Use of a directly conjugated monoclonal anti-D (BRAD-3) for quantification of fetomaternal hemorrhage by flow cytometry

Comparative study of cartilaginous fish divulges insights into the early evolution of primary, secondary and mucosal lymphoid tissue architecture

Cartilaginous fish are located at a pivotal point in phylogeny where the adaptive immune system begins to resemble that of other, more-derived jawed vertebrates, including mammals. For this reason, sharks and other cartilaginous fish are ideal models for studying the natural history of immunity. Insights from such studies may include distinguishing the (evolutionarily conserved) fundamental aspects of adaptive immunity from the (more recent) accessory. Some lymphoid tissues of sharks, including the thymus and spleen, resemble those of mammals in both appearance and function. The cartilaginous skeleton of sharks has no bone marrow, which is also absent in bony fish despite calcified bone, but cartilaginous fish have other Leydig's and epigonal organs that function to provide hematopoiesis analogous to mammalian bone marrow. Conserved across all vertebrate phylogeny in some form is gut-associated lymphoid tissues, or GALT, which is seen from agnathans to mammals. Though it takes many forms, from typhlosole in lamprey to Peyer's patches in mammals, the GALT serves as a site of antigen concentration and exposure to lymphocytes in the digestive tract. Though more complex lymphoid organs are not present in agnathans, they have several primitive tissues, such as the thymoid and supraneural body, that appear to serve their variable lymphocyte receptor-based adaptive immune system. There are several similarities between the adaptive immune structures in cartilaginous and bony fish, such as the thymus and spleen, but there are mechanisms employed in bony fish that in some instances bridge their adaptive immune systems to that of tetrapods. This review summarizes what we know of lymphoid tissues in cartilaginous fishes and uses these data to compare primary and secondary tissues in jawless, cartilaginous, and bony fishes to contextualize the early natural history of vertebrate mucosal immune tissues.

Enumeration of Fetal Red Blood Cells, Hemoglobin-Specific RBC Cells, and F Reticulocytes in Human Blood

Recent advances in analytical cytometry have improved diagnostic tools for the study of erythropoiesis in anemic patients and resolution of differential diagnosis in diseases of the erythron. This article presents three applications of red blood cell (RBC) analysis-quantitation of fetal red cells, F-cell enumeration, and F-reticulocyte analysis-which improve diagnostic precision, sensitivity, and specificity, and provide better laboratory indicators of therapeutic efficacy in a variety of hematologic and obstetric disorders. Such advances also include the measurement and quantitation of RBC hemoglobins and their relative ribonucleic acid levels. These advances not only promise to improve diagnostic accuracy and laboratory precision over techniques such as the traditional manual reticulocyte counting method and the Kleihauer-Betke stain method for evaluating fetomaternal hemorrhage (FMH), but also serve as tools for newer assays of anemia diagnosis and improved clinical outcomes. In addition to the primary methods, supporting techniques for preparing spiked controls, automating data analysis, setting up a fetal hemoglobin acquisition protocol, and assaying reticulocytes using thiazole orange are also presented. © 2019 by John Wiley & Sons, Inc.

Accurate quantitation of D+ fetomaternal hemorrhage by flow cytometry using a novel reagent to eliminate granulocytes from analysis

BACKGROUND

Quantitation of fetomaternal hemorrhage (FMH) is performed to determine the dose of prophylactic anti-D (RhIG) required to prevent D immunization of D- women. Flow cytometry (FC) is the most accurate method. However, maternal white blood cells (WBCs) can give high background by binding anti-D nonspecifically, compromising accuracy.

STUDY DESIGN AND METHODS

Maternal blood samples (69) were sent for FC quantitation of FMH after positive Kleihauer-Betke test (KBT) analysis and RhIG administration. Reagents used were BRAD-3-fluorescein isothiocyanate (FITC; anti-D), AEVZ5.3-FITC (anti-varicella zoster [anti-VZ], negative control), anti-fetal hemoglobin (HbF)-FITC, blended two-color reagents, BRAD-3-FITC/anti-CD45-phycoerythrin (PE; anti-D/L), and BRAD-3-FITC/anti-CD66b-PE (anti-D/G). PE-positive WBCs were eliminated from analysis by gating. Full blood counts were performed on maternal samples and female donors.

