Background: Anaphylaxis, the most severe and potentially life-threatening form of immediate hypersensitivity reaction, involves mainly a classical pathway mediated by antigen-specific immunoglobulins (IgE) and their high-affinity Fc receptor (FcERI) present on mast cells and basophils. It has been suggested that platelets contribute to IgE-mediated anaphylaxis, particularly the most severe reactions, but the mechanism of their activation is not clearly established.

Aims: We assessed the effective presence and functionality of the FcERI receptor on human platelets.

Methods: The presence of FcERI on human platelets from healthy donors was evaluated by flow cytometry and Western blotting using two mouse monoclonal antibodies (mAbs) (CRA-1 and 9E1) against the human FcERI alpha-chain. The functionality of FcERI was investigated on platelets from healthy donors and allergic patients.

Results: FcERI was undetectable on platelets from healthy donors by Western blot and flow cytometry analyses using the mAbs CRA-1 and 9E1, while these antibodies detected FcERI on human basophils. Incubation of washed platelets from healthy donors with anti-TNP (trinitro-phenyl) IgE for 1 h, followed by washing and challenge with TNP-BSA did not induce platelet aggregation. In addition, exposure of citrated whole blood from allergic patients to their specific allergen or to an anti-human IgE mAb (G7-18), a specific FcERI activator, did not induce P-selectin exposure or activation of integrin alphaIIbbeta3 (PAC-1) on platelets, whereas activation of basophils was evidenced by their significant increase in surface CD63 exposure. Finally, stimulation of citrated platelet-rich plasma from allergic patients with their specific allergen or with the mAb G7-18 did not result in platelet aggregation.

Conclusion(s): Human platelets do not have a functional FcERI receptor on their surface. These results do not however exclude a contribution of platelets to IgE-mediated anaphylaxis, which could be indirect, potentially involving other effectors.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/human-platelets-do-not-express-a-functional-fceri-receptor-on-their-surface/