Familial clustering of multiple sclerosis in a Dutch genetic isolate.

Multiple sclerosis (MS) is a complex disease with a substantial, yet poorly identified, genetic influence. We estimated the pattern of familial aggregation of MS in a recent genetically isolated population in The Netherlands. Forty-eight MS patients were identified. Their relationship was evaluated by tracing extended pedigrees, making use of municipal and church records. Of the 48 MS patients, 24 could be linked to a common ancestor in 14 generations. However, multiple relationships exist between patients and, to take these into account, we calculated inbreeding and kinship coefficients. We found that MS patients from the isolate were significantly more often related to each other and significantly more often inbred than a non-MS control group, drawn from the same isolate. There was no clustering of Type 1 diabetes and autoimmune thyroid diseases in families of MS patients from this isolate. Finally, HLA typing was performed. Although there was a trend towards a higher prevalence of the HLA DRB1*15 allele in patients compared to controls, differences did not reach significance. This study suggests familial aggregation in the genetically isolated population. The high level of inbreeding makes this population valuable for finding novel genes involved in MS.

An increased MRP8/14 expression and adhesion, but a decreased migration towards proinflammatory chemokines of type 1 diabetes monocytes.

In the early development of type 1 diabetes macrophages and dendritic cells accumulate around the islets of Langerhans at sites of fibronectin expression. It is thought that these macrophages and dendritic cells are derived from blood monocytes. Previously, we showed an increased serum level of MRP8/14 in type 1 diabetes patients that induced healthy monocytes to adhere more strongly to fibronectin (FN). Here we show that MRP8/14 is expressed and produced at a higher level by type 1 diabetes monocytes, particularly after adhesion to FN, creating a positive feedback mechanism for a high fibronectin-adhesive capacity. Also adhesion to endothelial cells was increased in type 1 diabetes monocytes. Despite this increased adhesion the transendothelial migration of monocytes of type 1 diabetes patients was decreased towards the proinflammatory chemokines CCL2 and CCL3. Because non-obese diabetic (NOD) mouse monocytes show a similar defective proinflammatory migration, we argue that an impaired monocyte migration towards proinflammatory chemokines might be a hallmark of autoimmune diabetes. This hampered monocyte response to proinflammatory chemokines questions whether the early macrophage and dendritic cell accumulation in the diabetic pancreas originates from an inflammatory-driven influx of monocytes. We also show that the migration of type 1 diabetes monocytes towards the lymphoid tissue-related CCL19 was increased and correlated with an increased CCR7 surface expression on the monocytes. Because NOD mice show a high expression of these lymphoid tissue-related chemokines in the early pancreas it is more likely that the early macrophage and dendritic cell accumulation in the diabetic pancreas is related to an aberrant high expression of lymphoid tissue-related chemokines in the pancreas.

How to improve the search for an unrelated haematopoietic stem cell donor. Faster is better than more!

Many patients do not reach haematopoietic stem cell transplantation. Shortage of unrelated donors (UDs) is still seen as the main cause. However, with a worldwide UD pool containing more than 8 million donors, it is possible that other impediments are becoming more important. We analysed 549 UD searches for Dutch patients, performed between 1987 and 2000, in order to find the reasons for failure or success to reach transplantation. Between 1996 and 2000, 59% of the patients of Northwest European origin received a graft from an UD with a median time span of 4.4 months from the start of the search. In all, 11% of the patients lacked a compatible donor, while 30% became medically unfit for transplantation. This is in contrast to the patients of non-Northwest European origin for whom UD shortage is still the most important impediment; only 32% were transplanted while 50% lacked a compatible donor. We conclude that the shortage of donors is no longer the biggest constraint in unrelated stem cell transplantation for patients of Northwest European origin. It may be more effective to optimize the chance on transplantation by making the search process more efficient.

HLA class II alleles are not a general susceptibility factor in Guillain-Barré syndrome.

