EFFECT OF HETEROLOGOUS ANTIBODY ON HUMAN PLATELETS

Abstract

The effect of heterologous anti-human platelet antibody on human platelet function was examined in the presence and absence of whole plasma as an in vitro model for antibody-induced immune damage to cells. Heterologous IgG [immunoglobulin G] anti-human platelet antibody mediated platelet aggregation and released serotonin from platelets in plasma and from platelets isolated by gel filtration. The anti-platelet antibody increased the availability of platelet acid phosphatase in a dose-response fashion. Anti-platelet antibody failed to release .beta.-glucuronidase (lysosomal enzyme marker) or cause lactic dehydrogenase loss (cytolysis). The effect of the antiplatelet antibody on platelets proceeded in the absence of complement. The active molecule in the anti-platelet antiserum was isolated in the IgG fraction, and all 3 indicators of platelet injury were mediated by purified monomeric IgG. Thrombin was not required for the antibody-mediated effects, as 3 thrombin inhibitors failed to block the reaction. EDTA was an effective inhibitor, suggesting a cation requirement, as little as 38 .mu.M Ca was sufficient for effective platelet aggregation and release. The inability of acetylsalicylic acid to inhibit the effect of the antiplatelet antibody suggests that heterologous antibody (IgG) induced platelet alteration proceeds by a different mechanism than that mediated by ADP and epinephrine, and does not involve endogenous platelet prostaglandin synthesis.