To evaluate the relevance of HL-A-specific antibodies in nonhemolytic transfusion reactions, sera from 72 patients with transfusion reactions were examined using platelet microcomplement fixation and microlymphocytotoxicity. Lymphocytotoxic antibodies were found in 24 and platelet complement-fixing antibodies in 18 patients. Thirteen positive sera were studied by absorption and elution with platelets. A total of 103 eluates (mean 7.9 eluates per serum) was tested serologically for antibody specificity. Results were statistically analyzed for fksociation with known HL-A antigens.All sera investigated contained HL-A-specific antibodies. Antibody specificities determined were directed against 7 antigens (1, 2.3,9. 10, l l and W28) of the first series and 10 antigens (5, 7, 8, 12, W5, W10, W15, W17, W21 and W27) of the second series of the HL-A system. By means of antibody concentration in the eluates, all sera revealed crossreacting HL-A-specific antibodies.The clinical importance of buffy coat-free red blood cells for the prevention of transfusion reactions is stressed.Non hemolytic transfusion reactions represent about 95% of all transfusion reactions [2]. The great majority of these are febrile transfusion reactions [2,21]. It is generally accepted that the major cause of febrile transfusion reactions are leukocyte alloantibodies in the serum of the recipient, whereas the role of leukocyte antibodies in urticaria1 reactions is still a matter of discussion [21].The importance of platelet alloantibodies in nonhemolytic transfusion reactions is also controversial [21, 191. Many investigations have been carried Supported by the Deutsche Forschungsgemeinschaft (Mu 27715).* Designations: (a) whole blood, 1 unit=500 ml ACD blood (formula B USP); (b) packed red blood cells (PRBC) = b d y coat-poor sediment of red blood cells of 1 unit of whole blood; (c) washed red blood cells (WRBC) = buffy coat-poor red blood cells of 1 unit of whole blood, washed 3 times in sterile saline.

To evaluate the relevance of HL-A-specific antibodies in nonhemolytic transfusion reactions, sera from 72 patients with transfusion reactions were examined using platelet microcomplement fixation and microlymphocytotoxicity. Lymphocytotoxic antibodies were found in 24 and platelet complement-fixing antibodies in 18 patients. Thirteen positive sera were studied by absorption and elution with platelets. A total of 103 eluates (mean 7.9 eluates per serum) was tested serologically for antibody specificity. Results were statistically analyzed for x^2-association with known HL-A antigens. All sera investigated contained HL-A-specific antibodies. Antibody specificities determined were directed against 7 antigens (1, 2, 3, 9,10,11 and W28) of the first series and 10 antigens (5, 7, 8, 12, W5, W10, W15, W17, W21 and W27) of the second series of the HL-A system. By means of antibody concentration in the eluates, all sera revealed crossreacting HL-A-specific antibodies. The clinical importance of buffy coat-free red blood cells for the prevention of transfusion reactions is stressed.