A role for glycoprotein IIb‐IIIa complex in the binding of IgE to human platelets and platelet IgE‐dependent cytotoxic functions

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Abstract
Summary. A possible relationship between binding sites for Immunoglobulin E (IgE) on human platelets, involved in IgE‐dependent cytotoxic functions of platelets against helminth parasites, and well‐characterized platelet constituents involved in haemostasis, was investigated. We first explored the interaction with IgE of platelets from patients with rare inherited deficiencies of defined platelet constituents and functions: Glanzmann's thrombasthenia, Bernard‐Soulier and grey platelet syndromes. We report that only type I and II thrombasthenic platelets, which lack the membrane glycoproteins (GP) lIb and IIIa, failed to bind IgE and to exhibit IgE‐dependent effector functions. Since thrombasthenic monocytes, however, showed normal interaction with IgE, this defect appeared restricted to platelets. Polyclonal and monoclonal antibodies directed against GP Ilb‐IIIa complex, but not monoclonal antibody directed against GP Ib, inhibited the binding of IgE to normal platelets, and their IgE‐dependent cytotoxicity. Taken together, these findings indicate a relation between the GP Ilb‐IIIa complex and the expression of IgE binding sites and IgE‐dependent effector functions in human platelets.