OBJECTIVE: To assess whether human leukocyte antigen (HLA)-DRB1 and HLA-DQB1 alleles confer susceptibility to Guillain-Barre syndrome (GBS) or are related to specific clinical or serologic subgroups of GBS. METHODS: The HLA-DRB1 and HLA-DQB1 loci were genotyped by PCR amplification with sequence-specific primers in 164 well-documented Dutch patients with GBS and 207 healthy Dutch control subjects. Patients with GBS were divided into subgroups based on clinical features, severity of disease, antecedent infection, and anti-ganglioside antibodies. Data were compared with those of all case-control HLA studies in GBS performed previously. RESULTS: In this case-control study, HLA-DRB1 and HLA-DQB1 alleles did not differ between GBS patients and control subjects. The frequency of HLA-DRB1*01 was increased in patients who needed mechanical ventilation (odds ratio 4.2; 95% CI 1.9 to 9.6; p(c) = 0.02). Multivariate logistic regression analysis showed that this association was independent of the severity of paresis and the presence of cranial nerve involvement (all p < 0.05). There was a tendency toward an association between certain HLA alleles and several anti-ganglioside antibodies. CONCLUSIONS: Human leukocyte antigen (HLA) class II antigens are not a general susceptibility factor in Guillain-Barre syndrome (GBS). However, HLA class II alleles may be a determinant in distinct subgroups of GBS, indicating the need for further exploration in large-scale studies.

A mutation in the HLA-B*2705-restricted NP383-391 epitope affects the human influenza A virus-specific cytotoxic T-lymphocyte response in vitro.

Viruses can exploit a variety of strategies to evade immune surveillance by cytotoxic T lymphocytes (CTL), including the acquisition of mutations in or adjacent to CTL epitopes. Recently, an amino acid substitution (R384G) in an HLA-B*2705-restricted CTL epitope in the influenza A virus nucleoprotein (nucleoprotein containing residues 383 to 391 [NP(383-391)]; SRYWAIRTR, where R is the residue that was mutated) was associated with escape from CTL-mediated immunity. The effect of this mutation on the in vitro influenza A virus-specific CTL response was studied. To this end, two influenza A viruses, one with and one without the NP(383-391) epitope, were constructed by reverse genetics and designated influenza viruses A/NL/94-384R and A/NL/94-384G, respectively. The absence of the HLA-B*2705-restricted CTL epitope in influenza virus A/NL/94-384G was confirmed by using (51)Cr release assays with a T-cell clone specific for the NP(383-391) epitope. In addition, peripheral blood mononuclear cells (PBMC) stimulated with influenza virus A/NL/94-384G failed to recognize HLA-B*2705-positive target cells pulsed with the original NP(383-391) peptide. The proportion of virus-specific CD8+ gamma interferon (IFN-gamma)-positive T cells in in vitro-stimulated PBMC was determined by intracellular IFN-gamma staining after restimulation with virus-infected autologous B-lymphoblastoid cell lines and C1R cell lines expressing only HLA-B*2705. The proportion of virus-specific CD8+ T cells was lower in PBMC stimulated in vitro with influenza virus A/NL/94-384G obtained from several HLA-B*2705-positive donors than in PBMC stimulated with influenza virus A/NL/94-384R. This finding indicated that amino acid variations in CTL epitopes can affect the virus-specific CTL response and that the NP(383-391) epitope is the most important HLA-B*2705-restricted epitope in the nucleoprotein of influenza A viruses.

Identification of a common HLA-DP4-restricted T-cell epitope in the conserved region of the respiratory syncytial virus G protein.

The cellular immune response to respiratory syncytial virus (RSV) is important in both protection and immunopathogenesis. In contrast to HLA class I, HLA class II-restricted RSV-specific T-cell epitopes have not been identified. Here, we describe the generation and characterization of two human RSV-specific CD4(+)-T-cell clones (TCCs) associated with type 0-like cytokine profiles. TCC 1 was specific for the matrix protein and restricted over HLA-DPB1*1601, while TCC 2 was specific for the attachment protein G and restricted over either HLA-DPB1*0401 or -0402. Interestingly, the latter epitope is conserved in both RSV type A and B viruses. Given the high allele frequencies of HLA-DPB1*0401 and -0402 worldwide, this epitope could be widely recognized and boosted by recurrent RSV infections. Indeed, peptide stimulation of peripheral blood mononuclear cells from healthy adults resulted in the detection of specific responses in 8 of 13 donors. Additional G-specific TCCs were generated from three of these cultures, which recognized the identical (n = 2) or almost identical (n = 1) HLA-DP4-restricted epitope as TCC 2. No significant differences were found between the capacities of cell lines obtained from infants with severe (n = 41) or mild (n = 46) RSV lower respiratory tract infections to function as antigen-presenting cells to the G-specific TCCs, suggesting that the severity of RSV disease is not linked to the allelic frequency of HLA-DP4. In conclusion, we have identified an RSV G-specific human T helper cell epitope restricted by the widely expressed HLA class II alleles DPB1*0401 and -0402. Its putative role in protection and/or immunopathogenesis remains to be determined.

