Removal Of White Cells Research Articles

Evaluation of performance of white blood cell reduction filters: An original flow cytometric method for detection and quantification of cell-derived membrane fragments

Contamination of blood products by white blood cells leads to a risk of transmission of infectious agents, particularly abnormal prion protein, the probable causative agent of new-variant Creutzfeldt-Jakob disease. Blood product filtration could reduce this risk, but the filtration systems might generate potentially infectious membrane fragments. We developed an original flow cytometric method that allows the detection and quantification of membrane fragments in filtered products and the evaluation of the quantity of destroyed cells.This method has four technical requirements: cytofluorometric acquisition of forward scatter parameters on a log scale, use of a fluorescent aliphatic reporter molecule (PKH26-GL) to identify membrane fragments, quantification with fluorescent beads, and the drawing up of a standard curve on the basis of cells destroyed by freezing/thawing to generate cell debris (i.e., quantity of membrane fragments measured versus quantity of destroyed cells).This original method can be used to test new filtration devices and it allows optimization of the filtration process or comparison of different filtration systems. We tested the method with three commercial white cell removal filters. We demonstrated that it is possible to evaluate the filter quality, particularly the likelihood of fragment removal during the filtration process.

Prevention of Infections Transmissible by Blood Derivatives

Agents that are transmissible by blood or its derivatives typically have long incubation periods, may often be asymptomatic for several years and can set up carrier or latent persistent infections. Examples are hepatitis B virus (HBV), hepatitis C virus (HCV), the human immunodeficiency viruses (HIV 1 and 2) and cytomegalovirus. The prevention of transfusion-transmitted infection (TTI) is based on the exclusion of potential blood donors who are not fit and well, the education of donors to exclude themselves if they are at risk of contracting TTIs, the laboratory screening of all blood donations for evidence of infection with a range of potential TTIs, physical removal of white cells in those cases where the agent is cell associated, viral inactivation procedures for pooled plasma derivatives, detection of viral genomes in plasma pools and the avoidance of unnecessary transfusions.

Factors influencing white cell removal from red cell concentrates by filtration.

The preparation of blood components by hard centrifugation results in red cell concentrates with a small amount of plasma. The influence of various plasma factors, temperature, and storage time on white cell reduction by filtration was studied. Red cell concentrates were suspended in 100 mL of saline-adenine-glucose-mannitol (SAGMAN) solution or in SAGMAN solution in which 5 or 10 mL had been replaced with an equal amount of fresh plasma, albumin (4%), or heat-inactivated plasma. After overnight storage at 4 degrees C, filtration at a slow flow rate (2 hours) was performed. The effect of temperature was studied by filtration at 4 degrees C and 37 degrees C. To study the influence of storage time, red cell concentrates were stored for 4 to 8 hours or 14 to 20 hours at 4 degrees C and filtered through another model of filter. The number of white cells was counted microscopically or by flow cytometry. When 5 or 10 mL of plasma was added, a significantly smaller number of white cells were found after filtration than were found in the SAGMAN control (the median difference between pairs: 23.6 x 10(6) for 5 mL [p = 0.006] and 14.9 x 10(6) for 10 mL [p = 0.003]). The number of white cells was significantly higher with 10 mL of albumin than with 10 mL of plasma (difference, 15.0 x 10(6); p = 0.006). When heat-inactivated plasma was used, the number of white cells was significantly lower than when fresh plasma was used (difference, 0.3 x 10(6); p = 0.009). Filtration at 37 degrees C resulted in a 64-percent reduction in white cells and that at 4 degrees C led to a 99.7-percent reduction (p = 0.006). When the second filter was used, a slight but significantly lower number of white cells was found in the red cell concentrate stored for 14 to 20 hours than in that stored for 4 to 8 hours (difference, 0.03 x 10(6); p < 0.001). The amount of plasma in the red cell concentrate and the storage time and temperature are important factors in the outcome of white cell reduction by filtration. The effect of plasma does not seem to be due to a general influence of protein or to the activity of complement or fibrinogen.

