Applications of flow cytofluorometry to transfusion science

Rh flow cytometry: An updated methodology for D antigen density applied to weak D types 164 and 165

BACKGROUND

An original methodology for determining the D antigen density on red cells was published in 2000 and has been applied in many publications since. This flow cytometry-based assay remained largely unrevised utilizing monoclonal anti-Ds that are not readily available anymore. We updated the methodology to quantify erythrocyte D antigen sites using microspheres and monoclonal anti-Ds that are commercially available today.

METHODS

The absolute D antigen density of a frozen standard CcDEe cell, drawn in 2003, a fresh blood donation from the same individual, drawn in 2022, and an internal control CcDEe cell, was quantified by flow cytometry using fluorescence-labeled microspheres. The internal control CcDEe cell was used in conjunction with 9 commercial anti-Ds to determine D antigen densities of 7 normal D, 4 partial D, and 11 weak D type samples, including 2 novel alleles.

RESULTS

The reproducibility of the updated assay was evaluated with red cells of published D antigen densities. The current results matched the known ones closely. The new weak D types 164 and 165 carried 4500 and 1505 D antigens/red cell, respectively. The absolute D antigen density decreased from 27,231 to 26,037 in an individual over 19 years.

DISCUSSION

The updated assay gave highly reproducible results for the D antigen densities of Rh phenotypes. Readily available anti-Ds allowed for the determination of the D antigen densities of 7 weak D types. The assay is suitable to evaluate the effects of distinct amino acid substitutions on the RhD phenotype.

A report on a modified protocol for flow cytometry-based assessment of blood group erythrocyte antigens potentially suitable for analysis of weak ABO subgroups

BACKGROUND

Flow cytometry (FC) has proven its utility in scrutinizing AB antigen expression in red blood cells (RBCs), cooperating with serological tests for accurate blood group typing. However, technical difficulties may impair the characterization of weak ABO subtypes when background noises appear at non-negligible levels.

STUDY DESIGN AND METHODS

We sought to establish an FC method that could prevent antibody-induced hemagglutination and an increase in cellular autofluorescence, two major issues inherent to RBC-FC analysis of AB expression. We optimized fixatives, multicolor-staining protocols, and sequential gating strategies. Blood samples from weak ABO subtype cases, B_m and A_el , were analyzed with the established protocol.

RESULTS

The optimized mixture of glutaraldehyde and formaldehyde successfully generated fixed RBCs resistant to agglutination while maintaining low autofluorescence. These features allowed co-staining of leukocyte- and erythrocyte-markers, which enabled sequential gating strategies facilitating the precise AB antigen analysis in purely single RBCs with minimum background noises. By the established FC analysis, we could detect in the B_m sample a small RBC population exhibiting weak B antigen expression. The assay also proved it feasible to identify a small population (0.04%) of RBCs weakly expressing the A antigen in the A_el sample confirmed as harboring a rare c.816dupG ABO variant allele.

CONCLUSION

The RBC-FC analysis described here allows the detection of AB antigens weakly expressed in RBCs while achieving minimum background noise levels in negative control samples. Overall, the modified protocol provides a quick and reliable assay valuable in transfusion medicine and is potentially applicable to the characterization of rare weak ABO variants.

The chemical and laboratory investigation of hemolysis

The abnormal breakdown of circulating red blood cells (RBCs), also known as hemolysis, is a significant clinical issue that can present as a primary disorder or arise secondary to another disease process. The evaluation for pathologic hemolysis (and the establishment of a hemolytic disorder) is heavily dependent on assays performed and overseen by the divisions of Hematology, Blood Bank/Transfusion Medicine, Clinical Chemistry, and Immunology in the clinical laboratory. Because of the wide variety of assays used across the spectrum of clinical pathology and potential pitfalls/limitations associated with this testing, the decision of which assay to choose and, perhaps more importantly, how to interpret results, can both be quite challenging. Thus, the aim of this manuscript is to provide a comprehensive review on the laboratory investigation of pathologic forms of hemolysis and hemolytic disorders. This chapter will: (1) introduce basic concepts on the pathophysiology of hemolysis and (2) examine assays available for hemolysis on a laboratory-by-laboratory basis, with a particular emphasis on the strengths, limitations, and clinical interpretations of each of these assays.

The Direct Antiglobulin Test: Indications, Interpretation, and Pitfalls

The direct antiglobulin test (DAT; sometimes referred to as the "Coombs" test) continues to be one of the most widely used assays in laboratory medicine. First described about 70 years ago, it is elegantly simple in design, yet it is widely complex in its applications and interpretations, and it is prone to false-positive and false-negative results. The overall objective of our review is to provide practicing pathologists with a guide to identify situations when the DAT is useful and to highlight disease-specific shortcomings as well as general pitfalls of the test. To accomplish these goals, this review will discuss the following: (1) the history of the DAT, (2) how the test is performed in the clinical laboratory, (3) clinical situations for its use, (4) its interpretation, and (5) the pitfalls associated with DAT assays, including causes of false positivity.