RESULTS

Elevated numbers of neutrophils were present in 80% of patients. Red blood cell (RBC) indices varied widely in maternal blood. D+ FMH values obtained with anti-D/L, anti-D/G, and anti-HbF-FITC were very similar (r = 0.99, p < 0.001). Correlation between KBT and anti-HbF-FITC FMH results was low (r = 0.716). Inaccurate FMH quantitation using the current method (anti-D minus anti-VZ) occurred with 71% samples having less than 15 mL of D+ FMH (RBCs) and insufficient RhIG calculated for 9%. Using two-color reagents and anti-HbF-FITC, approximately 30% patients had elevated F cells, 26% had no fetal cells, 6% had D- FMH, 26% had 4 to 15 mL of D+ FMH, and 12% patients had more than 15 mL of D+ FMH (RBCs) requiring more than 300 μg of RhIG.

CONCLUSION

Without accurate quantitation of D+ FMH by FC, some women would receive inappropriate or inadequate anti-D prophylaxis. The latter may be at risk of immunization leading to hemolytic disease of the newborn.

Reference values of fetal erythrocytes in maternal blood during pregnancy established using flow cytometry

The aim of our study was to assess the fetal RBC count in maternal blood during uncomplicated pregnancies from 26 weeks onward. We used a flow cytometric method specifically designed for use in a routine hematology analyzer. Pregnant women were recruited through midwives. The participating laboratories used the FMH QuikQuant method (Trillium Diagnostics, Brewer, ME) in a CELL-DYN Sapphire hematology analyzer (Abbott Diagnostics, Santa Clara, CA). The method is based on a monoclonal antibody to hemoglobin F. Flow cytometric data were analyzed by 2 independent observers. The 95th percentile reference range was estimated according to Clinical and Laboratory Standards Institute guidelines. A total of 236 samples were statistically analyzed. Gestational ages ranged from 21.6 to 41 weeks (mean, 32.0 weeks), and the fetal RBC count in maternal blood ranged from 0.00% to 0.50% (median, 0.025%). The fetal RBC count in maternal blood shows no correlation with gestational age. The established reference range during normal pregnancy is less than 0.125%.

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.

A rapid gel agglutination test for the determination of fetomaternal haemorrhage

Determination of fetomaternal haemorrhage (FMH) remains an area of difficulty. In most cases, prophylactic Rh immunoglobulin is usually administered to affected women without testing for foetal red blood cells (RBC). Here, we describe a new particle gel immunoassay (PaGIA) for the determination FMH (FMH-PaGIA). Superparamagnetic particles were coated with monoclonal anti-D and mixed with ethylenediaminetetraacetic acid-anticoagulated blood samples from D-negative pregnant women. The particles were isolated using a magnetic particle concentrator and then placed into the reaction chamber of a gel card. Agglutinated particles on top or dispersed through the gel matrix indicated the presence of D-positive cells. After the test was adapted to detect >or=0.3% D-positive RBC, randomly selected postpartum samples from 208 women were analysed in parallel with the Kleihauer-Betke test (KBT). In addition, all discrepancies were further analysed by flow cytometry. A total of 203 of the 208 postpartum samples were negative in both tests. One sample reacted positive with both assays. Two samples were strongly positive in the new FMH-PaGIA, but negative in the KBT. A serological re-examination revealed that both women were D positive. The KBT gave a false-positive result in two cases because of hereditary persistence of haemoglobin F. The new test is specific, easy to perform and can be done at any time in all laboratories.

Assessment of Fetomaternal Hemorrhage by Flow Cytometry and Kleihauer-Betke Test in Rh-Negative Pregnancies

OBJECTIVES

To assess the efficacy of flow cytometry (FC) in the detection and quantification of fetomaternal hemorrhage (FMH) in comparison to the Kleihauer-Betke test (KBT).