Influenza A virus specific T cell immunity in humans during aging.

To study the decreasing responsiveness of the immune system during aging, influenza virus specific cellular immunity was investigated in a cohort of healthy blood donors between 18 and 70 years of age. The percentage of influenza A virus specific T cells was determined by flow cytometry and found not to change during aging. After stimulation with phorbol 12-myristate 13-acetate and ionomycin, an increase in the percentage of IFN-gamma and IL-4 producing CD8(+) T cells was observed during aging. In addition, the cytotoxic T lymphocyte (CTL) activity was investigated in two additional groups of five donors, 18-20 and 68-70 years of age. The lytic capacity of purified CD8(+) T cells, after in vitro stimulation of peripheral blood mononuclear cells with influenza A virus, seemed lower in 68- to 70-year-old donors than in 18- to 20-year-old donors. Therefore we conclude that the reduced CTL activity in the elderly is not the result of a lower frequency of virus-specific T cells, but more likely the result of impaired antigen-specific proliferation or lower lytic capacity of these cells.

Sequence variation in a newly identified HLA-B35-restricted epitope in the influenza A virus nucleoprotein associated with escape from cytotoxic T lymphocytes.

Here, we describe a new HLA-B*3501-restricted cytotoxic T lymphocyte (CTL) epitope in the influenza A virus (H3N2) nucleoprotein, which was found to exhibit a high degree of variation at nonanchor residues. The influenza virus variants emerged in chronological order, and CTLs directed against old variants failed to recognize more recent strains of influenza A virus, indicating an escape from CTL immunity.

The magnitude and specificity of influenza A virus-specific cytotoxic T-lymphocyte responses in humans is related to HLA-A and -B phenotype.

The repertoire of human cytotoxic T-lymphocytes (CTL) in response to influenza A viruses has been shown to be directed towards multiple epitopes, with a dominant response to the HLA-A2-restricted M1(58-66) epitope. These studies, however, were performed with peripheral blood mononuclear cells (PBMC) of individuals selected randomly with respect to HLA phenotype or selected for the expression of one HLA allele without considering an influence of other HLA molecules. In addition, little information is available on the influence of HLA makeup on the overall CTL response against influenza viruses. Here, the influenza A virus-specific CTL response was investigated in groups of HLA-A and -B identical individuals. Between groups the individuals shared two or three of the four HLA-A and -B alleles. After in vitro stimulation of PBMC with influenza virus, the highest CTL activity was found in HLA-A2(+) donors. A similar pattern was observed for the precursor frequency of virus-specific CTL (CTLp) ex vivo, with a higher CTLp frequency in HLA-A2-positive donors than in HLA-A2-negative donors, which were unable to recognize the immunodominant M1(58-66) epitope. In addition, CTL activity and frequency of CTLp for the individual influenza virus epitopes were determined. The frequency of CTLp specific for the HLA-B8-restricted epitope NP(380-388) was threefold lower in HLA-B27-positive donors than in HLA-B27-negative donors. In addition, the frequency of CTLp specific for the HLA-A1-restricted epitope NP(44-52) was threefold higher in HLA-A1-, -A2-, -B8-, and -B35-positive donors than in other donors, which was confirmed by measuring the CTL activity in vitro. These findings indicate that the epitope specificity of the CTL response is related to the phenotype of the other HLA molecules. Furthermore, the magnitude of the influenza virus-specific CTL response seems dependent on the HLA-A and -B phenotypes.

Macrophage tropism of human immunodeficiency virus type 1 facilitates in vivo escape from cytotoxic T-lymphocyte pressure.

Early after seroconversion, macrophage-tropic human immunodeficiency virus type 1 (HIV-1) variants are predominantly found, even when a mixture of macrophage-tropic and non-macrophage-tropic variants was transmitted. For virus contracted by sexual transmission, this is presently explained by selection at the port of entry, where macrophages are infected and T cells are relatively rare. Here we explore an additional mechanism to explain the selection of macrophage-tropic variants in cases where the mucosa is bypassed during transmission, such as blood transfusion, needle-stick accidents, or intravenous drug abuse. With molecularly cloned primary isolates of HIV-1 in irradiated mice that had been reconstituted with a high dose of human peripheral blood mononuclear cells, we found that a macrophage-tropic HIV-1 clone escaped more efficiently from specific cytotoxic T-lymphocyte (CTL) pressure than its non-macrophage-tropic counterpart. We propose that CTLs favor the selective outgrowth of macrophage-tropic HIV-1 variants because infected macrophages are less susceptible to CTL activity than infected T cells.