Clinically and/or Serologically Misleading Findings Surrounding Immune Haemolytic Anaemias

Autoimmune haemolytic anaemias (AIHAs) are well-characterized disorders. They can be differentiated from one another and from other non-immune haemolytic anaemias by clinical, laboratory and serological testing. However, several misleading clinical presentations and/or serological findings may result in misinterpretation, delay and/or misdiagnosis. Such failures are avoidable by adequate clinical and serological experience of the responsible physicians and serologists or, at least, by an optimised bidirectional communication. As long as this has not been achieved, unpleasant failures are to be expected. A true diagnosis of AIHA can neither be verified by clinical nor serological findings alone. Thus, a collective clinical and serological picture remains obligatory for fulfilling the criteria of optimal diagnosis and therapy. Ultimately, the majority of pioneer scientific and practical work in this field stems from scientists who were simultaneously involved in both the clinic and serology.

New approaches to understanding the immune response to vaccination and infection

The immune system is a network of specialized cell types and tissues that communicates via cytokines and direct contact, to orchestrate specific types of defensive responses. Until recently, we could only study immune responses in a piecemeal, highly focused fashion, on major components like antibodies to the pathogen. But recent advances in technology and in our understanding of the many components of the system, innate and adaptive, have made possible a broader approach, where both the multiple responding cells and cytokines in the blood are measured. This systems immunology approach to a vaccine response or an infection gives us a more holistic picture of the different parts of the immune system that are mobilized and should allow us a much better understanding of the pathways and mechanisms of such responses, as well as to predict vaccine efficacy in different populations well in advance of efficacy studies. Here we summarize the different technologies and methods and discuss how they can inform us about the differences between diseases and vaccines, and how they can greatly accelerate vaccine development.

Blood doping in athletes--detection of allogeneic blood transfusions by flow cytofluorometry

Athletes may undergo blood transfusion to increase their red cell mass and the oxygen carrying capacity of their blood in order to confer a competitive advantage. Allogeneic transfusions are normally mismatched at one or more minor blood group antigens. The most sensitive and accurate method known to detect this form of blood doping is flow cytometry. Low percentages of antigen-positive and antigen-negative red blood cells (RBCs) can be quantitated using suitable specific alloantibodies and careful analysis. By testing blood samples taken at various times, a reduction in the percentage of a minor population of RBCs will indicate transfusion has occurred.

Identification and quantification of fetal red blood cells in maternal blood by a dual-color flow cytometric method: evaluation of the Fetal Cell Count kit

BACKGROUND

As an alternative to the cumbersome Kleihauer-Betke test (KBT), flow cytometry represents a powerful method for the identification and quantification of fetal red blood cells (RBCs) in maternal circulation.

STUDY DESIGN AND METHODS

The aim of this study was to evaluate the Fetal Cell Count kit (IQ Products), an innovative flow cytometric method, based on the combination of antibodies directed, respectively, against fetal hemoglobin (HbF) and carbonic anhydrase (CA), a marker expressed after birth, to discriminate fetal RBCs from adult F cells containing HbF. The investigation was performed by two French laboratories that compared the data obtained by flow cytometry and KBT in 455 pregnant or just-delivered women as well as in 124 artificial mixtures containing from 0.01 to 5.00 percent cord cells.

RESULTS

The FL1/FL2 histogram allowed distinction between fetal RBCs (HbF+, CA-), F cells (HbF+, CA+), and adult RBCs (HbF-, CA+). The limits of detection and quantification were determined at 0.03 and 0.10 percent or 0.02 and 0.05 percent when analyzing 100,000 or 200,000 events, respectively. Linearity was demonstrated between 0.01 and 5.00 percent fetal cells in the mixtures (r = 0.95, p < 0.01). A good correlation between fluorescence-activated cell sorting (FACS) and KBT results was obtained with artificial mixtures (r = 0.94, p < 0.01). From the 405 Kleihauer-negative samples, none were identified as positive by FACS. Among the 50 Kleihauer-positive samples, 6 were shown not to contain fetal cells but F cells by FACS.

CONCLUSION

With this new dual-color flow cytometric method, accurate evaluation of fetomaternal hemorrhage was achieved even in the face of HbF of maternal origin.

Immune hemolytic anemia associated with negative routine serology

Immune hemolytic anemia can occur in patients who have no antibodies detectable by routine procedures (direct [DAT] and indirect [IAT] antiglobulin tests). DAT-negative autoimmune hemolytic anemias (AIHAs) represent 5% to 10% of all AIHAs. Three causes have been identified: (1) small numbers of red blood cell (RBC)-bound IgG molecules below the threshold of the DAT; (2) IgA and IgM autoantibodies; and (3) low-affinity autoantibodies. Antibody-independent cytotoxic events caused by natural killer (NK) cells have also been implicated. DATs are sometimes found to be positive when tested by reference laboratories, due to poor technique in reading antiglobulin tests in hospital laboratories. Hemolytic transfusion reactions also can occur when no alloantibodies are detectable by routine procedures. In some cases antibodies can be detected by special serologic procedures (such as the Polybrene test); in other instances phenotypically matched RBCs survive well and a specific antigen can be shown to be involved, suggesting a specificity (like anti-C) that is undetectable by any technique. Antibodies other than to blood group antigens, such as human leukocyte antigen (HLA) antibodies, may sometimes be involved.