Prevention of transfusion-associated Chagas' disease: efficacy of white cell-reduction filters in removing Trypanosoma cruzi from infected blood.

Transfusion-associated Chagas' disease (TA-CD) is a worldwide problem. Measures adopted to prevent TA-CD include the clinical and serologic screening of blood donors and/or the inactivation of Trypanosoma cruzi present in collected blood, using gentian violet as the trypanocidal agent. This study investigated the efficacy of white cell-reduction filters in removing T. cruzi from infected blood. Human blood was contaminated with 2 or 150 T. cruzi parasites per mL and then left unfiltered or filtered with white cell-reduction filters that provided either 2, 3, or 6 log10 white cell removal. The efficacy of the parasite removal of these filters was evaluated by microscopic enumeration of active forms of T. cruzi both in vivo and in vitro. The in vivo experiments were done in Swiss mice that had been intraperitoneally inoculated with T. cruzi-infected human blood. The in vitro experiments were performed with fresh human blood that had been deliberately contaminated with T. cruzi. The number of parasites seen in mice inoculated with unfiltered blood containing 2 or 150 parasites per mL was significantly higher than the number of parasites seen in mice inoculated with blood from the same sample, but filtered with white cell-reduction filters providing 3 or 6 log10 white cell removal. Fifty to 70 percent of the mice given T. cruzi-infected (2 parasites/mL) filtered blood did not develop T. cruzi infection. In vitro, the use of white cell-reduction filters, providing 2, 3, or 6 log10 white cell removal, significantly reduced the number of parasites seen in culture. The present experimental data provide evidence that white cell-reduction filters are effective in reducing the number of parasites in T. cruzi-infected blood and that this efficacy depends, in part, on the concentration of parasites in the artificially infected blood. Properly designed clinical studies of known carriers of T. cruzi must be conducted to determine whether the use of white cell-reduction filters may be an alternative method of reducing the incidence of TA-CD.

Effects of 3‐5 log10 pre‐storage leucocyte depletion on red cell storage and metabolism

A new, in-line high-efficiency 3-5 log10 leucodepletion filter system (Leukotrap RC system) was used to investigate the effect of pre-storage white cell removal on the quality of AS-3 red cell concentrates stored for 42 d at 4 degrees C. Median residual white cell content was 4 x 10(5) when filtration was performed at 22 degrees C within 8 h of phlebotomy (n = 20) and 3.2 x 10(4) when filtration was performed at 4 degrees C 12-24 h after phlebotomy (n = 24). None exceeded 1 x 10(6) WBC per red cell product. Filtration was rapid (median 28 min), and red cell loss averaged (mean +/- 1 SD) 6.4 +/- 0.7%. In a paired study design, post-transfusion recoveries of 42 d stored red cells in the filtered units averaged 84 +/- 6% v 82 +/- 8% for unfiltered units (P < 0.05) and post-storage haemolysis. ATP, osmotic fragility, K+ and pH were significantly (P < 0.05) better in the filtered units. Reduced glycolytic activity was also observed in the filtered units, and there was a correlation between osmotic fragility, glucose consumption, and lactate produced in standard units that was not present in leucodepleted units. In conclusion, this study suggests that leucodepletion of AS-3 red cell concentrates prior to storage results in better maintenance of the integrity of the red cell membrane with reduced glycolytic activity. There was a modest improvement in post-infusion viability sufficient to offset the filtration-induced loss and to result in an equivalent red cell product.

