Insight into the hypercoagulable state of high‐risk thrombotic APS patients: Contribution of aβ2GPI and aPS/PT antibodies

Abstract

Objective Most high‐risk thrombotic antiphospholipid syndrome (APS) patients test positive for anti‐β2‐glycoprotein I (aβ2GPI) and anti‐phosphatidylserine/prothrombin (aPS/PT) antibodies. Information on the influence of these antibodies on thrombin generation and activated protein C resistance (aPCr) is still sparse and contradictory. Methods Plasma of 16 patients poured into a β2GPI affinity column allowed the perfect separation of aβ2GPI and aPS/PT antibodies. aPS/PT antibodies were further purified through a prothrombin affinity column. Obtained material was spiked into normal pooled plasma (NPP) and tested in the thrombin generation assay in the absence or presence of aPC. Results aPS/PT antibodies showed a marked anticoagulant effect. Affinity purified aPS/PT and aβ2GPI antibodies from five patients were compared. aPS/PT antibodies showed significantly prolonged lag time and time to peak (5.0 minutes [interquartile range (IQR)3.5–6.1] versus 2.7 minutes [IQR2.2–3.5], P = .03 and 8.7 minutes [IQR6.7–10.3] versus 5.7 minutes [IQR4.5–6.2], P = .05, respectively) and significantly lower peak and velocity index (143 nmol/L [IQR131–163] versus 171 nmol/L [IQR157–182], P = .03 and 35 nmol/L/min [IQR32–59] versus 72 nmol/L/min [IQR54–77], P = .03, respectively). When aPC was added to the system, aPCr was significantly increased compared to controls for both aβ2GPI and aPS/PT antibodies. However, it was significantly stronger using aPS/PT antibodies. Median inhibition of endogenous thrombin potential was 22% (IQR16–33) with aPS/PT compared to 52% (IQR46–56) with aβ2GPI antibodies (P = .002). Conclusions Aβ2GPI antibodies show a mild anticoagulant and moderate procoagulant effect in thrombin generation and moderate aPC resistance. Conversely, aPS/PT antibodies show a strong anticoagulant effect and a strong aPCr.

International multicenter, multiplatform study to validate Taipan snake venom time as a lupus anticoagulant screening test with ecarin time as the confirmatory test: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

“…Only 13/175 (7.4%) of triple‐positive patients were LA‐negative by TSVT/ET compared with 61/371 (16.4%) non‐triple‐positive APS patients. A possible explanation comes from a recent report indicating that aβ2GPI exert LA activity through interference with FV activation, to which oscutarin C and ecarin would be insensitive, whereas prothrombin‐directed antibodies compete for phospholipid‐binding sites, 62 and other recent studies report that LA activity in high‐risk patients is largely attributable to prothrombin‐directed antibodies 63,64 2,65 …”

“…A possible explanation comes from a recent report indicating that aβ2GPI exert LA activity through interference with FV activation, to which oscutarin C and ecarin would be insensitive, whereas prothrombin-directed antibodies compete for phospholipid-binding sites, 62 and other recent studies report that LA activity in high-risk patients is largely attributable to prothrombin-directed antibodies. 63,64 This high sensitivity of TSVT/ET for the clinically significant LA in triple-positive patients provides a vehicle for LA detection in patients already anticoagulated with VKAs or DFXaIs at a diagnostic juncture where antibody profiling is clinically and prognostically valuable. 2,65 Although TSVT/ET did not detect all LA from triplepositive patients, not all were positive in both dRVVT and APTT, which we have reported previously.…”

Platelet- and endothelial-derived microparticles in the context of different antiphospholipid antibody profiles

“…The approximate cut-off values for the immunological tests were calculated by means of the 99°p ercentile of results obtained in 40 healthy subjects: 10 U/ mL, 13 and 14 Chemiluminescence Units (CU) for IgG aCL, IgG aβ2GPI and IgG aβ2GPI-Domain1, respectively. 16 Cut-off value used for IgG antiphosphatidyl-serine/ prothrombin (aPS/PT) antibodies was 30 U/mL. Data were confirmed after 12 weeks and the first determination was used for data analysis.…”

Recommendations for the measurement of thrombin generation: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

“…Used in the context of antiphospholipid antibody testing, TG can be applied beyond this field, as a suitable assay to investigate hypo-or hypercoagulability. [32][33][34]…”

“…Our main aim is to reach a reduced interlaboratory variation by following this guidance protocol, which will be helpful to further integrate TG assay for patient management. Used in the context of antiphospholipid antibody testing, TG can be applied beyond this field, as a suitable assay to investigate hypo‐ or hypercoagulability 32‐34 …”