Immunocytometric quantitation of foeto-maternal haemorrhage with the Abbott Cell-Dyn CD4000 haematology analyser

This study evaluated the extended use of a haematology analyser (Abbott Cell-Dyn CD4000) for the immunofluorescent enumeration of foeto-maternal haemorrhage (FMH) with fluorescein isothiocyanate-labelled monoclonal anti-RhD. Method performance was assessed with artificial FMH standards, and a series of 44 clinical samples. Within run precision was <15% (coefficient of variation, CV) for FMH volumes of 3 ml and above, 18.8% at an FMH volume of 2 ml and 31.7% at an FMH volume of 1 ml. Linearity analysis showed excellent agreement (observed FMH% = 0.98x expected FMH% + 0.02), and a close relationship (R(2) = 0.99) between observed and expected FMH percentages. The lower limit of quantification of the CD4000 (SRP-Ret) method with a maximum CV of 15% was 1.6 ml, and the limit of detection was <1 ml. Parallel Kleihauer-Betke test (KBT) assessments of FMH standards showed an overall trend for higher KBT values (observed = 1.25x expected - 0.38). At an FMH level of 4 ml, KBT observer estimates ranged from 0.57 to 11.94 ml with a mean inter-observer CV of 63%. For 44 clinical samples, there was decision point agreement between KBT and SRP-Ret results for 42 samples with an FMH of <2 ml. Analysis in the low FMH range (<1 ml) showed that small volume foetal leaks could be detected with the SRP-Ret method in most of 23 samples with negative KBT results. CD4000 SRP-Ret method performance for FMH determination was similar to that reported for flow cytometry.

Human platelet antigen-specific alloantibodies implicated in 1162 cases of neonatal alloimmune thrombocytopenia

BACKGROUND

Neonatal alloimmune thrombocytopenia (NATP) caused by fetomaternal mismatch for human platelet (PLT) alloantigens (HPAs) complicates approximately 1 in 1000 to 1 in 2000 pregnancies and can lead to a serious bleeding diathesis, intracranial hemorrhage, and sometimes death of the fetus or neonate. As a national reference center for NATP investigations, our experience with this entity over a 12-year period was reviewed.

STUDY DESIGN AND METHODS

The laboratory records of all cases of suspected NATP referred for evaluation from January 1, 1990, to December 31, 2002, were analyzed. The spectrum of PLT alloantibody specificities identified was compared with an earlier reported series of serologically verified NATP cases.

RESULTS

HPA-specific alloantibodies were identified in 1162 (31%) of 3743 sera of mothers of infants with clinically suspected NATP. Maternal HPA-1a (PlA1) alloimmunization accounted for the majority (79%) of confirmed NATP cases, with HPA-5b (Bra), HPA-3a (Baka), and HPA-1b (PLA2) alloantibodies accounting for 9, 2, and 4 percent of cases, respectively. In addition, an increase in the number of cases in which multiple HPA-specific alloantibodies were present in maternal sera was observed during the study period.

CONCLUSION

Although, as with the earlier series, maternal HPA-1a alloimmunization was the dominant cause of NATP, the identification of an increasing number of cases due to alternative HPA polymorphisms suggests that investigation for HPA-1 incompatibility alone is no longer sufficient to fully evaluate clinically suspect NATP cases.

Detection and identification of platelet antibodies in clinical disorders

Serologic assays to detect and identify platelet-reactive antibodies have progressed from less sensitive and specific Phase I tests based on platelet functional endpoints through more sensitive Phase II assays that detect platelet-associated immunoglobulins, to highly specific Phase III assays that detect antibodies bound to alloantigens located on isolated platelet surface glycoproteins. Phase II and III assays are useful in the evaluation of patients with suspected platelet alloimmune syndromes neonatal alloimmune thrombocytopenia (NATP) and post-transfusion purpura (PTP) as well as in platelet crossmatching. Flow cytometry, a Phase II assay, can be modified to detect drug-dependent platelet-reactive antibodies. 14C-serotonin release, a Phase I assay and the platelet factor 4 ELISA, a Phase III assay, are now used to diagnose patients with heparin-induced thrombocytopenia (HIT). A sufficiently sensitive and specific assay to diagnose idiopathic (autoimmune) thrombocytopenia (ITP) remains elusive.

Binding of activated platelets to WBCs in vivo after transfusion

BACKGROUND

During preparation and storage of apheresis concentrates, platelets are being activated. One of the alterations that occur during this process is an increased expression of P-selectin (CD62p) on the cytoplasmic surface of platelets. This neoepitope represents a ligand for the binding of platelets to WBCs. It has been suggested that the activation of platelets is associated with the sequestration of platelets after transfusion. In this in vivo study, the binding of platelets to WBCs was analyzed following transfusion of platelet concentrates (PCs).