METHODS

25 unsensitized Rh-negative mothers who had delivered Rh-positive infants were included. Presence of FMH was determined by KBT and FC using FITC-labeled BRAD-3 antibodies.

RESULTS

FMH was detected in 19 (76%) patients by FC and 23 (92%) patients by KBT prior to delivery, and in 21 (84%) patients by FC and 23 (92%) patients by KBT after delivery. The mean volume of FMH in the post-delivery samples by KBT and FC were 0.34 +/- 0.26 ml (range 0.05-1.2 ml) and 0.37 +/- 0.57 ml (range 0.02-2.6 ml) respectively. The volume of post-delivery FMH estimated by KBT and FC correlated well (r = 0.75; ICC alpha = 0.73). A higher agreement between KBT and FC was seen in the 0.1-0.5 ml range (kappa = 0.65; p < 0.01).

CONCLUSIONS

Both manual KBT and FC using FITC-BRAD-3 antibodies show good sensitivity in detecting and quantifying fetal red cells. There is a good correlation between the methods in the 0.1- to 0.5-ml range of FMH.

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.

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.

Quantification of fetomaternal hemorrhage: a comparative study of the manual and automated microscopic Kleihauer-Betke tests and flow cytometry in clinical samples

OBJECTIVE

The purpose of this study was to evaluate the quantification of fetomaternal hemorrhage by the manual and automated microscopic analysis of Kleihauer-Betke stained slides and by flow cytometry.

STUDY DESIGN

Blood smears were stained and evaluated manually according to the Kleihauer-Betke test. The same slides were used for automated microscopy. In addition, blood flow cytometry was performed by anti-hemaglobin F immunostaining.

RESULTS

Fetomaternal hemorrhage >0.1% was detected in 4 patients by manual and automated Kleihauer-Betke test and by blood flow cytometry. Fetomaternal hemorrhage was absent according to all 3 methods in 13 patients; fetomaternal hemorrhage<0.1% was detected in 27 patients by either manual or automated Kleihauer-Betke test or both. Moderate agreement was observed between the manual and automated Kleihauer-Betke test (weighted kappa, 0.56; 95% CI, 0.33-0.78). Agreement between the manual Kleihauer-Betke test and blood flow cytometry was fair (weighted kappa, 0.40; 95% CI, 0.15-0.66).

CONCLUSION

Automated microscopic detection of fetal blood cells in clinical samples provides accurate quantification that is comparable to the manual Kleihauer-Betke test in both small and large fetomaternal hemorrhage. Blood flow cytometry is capable only of quantifying fetomaternal hemorrhage of >0.1%.

Improved method for fluorescence cytometric immunohematology testing

BACKGROUND

A method for accurate immunohematology testing by fluorescence cytometry (FC) was previously described. Nevertheless, the use of vacuum filtration to wash RBCs and a standard-flow cytometer for data acquisition hindered efforts to incorporate this method into an automated platform.

STUDY DESIGN AND METHODS

A modified procedure was developed that used low-speed centrifugation of 96-well filter plates for RBC staining. Small-footprint benchtop capillary cytometers (PCA and PCA-96, Guava Technologies, Inc.) were used for data acquisition. Authentic clinical samples from hospitalized patients were tested for ABO group and the presence of D antigen (n = 749) as well as for the presence of RBC alloantibodies (n = 428). Challenging samples with mixed-field reactions and weak antibodies were included. Results were compared to those obtained by column agglutination technology (CAT), and discrepancies were resolved by standard tube methods. Detailed investigations of FC sensitivity and reproducibility were also performed.