External quality assessment of flow cytometric HLA-B27 typing.

A biannual external quality assurance (EQA) scheme for flow cytometric typing of the HLA-B27 antigen is operational in The Netherlands and Belgium since 1995. We report here on the results of the first seven send-outs to which 36 to 47 laboratories participated. With the send-out, four specimens from blood bank donors, who had been typed for HLA Class I antigens by complement-dependent cytotoxicity, were distributed. Subtyping of the HLA-B27 allele was performed by PCR-SSP. Ten samples were HLA-B27(pos) (all HLA-B*2705) and 18 were HLA-B27(neg). For flow cytometry, the most widely monoclonal antibody (MoAb) used was FD705, followed by GS145.2 and ABC-m3. The majority of laboratories used more than 1 anti-HLA-B27 MoAb for typing. The HLA-B27(pos) samples were correctly classified as positive by the large majority of participants (median 95%; range 85% to 100% per send out); some participants considered further typing necessary and misclassification as negative was only sporadically seen. The classification of HLA-B27(neg) samples as negative was less straightforward. Ten samples were correctly classified as such by 97% (82% to 100%) of the participants, whereas 64% (range 53% to 70%) of the participants classified the remaining eight samples as HLA-B27(neg). There was no significant prevalence of a particular HLA-B allele among these eight "poor concordancy" samples as compared to the ten "good concordancy" samples. Inspection of the reactivity patterns of the individual MoAb with HLA-B27(neg) samples revealed that ABC-m3 showed very little cross-reactivity apart from its well-known cross-reactivity with HLA-B7, whereas the cross-reactivity patterns of GS145.2 and FD705 were more extensive. The small sample size (n = 18) and the distribution of HLA-B alleles other than HLA-B27 did not allow assignment of specificities to these cross-reactions. Finally, we showed that standardized interpretation of the combined results of two anti-HLA-B27 MoAb reduced the frequency of false-positive conclusions on HLA-B27(neg) samples. In this series, the lowest frequency of false-positive assignments was observed with the combination of the FD705 and ABC-m3 MoAb.

Expression of MAGE, gp100 and tyrosinase genes in uveal melanoma cell lines.

In order to determine the possible use of uveal melanoma cell lines as stimulators in immunotherapy, we evaluated the expression of the human genes for MAGE-1, -2 and -3, gp100 and tyrosinase in uveal melanoma cell lines. mRNA expression of the MAGE-1, -2 and -3, gp100 and tyrosinase genes and the HLA class I specificity were determined in five primary and three metastatic uveal melanoma cell lines. Expression of the examined genes was heterogeneous in the primary and metastatic cell lines. The cell lines OCM-1 and OMM-1 expressed MAGE-1, -2 and -3, whereas EOM-3, MEL202, 92-1 and OMM-3 were negative for these antigens. gp100 was expressed in all cell lines, and tyrosinase in all but three (EOM-29, OMM-2 and OMM-3). Except for EOM-3, the HLA-A type of all the cell lines could be determined by complement-dependent microlymphocytotoxicity assay. Since at least two melanoma-associated antigens can be found in uveal melanoma cell lines, as well as the HLA class I molecules, these cell lines may be applicable as immunogens for specific immunotherapy against metastatic uveal melanoma.

[Allogeneic bone marrow transplantation of unrelated donors; fewer complication, more donors]. / Allogene transplantaties met beenmerg van onverwante donors; minder complicaties, meer donors.

A female patient aged 37 years who suffered from chronic myeloid leukemia received an allogeneic bone marrow transplantation (BMT) from an HLA-matched unrelated donor. No life-threatening complications ensued; 2.5 years after BMT she is still in complete remission. Survival after BMT from an unrelated donor for the time being is still lower than that after BMT from a related donor, but is improving due to better prevention and treatment of opportunistic infections and better selection of registered donors by meticulous HLA matching.