Prevention of primary transfusion‐associated cytomegalovirus infection in bone marrow transplant recipients by the removal of white cells from blood components with high‐affinity filters

A prospective study was carried out to determine whether use of cytomegalovirus (CMV) unscreened red blood cells and platelet concentrates, white blood cell (WBC) depleted with high-efficiency filters, would prevent transfusion-associated (TA) CMV infection in CMV seronegative bone marrow transplant recipients. Blood components were filtered in the bloodcentre under quality control and after filtration residual WBC counts were always below 5 x 10(6) cells/U. Since 1990, 23 consecutive allogeneic and 37 autologous CMV seronegative marrow transplant recipients, have been transfused with filtered blood components and followed for 6 months for evidence of CMV infection by monitoring culture and CMV serology. None of the patients showed clinical symptoms of CMV infection, and CMV cultures during episodes of fever were always negative. IgM anti-CMV antibodies were negative during the study in all patients. Low titres of IgG anti-CMV antibodies (5-12 relative ELISA units) were found in 24/60 patients during the first month after bone marrow transplantation (BMT), probably due to passive transfer of IgG administered with the platelet transfusions. 3 and 6 months after BMT, 56 and 48 patients respectively were still alive; and CMV serology was negative in all patients. The results show that TA-CMV infection is preventable by filtration of blood through high-efficiency filters in patients undergoing autologous and allogeneic BMT.

Leucocyte depleting filters and cardiothoracic surgery

Leucocyte filtration technology is now beginning to be used in cardiothoracic surgery. The leucocyte depletion of banked homologous blood has been shown to reduce its immunosuppressive effects, along with a range of other benefits. Use of such a blood product appears to be an attractive option during cardiopulmonary bypass (CPB) as this procedure is recognized as causing immune disturbance and long-term immunosuppression. White-cell removal filters also appear to have a novel application in the reduction of neutrophil-mediated damage associated with CPB procedures. A strong database from animal work has been recently supplemented by human data that shows clinical benefits from autologous white-cell removal by filtration.

Mechanisms of white cell reduction in red cell concentrates by filtration: the effect of the cellular composition of the red cell concentrates.

The effect of platelets on the removal of white cells (WBCs) from 16 to 24-hour-old red cell (RBC) concentrates by filtration was studied. RBC concentrates with various concentrations of platelets and WBCs were filtered on a cellulose acetate column filter and on three polyester flatbed filters. The microscopic study revealed that lymphocytes and most monocytes were captured in the smaller pores of the fiber network, irrespective of the brand of filter, the type of filter material, or the prefiltration platelet amount in the RBC concentrates. In contrast, efficient granulocyte depletion depended on granulocyte-platelet interaction and on the filter material. In the presence of platelets, granulocytes were captured in the top part of the column filter or in the coarse layers of two of the flatbed filters, where platelets covered the fibers. Platelet depletion of the RBC concentrates prior to filtration diminished the contribution of these parts of the filters to granulocyte capture. A larger part of the column filter or the fine layers of the flatbed filters were now required for granulocyte capture. In one of the flatbed filters, granulocyte-platelet interaction occurred mainly in the fine layers, which ended in blockage of this filter after the filtration of variable volumes (250-600 mL) of standard RBC concentrates. A quantitative estimation of the effect of platelets on the WBC-reduction capacity found that all three flatbed filters had a highly significant decrease (p = 0.001) in WBC-reduction capacity for platelet-depleted or buffy coat-depleted RBC concentrates, as compared with standard RBC concentrates.(ABSTRACT TRUNCATED AT 250 WORDS)

