Epidemiological, clinical and immune factors that influence the persistence of antiphospholipid antibodies in leprosy

Abstract Introduction: Antiphospholipid antibodies (aPL) are described in individuals with leprosy without the clinical features of antiphospholipid antibody syndrome (APS), a condition involving thromboembolic phenomena. We have described the persistence of these antibodies for over 5 years in patients with leprosy after specific treatment. Objectives: To determine whether epidemiological, clinical and immunological factors played a role in the longterm persistence of aPL antibodies in leprosy patients after multidrug therapy (MDT) had finished. Methods: The study sample consisted of 38 patients with a diagnosis of leprosy being followed up at the Dermatology and Venereology Outpatient Department at the Alfredo da Matta Foundation (FUAM) in Manaus, AM. ELISA was used to detect anticardiolipin (aCL) and anti-β2 glycoprotein I (anti-β2GPI) antibodies. Patients were reassessed on average of 5 years after specific treatment for the disease (MDT) had been completed. Results: Persistence of aPL antibodies among the 38 leprosy patients was 84% (32/38), and all had the IgM isotype. Mean age was 48.1 ± 15.9 years, and 23 (72.0%) were male. The lepromatous form (LL) of leprosy was the most common (n = 16, 50%). Reactional episodes were observed in three patients (9.4%). Eighteen (47.37%) were still taking medication (prednisone and/or thalidomide). Mean IgM levels were 64 U/mL for aCL and 62 U/mL for anti-β2GPI. In the multivariate binary logistic regression the following variables showed a significant association: age (p = 0.045, OR = 0.91 and CI 95% 0.82-0.98), LL clinical presention (p = 0.034; OR = 0.02 and CI 95% = 0.0-0.76) and bacterial index (p = 0.044; OR = 2.74 and CI 95% = 1.03-7.33). We did not find association between prednisone or thalidomide doses and positivity for aPL (p = 0.504 and p = 0.670, respectively). No differences in the variables vascular thrombosis, pregnancy morbidity, diabetes, smoking and alcoholism were found between aPL-positive and aPL-negative patients. Conclusion: Persistence of positivity for aPL antibodies was influenced by age, clinical presentation and bacterial index. However, further studies are needed to elucidate the reason for this persistence, the role played by aPL antibodies in the disease and the B cell lineages responsible for generation of these antibodies.

The Clinical Performance of a New Chemiluminescent Immunoassay in Measuring Anti-ß2 Glycoprotein 1 and Anti-Cardiolipin Antibodies.

BACKGROUND Laboratory criterion is needed for the classification of antiphospholipid syndrome (APS), which contain anticardiolipin antibodies (aCL) and anti-ß2-glycoprotein 1 antibodies (aß2GP1). They are commonly identified by enzyme-linked immunosorbent assay (ELISA), but lack standardized kits, resulting in substantial variations in the antibody positivity between different laboratories. The emergence of chemiluminescence automated -BIO-FLASH may improve the situation. MATERIAL AND METHODS We selected 185 patients with APS, systemic lupus erythematosus (SLE), infertility, connective tissue disease (CTD), and other conditions in Peking University Third Hospital. We tested the aCL and aß2GP1 levels by EUROIMMUN ELISA and 105 patients had at least one positive result for aCL and aß2GP1, while the others had negative results. We retested them by chemiluminescence assay (CIA) and analyzed the result and compared the coincidence rate. The IgM levels were retested by AESKU ELISA. Data were analyzed using SPSS. RESULTS Our result suggested that CIA had good performance for IgG isotype of aCL and aß2GP1 in the coincidence rate. The positive coincidence rate of aCL IgM between CIA and EUROIMMUN ELISA was only 41.67%, but two ELISA kits showed good coincidence, CIA and AESKU ELISA had an obviously higher positive rate. CIA and AESKU had a higher coincidence than that of AESKU and EUROIMMUN in aß2GP1-IgM. CONCLUSIONS The new automated CIA BIO-FLASH is suitable for detecting aCL and aß2GP1 antibodies, especially IgG isotype, which may provide an alternative to time-consuming conventional ELISA method.

Clinical value of anti-domain I-ß2Glycoprotein 1 antibodies in antiphospholipid antibody carriers. A single centre, prospective observational follow-up study.