Problems and possible solutions in finding an unrelated bone marrow donor. Results of consecutive searches for 240 Dutch patients.

To evaluate the efficiency of our protocol for finding an HLA matched unrelated bone marrow donor, search results obtained between 1990 and 1995 for 240 Dutch patients were analyzed. The percentage of patients for whom, according to information given by the registries, a fully split-HLA antigen matched donor is available, increased from 24% in 1990 to over 70% in 1995. As a result the percentage of patients transplanted rose from about 24% in 1990-1991 to 44% in 1994-1995. The median time between the start of the search and transplantation was about 6 months. The systematic use of Bone Marrow Donors Worldwide (BMDW) which comprises the HLA groups of all volunteer bone marrow donors in Europe, Israel, South Africa, North America, Canada, India, Australia and New Zealand has been essential in this context. While searching for a suitable donor several problems were encountered such as unavailability of donors (12%) and discordant typing results (8%; range < 1% to > 25%). Thus it is advisable to select several donors for a patient. For 86% of patients with at least one HLA identical donor on the serological level for HLA-A,-B,-DR,-DQ, an HLA-DRB1/3/4/5, and -DQB1 identical donor could be identified. As expected, patients with two frequent haplotypes in strong linkage disequilibrium had the best chance of obtaining an HLA matched donor. Unexpectedly, patients with only one such haplotype had an almost similar chance. It could be calculated that HLA-DR typing of HLA-A,-B identical donors was rarely cost-effective after 1992. Only 12 of the 75 transplanted patients (16%) typeable at DNA level for class II, turned out to be completely matched for HLA-A,-B,-C,-DRB1/3/4/5,-DQB1,-DPB1 and had a negative MLC test. In the group of patients transplanted with a fully matched donor and for whom a CTLp test was performed, only 7% (4/54) of the tests were negative. Search results for patients of non-European origin were dismal, with only four of 26 patients referred being transplanted. In summary, of the 240 patients for whom the Europdonor office searched for a donor, about one-third were transplanted, one-third had a potential donor but did not reach transplantation, while for the remaining one-third of patients no suitable donor could be found.

A flow cytometric platelet immunofluorescence crossmatch for predicting successful HLA matched platelet transfusions.

Platelet crossmatching may provide a useful way of selecting donors for effective platelet transfusions in patients refractory to random donor platelet concentrates due to alloimmunization. We assessed the predictive value of a flow cytometric platelet immunofluorescence crossmatch test for the outcome of HLA matched platelet transfusions in a group of alloimmunized patients. Platelet immunofluorescence (PIFT) crossmatches were performed for 104 HLA-matched platelet transfusions administered to 30 patients. A negative PIFT crossmatch correctly predicted a successful platelet transfusion (1 h post-transfusion platelet recovery >20%) in 56/75 (75%) cases. We also considered non-immunological factors that, in combination with alloimmunization, might have contributed to an unsuccessful transfusion result, i.e. fever, septicaemia, splenomegaly, disseminated intravascular coagulation and bleeding. The predictive value of a negative PIFT crossmatch was better when these non-immunological factors were absent [48/59 (81%) correct predictions] than when these factors were present [8/16 (50%) correct predictions] (P=0.01; chi-square test). The effect of ABO incompatibility between donor and recipient on the predictive value of the PIFT crossmatch was also analysed. Positive PIFT crossmatches occurred more frequently in ABO incompatible donor-recipient combinations [in 18/28 (64%) cases] than in ABO-compatible donor-recipient combinations [in 11/76 cases (14%)] (P<0.001, chi-square test). Successful platelet transfusions were observed on 53/76 (70%) occasions in ABO compatible transfusions as compared to 16/28 (57%) in ABO incompatible transfusions. This difference was not statistically significant (P=0.23; chi-square test). Consequently, a negative PIFT crossmatch appeared to be non-predictive for the transfusion outcome in cases of ABO incompatibility between donor and recipient. We conclude that the PIFT crossmatch for platelet donor selection in addition to matching for HLA antigens, is predictive for the outcome of ABO compatible transfusions in alloimmunized recipients and prediction levels are increased when non-immunological causes for platelet refractoriness are absent.

Leukocyte depletion of random single-donor platelet transfusions does not prevent secondary human leukocyte antigen-alloimmunization and refractoriness: a randomized prospective study.