STUDY DESIGN AND METHODS

Double apheresis concentrates were prepared with two different cell separators. One of the split products was stored for 1 to 2 days and the other one for 3 to 5 days. Flow cytometry was applied to analyze the degree of platelet activation in vitro, and also to measure the extent of platelet binding to WBC subclasses in vivo after transfusion into patients.

RESULTS

The results of this study show that platelet activation occurs during apheresis and storage of PCs. After transfusion of the PCs, no significant binding of platelets to T or B-cells could be detected. However, a significant binding of platelets to monocytes and neutrophil granulocytes occurs. While in Baxter PCs stored for 1-2 days the amount of platelet-leukocyte aggregates in vivo was higher compared to COBE PCs, no such difference could be detected anymore for the PCs stored for 3-5 days.

CONCLUSION

This study demonstrates that binding of activated platelets occurs to monocytes and neutrophil granulocytes but not to T- and B-cells in the circulation after transfusion. In addition, the interaction of platelets and WBCs is dependent on the degree of P-selectin expression. Platelets showing a higher degree of activation adhere to WBCs to a higher degree than nonactivated platelets.

Platelet function testing in apheresis products: flow cytometric, resonance thrombographic (RTG) and rotational thrombelastographic (roTEG) analyses

During storage of platelet concentrates, quality control of the units is mandatory. This includes the important testing of the hemostatic function of platelets. So far, mostly platelet aggregation analyses have been performed. In this study, new approaches were tested to evaluate the applicability of modern techniques for quality monitoring. Plateletpheresis was performed with two different cell separators (AMICUS cell separator, Fenwal, Baxter Healthcare, Deerfield, USA; COBE Spectra, COBE BCT, Lakewood, USA). In each procedure split products (n = 22) were prepared and stored for 1-2 days (n = 22) or 3 5 days (n = 22). Platelet hemostatic capacity was tested by applying flow cytometry. platelet aggregation (platelet-rich-plasma [PRP]+agonist), resonance thrombography (RTG; PRP, no agonist) and rotational thrombelastography (roTEG; PRP+agonist). Flow cytometric analyses did not reveal significant changes in structural (CD41a. CD42b) or activation-dependent antigens (CD62p, CD63, LIBS, RIBS). Also, differences in the data from the flow cytometric reactivity tests were not significant between the two groups. In platelet aggregation assays, shape change (p = 0.8), maximum aggregation (p = 0.4), and maximum gradient (p = 0.8) did not show significant differences between the two groups. In the RTG test, differences between r-time (reaction time; p = 0.4), and f-time (clot formation time [fibrin influence]; p = 0.3), and in roTEG r-time (coagulation time; p = 0.1) and k-time (clot formation time; p = 1.0) were not significant. P-time (clot formation time [platelet influence]) and M (maximum amplitude) in RTG, and k-time and MA (maximum amplitude) in roTEG showed a slight decrease in platelet function (p < or = 0.05). We conclude that platelet function is well maintained during storage. This is reflected by the results of immunological and platelet function assays. Rotational thrombelastography (in the case of PRP) and especially resonance thrombography represent promising methods for quality control of platelet concentrates and rapidly provide information about the status of platelet function and the whole clotting process.

Influence of storage time on activation of platelets collected with CS 3000 Plus and Cobe Spectra using platelet storage containers

The aim of this study was to evaluate the in vitro activation in platelet suspensions collected with CS 3000 Plus and Cobe Spectra cell separators using platelet storage containers and the role of white blood cell (WBC) concentration of the suspension in this activation. Seventy-seven donors were subjected to automated platelet donations with 1 type of equipment (37 with Cobe Spectra and 40 with CS 3000 Plus). Blood samples were obtained immediately after separation and on the third day of storage at 22 degrees C in constant agitation. The WBC concentrations of these samples were studied before storage. Paraformaldehyde-fixed platelets were incubated with 2 murine monoclonal antibodies: CD42b and CD62. Murine monoclonal antibody immunoglobulin G was used as a negative isotypic control. Bound antibody was then quantitated by flow cytometry. On the third day of storage, a significant increase in CD62 expression rate was observed in platelet suspensions collected with both kinds of equipment. Mean expression rates for Cobe Spectra on Day 0 and Day 3 were 25.6 +/- 6.2% and 69.2 +/- 9.7%, respectively. Mean expression rates for CS 3000 Plus on Day 0 and Day 3 were 23.4 +/- 8.2% and 67.0 +/- 8.2%, respectively. The mean results for both devices were 22.8 +/- 4.56% for Day 0 and 68.7 +/- 13.2% for Day 3. There was no difference between CD42b mean fluorescence intensity on Days 0 and 3 for the 2 devices (p > 0.5). Mean WBC concentrations in the platelet suspensions for Cobe Spectra and CS 3000 Plus were 0.37 x 10(3)/microl and 0.42 x 10(3)/microl, respectively, and there was no relation between WBC concentration and increase in CD62 expression. Both kinds of equipment were found to be similar according to in vitro activation markers.