BACKGROUND: There seems to be a clear correlation between antibodies against domain I (anti-DI) of ß2Glycoprotein I and severe clinical profiles in antiphospholipid syndrome (APS) patients. We investigated the clinical significance of anti-DI antibodies in a cohort of aPL carriers. METHODS: One hundred and five carriers persistently positive for IgG anti-ß2Glycoprotein 1 antibodies (a-ß2GPI) and/or IgG anticardiolipin (aCL) and/or lupus anticoagulants (LAC) were tested for the presence of anti-DI antibodies using the QUANTA Flash® Beta2GPI-Domain I chemiluminescence immunoassay. RESULTS: Anti-DI antibodies were detected in 44 aPL carriers (41.9%) and they were significantly associated to triple aPL positivity (LAC plus IgG a-ß2GPI plus IgG aCL antibodies). Isolated LAC and a-ß2GPI antibodies were significantly associated to anti-DI negative aPL carriers. During a 82.2 month mean follow-up, ten aPL carriers (9.5%) developed a first thrombotic event so becoming APS patients. Anti-DI antibodies, triple aPL positivity, thromboembolic risk factors and autoimmune disorders significantly prevailed in carriers becoming APS. Logistic regression analysis showed that anti-DI positivity was an independent risk factor for thrombosis. CONCLUSIONS: Anti-DI antibody positivity can be considered a new risk factor predictive of the first thrombotic event in aPL carriers, instead, negative anti-DI may be useful to identify low-risk aPL carriers.

Assessment of diagnostic methods for the detection of anticardiolipin and anti-ßeta2 glycoprotein I antibodies in patients under routine evaluation for antiphospholipid syndrome.

BACKGROUND: We assessed the performance characteristics and correlations of the traditional enzyme-linked immunosorbent assay (ELISA) and chemiluminescence immunoassay (CIA) for detecting IgG and IgM antibodies to cardiolipin (aCL) and beta2 glycoprotein (anti-ß2GPI) antibodies in patients under routine evaluation for APS. METHODS: Patients (n = 216) referred to ARUP Laboratories for lupus anticoagulant (LAC) and/or aCL or anti-ß2GPI IgG/IgM antibodies evaluation were assessed by ELISA and CIA methods. Diagnostic accuracies, correlations between methods and specific clinical manifestations in APS were investigated. RESULTS: The areas under the curve (%) for APS using LAC with CIA (74, 95% CI: 65-82) or ELISA (70, 95% CI: 61-79) aPLs were comparable. The overall agreements and linear regression correlations between methods for aPL antibody of the same specificity were variable: aCL IgG 87.3%; R2 = 0.7491, aCL IgM 71.6%; R2 = 0.2656, anti-ß2GPI IgG 77.2%; R2 = 0.7688 and anti-ß2GPI IgM 81.7%; R2 = 0.3305. CONCLUSIONS: With inclusion of LAC, the ELISA and CIA show comparable performance for the diagnosis of APS. However, correlations of APS-specific manifestations were dependent on method of detecting the aPL antibodies suggesting platforms may not be used interchangeable.

Reversible drug-induced antiphospholipid syndrome.

We report an original case of reversible antiphospholipid syndrome (APS) due to minocycline in a young male patient who experienced recurrent strokes while taking minocycline. He started minocycline therapy (50 mg twice daily) at 15 years old for acne. After three years of treatment, the patient experienced a lateral medullary syndrome. He was treated with aspirin while minocycline was continued. Eighteen months later, the patient complained about horizontal binocular diplopia. MRI revealed an infarct of the oculomotor nerve nucleus. Laboratory investigations revealed high titers of anti-beta 2 glycoprotein 1 (antiß2GP1) antibodies of 470 U/ml (normal range <15 U/ml) and antiphosphatidylethanolamine antibodies of 137.4 U/ml (normal range <18 U/ml). Other laboratory tests were normal. Six weeks after discontinuation of minocycline, anti-ß2GP1 antibodies decreased to 335 U/ml and to 36 U/ml at six months and then remained negative for six years. Many drugs have been considered as possibly causing APS but only in a limited number of patients. To our knowledge this is the first case of drug-induced APS with complete disappearance of high titers of anti-ß2GP1 antibodies after minocycline withdrawal. This case also illustrates the need to monitor the levels of antiphospholipid antibodies, even though initial values are high and confirmed after 12 weeks.

Novel diagnostic and therapeutic frontiers in thrombotic anti-phospholipid syndrome.

