PB0664 - The effects of complement-independent, autoantibody-induced apoptosis of platelets in immune thrombocytopenia

Background: Immune thrombocytopenia (ITP) is characterized by increased platelet clearance. It is commonly believed that autoantibodies cause platelet apoptosis play a role in the development of ITP, specifically targeting GPIIbIIIa and GPIbα. Recent research has shown the destruction of platelets in ITP caused by antibodies may involve a complement independent mechanism.

Aims: To compare the impact of antigen specificity of antiplatelet antibodies on normal platelets under the complement independent conditions.

Methods: We detected the levels of autoantibodies against specific platelet membrane glycoproteins in the plasma of 38 ITP patients with modified MAIPA. Protein A agarose affinity chromatography columns were used to isolate and purify IgG. Flow cytometry was used to analyze markers of apoptosis, including phosphatidylserine (PS) exposure, mitochondrial inner membrane potential (ΔΨm), and formation of platelet-derived microparticles.

Results: Our results showed that plasma-purified IgG from patients with positive GPIb/IX antibodies significantly promoted normal platelet apoptosis , in patients with positive GPIIb/IIIa antibodies, their plasma-purified IgG did not significantly impact platelet apoptosis. These results were further confirmed by detecting PS exposure on the platelet surface. It was observed that plasma-purified IgG from patients with positive GPIb/IX antibodies promoted the formation of platelet microparticles. However, this effect was not found in GPIIb/IIIa antibody positive patients.We incubated purified IgG from GPIb/IX antibody-positive plasma from patients and healthy controls plasma with normal platelets, found the formation of platelet particles is not caused by platelet activation, which further indicating that the formation of PMPs is a cellular-level indicator of anti-GPIb/IX antibody action on platelets and subsequent platelet apoptosis.

Conclusion(s): Our results indicate that ITP patients with GPIb/IX-specific autoantibodies can induce platelet apoptosis through complement-independent pathways, while GPIIb/IIIa-specific autoantibodies do not have this effect. Patients with anti-GPIb/IX antibodies promote the formation of platelet microparticles without affecting platelet activation.