RESULTS

The modified FC method with the PCA determined the correct ABO group and D type for 98.7 percent of 520 samples, compared to 98.8 percent for CAT (p > 0.05). No-type-determined (NTD) rates were 1.2 percent for both methods. In testing for unexpected alloantibodies, FC determined the correct result for 98.6 percent of 215 samples, compared to 96.3 percent for CAT (p > 0.05). When samples were automatically acquired in the 96-well plate format with the PCA-96, 98.7 percent of 229 samples had correct ABO group and D type determined by FC, compared to 97.4 percent for CAT (p > 0.05). NTD rates were 0.9 and 2.6 percent, respectively. Antibody screens were accurate for 99.1 percent of 213 samples with the PCA-96, compared to 99.5 percent for CAT (p > 0.05). Further investigations demonstrated that FC with the PCA-96 was better than CAT at detecting weak anti-A (p < 0.0001) and alloantibodies.

CONCLUSIONS

An improved method for FC immunohematology testing has been described. This assay was comparable in accuracy to standard CAT techniques, but had better sensitivity for detecting weak antibodies and was superior in detecting mixed-field reactions (p < 0.005). The FC method demonstrated excellent reproducibility. The compatibility of this assay with the PCA-96 capillary cytometer with plate-handling capabilities should simplify development of a completely automated platform.

Improvement of the Kleihauer-Betke test by automated detection of fetal erythrocytes in maternal blood

BACKGROUND

Reliable detection and quantification of fetal red cells in maternal blood is important in routine obstetric practice. The manual Kleihauer-Betke test (KBT) is widely used, but it is imprecise and subjective. This study investigated whether automated readout of the KBT could improve sensitivity and accuracy.

METHODS

Glass slides containing dilutions of fetal red cells in adult blood were prepared and stained by using acid elution. Standard manual evaluation of the KBT was performed for all slides by one investigator. In addition, automated microscopy and image analysis of the same slides were performed, whereby detected fetal cells were reviewed by two independent investigators.

RESULTS

Ten replicate measurements of fetal cell numbers showed high reproducibility and very small interobserver and intraobserver variabilities. Typical coefficients of variation were 3-4% for concentrations ranging from 0.001% to 0.1%. The automated KBT showed strong correlation between theoretical and detected concentrations of fetal cells (r2 = 0.999). In the range from 0.0001% to 0.001%, the standard KBT underestimated the fetal cell percentage, whereas the automated KBT was very precise. The correlation between methods was good (r2 = 0.999).

CONCLUSION

Automated readout of the KBT improved accuracy of fetal cell detection in the range from 0.0001% to 1% fetomaternal hemorrhage, particularly when larger numbers of cells were analyzed.

An automatable format for accurate immunohematology testing by flow cytometry

BACKGROUND

Current immunohematology testing methods have limitations including cost, throughput, and adaptability to automation. Furthermore, current automated and semiautomated workstations cannot accommodate many other tests relevant to blood transfusion.

STUDY DESIGN AND METHODS

Authentic clinical samples from hospitalized patients were tested for ABO group, D type, and presence of RBC alloantibodies by column agglutination technology (CAT), standard tube methods, and a recently developed flow cytometry (FC) technique. Included were challenging samples with rouleaux, autoantibodies, mixed-field reactions, and weak antibodies. Antibody staining of RBCs for FC was initially performed in test tubes and subsequently in microtiter filter plates interfaced with a vacuum manifold.

RESULTS

When antibody staining was performed in tubes, FC testing determined the correct ABO group and D type for 99.1 percent of 222 clinical samples, as compared to accuracies of 91.9 percent for CAT and 95.0 percent for standard tube testing. FC testing also detected 99.5 percent of clinically relevant RBC alloantibodies in 239 patient samples, as compared to 98.9 percent for CAT and 94.7 percent for LISS-IAT. Using the FC filter plate technique, 104 of 109 samples (95.4%) were correctly typed for ABO and D (the remaining five samples were read as "no type determined" due to RBC and serum testing discrepancies), and RBC alloantibodies of the IgG and IgM classes were correctly identified in 98.3 percent of samples.

CONCLUSIONS

Optimized FC testing methods that are comparable in accuracy to standard CAT and tube methods are described. When used with filter plates, this methodology should allow rapid and cost-effective immunohematology testing of both patient and donor samples in an automated workstation format. The same workstation should support automation of other pretransfusion assays that can be analyzed by FC.

