Leukocyte filtration mechanisms. Factors influencing the removal of infectious agents from red cell concentrates

The purpose of the present overview was to determine the factors influencing the removal of infectious agents from red cell concentrates by filtration. In general, the efficacy of the filtration method depends on the physical as well as the functional properties of blood cells. These properties are highly influenced by the changes exerted on the blood cells during blood collection, processing and storage and the filtration method itself. In particular, the removal of infectious agents of red cell concentrates by filtration will be determined by the type of virus and therewith the binding towards leukocytes, the type of bacteria and holding period before filtration, the deformability of infected cells and the disintegration of cells in the filte

Asymmetric membrane filters for the removal of leukocytes from blood

As part of a study on the mechanisms of leukocyte filtration, the influence of pore size distribution on filter efficiency was investigated. Conventional leukocyte filters are not suitable for model studies, as these filters are composed of tightly packed synthetic fibers, with a poorly defined porous structure. Therefore, open cellular polyurethane membranes with pore size distributions varying from approximately 15 to 65 m were prepared. Filtration experiments with stacked packages of these membranes showed that leukocytes are best removed (>99%) by filters with a pore size distribution of 11-19 m. These pore sizes approach the size of leukocytes (6-12 m). However, due to fast clogging, blood flow through these filters is rapidly reduced, which results in a low filter capacity. With an asymmetric membrane filter, in which the pore size decreases from about 65 to 15 m in the direction of blood flow, both moderate removal of leukocytes (>80%) and maintenance of flow (0.2 mL/s) are obtained. This results in efficient leukocyte removal. From cell analysis of both filtrate and filter, it is concluded that adhesion rather than sieving is the major filtration mechanism. Thus, further optimization of the filter may be achieved by surface modification

Comparison of five different filters for the removal of leukocytes from red cell concentrates

The leukocyte depletion capacity and performance of 5 filters designed for filtration of red cell concentrates (RCC) were compared by counting leukocytes, measuring red cell volumes and by histological examination of the filters after use. To eliminate interdonor differences, 5 buffy-coat-poor RCC were pooled (in each of 10 experiments) and subsequently split up into the original bags. The RCC were passed over the Cellselect filter, a column filled with cellulose acetate, and over flat-bed polyester filters: the Cellselect Optima, the Pall RC 50, the Leukostop and the Sepacell R-500. The filtration was shortest with the Pall RC 50 (p less than 0.001 compared to the other 4 filters). Leukocyte removal was most effective with the cellulose acetate filter (p less than 0.01 compared to the other 4 filters) followed by the Cellselect Optima polyester filter (p less than 0.02 compared to the remaining 3 filters). Residual leukocytes did not exceed 50 x 10(6) for any brand of filter. Red cell recovery was similar for all 5 filters with mean values from 86.1 to 89.2%. The leukocyte numbers, counted in Türk's solution or in propidium iodide, gave comparable values in hemocytometers applying light microscopy or fluorescent microscopy, respectively. Histological examination showed that lymphocytes were mainly removed by trapping, whereas granulocytes showed a variable pattern: adhesion in presence of platelets or trappin

Effect of filtration on subsequently stored platelet concentrates

The effect of filtration on the quality of platelet concentrates (PC) during storage was investigated. Two leukocyte depletion filters (Pall PL50HF and Sepacell PL-10A) were applied to filter PC made from a pool of 4 buffy coats. For each experiment 3 PC were pooled and divided into 3 identical PC to eliminate differences between the PC. Two PC were filtered, and the third PC served as an unfiltered control. A total of 12 experiments was performed. Before filtration, volumes of the PC were 263 +/- 11.7 ml (mean +/- SD). Platelet and leukocyte counts per PC were 241 +/- 25.9 x 10(9) and 7.2 +/- 1.8 x 10(6), respectively. After filtration leukocyte counts did not exceed 5 x 10(4) in any of the PC. In the PC filtered with the Pall PL50HF the mean platelet loss was approximately 14% and with the Sepacell PL-10A, 17%. During a 9-day storage period the pH, PO2, PCO2, bicarbonate, lactate and glucose concentration and LDH release as well as the morphology, examined by the swirling effect and microscopically, were not significantly different in filtered and unfiltered units. Filtration through the 2 investigated leukocyte depletion filters for PC did not adversely affect in vitro viability of the platelets during storag

