PB1374 - Anti-αIIbβ3 antibodies in Glanzmann thrombasthenia patients may generate procoagulant platelets by complement activation

Tuesday, June 27, 2023

18:30 – 19:30 ET

Room: Exhibition

Presenting Author(s)

Christine S M Lee, PhD

Postdoctoral Research Fellow
ANZAC Research Institute, University of Sydney
Sydney, New South Wales, Australia

Co-Author(s)

YH

Yoann Huguenin

Consultant Haematologist
Competence Centre for Inherited Bleeding Disorders, University Hospital of Bordeaux
Bordeaux, Aquitaine, France
XP

Xavier Pillois

Researcher
French Reference Centre for Inherited Platelet Disorders; University Hospital of Bordeaux
Bordeaux, Aquitaine, France
MM

Mikeldi Moulieras

Researcher
French Reference Centre for Inherited Platelet Disorders; University Hospital of Bordeaux
Bordeaux, Aquitaine, France
EM

Ella Marcy

Researcher
French Reference Centre for Inherited Platelet Disorders; University Hospital of Bordeaux
Bordeaux, Aquitaine, France
SW

Shane Whittaker

Research Assistant
ANZAC Research Institute, University of Sydney
Sydney, New South Wales, Australia
Vivien M. Chen, MBBS PhD FRACP FRCPAA (she/her/hers)

Group Leader, Staff Specialist Haematologist
ANZAC Research Institute, University of Sydney
Sydney, New South Wales, Australia
MF

Mathieu Fiore

Haematologist
French Reference Centre for Inherited Platelet Disorders; University Hospital of Bordeaux
Bordeaux, Aquitaine, France

Background: Glanzmann thrombasthenia (GT) is a rare bleeding disorder caused by inherited defects of the platelet αIIbβ3 integrin. Platelet transfusions can trigger an immune response that blocks integrin function by interfering with fibrinogen binding.

Aims: We aim to determine the prevalence of such isoantibodies and better characterize their pathogenic properties.

Methods: Twelve GT patients were evaluated for anti-αIIbβ3 isoantibodies. Sera or total immunoglobulin G (IgG) from GT patients with or without anti-αIIbβ3 isoantibodies were then used to study their in vitro effect on healthy donor platelets. Immunofluorescence staining, flow cytometry and microchip flow chamber techniques were used to characterize the pathogenic properties of the anti-αIIbβ3 isoantibodies. One-way ANOVA with multiple comparisons test was used to assess differences.

Results: Two of twelve GT sera (patients GT3 (July sample) and GT12) were able to completely block αIIbβ3 integrin function in donor platelets (Figure 1). We observed that these two sera caused a reduction in donor platelet size similar to that observed when platelets become procoagulant. When mixed with patients’ sera or purified IgG, microvesicle formation, phosphatidylserine exposure, calcium influx and procoagulant platelet formation (Figure 2) were observed in healthy donor platelets. We also observed enhanced C5b-9 complement deposition at the platelet surface resulting in the formation of membrane attack complex (MAC). This process was inhibited by the complement C5 inhibitor eculizumab or reduced by polyvalent human immunoglobulins.

Conclusion(s): These results suggest that complement activation induced by rare blocking anti-αIIbβ3 isoantibodies may lead to the formation of a MAC with subsequent pore formation, resulting in calcium influx and procoagulant phenotype.