Inverse expression of P(k) and Luke blood group antigens on human RBCs

BACKGROUND

Luke (LKE) is a high-frequency RBC antigen, related to the P blood group system. A LKE-negative phenotype is found in 1 to 2 percent of donors and may be associated with increased P(k). Because P(k) and similar glycolipids are receptors for shiga toxin on cell membranes, a LKE-negative phenotype could have implications for infections by Shigella dysenteriae and enterohemorrhagic Escherichia coli.

STUDY DESIGN AND METHODS

Volunteer donors (n = 257) were serologically typed for LKE with a LKE MoAb, MC813-70. LKE-strong-positive, LKE-weak-positive and LKE-negative RBCs were analyzed for P(k), P, LKE, and shiga toxin binding by immunofluorescence flow cytometry, high-performance thin-layer chromatography, scanning densitometry, and high-performance thin-layer chromatography immunostaining.

RESULTS

Among Iowa donors, 78.6 percent were LKE-strong-positive, 20.2 percent were LKE-weak-positive, and 1.2 percent were LKE-negative. There was an inverse expression of P(k) and LKE on RBCs. P(k) expression was increased on LKE-negative RBCs and was associated with increased shiga toxin binding. A LKE-active glycolipid was identified in the ganglioside fraction of LKE-strong-positive RBCs.

CONCLUSION

A LKE-negative phenotype is associated with increased expression of P(k) on RBCs. Differences in P(k) and LKE expression may play a role in host susceptibility to infection with S. dysenteriae and E. coli.

Analysis of factors affecting quantification of fetomaternal hemorrhage by flow cytometry

BACKGROUND

An analysis was carried out to determine the sources and extent of errors encountered in the quantitation of the volume of fetomaternal hemorrhage (FMH) by flow cytometry. Different assay conditions were compared, to define the simplest, most accurate protocol.

STUDY DESIGN AND METHODS

D-, D+, and artificial FMH (mixtures of D+ and D- RBCs) were stained either by a direct method (using FITC-conjugated IgG3 D MoAb [BRAD-3]), with or without dual labeling with PE-conjugated anti-GPA, or by indirect methods (using polyclonal anti-D followed by FITC- or biotin-conjugated anti-IgG reagents). Cells were selected for flow cytometric analysis on the basis of either forward or side scatter (log FSC/log SSC) characteristics or of GPA+ labeling or were unselected. The numbers of events labeled with anti-D were determined from histograms. For some samples, 10 replicates of 500,000 events each were analyzed.

RESULTS

Background fluorescent events in 10 directly labeled gated D- samples ranged from 0.007 to 0.023 percent, equivalent to 0.15- to 0.51-mL FMH. Both the use of a gate on log FSC/SSC or the selection of GPA+ events only resulted in a reduction in FMH of 0.3 mL or less. The intra-assay variation in FMH, or sampling error, was found to be approximately 10 percent at low artificial FMH (<10 mL) but greater (< or =50% with a CV of 15%) with D- samples. Direct staining was quicker and produced a lower background than indirect staining.

CONCLUSION

The inherent sampling error that is due to the random distribution of rare events throughout the blood sample contributed greatly to the variation in the volume of FMH calculated by flow cytometry. The FMH should not be underestimated. For a routine assay, a simplified protocol and calculation will be sufficiently accurate to determine the dose of prophylactic anti-D that should be given to the patient.

Cefotetan-induced hemolytic anemia: a case report and review of the literature

Cefotetan disodium-induced hemolytic anemia has been reported previously, and some of these cases have been severe or fatal. We describe a case of severe hemolytic anemia that occurred in an 80-year-old woman who received cefotetan prophylactically after surgery for a small bowel obstruction. Eight days after the first dose of cefotetan, the patient developed a severe Coomb test-positive hemolytic anemia. Using flow cytometry, we demonstrated cefotetan-specific antibodies in her posttreatment serum, which were detectable at a serum dilution up to 1:10 000. The patient received corticosteroid therapy and blood transfusions, with improvement of her hematologic parameters, but died 54 days after admission for respiratory failure. To our knowledge, this is the first use of flow cytometry for the detection of cefotetan-induced red blood cell antibodies. This technique offers a sensitive, rapid, objective method for detecting drug-induced antibodies.

Assessment of donor T-cell function in cellular blood components by the CD69 induction assay: effects of storage, gamma radiation, and photochemical treatment

BACKGROUND

Functional donor T-lymphocytes in blood components may cause a variety of transfusion complications. A flow cytometric assay based on the measurement of induced CD69 expression may be an alternative to cell proliferation methods in determining the functional status of these cells in blood components.

STUDY DESIGN AND METHODS

Seven units of whole blood, RBCs, and platelet concentrates (PCs) were stored under blood bank conditions. Half of 3 PCs each were gamma-radiated or treated with UVA+psoralen; the other half served as controls. Samples were analyzed for phorbolester-induced expression of CD69 as an indicator of cell responsiveness and for exclusion of propidium iodide as a measure of cell membrane integrity and viability.