The anti-phospholipid syndrome (APS) is an autoimmune disorder characterized by vascular thrombosis and/or pregnancy morbidity, associated with a persistent positivity for anti-phospholipid antibodies (aPL). The current classification criteria for APS include three laboratory tests: lupus anti-coagulant (LA), anti-cardiolipin (aCL), and anti-ß2 glycoprotein-I (ß2GPI). To date, the therapeutic approach for thrombotic APS mainly centers on long-term anti-coagulation with a vitamin K antagonist (VKA). APS management may represent a challenge for the treating physicians. Patients with different aPL profiles need a tailored risk-stratified approach. Moreover, in patients with recurrent thrombotic events despite therapy with VKA, or in those with microvascular involvement, new therapeutic options are highly needed. In this review, we aim to elucidate recent findings about new aPL specifities, available risk scoring models, and novel therapeutic approaches in APS management.

[Preparation and application of a polyclonal antibody against the peptides of ß2glycoprotein 1].

OBJECTIVE: To prepare a polyclonal antibody against human and murine ß2 glycoprotein 1 (ß2GP1) antigen with chemically synthesized ß2GP1 peptides, and identify its specificity and pathogenicity. METHODS: The peptides from the NH2-terminal 35th-51th amino acids of ß2GP1 were synthesized by standard Fmoc assay, and then used to immunize New Zealand white rabbits after coupling with keyhole limpet hemocyanin (KLH). The polyclonal antibody in the rabbit sera was purified by protein G column. The titer and specificity of the polyclonal antibody were determined by ELISA and Western blot analysis. The total RNA was extracted and the protein lysates were collected from C3H/HeN mouse peritoneal macrophages treated with the above anti-ß2GP1 peptides antibody/ß2GP1 complexes in vitro. And the tissue factor (TF) mRNA and protein expression in the peritoneal macrophages were detected by real-time quantitative PCR and Western blotting. The activation of p38 and NF-κB p65 induced by anti-ß2GP1 peptides antibody/ß2GP1 complexes was determined by Western blotting using phosphor-specific antibodies. Experimental antiphospholipid antibody syndrome (EAPS) mouse model was established in C3H/HeN mice by intraperitoneal injection of anti-ß2GP1 peptides antibody in vivo. The titers of anti-ß2GP1 antibodies in the mouse peripheral blood and the activated partial thromboplastin time (APTT) were detected. RESULTS: The purity of chemically synthesized ß2GP1 peptides was 94%, which met the immunogen standard. The titer of antiserum of the rabbit immunized with ß2GP1 peptide coupling with KLH was over 1:32 000. Western blotting showed that the anti-ß2GP1 peptides antibody could specifically recognize both human and mouse ß2GP1. Furthermore, ELISA showed that the antibody could specifically bind to ß2GP1 cryptic epitope. In vitro experiments demonstrated that the anti-ß2GP1 peptides antibody/ß2GP1 co mplexes could enhance p38 and NF-κB p65 phosphorylation in mouse peritoneal macrophages and induce TF mRNA and protein expression. Moreover, EAPS mouse model induced by anti-ß2GP1 peptide antibody was successfully established, in which the titers of anti-ß2GP1 antibody in mouse peripheral blood were greater than 1:3200 and APTT was significantly shorter that that of control group. CONCLUSION: The anti-ß2GP1 peptide antibody we prepared could specifically recognize both human and mouse ß2GP1 and specifically bind to ß2GP1 cryptic epitope. It was also proved to have the pathogenic effect.

Antiphospholipid antibody testing for the antiphospholipid syndrome: a comprehensive practical review including a synopsis of challenges and recent guidelines.

The antiphospholipid (antibody) syndrome (APS) is an autoimmune condition characterised by a wide range of clinical features, but primarily identified as thrombotic and/or obstetric related adverse events. APS is associated with the presence of antiphospholipid antibodies (aPL), including the so-called lupus anticoagulant (LA). These aPL are heterogeneous in nature, detected with varying sensitivity and specificity by a diverse range of laboratory tests. All these tests are unfortunately imperfect, suffer from poor assay reproducibility (inter-method and inter-laboratory) and a lack of standardisation and harmonisation. Clinicians and laboratory personnel may struggle to keep abreast of these factors, as well as the expanding range of available aPL tests, and consequent result interpretation. Therefore, APS remains a significant diagnostic challenge for many clinicians across a wide range of clinical specialities, due to these issues related to laboratory testing as well as the ever-expanding range of reported clinical manifestations. This review is primarily focussed on issues related to laboratory testing for APS in regards to the currently available assays, and summarises recent international consensus guidelines for aPL testing, both for the liquid phase functional LA assays and the solid phase assays (anticardiolipin and anti-beta-2-Glycoprotein-I).

