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Leukocytes in RBC preparations have a variety of immunologic effects in transfused patients. Not only their elimination at time of transfusion but before storage seems to be advantageous. Filtration with the Leukotrap system at the day of preparation led to an overall reduction of leukocytes of 82.2%, i.e. an average of 5.4 x 10(8) leukocytes/RBC concentrate. Filtration with a Sepacell R 500 A eliminated 99.0% of leukocytes, 3.4 x 10(7) cells remained per blood unit. The determination of lymphocyte subpopulations by flow cytometry after filtration with the Leukotrap system showed a more effective adsorption of B cells than of T and natural killer cells.

Immunocompetent cells have been shown to be effective in immunosuppression after blood transfusion. The analysis of leukocytes by electronic cell counter and of lymphocyte subsets by flow cytometry in stored whole blood revealed a decay of granulocytes within the first day of storage. T-lymphocyte subpopulations and natural killer cells continuously decrease over the time of storage, whereas B lymphocytes are very stable during the first 2 weeks. After 4 weeks lymphocyte subsets had decreased by the following values: total lymphocytes 46.0%, CD3+ 78.3%, CD4+ 80.1%, CD8+ 81.3%, CD19+ 65.9%, CD16/56+ 74.8% and CD3/DR+ 89.5%. Therefore leukocyte removal should be achieved as soon as possible after collection.