We studied the value of leukocyte depletion of platelet transfusions for the prevention of secondary human leukocyte antigen (HLA)-alloimmunization in patients with a high-risk of prior immunization induced by pregnancies. Seventy-five female patients with hematologic malignancies (mostly acute leukemia) and a history of pregnancy were randomized to receive either standard random single-donor platelet transfusions (mean leukocytes, 430 x 10(6) per transfusion) or leukocyte-depleted random single-donor platelet transfusions. Leukocyte depletion to less than 5 x 10(6) leukocytes per platelet transfusion (mean leukocytes, 2 x 10(6) per transfusion) was achieved by filtration. Of the 62 evaluable patients, refractoriness to random donor platelets occurred in 41% (14 of 34) of the patients in the standard group and in 29% (8 of 28) of the patients in the filtered group (P = .52); anti-HLA antibodies developed in 43% (9 of 21) of individuals in the standard group and 44% (11 of 25) of cases in the filtered group. The time toward refractoriness and development of anti-HLA antibodies was similar for both groups. We conclude that leukocyte depletion of random single-donor platelet products to less than 5 x 10(6) per transfusion does not reduce the incidence of refractoriness to random donor platelet transfusion because of boostering of anti-HLA antibodies.

Detection of multiple 'Ebnotypes' in individual Epstein-Barr virus carriers following lymphocyte transformation by virus derived from peripheral blood and oropharynx.

Transformation of a B lymphocyte into a lymphoblastoid cell line (LCL) by Epstein-Barr virus (EBV) results in the expression of EBV nuclear antigens (EBNAs) of which the size spectrum ('Ebnotype') is characteristic for the transforming virion. Ebnotyping has been used as an epidemiological tool for studies of EBV infection. We compared the occurrence of a single and of multiple Ebnotypes, as defined by EBNAs 1, 2 and 6, in healthy and diseased EBV carriers. Cases from which two or more LCLs could be established from peripheral blood or oropharyngeal cultures were considered informative. The frequency of multiple Ebnotypes was relatively low in healthy individuals and in patients with infectious mononucleosis or with haematological diseases who were awaiting a bone marrow transplant [blood, 11 of 74 patients (15%); oropharynx, 12 of 49 patients (24%)], whereas it was relatively high in recipients of bone marrow or cardiac allografts and one patient with AIDS [blood, 12 of 34 patients (35%); oropharynx, 11 of 16 patients (69%)]. Three patterns of the simultaneous presence of multiple Ebnotypes were distinguished. The first, most frequent, pattern observed predominantly in oropharyngeal cultures of all groups consisted of minority Ebnotypes differing from the majority type by only a single EBNA protein (usually EBNA 1). The second, less frequent, pattern observed in the healthy carriers and the (candidate) transplant recipients consisted of minority Ebnotypes differing from the majority type by two EBNA proteins (mostly EBNAs 1 and 6). The third pattern, characterized by the simultaneous presence of totally different Ebnotypes, was restricted to the (candidate) transplant recipients and the AIDS patient and was more frequently observed in the blood than in the oropharynx. We suggest that the first two patterns result from heterologous recombinations occurring during viral replication at repeat sequences within the EBNA coding regions, whereas the third pattern reflects multiple infections with exogenous viruses.

Comparison of four filters for leukocyte depletion of single donor plateletapheresis products.

Removal of leukocytes from platelet suspensions is important in preventing the development of alloimmunization to HLA antigens in repeatedly transfused patients. Several types of filters have recently become available to remove leukocytes from platelet suspensions. We have compared the results obtained with Pall PL100S, Pall PL50S, Sepacell PL-10N and Sepacell PL-5N filters. Platelets were obtained by plateletapheresis using the Haemonetics V-50 TSPP surge procedure. A total of 160 platelet suspensions were studied, 40 for each type of filter used. The median number of leukocytes pre-filtration was 321x10 6 (range: 16-4068). The median number of leukocytes post-filtration was 2x10 6 ( less than 1-521) and was dependent on the number of leukocytes present pre-filtration but not on the type of filter used. All filters tested showed approximately a 2 log 10 reduction of leukocytes. When the number of leukocytes was below 500x10 6 pre-filtration, the number of leukocytes post-filtration did not exceed 10x10 6. Overall platelet loss was 11+/-7% and was lowest with the Pall PL50S filters (7+/-7%). Mean platelet volumes post-filtration were decreased with all types of filters used.