RESULTS

CD69 inducibility and propidium iodide exclusion decreased exponentially (half-life, 3. 3 and 8.1 days, respectively) during cold blood storage. Irradiation and UVA+psoralen treatment of PCs immediately reduced CD69 inducibility to 21 percent (controls, 82%; p = 0.004) and 12 percent (controls, 95%; p = 0.0008), respectively. The proportion of cells capable of propidium iodide exclusion was similar in treated samples and controls, but it declined faster in the treated samples during subsequent storage.

CONCLUSION

Flow cytometric measurement of CD69 induction can be adapted to provide quantitative assessment of T-cell function in blood components. Results obtained by the CD69 assay are in general agreement with those previously reported by use of proliferation methods; the assay may be useful for special applications in transfusion medicine.

[Evolving methods in immunohematology]

The immunogenic nature of erythrocyte polymorphism is in variance with the incompatible transfusion. Indeed, the fixing of an antibody on the corresponding antigen generally condemns the cell concerned with its destruction. Therefore, in order to ensure the immunohemolytic safety of the transfusions, it is necessary to avoid an in vivo encounter between antigens and antibodies, whose feasibility study in vitro is a determining element. Because of the requirement standards of such analyses and the preoccupation with the continuous improvement of transfusion safety, the evolution of the methods used in immunohematology is a constant concern for all those involved in the process. Thus, during the last few years, new technologies have been introduced which aim at improving performance and sometimes implementing alternatives to agglutination. This improvement is not limited to the search for an overall increase in specificity-sensitivity; it also takes into account the capability to detect "the clinically significant" as well as the limitations of human reliability, which justifies the introduction of automation and computerization. The whole of these methodological evolutions associated with that of the performance of reagents, legitimate the need to reconsider the realization of erythrocyte typing and the search for anti-erythrocyte antibodies.

Severe HDN due to anti-Ce that required exchange tranfusion

BACKGROUND

Rh system antibodies are commonly encountered in blood bank practice as well as during pregnancy. Nevertheless, no examples of anti-Ce (RH7) have been reported as a cause of HDN that requires exchange transfusion.

CASE REPORT

A 38-year-old woman in her fourth pregnancy was typed as blood group O D+, C-, c+, E+, e-. Anti-C and anti-e were detected in her serum during a routine prenatal work-up. Further evaluation, including flow cytometric analysis, revealed the presence of a strong anti-Ce and a weak anti-e. Her partner was typed as group A D+, C+, c-, E-, e+. A seemingly healthy male infant was delivered at 40 weeks of gestation. The infant's RBCs were typed as group O D-, C+, c+, E+, e+ with a positive DAT (titer 128). Twenty-five hours after birth, the baby had to be transferred to the neonatal intensive care unit because of rapidly rising total serum bilirubin. Despite intensive treatment, including double phototherapy, albumin infusion, and the administration of furosemide and IVIG, the total serum bilirubin level increased during the following day and exchange transfusion with 2 units of type O D-, C-, c+, E+, e- had to be performed; this resulted in a prompt decrease in total serum bilirubin without relapse.

CONCLUSION

Anti-Ce caused severe HDN requiring exchange transfusion. This highlights the need for a close follow-up throughout pregnancy if unexpected RBC antibodies are present, to permit the provision of compatible blood in case of a rare antibody.

Comparison of flow cytometric assays with isotopic assays of (51)chromium-labeled cells for estimation of red cell clearance or survival in vivo

BACKGROUND

A comparison was made between flow cytometric and conventional radioisotopic assays in the determination of the clearance or survival of small volumes of (51)chromium-labeled D+ red cells after injection into volunteers.

STUDY DESIGN AND METHODS

Four clearance studies were performed using 4 mL of autologous D+ cells coated with anti-D at two concentrations (5 or 10 microg anti-D/mL red cells) transfused to two subjects at separate times. Five survival studies were carried out using 5 mL of frozen-thawed D+ cells transfused to five D- subjects with no detectable anti-D. Sequential blood samples were taken for gamma counting and flow cytometry. Several methods were used to stain the transfused red cells, and the data were analyzed by using three flow cytometers.

RESULTS

The determination of red cell clearance or survival by radioactivity measurements gave results consistent with published data. However, none of the flow cytometric assays exhibited the necessary sensitivity or accuracy in quantitation of the rare events to provide reliable data for the calculation of the initial clearance rate, the red cell half-life, or the mean cell lifespan, although rough estimates of red cell clearance were obtained in some subjects. This inability to accurately enumerate rare fluorescence-labeled cells was due mainly to the presence of "background" events, which were a considerable problem in some samples, when the coating level of anti-D was less than 3000 molecules of IgG per cell.

CONCLUSION

Flow cytometry may enable the crude estimation of the percentage of small volumes (<5 mL) of transfused D+ red cells, but in this study it was found that this method was not sufficiently accurate to determine the initial clearance rate, red cell half-life, or mean cell lifespan. If the proportion of transfused cells in the recipient is about 0.2 percent or less, the use of radioisotopes for labeling cells for quantitative in vivo red cell clearance or survival data should remain the method of choice.

