Pseudothrombocytopenia: an immunologic study on platelet antibodies dependent on ethylene diamine tetra-acetate

Antibodies specifically reacting with platelets only in the presence of EDTA, by the platelet immunofluorescence test, were found in the serum of 20 patients with pseudothrombocytopenia due to in vitro EDTA-dependent platelet agglutination. These antibodies reacted optimally at 0-4 degree C. In 19 patients, IgG antibodies were detected; in 8 patients, IgM or IgA antibodies were also found. In one patient, only IgM antibodies were found. In 14 patients, the IgG antibodies were IgG1, but IgG2, IgG3, and IgG4 antibodies were also seen in 7 patients. The reaction of platelets with the antibodies was detectable in the presence of Na2EDTA, the K, Ca, and Mg salts of EDTA, and K2EGTA. F(ab')2 or F(ab') fragments of the IgG antibodies reached as strongly as the intact antibodies, indicating that the reaction is dependent on the antibody-combining site. The EDTA-dependent antibodies did not show platelet-group specificity. However, platelets from patients with Glanzmann disease did not react with the antibodie

Elution of granulocyte and platelet antibodies

By lowering the pH of the medium, allo- and autoantibodies bound to granulocytes and platelets could be eluted from these cells and their presence in the eluate could subsequently be detected with normal donor granulocytes and platelets, respectively, in the immunofluorescence test and/or agglutination test. IgG- as well as IgM- and IgA-containing antibodies were detectable in the eluates. Depending on the attraction mechanism between antigen and antibody, some antibodies were also eluted by dimethylsulphoxide at pH 9.5, ether and/or by heating at 56 degrees C. By differential elution of antibodies from donor platelets, we demonstrated the simultaneous presence of platelet-specific antibodies and HLA antibodies in the serum of a mother whose newborn suffered from transient neonatal thrombocytopeni