ＩＬ‐ＩＩ活性化リンパ球を用いた抗ＨＬＡ抗体検出法の有用性と抗ＨＬＡ抗体保有率

We developted a new lymphocyte cytotoxicity test using proidium iodide and IL-II activated lymphocytes as panel cells for the detection of anti-HLA antibody. IL-II L which had been obtained by the continuous culture with 5μg/ml PHA and 40U/ml hrIL-II showed much better sensitivity than PBL.Subsequently, we investigated the prevalence of anti-HLA antibody in the 139 patients. Nineteen patients (19.8%) out of 96 patients who had the history of blood transfusion and 5 patients (11.6%) out of 43 patients who had no history of blood transfusion had the positive anti-HLA antibody. One (3.6%) patients out of 29 child patients who had been treated with filtered platelets from single donors and 6 patients (26.1%) out of 23 adult patients who had been treated with the filtered platelets from multiple donors had anti-HLA antibody (p<0.005). These results suggest that the removal of white cells by the filtration from the platelet products from single donors might be effective to prevent the antibody production.In addition, there was a reciprocal relationship between the score and the unit of transfused blood products in the patients whose scores on LCT were up to 6. This leads to a conclusion that the production of anti-HLA antibody depends on the immune responsiveness of each patient.

Prevention of transfusion-associated cytomegalovirus infection in neonatal patients by the removal of white cells from blood.

The usual methods employed to reduce the risk of transfusion-associated cytomegalovirus (TA CMV) disease have been to transfuse blood or cellular blood components that are CMV antibody-negative or to administer deglycerolized frozen red cells. To determine if the reduction of white cells (WBCs) in blood by filtration will also eliminate TA CMV disease in a high-risk population, 48 surviving very low birth weight (less than 1250 g) neonatal infants born to CMV-seronegative mothers at three participating institutions in the Hartford, Connecticut area and receiving at least one CMV-seropositive blood transfusion were studied. The incidence of TA CMV disease in 26 neonatal patients who received blood prepared by a modified spin-cool-filter technique and in 22 neonatal patients who received blood filtered through a WBC-reduction filter was compared with the incidence of transfusion-associated disease in similar populations reported in other studies. The CMV antibody prevalence of the blood donor population was found to be 37 percent. At the time of discharge of the individual neonatal infants in the population studied, and/or 2 to 6 months later, 47 of the 48 who had undergone transfusion had CMV antibody-negative serologic tests and/or urine culture. The other infant transiently seroconverted because of passive transfer of the antibody. None of the 48 neonatal infants had clinical evidence of CMV infection. This study indicates that WBC reduction of donor blood can reduce and perhaps prevent TA CMV disease in high-risk neonatal patients.

Density separation of human red blood cells on self forming Percoll R gradients: correlation with cell age

Human red blood cells were density separated on self-forming Percoll R gradients. Redistribution of density fractionated red blood cells was studied by recentrifugation on self-forming Percoll gradients. A protocol that avoids centrifugation of red cells prior to removal of white cells and introduces EDTA before red cell pelleting completely avoided redistribution. Dense red cells separated according to this method were senescent on the basis of a biochemical and a physical criterion: the increase in the band 4.1a:4.1b ratio (Mueller , T., Jackson, C.W., Dockter, M.E. and Morrison, M. (1987) J. Clin. Invest. 79, 492–499) and the loss of maximum deformability. Characterization also included the relative content of two proteins (complement receptor 1, CR1 (Ripoche, J. and Sim, R.B. (1986) Biochem. J. 235, 815–821); decay accelerating factor, DAF) on density fractionated red cells. Unlike cytoplasmic proteins, these proteins face similar conditions , whether located on circulating reticulocytes or aging red cells. Both components were lost linearly within experimental errors with cell and were lower by 60 and 40% in dense than light cells, respectively.

White cell depletion of single‐donor platelet preparations by a new adsorption filter

A newly developed adsorption filter has been evaluated for the removal of white cells (WBCs) from platelet concentrates. It consists of surface-modified polyester fibers and can be used at the patient's bedside. WBC mean removal rate was 98.8 +/- 0.9 percent, and platelet recovery was 99.0 +/- 0.7 percent. The aggregation curves (ADP, collagen) and hypotonic shock response of platelets were not influenced by the filtration, and the plasma electrolyte and lactate dehydrogenase concentrations were unaffected. Transmission and scanning electron micrographs showed no difference in platelet ultrastructure before and after filtration. Determination of posttransfusion platelet recovery did not reveal any significant difference from that of nonfiltered platelets. The tested filter seems to be a suitable device for WBC depletion of single-donor platelet concentrates at the bedside.