Quantification of feto-maternal haemorrhage (FMH) by flow cytometry: anti-fetal haemoglobin labelling potentially underestimates massive FMH in comparison to labelling with anti-D

Many centres now routinely use flow cytometry to quantify feto-maternal haemorrhage (FMH). However, which flow cytometric method is the most accurate in quantifying FMH is currently unknown. An audit of clinical results in which FMH had been estimated by both directly conjugated monoclonal anti-D and anti-fetal haemoglobin (HbF) labelling suggested that the anti-HbF labelling method may underestimate massive FMH in comparison to labelling with anti-D. Subsequent to this audit, 46 samples of adult D-negative blood were spiked with varying amounts of D-positive cord blood (0.05-10% fetal cells per sample), and the number of fetal cells present was quantified by both labelling methods. The percentage of fetal cells detected by anti-D was not significantly different to the estimated percentage of fetal cells added to each sample (P = 0.636). However, anti-HbF labelling significantly underestimated the percentage of fetal cells present (P = 0.0001). In comparison to anti-D, the percentage of fetal cells detected by anti-HbF was also significantly lower (P < 0.0001). The difference in fetal cell detection between anti-D and anti-HbF labelling was only apparent in the spiked samples containing > or =1% fetal cells per sample. In samples containing < or =0.6% fetal cells, no significant difference in the detection of fetal cells between anti-D and anti-HbF labelling was observed (P = 0.11). To allow adequate immunoprophylaxis in D-negative mothers with massive FMH, we recommend that anti-D labelling should be used in the routine flow cytometric estimation of FMH.

Evaluation of flow cytometric enumeration of foetal erythrocytes in maternal blood

In pregnant women subject to abdominal trauma or other foetomaternal haemorrhage, foetal red blood cells containing haemoglobin-F (HbF) can be found in the circulation. Recently, a monoclonal antibody to HbF has become commercially available, enabling application of a flow cytometric immunofluorescence method for accurately determining the concentration of HbF+ red blood cells. We demonstrate that white blood cells are included in the cluster selected as red blood cells and that these white blood cells exhibit a level of autofluorescence that coincides with the fluorescence signal from HbF+ red blood cells. However, these white blood cells can be excluded from the analysis, thus preventing spuriously increased HbF+ red blood cell counts. We present the results of patient samples containing HbF+ red cells as illustrations of the technique and as a potential interference by HbF-containing cells of nonfoetal origin. Using samples spiked with cord blood, the method is exactly linear with a high coefficient of correlation (r=0.997). Furthermore, the assay has excellent precision (CV < 2.4%), a low limit of detection (0.12% HbF+ RBC), is independent of Rhesus D and can be completed within 1.5 h. This method is suitable for accurate determination of foetomaternal haemorrhage.

Quantification of foetomaternal haemorrhage. An analysis of two cytometric techniques and a semiquantitative gel agglutination test

Traditional tests to screen for foetomaternal haemorrhage are time-consuming and difficult to perform. The Kleihauer test is widely used but difficult to standardize. We evaluated three techniques for quantifying foetomaternal haemorrhage: a semiquantitative gel agglutination test and two flow cytometric techniques. The gel agglutination test is based on the consumption of anti-D reagent by D+ cells, analysing the reaction of the supernatant against indicator cells in a Coombs-gel card. In the two colour direct immunofluorescent technique, the sample is incubated with Per-CP labelled anti CD45 antibody, fixed with glutaraldehyde and permeabilized by exposure to Triton X-100. An aliquot is stained with an antibody to foetal haemoglobin, conjugated with fluorescein isothiocyanate or phycoerythrin. The indirect immunofluorescent technique is based on the labelling of Rh (D) antigen with an anti D reagent, followed by the addition of an anti IgG antibody conjugated with phycoerythrin. Foetomaternal haemorrhage was not detected in 75 of the 85 samples analysed by the direct immunofluorescent technique. In the remaining 10 samples, the volume was very low. Thirty-five samples with Rh (D) antigen incompatibility were analysed in parallel by the indirect immunofluorescent technique and in 15 of the 35 samples, the gel agglutination technique was also carried out. The three techniques gave similar results. The gel agglutination test can be used to screen for foetomaternal haemorrhage, while greater volumes should be quantified by flow cytometric techniques.