Clinical performance of anticardiolipin and antiß2 glycoprotein I antibodies using a new automated chemiluminescent assay: superior thrombotic prediction of combined results measured by two different methods.

The anticardiolipin (aCL) and antibeta2-glycoprotein I (aß2GPI) antibodies are used to diagnosis antiphospholipid syndrome. It would be possible to use two or more methods to improve the diagnostic sensitivity of aCL and aß2GPI. In this study, we investigated the laboratory performance of a new chemiluminescent assay and explored whether the combined results of aCL and aß2GPI measured by two different methods predict thrombotic risk better. The cut-off values were assessed with 99 healthy controls. The coefficient of variations was determined using control materials. Using the plasma of 109 patients, AcuStar chemiluminescent assay and QUANTA Lite ELISA were carried out according to the manufacturers' instructions. The AcuStar cut-off points were 13.5 U/ml for aCL IgG, 19.1 U/ml for aCL IgM, 16.3 U/ml for aß2GPI IgG and 12.6 U/ml for aß2GPI IgM. Total coefficient of variations ranged from 4.6 to 8.8%. For both aCL and aß2GPI, the AcuStar odds ratio for thrombosis prediction was higher than that of QUANTA Lite. When the results for both AcuStar and QUANTA Lite are positive, the odds ratios of aCL and aß2GPI were higher than that interpreted by a single positive result each. The new automated chemiluminescent assay exhibited good precision, concordance rate, and clinical performance. The combined results of aCL and aß2GPI as measured by two different methods are expected to increase the prediction power for thrombosis.

Risk assessment in patients with antiphospholipid antibodies.

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by the association of antiphospholipid antibodies (aPL) with thrombosis and/or pregnancy loss: classification criteria were defined in the updated international consensus held in Sidney in 2005. Vascular and obstetric manifestations display partially different pathogenetic mechanisms. Thrombosis develop as a result of local procoagulative changes upon triggers influence (second-hit theory). Pregnancy morbidity is thought to be dependent on placental thrombosis and complement activation. The laboratory tests include Lupus Anticoagulant (LA), a functional assay, and anticardiolipin (aCL) and anti-ß2-glycoprotein I antibodies detected by solid phase enzyme-linked immunosorbent assay (ELISA). The LA testing is relatively standardized while there's still significant interlaboratory discrepancy in ELISA tests. Current APS criteria are under discussion: since for vascular and obstetric APS, different pathogenetic mechanisms have been shown, some criteria variation could also be contemplated. What is the weight of aPL antibodies in provoking thrombosis and which contribution could be expected from aPL per se is debated. As thrombosis is generally considered to be multi-factorial, each case needs a risk-stratified approach. Any primary prophylaxis, intensity and duration of secondary prophylaxis should take into account aPL profile, other cardiovascular risk factors and systemic autoimmune diseases associated. We look forward to the publication of recommendations of the leading experts in the field, developed during the recent 14th International Congress in Rio de Janeiro, Brazil.

Estimation of the amount of ß2-glycoprotein I adsorbed at the inner surface of fused silica capillaries after acidic, neutral and alkaline pretreatment.

Sample adsorption to the inner surface of fused silica capillaries is a common problem in CE when analyzing macromolecules and is harmful to the analysis. We previously utilized the pH hysteresis effect of fused silica to facilitate electrophoresis of the strongly adsorbing protein ß(2) gpI in plain-fused silica capillaries at neutral pH. In the present paper, the effect of different pretreatments of the capillary on the adsorption of the ß(2) -glycoprotein I has been investigated using electroosmosis markers, SDS mobilization, and imaging based on indirect immunofluorescence microscopy for direct visualization. The amount of ß(2) gpI adsorbed on the surface was probed using all these independent techniques after electrophoresis at neutral pH on capillaries pretreated with HCl, background electrolyte (BGE), and NaOH. BGE pretreatment was included as a positive control. We found that 80% or more of the starting material was adsorbed to the inner surface of the silica capillaries during electrophoresis after pretreatment with only BGE or with NaOH, but after acidic pretreatment the loss was consistently less than 20%. NaOH most efficiently removes adsorbed protein between runs. A theoretical calculation of the pH change of the BGE showed that electrolysis affects the pH more than the deprotonation of silanols during electrophoresis. We conclude that acidic pretreatment of fused silica capillaries diminishes adsorption of ß(2) gpI by decreasing charge-dependent wall adsorption.

