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Summary. The purpose of this study was to determine whether quantitative or qualitative factors are of major importance in the destruction of red cells sensitized with incomplete warm autoantibodies of subclass IgG1. To that end, the relative amount of IgG1 antibody present on the red cells of patients with autoantibodies of this subclass only, was measured by means of continuous flow cytofluorometry. This method appeared to give an idea of the amount of antibody on red cells and was reproducible. The intensity of the fluorescence of patient's red cells, measured after incubation with a FITC-labelled anti-IgG1, was compared with the presence or absence of signs of increased haemolysis in vivo and the cytotoxic activity of normal monocytes towards these red cells in vitro. It appeared that it was predominantly the amount of IgGl autoantibody that determined whether or not these antibodies induced haemolysis in vivo or cytotoxicity of monocytec in vitro. This was also true with methyldopa-induced IgG1 autoantibodies.

Summary. By applying the platelet suspension immunofluorescence test (PSIFT), platelet-specific alloantibodies responsible for post-transfusion purpura were detected in eight patients within a period of 2 years. All patients were female and had previously received blood or had been pregnant. The platelet-specific alloantibodies had the specificity anti-Zwa in all the patients, who were all Zw(a -). In two patients the platelets were tested in the acute phase of the disease and found to be coated with IgG. In one patient an ether eluate was prepared from the platelets that reacted strongly with Zw(a +) platelets, but weakly with platelets from Zwb-homozygous individuals. The sera of these two patients, and of two others whose platelets were not directly tested, taken in the acute phase of the purpura, reacted strongly with Zwa-positive platelets. The four sera also reacted, however weakly, with Zwa-negative platelets, with autologous platelets taken during remission and with platelets from patients with Glanzmann's disease. It is postulated that Zwa-anti-Zwa complexes, present in the eluate and the sera, caused the reaction with Zwa-negative platelets and the patients’own platelets. Immunochemical characterization of the post-transfusion purpura antibodies showed that in all patients these were IgG, in two combined with IgM antibodies. Antibodies of the sub-class IgG1 were found in all patients, sometimes together with IgG3. In the indirect immunofluorescence test with anti-complement serum, the PTP antibodies in only four sera were able to fix complement. In only two of these sera were these complement-binding antibodies detectable in the 51Cr-lysis technique and then in a much lower titre than in the immunofluorescence technique.

Summary. A serological follow-up study was undertaken in 47 patients with bone-marrow failure, who were repeatedly transfused with random donor granulocytes and/or platelets. Sera, obtained at regular intervals, were investigated in the leucoagglutination test, the lymphocytotoxic test and the immunofluorescence test on paraformaldehyde-fixed platelets, granulocytes and lymphocytes. The frequency of alloimmunization was high (73%). Not only HLA antibodies, but also blood-cell-specific alloantibodies were detected in the sera of the alloimmunized patients, e.g. lymphocyte-specific, platelet-specific and granulocyte-specific antibodies. The immunofluorescence test on platelets was also used as a crossmatch, and when this test was positive it was always found that after platelet transfusion the increment value was nil.