An overview of the use of flow cytometry in the analysis of mixed red cell populations

This paper reviews the application of flow cytometric techniques to the analysis and quantitation of mixed red cell populations. Such mixtures may arise in a variety of ways, for example: through transplacental hemorrhage during pregnancy or upon delivery; through iatrogenic procedures such as blood transfusion, bone marrow or peripheral blood stem cell transplantation; or through disease, when a loss of surface antigen expression may occur due to the expansion of abnormal progenitors lacking the appropriate gene or lacking the ability to translate the product of the gene. Flow cytometry can offer a simple and accurate means of identifying and quantitating mixed red cell populations through detection of antigens specific for either donor or recipient, and in many cases it is possible to distinguish homo- or heterozygous expression of a common antigen. Internal antigens may be accessed after fixation and permeabilisation of the red cells. These latter techniques are relatively new and expand the spectrum of antigenic differences available for the identification of individual species in mixed populations.

Immunoglobulin isotype identification in red cell antibodies using flow cytometry

BACKGROUND

Identifying the isotype of an immunoglobulin (IgM vs. IgG) detected in a patient sample is especially important in anticipating the risk of hemolytic disease of the newborn. Currently, 2-mercaptoethanol (2-ME) treatment of a sample is used in the authors' laboratory to degrade IgM, and this is followed by retesting. This method has multiple drawbacks. The purpose of this study was to develop a flow cytometry (FC) assay that would replace the 2-ME treatment protocol (2-ME treatment).

STUDY DESIGN AND METHODS

A preliminary FC assay was developed, modified, and refined through the use of stock antibodies. Then, 10 samples containing antibodies were tested in parallel by the FC assay and 2-ME treatment.

RESULTS

When a 10-unit mean channel fluorescence change was used as an index of a positive result, the FC assay detected all isotypes identified by 2-ME treatment. The FC assay was also able to identify mixtures of isotypes. One antibody that had not reacted in conventional agglutination testing was detected by the FC assay. The amount of fluorescence and the agglutinating strength of the antibody did not parallel each other. In one case, this discrepancy may have reflected an antibody that was primarily IgA.

CONCLUSIONS

The FC assay appears to be as accurate as 2-ME treatment in differentiating IgG from IgM. The FC assay produces a positive endpoint for both isotypes, will identify IgA, requires less sample, and has no odor.

Biocompatibility of a new cell separator studied by flow cytometry: analyses of platelet antigens during apheresis and storage

BACKGROUND

Alterations of platelet antigens are known to occur during cytapheresis and storage. These changes have been shown to be dependent on the biomaterials, techniques, and devices used. In this study, the influence of a new cell separator (AMICUS) and storage container (PL-2410) on platelet glycoproteins was analyzed.

STUDY DESIGN AND METHODS

During plateletpheresis and storage, the levels of platelet glycoproteins and binding of fibrinogen were determined by flow cytometry.

RESULTS

During apheresis, mean channel fluorescence intensity of CD41 a did not change significantly (p = 0.06). A small increase was evident in CD42b mean channel fluorescence intensity, which rose from a baseline level of 178.6 +/- 68.3 to 231.5 +/- 97.9 at the end of the procedure (p<0.05); in CD62p-positive platelets, which increased from 2.0 +/- 0.9 percent to 9.9 +/- 3.9 percent (p<0.05); in CD63-positive platelets, which increased from 1.7 +/- 0.7 percent to 7.9 +/- 2.6 percent (p<0.05); and in the binding of fibrinogen, which increased from 1.9 +/- 0.8 percent positive platelets to 10.5 +/- 2.6 percent (p<0.05). During storage, the mean channel fluorescence intensity of CD41a and CD42b, the percentage of CD62p- and CD63-positive platelets, and the binding of fibrinogen to platelets showed no significant change.

CONCLUSION

These studies show that alterations in platelet antigens and platelet activation occur to a small degree during apheresis and storage. These findings demonstrate generally good biocompatibility of this new cell separator.

Annexin V and platelet antigen expression is not altered during storage of platelet concentrates obtained with the AMICUS cell separator

During storage of platelet concentrate the so-called "storage lesion" occurs. During this time, platelets loose their morphological and functional capacities that are necessary for proper in vivo efficacy following transfusion. Annexin V represents a marker for apoptosis. In this study, Annexin V and additional antigens were analyzed by flow cytometry. Platelet concentrates were obtained with a new cell separator (AMICUS Separator, Fenwal). Following apheresis, platelet units were stored for an experimentally prolonged time of seven days. Daily aliquots of the platelet-rich plasma were obtained to measure Annexin V and platelet antigens CD62p, CD63, CD41a, CD42b, and the binding of fibrinogen. All analyses were performed using flow cytometry. During storage, no significant changes in mean channel fluorescence intensity (MCFI) of CD41a (P = 0.99) and CD42b (P = 0.29), percentage of CD62p+ and CD63+ platelets (P = 0.23 for CD62p; P = 0.52 for CD63), and the binding of fibrinogen to platelets occurred (P = 0.85). Also, the expression of Annexin V remained constant with no significant change (P = 0.36). This study shows that antigens of platelets, obtained with the AMICUS cell separator are well preserved during storage. Regarding Annexin V, no obvious signs of apoptosis can be detected by flow cytometry. These findings demonstrate the high degree of biocompatibility of the apheresis device and storage container.