Interference in antiphospholipid antibody assays.

Antiphospholipid antibodies (aPL) are detected with two types of laboratory tests: first, antigen-specific immunoassays for the determination of antibodies against cardiolipin, ß2-glycoprotein I and other phospholipids, and phospholipid-protein complexes; second, functional (coagulation) assays for the detection of lupus anticoagulants. Both aPL immunoassays and coagulation assays are prone to interferences, and clinicians need to be aware of the limitations of these assays. Interference is a clinically significant bias in the measured analyte concentration due to the effect of another component or property of the sample. Besides immune-mediated interferences (such as heterophile or human anti-animal antibodies, rheumatoid factor, high immunoglobulin levels, or factor inhibitors), aPL assays are uniquely affected by anticoagulants and the presence of residual platelets in test plasma. Interferences are usually analyte- and assay-specific and may go unrecognized in routine laboratory practice. Despite advances in our knowledge on the mechanisms of interferences in aPL assays, it is unlikely that total elimination will be possible.

The future of antiphospholipid antibody testing.

The presence of antiphospholipid antibodies (aPL) is essential to diagnose the antiphospholipid syndrome (APS). Three assays are available to detect the presence of these autoantibodies, but all three assays suffer from several important drawbacks. First, the assays lack standardization because the results of the assay partially depend on the laboratory that performs the assay. Second, we do not know whether the assays detect the autoantibody population responsible for the clinical manifestations that characterize the syndrome. Finally, the assays do not predict the risk of recurrence. There is an absolute need for novel assays that generate prognostic information that can be used for a more tailored treatment of patients with APS. In 2011, important information became available on the protein against which the autoantibodies are directed, ß2-glycoprotein I (ß2GPI). Based on the progress we have made in our understanding of the physiology of ß2GPI, it should be possible to design assays that can better predict the consequences of the presence of aPL in the circulation.

Glycopeptide profiling of beta-2-glycoprotein I by mass spectrometry reveals attenuated sialylation in patients with antiphospholipid syndrome.

Beta2-glycoprotein I (beta2GPI) is a five-domain protein associated with the antiphospholipid syndrome (APS), however, its normal biological function is yet to be defined. beta2GPI is N-glycosylated at several asparagine residues and the glycan moiety conjugated to residue 143 has been proposed to interact with the Gly40-Arg43 motif of beta2GPI. The Gly40-Arg43 motif has also been proposed to serve as the epitope for the anti-beta2GPI autoantibody associated with APS. We hypothesized that the structure or composition of the glycan at Asn-143 might be associated with the APS symptom by shielding or exposing the Gly40-Arg43 motif towards the anti-beta2GPI autoantibody. To test this hypothesis we used mass spectrometry (MS) for comparative glycopeptide profiling of human beta2GPI obtained from blood serum from four healthy test subjects and six APS patients. It revealed significant differences in the extent of sialylation and branching of glycans at Asn-143. Biantennary glycans were more abundant than triantennary glycans at Asn-143 in both healthy subjects and patients. In APS patient samples we observed a decrease in sialylated triantennary glycans and an increase in sialylated biantennary glycan structures, as compared to controls. These data indicate that some APS patients have beta2GPI molecules with a reduced number of negatively charged sialic acid units in the glycan structure at Asn-143. This alteration of the electrostatic properties of the glycan moiety may attenuate the intramolecular interactions with the positively charged Gly40-Arg43 motif of beta2GPI and, in turn, leads to conformational instability and exposure of the disease-related linear epitope Gly40-Arg43 to the circulating autoantibody. Thus, our study suggests a link between site-specific glycan profiles of beta2GPI and the pathology of antiphospholipid syndrome.

Antiphospholipid antibodies and the antiphospholipid syndrome: clinical significance and treatment.