In vitro evaluation of platelet concentrates, prepared from pooled buffy coats, stored for 8 days after filtration

BACKGROUND: Posttransfusion complications can be prevented by pretransfusion removal of donor white cells from platelet concentrate. The filtration used for this removal seems to have little effect on platelet function and activation, but more information is needed on its effect on function during subsequent long-term storage of concentrate. STUDY DESIGN AND METHODS: The effect of prestorage filtration of buffy coat-prepared platelet concentrates (PCs) on platelet function, metabolism, and activation was investigated. A pool of three PCs, each made of four buffy coats, was split into three equal volumes; two were filtered over two different filters and the third served as a control. Variables monitored immediately after filtration and during the subsequent 8-day storage period at 22 degrees C included aggregation upon stimulation with collagen and/or ADP, platelet adhesion capacity to collagen and fibrinogen in flowing blood, nucleotide content of and nucleobase release by the platelets, expression of activation-dependent antigens, and beta-thromboglobulin release by the platelets. RESULTS: No differences were observed between the PCs filtered over two different filters and the nonfiltered control PCs immediately after filtration and during storage, except for a selective removal (20%) of beta-thromboglobulin by one filter. CONCLUSION: PCs prepared from a pool of four buffy coats can be filtered and subsequently stored for 8 days (starting +/- 24 hours after whole blood collection) without detriment to platelet function, metabolism, or activatio

Preparation of leukodepleted platelet concentrates from pooled buffy coats: prestorage filtration with Autostop BC

BACKGROUND AND OBJECTIVES: Our requirements for leukocyte-depleted platelet concentrates (LD-PC) for an adult patient are: platelets >240x10(9), leukocytes <5x10(6), volume of 150-400 ml; and at the end of storage a pH between 6.8 and 7.4 and presence of the swirling effect. Our aim was to develop a standardized, semiautomated method for the production of LD-PC, by pooling of buffy coats (BC), and prestorage leukoreduction by filtration. MATERIALS AND METHODS: Whole blood was collected in Top and Bottom systems, and separated automatically with the Compomattrade mark G3 equipment into a red cell concentrate, a plasma and a BC. Subsequently, a pool of 5 BC was made, and 200 g plasma from one of the donors was added. Then, after soft spin centrifugation, the platelet rich plasma was leukocyte depleted by filtration using the Autostoptrade markBC filter, and stored in a 1,000 ml polyolefin platelet storage bag. RESULTS: BC (n = 60) had a volume of 51+/-2 ml (mean +/- SD) with a hematocrit of 0.44+/-0.03 l/l and contained 80+/-5% of the platelets and 74+/-12% of the leukocytes of the whole blood. Routinely prepared LD-PC (n = 15,037) contained a median of 341x10(9) platelets (range 49-599x10(9)), with only 104/15,037 (0.7%) containing fewer than 240x10(9) platelets; the median volume was 263 ml (range 134-373 ml). In 118/917 (13%) LD-PC leukocytes were observed in the Nageotte hemocytometer, but only twice exceeding 1x10(6) leukocytes per unit, and none exceeding 5x10(6) (median <0. 6x10(6); range <0.6-1.41x10(6)). Storage experiments of the LD-PC (n = 12) revealed adequate oxygenation and maintenance of pH and swirling effect up to 9 days. CONCLUSIONS: This method warrants with 99% confidence that LD-PC contain more than 240x10(9) platelets; with 97.5% confidence that 100% of the LD-PC contain <5x10(6) leukocytes, and with 95% confidence that more than 99% of the LD-PC contain fewer than 1x10(6) leukocytes; these LD-PC can be stored satisfactorily for up to 9 day