Removal of white cells from red cells by transfusion through a new filter

The effectiveness of a new filter (RC100) for the preparation of white cell-depleted red cells (RBCs) at the bedside was evaluated in vitro and in vivo using three RBC products: standard RBC concentrate (CPDA units), RBCs suspended in saline-adenine-glucose-mannitol additive solution after the removal of plasma (SAGM units), and RBCs suspended in SAGM after the removal of plasma and buffy coat (SAGM-BC units). Median RBC recovery was at least 92 percent when 2 units were administered through one filter; median values for residual white cells and platelets were less than or equal to 20 x 10(6) and less than or equal to 2.5 x 10(9) per 2 units, respectively. The in vivo study was carried out in 80 multiply transfused patients with thalassemia, 35 of whom had experienced frequent nonhemolytic transfusion reactions when given standard or buffy coat-free RBCs. During the 6-month study, each patient was given two transfusions of each type of RBC product One febrile nonhemolytic transfusion reaction occurred in each of two patients receiving SAGM-BC units, but in no other case. If the flow rate is not reduced, the median transfusion time is 35 minutes per CPDA unit and 15 minutes per SAGM and SAGM-BC unit. It is concluded that the transfusion of RBCs through the RC100 is a simple and effective procedure to administer white cell-depleted RBCs prepared at the bedside.

Preparation of white cell-depleted red cells for 42-day storage using an integral in-line filter.

A new blood pack system for the preparation of white cell-depleted red cells was studied. The system is a modified additive-solution quadruple-unit blood pack that incorporates a cellulose-acetate fiber depth filter in-line between the AS-3 additive bag and the CP2D collection bag. Mean +/- SD white cell removal from 156 units processed under standard production conditions was 97.7 +/- 2.7 percent; residual white cells were 1.1 +/- 1.0 x 10(8) per unit. Red cell loss was 10.0 +/- 1.0 percent (n = 43). Mean platelet removal was 80.9 percent from units from which platelet concentrates were not prepared (n = 47). Microaggregates did not form during storage, and hemolysis of filtered red cells was lower than that of unfiltered controls. Filtered AS-3 red cells stored for 42 days had a 51Cr survival of 80.1 +/- 5.7 percent (mean +/- SD) as compared with 78.9 +/- 6.2 percent for unfiltered controls (n = 17). This in-line filter system provides white cell-depleted, microaggregate-free red cells that can be stored for 42 days.

Depletion of white cells from platelet concentrates with a new adsorption filter.

Removal of white cells (WBCs) from platelets may reduce alloimmunization to WBC antigens, prevent febrile reactions, and improve platelet increments in multiply transfused patients receiving HLA-matched platelets. A new surface-modified fibrous polyester filter was evaluated; it requires no special processing of pooled platelet concentrates and can be used at the patient's bedside. The studies were designed to measure WBC removal, platelet function, in vitro platelet recovery, and in vivo platelet survival. WBC mean removal was 99.8 percent +/- 0.56 (n = 37) when a pool similar in volume to 6 platelet concentrates was tested. The mean number of residual WBCs after filtration was 5.6 x 10(5). In vitro mean platelet recovery was 86.9 percent for a pool size of 6 units (n = 37). Clot retraction and platelet aggregation were unaffected by filtration. Survival studies of 111Indium-labeled platelets done with filtered autologous platelets showed no reduction in the normally expected survival. These studies indicated that the filter efficiently removes WBCs without substantially decreasing platelet number, survival, or function. This device offers the potential of considerably improving platelet transfusion therapy.

