Scientific Research Question: Immune thrombocytopenia (ITP) is a bleeding disorder characterized by autoantibodies
(AAbs) that target glycoproteins (GPs) expressed on platelets (PLTs) surface. Desialylation
was recently identified to be a new mechanism that leads to an Fc-independent PLT
clearance through the Ashwell-Morell-Receptor (AMR) expressed on hepatocytes. In this
work, we investigated AAb-mediated glycan pattern modification on PLTs and megakaryocytes
(MKs) as well as its impact on PLT survival in vivo.
Methodology: Glycan modification of GPs induced by AAbs from ITP sera was analyzed using the lectin
binding assay (LBA). In the LBA two lectins; Ricinus communis agluttinin (RCA) and
Erythrina cristagalli lectin (ECL) that bind to galactose and N-Acetylgalactosamin
residues, respectively, were used. After incubation of MKs or PLTs with ITP or healthy
donor sera the glycan changes were detected by flow cytometry (FC). To investigate
the impact of desialylation on PLTs´ lifespan, the NOD/SCID mouse model was used.
Findings: In this study 37 sera from ITP patients were investigated. Different modifications
of glycan pattern were observed. 17/37 ITP sera induced a significant increase in
RCA binding compared with sera from healthy donors: (mean fold increase (FI): 3.69,
range: 1.69–13.61, p = 0.0001), whereas 17/37 sera caused an increased binding of ECL (mean FI: 1.94,
range: 1.56–5.47, p = 0.001). The impact of PLTs desialylation on their lifespan was analyzed in vivo
using the NOD/SCID mouse model. The injection of ITP AAbs resulted in accelerated
clearance of human PLTs from the mouse circulation. The destruction of human PLTs
by ITP AAbs was reduced but not completely blocked by a specific neuraminidase inhibitor
that prevents glycan changes on PLT surface (survival of human PLTs after 5h: 29%,
range 22–40% versus 48%, range 41–53%, p = 0.014, respectively). Furthermore, we observed that the glycan expression of mature
MKs can be modify by exogenous neuraminidase. Interestingly, ITP-AAbs were also able
to change glycan patterns on MKs surface. In particular, 7/10 sera induced a significant
increase in RCA binding (mean FI: 2.24, range: 1.15–3.66, p = 0.001) whereas 7/10 sera caused higher ECL binding (mean FI: 1.31, range: 1.10–1.69,
p = 0.01).
Conclusions: Our findings suggest that ITP AAbs are able to induce changes in glycan pattern on
PLTs as well as on MKs surface. The mechanism of AAbs mediated modifications of glycan
pattern seems to contribute to PLT destruction and impaired production in ITP patients.
