a carrier protein and tested as a vaccine. Mice immunized with the peptide containing amino acids 240 to 255 of protein E2 were protected against a challenge with virulent SFV but protection of mice immunized with the peptides containing amino acids 126 to 141 or 178 to 186 was only marginally better than that of controls. The prechallenge sera of most peptide-immunized mice reacted with SFV-infected cells but none of these sera neutralized the virus in vitro. However, protection of mice correlated well with SFV-specific antibody titre, suggesting antibody-mediated protection.

Animals↗
PubMed1989

Identification of a DTH-inducing T-cell epitope on the E2 membrane protein of Semliki Forest virus.

Mapping of T-cell epitopes on the structural proteins of Semliki Forest virus (SFV) was performed by measuring the ability of cloned SFV protein fragments to induce delayed-type hypersensitivity (DTH). The cloned SFV protein fragments were expressed as hybrid proteins with cro-beta-galactosidase in Escherichia coli from constructed recombinant plasmids. DTH reactions were measured, as footpad swelling, in BALB/c mice after immunization with whole, UV-inactivated SFV and challenge with the hybrid proteins, and vice versa, using the adjuvant dimethyl dioctadecyl ammonium bromide to enhance DTH. Only two of the tested hybrid proteins induced DTH, and these DTH reactions were equally strong. The largest DTH-inducing hybrid protein contained the N-terminal 350 amino acids of E2 and part of E3, the smallest contained only the region from amino acid residues 115 to 151 of the E2 membrane protein without any other SFV protein parts. It was concluded that the segment between amino acid residues 115 and 151 of the E2 membrane protein of SFV was responsible for the observed DTH, and thus, contains a T-cell epitope. Sequence homology with known T-cell epitopes on other proteins makes it likely that the DTH-inducing T-cell epitope is located from amino acid residues 120 to 128 of E2.

Adjuvants, Immunologic↗
PubMed1989

Synergistic effect of low doses of tumor necrosis factor and sera from patients with systemic lupus erythematosus on the expression of procoagulant activity by cultured endothelial cells.

The effect of 15 antiphospholipid antibody (APA) positive SLE sera, 13 APA negative SLE sera, 10 APA negative sera from patients with other connective tissue diseases (CTD) and 15 control sera on the expression of endothelial procoagulant activity (PCA) was studied. Endothelial cells (EC) were stimulated with tumor necrosis factor (TNF) and 20% serum for 4 hr and the surface PCA expression was measured. Without TNF, none of the sera stimulated PCA expression. With suboptimal TNF stimulation, 14/15 APA positive SLE sera, 7/13 APA negative SLE sera, 2/10 CTD sera and 2/15 control sera enhanced PCA expression. This stimulating effect resided in the IgG fraction and was associated with the presence of APA, but not with a history of thrombosis. Purified APA had no PCA stimulating activity. PCA expression was inhibited by cycloheximide and heat treatment (30 min, 56 degrees C) of serum. In conclusion, 21/28 (75%) SLE sera increase the TNF-induced endothelial PCA expression. Although this effect predominantly occurs with APA positive serum, a causative role of APA was not demonstrated.

Adult↗