Characteristics and clinical application of blood filters

Microaggregate blood filters (MAFs) may be beneficial for patients at increased risk of ARDS receiving massive transfusion, although their use is not uniformly recommended. While new leukocyte adsorption filters (LAFs) are more efficient for white cell removal, both MAFs and LAFs successfully reduce the incidence of febrile reactions to red cell components by reducing the residual leukocyte content below 10 9. It is likely that leukocyte removal delays or prevents recipient HLA alloimmunization from transfusion. LAFs offer a simple means of providing both red cells and platelets, depleted of leukocytes to levels below 10 8 and may prevent or delay the onset of HLA alloimmunization. A promising area of application of LAFs is for prevention of transfusion-transmitted CMV where leukocyte-depleted components may be noninfectious. Several secondary benefits of leukocyte-depleted components are anticipated, including a decreased risk of HTLV-1 transmission, reduced degree of transfusion-mediated immunosuppression and a lowered risk of graft-vs-host disease.

Leukotrap, a device for white cell poor platelets quality control studies In vitro and In vivo

Most febrile transfusion reactions are due to leucoagglutinins. Cutter's Leukotrap platelet pooling bag has a distal conic pouch for depleting the platelets of white blood cells by centrifugation. We tested 33 Leukotraps each containing six platelet units in vitro and 32 in vivo. The mean in vitro platelet count was 3.7 ± 0.5 × 10 11 platelets before, and 3.0 ± 0.5 × 10 11 after spinning, representing a platelet recovery of 80.2 ± 9.6% Mean white blood cells were 3.8 ± 0.6 × 10 8 before, and 0.6 ± 0.1 × 10 8 after centrifugation, this constituting a white cell removal of 83.5 ± 7.7%. pH ranged from 7.37 for 24-h platelets to 7.19 for 96-h platelets. 24-h after platelet pooling, all Leukotraps were sterile. Platelet aggregation with physiologic agents showed little change compared to individual platelet units. Glucose ranged between 418 and 336 mg/dL, pCO 2 between 27.8 and 19.1 mmHg, but pO 2 dropped drastically from 74.8 mmHg to 11.6 mmHg. Hypotonic osmotic recovery was satisfactory. In vivo studies were carried out with pooled, leucocyte-poor platelets which were transfused to six bone marrow transplant patients with no splenomegaly or septicemia at the outset. These patients had all demonstrated febrile transfusion reactions to standard donor units. The mean platelet increment was 16.8 × 10 9/L. A single febrile transfusion reaction witnessed in one patient, was accompanied by an adequate platelet response. Hence Leukotrap is a useful clinical tool for reducing febrile transfusion reactions related to white blood cells.

The in vitro evaluation of two filters (Erypur and Imugard IG 500) for white cell-poor platelet concentrates.

White cell-poor blood components are useful in patients with white cell antibodies. White cells are efficiently removed by two different filters, Imugard and Erypur, which have used saline as the filter solution. This study evaluated these filters as to their production of white cell-poor platelets. Pools of random-donor platelet concentrates were filtered. Prefiltration and postfiltration samples were evaluated for percentages of platelet recovery, white cell (WBC) removal, and platelet function. The two filter solutions tested were normal-strength saline (NSS) and fresh-frozen plasma (FFP). Postfiltration samples using NSS showed no measurable platelet aggregation with ADP, epinephrine, or collagen. However, with FFP, both filters showed 100 percent platelet aggregation with ADP, epinephrine, and collagen. The FFP filter solution provided excellent white cell removal in both filters (Imugard: 100% WBC removal or less than 1.0 X 10(6) residual WBC; Erypur: 99.5% removal or greater than 1.0 X 10(7) residual WBC); however, platelet recovery was better with Imugard (95%) than with Erypur (55%). The filtration procedure is an excellent method for the preparation of white cell-poor platelets; however, the quantity of the saline solution recommended for the filtering of red cells must be minimized for platelets.

Application of a low-pressure differential filtration technique to suspensions of red blood cells.

