PB0036 - Increased complement activation markers in antiphospholipid syndrome-related ischemic stroke correlate with platelet hyperreactivity

Sunday, June 23, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Presenting Author(s)

IT

Ibrahim Tohidi-Esfahani

Consultant haematologist
Haematology Department, Concord Repatriation General Hospital, Sydney, Australia
Pennant Hills, New South Wales, Australia

Co-Author(s)

VV

Veronica Venturelli

Clinical Fellow
Department of Haematology, Cancer Institute, University College London
London, England, United Kingdom
YX

Yiran Xing

Student
Department of Haematology, Cancer Institute, University College London
London, England, United Kingdom
EG

Eleni Gavriilaki

Dr
2nd Propaedeutic Department of Internal Medicine, Hippokration General Hospital, Aristotle University of Thessaloniki, Thessaloniki, Greece
Thessaloniki, Thessaloniki, Greece
XK

Xi Kang

Student
Department of Haematology, Cancer Institute, University College London
London, England, United Kingdom
DI

David Isenberg

Professor
Centre for Rheumatology, Division of Medicine, University College London, London, UK
London, England, United Kingdom
Hannah Cohen, MD

University College London Hospitals, United Kingdom
London, England, United Kingdom
ME

Maria Efthymiou

Senior Research Fellow
Department of Haematology, University College London
London, England, United Kingdom

Background: Antiphospholipid syndrome (APS)-related ischemic stroke has high rates of recurrent thrombosis despite standard-of-care treatment. The precise role of complement activation has not been fully evaluated.

Aims: To determine prevalence of complement activation in APS-related ischemic stroke patients and possible relationships with platelet hyperreactivity.

Methods: The following patients were recruited: patients with confirmed APS by Sydney Criteria and imaging-proven brain ischemia (n=71), patients with ischemic stroke without antiphospholipid antibodies (n=40) and healthy donors (n=40). Complement activation markers (C3a-desArg (C3a), C5a-desArg (C5a), sC5b-9 and Bb fragment) were measured using commercial ELISAs. Complement-mediated cell killing was measured by the modified Ham (mHam) test: patient serum added to PIGA-null TF-1 cells (paroxysmal nocturnal hemoglobinuria cell line) lacking cell surface complement regulators. Plasma was added to healthy donor whole blood and procoagulant platelet (annexin-V+/P-selectin+) response was measured (flow cytometry) as the absolute change in proportion of platelets following stimulation (thrombin 2U/mL) compared to autologous plasma.

Results: Complement activation markers other than C5a, and mHam results were increased in APS patients compared to ischemic stroke and healthy controls, most significantly with C3a (Figure 1). Following thrombin stimulation, samples from APS patients (n=14) induced a significantly higher procoagulant platelet response in healthy donor whole blood: median 24.2% (interquartile range, IQR, 7.6-38.5%), compared to healthy control cohort plasma (n=6): median 0% (IQR -6.8-5%, p=0.002) (Figure 2A). Spearman’s correlation identified only activation markers C3a and sC5b-9 as significantly (positively) correlated with the degree of platelet reactivity; r=0.64 (p=0.002) and r=0.55 (p=0.02), respectively (Figure 2B-E). Correlation with complement-mediated cell killing by the mHam assay also trended to significance, r=0.44 (p=0.0503, Figure 2F).

Conclusion(s): Preliminary results suggest that increased complement activation, particularly C3a, is present in APS-related ischemic stroke, and appears to correlate with platelet hyperreactivity. The role of complement-mediated platelet hyperreactivity in thrombotic recurrence remains to be established.