Monoclonal anti-D for immunoprophylaxis

Routine antenatal prophylaxis with anti-D has become accepted as desirable, but concerns have been expressed about the adequacies of supply and safety of polyclonal anti-D. Human monoclonal anti-D has been produced using Epstein-Barr virus (EBV)-transformed peripheral B cells, sometimes coupled with fusions to myeloma cell lines. More recently, molecular biology techniques have been used to produce human monoclonal anti-D in a variety of different ways. Many monoclonal antibodies (mAbs) have been characterized for fine specificity and in vitro functional activity in International Workshops. Two mAbs have been shown to cause red cell clearance and immunosuppression in male volunteers. Considerations for the future development of monoclonal anti-D for prophylactic use are reviewed.

Labeling D+ RBCs for flow cytometric quantification of fetomaternal hemorrhage after the RBCs have been coated with anti-D

BACKGROUND

D- patients may receive Rh immunoglobulin (RhIg) before blood samples are taken for estimation of the volume of fetomaternal hemorrhage (FMH) by flow cytometry. Anti-D bound to the fetal D+ cells may then block the binding of conjugated D MoAb. This may reduce the fluorescence of the D+ cells, which would lead to ambiguity over setting the positions of the markers on histograms and may result in erroneous values of FMH.

STUDY DESIGN AND METHODS

Labeling methods were compared by using FITC-BRAD 3 (anti-D) and/or FITC-anti-IgG (Fab fragment) with mixtures of D+ (R1r) and D- (rr) cells when the D+ cells had first been coated with various amounts (0 molecules/cell and 600-13,000 molecules/cell) of anti-D (RhIg). Variables examined were antibody concentrations, the order and times of incubation with the antibodies, and the effect of washing between the uptake of the antibodies used.

RESULTS

In all cases, D+ cells were strongly labeled after incubation with 50 microL of FITC-BRAD-3 and then after washing with 50 microL of FITC-anti-human IgG, with both incubations being for 30 minutes at 37 degrees C. With this double-staining procedure, the fluorescence of D+ cells was found to be similar regardless of how much anti-D (RhIg) was previously bound and greater than that with FITC-BRAD-3 alone, giving an enhanced signal-to-noise ratio.

CONCLUSION

As the testing laboratory may not know if the patient has received prophylactic RhIg, this labeling method would be suitable for all samples.

Detection of massive transplacental haemorrhage by flow cytometry

Flow cytometry has been shown to be a more accurate and sensitive method than the Kleihauer-Betke test for the measurement of feto-maternal haemorrhage in Rh(D) incompatibility. This report describes the successful use of flow cytometry to detect and monitor the management of a massive transplacental haemorrhage (105 ml) of fetal Rh(D) positive cells in a Rh(D) negative woman. The report highlights the accuracy and reproducibility of the test and the stability of a blood sample when transferred 596 kilometres to a central testing facility.

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.

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.

Monitoring the clearance of fetal RhD-positive red cells in FMH following RhD immunoglobulin administration

Anti-RhD immunoglobulin was administered to RhD-negative women based on estimates of fetal bleed size obtained using a direct immunofluorescence flow cytometric technique employing a FITC-conjugated monoclonal human anti-D (BRAD 3). The effectiveness of the dose administered was assessed by (i) measuring the fraction of RhD-positive fetal cells in the maternal circulation at d0, and between d2 and d10 post RhD Ig administration, (ii) quantifying the amount of anti-D detectable in maternal plasma following RhD Ig injection in the perinatal period and (iii) assessing maternal serum for the presence of immune anti-D in follow-up samples taken 3 months to 3 years after delivery. Fifty-four women were assessed, 29 having fetal bleeds in excess of 4 mL. Follow-up samples were received from 20/29 mothers after RhD Ig administration; 43-99% and 69-99% of fetal cells had been cleared by d2/3 and d5/6, respectively, in 14/20 mothers, whereas less than 50% had been cleared in the remaining mothers. Long-term follow-up samples were obtained from eight of the 29 mothers (four with bleeds >/=20 mL, two with bleeds >95 mL): none had detectable anti-D in the serum 4 months to 3 years after delivery despite the persistence of up to 36% fetal RhD-positive cells in the maternal circulation six days after delivery.