The role of flow cytometry in improving biocompatibility in transfusion medicine

In transfusion medicine, blood and blood components, donors and patients are increasingly confronted with biomaterials. The need to understand the response of human blood to contact with these artificial surfaces has led to multiple studies on the biocompatibility of biomaterials. Up to this time, these investigations have predominantly been performed using physical, immunological and biochemical methods. Many of these approaches are useful in investigating the multiple factors involved in blood-biomaterial interactions. However, they always reflect the overall behaviour of whole cellular populations in local or systemic reactions. The application of multiparameter flow cytometry, on the other hand, provides insight into antigenic expression and changes at the single-cell level. Therefore, the technique of flow cytometry represents a new and powerful way of analysing and improving the biocompatibility of these materials in blood-contacting applications in this field.

Blood group antibodies are made by CD5+ and by CD5- B cells

The B1 subset of B lymphocytes is associated with the production of low-affinity, polyspecific antibodies. B1 cells are generally recognized by their expression of CD5, and comprise the majority of neonatal B cells. The neonate responds to a restricted range of antigens, and generally makes low-affinity IgM antibody. Published data suggest that antibodies against the blood group antigens A and B are found occasionally in cord blood, and develop rapidly in infants as a result of cross-reactivity with bacterial carbohydrate antigens. This suggests that CD5+ B1 cells may be specialized to make antibodies against such carbohydrate antigens. In this study we evaluated the appearance of antibodies against the blood group (ABO) antigens in human infants, using reagents which specifically distinguish between IgM (made by the infant) and IgG (mainly of maternal origin) and immunofluorescence to detect low levels of antibody. Having established that antibody is always detectable by 8 months of age, and frequently much earlier, we developed a plaque assay to examine the phenotype of cells making antibody against blood group antigens. At 8 months of age, CD5+ and CD5- cells were both capable of making anti-blood group antibody.

Thrombocytopenia induced by vancomycin-dependent platelet antibody

BACKGROUND AND OBJECTIVES

Many drugs are associated with thrombocytopenic purpura through immune-mediated platelet destruction. The case of a woman who suffered life-threatening thrombocytopenia during vancomycin treatment for Staphylococcus aureus septicemia is reported.

MATERIALS AND METHODS

Conventional clinical and laboratory methods, including flow cytometry.

RESULTS

After treatment of septicemia with vancomycin, severe thrombocytopenia and bleeding occurred, without detection of drug-dependent platelet antibodies (DDPA). This was followed by vegetative endocarditis, whereupon antibiotics were withdrawn so as to isolate the organism. The thrombocytopenia was corrected. On day 34, antibiotics including vancomycin were reinstituted, and three days later thrombocytopenia recurred. With a change in antibiotics, the platelet count corrected itself within four days.

CONCLUSIONS

Vancomycin may induce potentially severe immunological thrombocytopenia.

Severe autoimmune hemolytic anemia associated with IgM warm autoantibodies directed against determinants on or associated with glycophorin A

BACKGROUND AND OBJECTIVES

Autoimmune hemolytic anemiA (AIHA) is rarely caused by IgM warm autoantibodies, and is sometimes difficult to diagnose. We describe three patients with severe AIHA caused by IgM warm autoantibodies; in two of the three, the hemolysis was fatal.

MATERIALS AND METHODS

Conventional hematologic and serologic procedures were used.

RESULTS

The IgM autoantibodies in all three cases were directed against determinants on or associated with glycophorin A (Ena, Wrb, and Pr). The IgM autoantibodies and unusual serological characteristics, in that the agglutinins were detected or greatly enhanced only by the presence of albumin or a low pH, and/or the agglutinins reacted optimally at 20-30 degrees C.

CONCLUSIONS

IgM warm autoantibodies directed at determinants on or associated with glycophorin A appear to cause severe (often fatal) hemolytic anemia.

Analysis of platelets by flow cytometry

Transfusion medicine has become a multi-disciplinary field with many recent technical developments and the flow cytometer has had a significant impact in transfusion medicine, especially at the level of platelet immunobiology. Many routine tests in platelet immunology are now performed by flow cytometry laboratories, including assessment of platelet-associated allo- and auto-antibodies and complement components. Platelet analysis by flow cytometry has been applied to detection of platelet antigens, platelet surface-bound proteins, platelet activation, measurement of reticulated platelets, intracellular calcium studies, and the measurement of platelet microparticles in vivo and in vitro. This review will focus on the use of the flow cytometer in these applications in investigations of platelet immunology.