PB0342 - Platelet phosphatidylserine is the critical mediator of thrombosis in heparin-induced thrombocytopenia

Sunday, June 25, 2023

18:30 – 19:30 ET

Room: Exhibition

Presenting Author(s)

Jan Zlamal, MD

Resident/PhD Student
Institute for clinical and experimental transfusion medicine Tübingen
Tübingen, Baden-Wurttemberg, Germany

Co-Author(s)

AS

Anurag Singh

Post Doc
Institute for clinical and experimental transfusion medicine Tübingen
Tübingen, Baden-Wurttemberg, Germany
KW

Karoline Weich

TA
Institute for clinical and experimental transfusion medicine Tübingen
Tuebingen, Baden-Wurttemberg, Germany
Günalp Uzun, MD (he/him/his)

Physician
Center for Clinical Transfusion Medicine, University Hospital of Tübingen
Tübingen, Baden-Wurttemberg, Germany
HJ

Hisham Jaffal

Student
Institute for clinical and experimental transfusion medicine Tübingen
Tuebingen, Baden-Wurttemberg, Germany
Karina Althaus, MD

Physician, Director of Platelet Immunology Lab.
Center for Clinical Transfusion Medicine, University Hospital of Tübingen
Tübingen, Baden-Wurttemberg, Germany
Tamam Bakchoul, MD (he/him/his)

Medical Director
Center for Clinical Transfusion Medicine, University Hospital of Tübingen
Tübingen, Baden-Wurttemberg, Germany

Background: Heparin-induced thrombocytopenia (HIT) is a severe adverse event caused by anti-platelet (PLT) factor 4/heparin antibodies (Abs) that contribute to an increased prothrombotic environment. While it is well recognized that HIT Abs harbour the potential to activate PLTs via the engagement of PLT Fc-gamma-RIIA, the biological relevance of different PLT subpopulations in the complex pathophysiology of HIT remains poorly understood.

Aims: In this study, we hypothesized that HIT Abs have the potential to induce a procoagulant PLT phenotype that contributes to the prothrombotic environment in HIT.

Methods: Using flow cytometry, we analyzed whether HIT Abs have the capability to induce changes in the expression level of the PLT surface activation marker P-selectin (CD62p) and the negatively charged procoagulant phospholipid phosphatidylserine (PS). To investigate whether HIT Ab-induced procoagulant PLTs contribute to an increased thrombin generation as well as thrombus formation, calibrated automated thrombogram (CAT) analysis and an ex vivo thrombosis model were utilized, respectively.

Results: HIT patient Abs induced a procoagulant (CD62p/phosphatidylserine double positive) PLT phenotype (p < 0.0001) that shows an increased thrombin generation potential (p < 0.0001). Notably, the perfusion of whole blood samples that were spiked with HIT Ab-induced procoagulant PLTs resulted in a significant increase of multicellular thrombus deposition in a heparin- as well as in a PLT Fc-gamma-RIIA dependent manner (p=0.0313 and p=0.0313, respectively). Interestingly, HIT Ab-induced thrombus formation remained unaffected by inhibiting the interplay of procoagulant PLTs with leukocytes via the P-selectin-glycoprotein ligand-1 (PSGL-1) axis (Figure 1). In great contrast, increased thrombin and most importantly, increased HIT Ab-induced thrombus formation were significantly reduced in the presence of the PS blocking protein, namely lactadherin (Figure 2).

Conclusion(s): Based on our mechanistic studies we conclude that increased PS on the surface of HIT Ab-induced procoagulant PLTs is a crucial factor that contributes to the increased prothrombotic potential in HIT.