Use of a phycoerythrin-conjugated anti-glycophorin A monoclonal antibody as a double label to improve the accuracy of FMH quantification by flow cytometry

The use of flow cytometry for quantifying fetomaternal haemorrhage is increasing, and has been shown to be more accurate than the Kleihauer-Betke test for evaluating larger bleeds of over 4 mL in volume. Red cells are stained with fluorescently labelled monoclonal anti-D. Cells for analysis are normally gated manually on the basis of forward and side scatter. We investigated whether the use of an antiglycophorin A monoclonal antibody conjugate (red cell specific) in a dual labelling technique would improve the gating of RBC and FMH quantification. Mixes of adult rr and cord R1r RBC were prepared to simulate 1, 0.5, 0.25, 0.12 and 0.06% fetal bleeds. Phycoerythrin-conjugated BRIC 256 (mouse monoclonal antiglycophorin A) was used to label all RBC, and FITC-BRAD-3 monoclonal anti-D was used to determine the proportion of D-positive cells. Results from the dual labelling experiments were compared to those from single labelling of the same mixtures with FITC-BRAD-3 alone, using gated and ungated data. The results showed that single labelling with manual gating gave falsely low FMH estimates. We conclude that use of a fluorescently labelled antiglycophorin A antibody improves the accuracy of the FMH measurement by flow cytometry, as manual subjective gating of RBC excludes a higher proportion of fetal than of adult RBC.

Detection of weak D and D(VI) red cells in D-negative mixtures by flow cytometry: implications for feto-maternal haemorrhage quantification and D typing policies for newborns

Quantitation of feto-maternal haemorrhage (FMH) by flow cytometry (FC) has been shown to be more accurate than the Kleihauer-Bekte test. Fetal cells will be predominately of R1r or R2r phenotype, with antigen site numbers per cell (SPC) of between 9900 and 16000. If the fetus is of weak D or partial D(VI) phenotype, fewer SPC will be present. Red cells from 20 adult weak D samples were mixed with rr red cells to give 1% mixes. Mixtures were stained and analysed by FC, using two different monoclonal reagents. The SPC of each sample was measured using SOL-ELSA with Scatchard plot analysis. 18 samples could not be distinguished and had <1000 SPC. Two samples that could be distinguished had 1350 and 3000 SPC. Red cells from seven samples of D(VI) were also analysed. None of these samples could be distinguished: SPC were all <1000. Although one of the reagents used reacts with D(VI) cells, quantitation of a D(VI) FMH would not be possible due to low SPC. The ability of fetal red cells with low Rh D SPC to cause immunization is questionable; failure to measure FMH in these cases is unlikely to cause clinical problems, as long as suitably sensitive serological reagents and techniques are used to type all weak D and D variant babies as Rh D positive, and thus ensure that the mother is given the appropriate dose of anti-D.

Strategies for rare-event detection: an approach for automated fetal cell detection in maternal blood