This article provides a review of the various types of antiphospholipid (aPL) antibodies and antiphospholipid syndromes, their prevalence, presumed origin, relationship to autoimmunity in general, and their role in the body's defenses and apoptosis. New hypotheses such as the role of antibodies to beta2 glycoprotein I (beta2GPI) and the signaling of toll-like receptors are also discussed, as is the spectrum of clinical manifestations associated with the demonstration of these antibodies, now assumed to be "pathogenic." A distinction is made between antibodies present in sera of patients with a variety of microangiopathic syndromes (MAPS; e.g., HELLP syndrome, thrombotic thrombocytopenic purpura, and thrombotic microangiopathic syndromes). In these conditions, the antibodies might not be "pathogenic" but, alternatively, generated by small vessel endothelial damage. These conditions are differentially referred to as microangiopathic antiphospholipid-associated syndromes, and they should be differentiated from the microvascular occlusions that are seen in the antiphospholipid syndrome. Current treatments of the antiphospholipid syndrome are briefly reviewed.

Anti-beta2-glycoprotein I antibodies induce monocyte release of tumor necrosis factor alpha and tissue factor by signal transduction pathways involving lipid rafts.

OBJECTIVE: To investigate the association of beta(2)-glycoprotein I (beta(2)GPI) with lipid rafts in monocytic cells and to evaluate the proinflammatory and procoagulant effects of anti-beta(2)GPI binding to its target antigen on the monocyte plasma membrane. METHODS: Human monocytes were fractionated by sucrose density-gradient centrifugation and analyzed by Western blotting. Immunoprecipitation experiments were performed to analyze the association of beta(2)GPI with lipid rafts and the possible interaction of beta(2)GPI with annexin A2 and Toll-like receptor 4 (TLR-4). Monocytes were then stimulated with affinity-purified anti-beta(2)GPI antibodies from patients with the antiphospholipid syndrome (APS). Interleukin-1 receptor-associated kinase (IRAK) phosphorylation and NF-kappaB activation were evaluated by immunoprecipitation and transcription factor assay, respectively. Supernatants from monocytes were tested for tumor necrosis factor alpha (TNFalpha) and tissue factor (TF) levels by enzyme-linked immunosorbent assay. RESULTS: We found beta(2)GPI and its putative receptor annexin A2 in lipid raft fractions of human monocytes. Moreover, there was an association between beta(2)GPI and TLR-4, suggesting that it was partially dependent on raft integrity. Triggering with anti-beta(2)GPI antibodies induced IRAK phosphorylation and consequent NF-kappaB activation, which led to the release of TNFalpha and TF. CONCLUSION: Anti-beta(2)GPI antibodies react with their target antigen, likely in association with annexin A2 and TLR-4, in lipid rafts in the monocyte plasma membrane. Anti-beta(2)GPI binding triggers IRAK phosphorylation and NF-kappaB translocation, leading to a proinflammatory and procoagulant monocyte phenotype characterized by the release of TNFalpha and TF, respectively. These findings provide new insight into the pathogenesis of APS, improving our knowledge of valuable therapeutic targets.

Effects of beta2-glycoprotein-I on platelet aggregation in cord versus adult whole blood.

We present a peculiarity of the neonatal hemostatic system that might contribute to establish a procoagulant readiness in neonatal blood by sensitizing neonatal platelets for ADP stimulation. beta2-glycoprotein-I (beta2-GP-I) is a plasma constituent capable of suppressing ADP-induced platelet aggregation. We found significant lower levels of beta2-GP-I in cord vs. adult plasma (120 +/- 27 vs. 180 +/- 37 microg/mL, P<0.001). We demonstrate dose-dependent inhibition of ADP-induced platelet aggregation in cord whole blood (WB) in the presence of increasing amounts of beta2-GP-I, evaluated by means of WB aggregometry employing the impedance method. Particularly, raising the beta2-GP-I concentration in cord WB from neonatal level up to the respective adult value caused significant reduction of amplitude (from 9.5 +/- 2.7 to 2.8 +/- 0.9 Omega, P<0.001) and of slope (from 5.9 +/- 2.4 to 1.89 +/- 0.9 Omega/min, P<0.001), and a significant prolongation of the aggregation time (from 51.8 +/- 22.9 to 110.8 +/- 60.3 s, P<0.001). In conclusion, physiological low levels of beta2-GP-I in cord WB cause enhanced responsiveness of neonatal platelets to ADP stimulation. This mechanism might help to explain the clinically observed well-functioning hemostasis in neonates.