Antibody-mediated platelet-desialylation: a potential role in platelet destruction in autoimmune thrombocytopenia

R. Jouni1, J. Alex2, I. Marini2, L. Janzen2, A. Greinacher2, T. Bakchoul1 (1Tuebingen, Germany, 2Greifswald, Germany)

Date: 18.02.2017,
Time: 10:00 - 11:15

Objective: Immune thrombocytopenia (ITP) is a bleeding disorder caused by autoantibodies (AAbs) directed against platelet (PLT) glycoproteins (GP). Recently, Fc-independent PLT clearance via Ashwell-Morell receptors (AMRs) has been suggested as a novel mechanism of antibody-mediated PLT destruction in mice. In this study we analyzed the impact of AAbs from ITP patients on the glycan pattern of human PLTs and the subsequent effect on their survival in vivo.

Methods: Sera from ITP patients and healthy donors were analyzed using monoclonal platelet antigen capture assay (MAIPA) and lectin binding assay (LBA). In LBA, sera were incubated with PLTs from healthy donors, and the change in glycan pattern was analyzed by flow cytometry using lectins; Ricinus communis agglutinin (RCA), Erythrina cristagalli lectin (ECL) and Peanut agglutinin (PNA) that bind to galactose, N-acetyllactosamine and N-acetylgalactosamine residues, respectively. The impact of different glycan patterns on the survival of human PLTs was investigated using the NOD/SCID mouse model.

Results: 37 sera from ITP patients and 25 sera from healthy donors were investigated in this study. Different patterns of glycan modification were observed after incubation with AAbs in the LBA. 17/37 sera induced a significant increase in PNA binding compared to heathy donors: (median fold increase (FI): 1.21, range: 1.08 – 1.40). 9/37 sera caused higher ECL binding (median FI: 1.02, range: 1.08 – 1.15). In contrast, 8/37 sera showed strong decrease in RCA binding (median FI: 0.52, range: 0.50 – 0.59). Interestingly, not only GP-Ib/IX AAbs but also GPIIb/IIIa AAbs were able to modify glycan pattern. No significant change was induced by sera from healthy donors. The injection of AAbs resulted in accelerated clearance of human PLTs from the circulation of the NOD/SCID mice. The destruction of human PLTs by ITP-AAbs was reduced but not completely inhibited by a specific neuraminidase inhibitor that prevents glycan changes on PLT surface (survival of human PLTs after 5h: 29%, range 22-40% vs. 48%, range 41-53%, p=0.014, respectively).

Conclusion: Our data demonstrate that AAbs from ITP patients are able to induce cleavage of glycan moieties on the PLT surface in distinct ways. Although, AAb-mediated glycan-modification eems to contribute to PLT destruction in ITP, the impact of GP-specificity needs further investigations.