This article explores the feasibility of the use of automated microscopy and image analysis to detect the presence of rare fetal nucleated red blood cells (NRBCs) circulating in maternal blood. The rationales for enrichment and for automated image analysis for "rare-event" detection are reviewed. We also describe the application of automated image analysis to 42 maternal blood samples, using a protocol consisting of one-step enrichment followed by immunocytochemical staining for fetal hemoglobin (HbF) and FISH for X- and Y-chromosomal sequences. Automated image analysis consisted of multimode microscopy and subsequent visual evaluation of image memories containing the selected objects. The FISH results were compared with the results of conventional karyotyping of the chorionic villi. By use of manual screening, 43% of the slides were found to be positive (>=1 NRBC), with a mean number of 11 NRBCs (range 1-40). By automated microscopy, 52% were positive, with on average 17 NRBCs (range 1-111). There was a good correlation between both manual and automated screening, but the NRBC yield from automated image analysis was found to be superior to that from manual screening (P=.0443), particularly when the NRBC count was >15. Seven (64%) of 11 XY fetuses were correctly diagnosed by FISH analysis of automatically detected cells, and all discrepancies were restricted to the lower cell-count range. We believe that automated microscopy and image analysis reduce the screening workload, are more sensitive than manual evaluation, and can be used to detect rare HbF-containing NRBCs in maternal blood.

Monoclonal anti-D for prophylaxis of RhD haemolytic disease of the newborn

The incidence of Rh D haemolytic disease of the fetus and newborn has been dramatically reduced by the prophylactic administration of anti-D immunoglobulin to Rh D-negative women. This preventive treatment depends on adequate supplies of anti-D derived from plasma of immunised donors, and replacement with monoclonal anti-D would be advantageous. Two monoclonal antibodies, BRAD-3 (IgG3) and BRAD-5 (IgG1) have been produced from EBV-transformed B-lymphoblastoid cell lines in Bristol and extensively characterised. Both have shown good (but differing) functional activities, determined by study of interactions of anti-D coated red cells with effector cells bearing IgG Fc receptors. Phase I clinical trials using Rh D negative male volunteers were undertaken in Bristol. The plasma half lives of BRAD-3 and BRAD-5 were characteristic for their IgG subclass, and both anti-D mediated accelerated circulatory clearance of D-positive red cells infused two days after i.m. injection of the antibodies. BRAD-3 and BRAD-5 were then shown to protect the volunteers from mounting a primary anti-D response to these D-positive red cells, and thus they may be suitable for Rh D prophylaxis of Rh D-negative women.

Monocyte-bound monoclonal antibodies inhibit the Fc gamma RI-mediated phagocytosis of sensitized red cells: the efficiency and mechanism of inhibition are determined by the nature of the antigen

Monocyte-binding monoclonal antibodies (mAbs) inhibited the Fc gamma receptor I (Fc gamma RI)-mediated phagocytosis of red cells sensitized with human monoclonal immunoglobulin G (IgG) anti-D (E-IgG) via three distinct mechanisms depending on their specificity. First, all monocyte-binding mAbs tested inhibited the adherence (and hence the phagocytosis) of E-IgG. They also inhibited the binding of fluorescein isothiocyanate (FITC) conjugated IgG anti-D. This inhibition of ligand binding was more efficiently promoted by murine (m) IgG2a than mIgG1 mAbs and presumably involved receptor blockade via the formation of antigen (Ag)-mAb-Fc gamma RI complexes on the monocyte membrane. Monocytes passively sensitized with human monoclonal anti-D (M-IgG) were used in experiments to distinguish between inhibition of ligand binding and inhibition of phagocytosis. In this way, it was shown that mAbs to transmembrane molecules (CD11b/CD18, CD44, and HLA) inhibited the phagocytosis of red cells adherent to M-IgG. Under the same conditions, mAbs to glycosylphosphatidylinositol (GPI) linked molecules (CD14, CD55 and CD59) did not inhibit phagocytosis. These data suggested a second mechanism of inhibition of Fc gamma RI-mediated phagocytosis that involved the cross-linking of a proportion of Fc gamma RI (i.e. those not ligated with IgG anti-D) to molecules which are relatively constrained in the cell membrane. A third mechanism of inhibition was revealed by the use of F(ab')2 fragments of mAb to CD11b which inhibited Fc gamma RI-mediated interactions with E-IgG in a manner that did not involve IgG (Fc) crosslinking or blockade of Fc gamma RI. In this respect, Fc gamma RI-mediated phagocytosis was more susceptible to inhibition than receptor-mediated adherence.