The paper describes a low-pressure 2 cm H2O, 5μm nuclepore filtration system for assessing red blood cell flexibility in suspensions of native plasma. Details are given of the white cell removal technique and filter handling methods for improved repeatability. Calibration of the system and filters using physiological saline controls is detailed and the advantages of a constant-pressure system are discussed. Data on filtration rates from normal controls and diabetics are given. Comparison of thisin votro system with literature data onin vivo systems is made.

Evaluation of a new filter for obtaining leucocyte-poor blood

Leucocyte-poor blood plays an important role in transfusion practice. Its use minimizes the possibility of a febrile reaction following transfusion in patients who are sensitized to white cell antigens. In addition, transfusion of leucocyte-poor blood will decrease the chances of leucocyte sensitization in patients who must receive multiple transfusions. It may be desirable for use in immuno-deficient or immunologically suppressed patients who run the risk of graft vs. host disease if viable lymphocytes are transfused. The ‘Imugard IG 500 (Terumo Corporation), which utilizes the raw cotton of G. barbadense, has recently been introduced for the preparation of leucocyte-poor blood. The filter was investigated to evaluate the efficiency of leucocyte and platelet removal from packed red cells. Filtration resulted in an average white cell removal of 97%. iNo selective removal of granulocytes or lymphocytes could be demonstrated. The age of the blood at filtration and anticoagulant (CPD or ACD) appeared to have no effect on the percentage white cell removal. The average platelet removal was 77%, and removal of platelets was less efficient and less consistent than removal of leucocytes. Red cell loss averaged 5% and red cells were judged to be unaffected by the filtration process on the basis of red cell indices, ATP and 2, 3 DPG levels, methylene blue uptake and osmotic fragility curves. This filtration technique has a number of advantages: it is simple, relatively inexpensive, takes less than 1 h to perform, requires no special ancillary equipment, results in a high red cell recovery with no overt damage to red cells, and the leucocyte removal is excellent in comparison with other techniques. Removal of platelet-rich plasma from the red cells prior to filtration may reduce residual platelet levels to clinically acceptable numbers. The potential problem of antigenic leucocyte fragments may be decreased if fresh blood is used for filtration. A true assessment of the white cell antigenicity of filtered blood can only be obtained by clinical trials in sensitized patients. Leucocyte-poor blood plays an important role in transfusion practice. Its use minimizes the possibility of a febrile reaction following transfusion in patients who are sensitized to white cell antigens. In addition, transfusion of leucocyte-poor blood will decrease the chances of leucocyte sensitization in patients who must receive multiple transfusions. It may be desirable for use in immuno-deficient or immunologically suppressed patients who run the risk of graft vs. host disease if viable lymphocytes are transfused. The ‘Imugard IG 500 (Terumo Corporation), which utilizes the raw cotton of G. barbadense, has recently been introduced for the preparation of leucocyte-poor blood. The filter was investigated to evaluate the efficiency of leucocyte and platelet removal from packed red cells. Filtration resulted in an average white cell removal of 97%. iNo selective removal of granulocytes or lymphocytes could be demonstrated. The age of the blood at filtration and anticoagulant (CPD or ACD) appeared to have no effect on the percentage white cell removal. The average platelet removal was 77%, and removal of platelets was less efficient and less consistent than removal of leucocytes. Red cell loss averaged 5% and red cells were judged to be unaffected by the filtration process on the basis of red cell indices, ATP and 2, 3 DPG levels, methylene blue uptake and osmotic fragility curves. This filtration technique has a number of advantages: it is simple, relatively inexpensive, takes less than 1 h to perform, requires no special ancillary equipment, results in a high red cell recovery with no overt damage to red cells, and the leucocyte removal is excellent in comparison with other techniques. Removal of platelet-rich plasma from the red cells prior to filtration may reduce residual platelet levels to clinically acceptable numbers. The potential problem of antigenic leucocyte fragments may be decreased if fresh blood is used for filtration. A true assessment of the white cell antigenicity of filtered blood can only be obtained by clinical trials in sensitized patients.