Platelet Fc Receptor as a Mechanism for Ag-Ab Complex-induced Platelet Injury

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Abstract
Antigen-antibody complexes immunologically unrelated to platelet antigens may produce thrombocytopenia in vivo and platelet aggregation and release in vitro. An in vitro platelet system (rabbit and human) was used to study the platelet receptor that mediates the attachment of the immune complex. Platelet aggregation induced by 7 S immune complexes or aggregated gammaglobulin was blocked by prior exposure of the platelet to isolated antibody Fc. Fab from the same antibody was not inhibitory. 5S complexes lacking the Fc piece did not produce aggregation. Serum, as a source of complement was included in the rabbit platelet test system. However, the role of complement is thought to be secondary as it did not bind to platelets in the absence of 7 S complexes and was fixed only secondarily to 7 S binding. On the basis of these studies it is suggested that the platelet membrane contains an Fc receptor and that the primary fixing of immune complexes to the platelet is through the antibody Fc rather than by complement mediated non-specific immune adherence. Antibody Fc fixation to the Fc receptor site of the platelet is probably the common pathway for platelet injury induced by a number of antigen-antibody complexes immunologically unrelated to the platelet.

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