Comparison of DATs using traditional tube agglutination to gel column and affinity column procedures.

BACKGROUND: Detection of immunoglobulin or complement bound to RBCs by using the DAT is valuable in the diagnosis of immune-mediated hemolytic anemia. Traditionally, the DAT has been performed by tube agglutination using anti-IgG or anti-C3d. The purpose of this study was to compare the tube agglutination DAT to gel microcolumn, affinity microcolumn, and flow cytometric DATs on RBCs coated in vitro and on patient RBC samples. STUDY DESIGN AND METHODS: RBCs from 84 patients were assessed by tube agglutination DAT, one gel microcolumn DAT, and two affinity microcolumn DATs. One affinity microcolumn assay was unmodified and one was modified by the addition of polyspecific antiglobulin or anti-IgG as a secondary antibody. RBCs from 15 of the 84 patients underwent analysis by flow cytometry with fluorescence-labeled anti-IgG. The assays were also compared by using D+ RBCs sensitized with serially adjusted concentrations of anti-D. RESULTS: Both tube agglutination and gel microcolumn DATs were positive in 49 patient samples; both assays were negative in 20 samples, and the results were discordant in 15. Gel microcolumn DATs were more likely than were tube agglutination DATs to detect IgG on RBCs. Affinity microcolumn DATs were less likely than gel microcolumn or tube agglutination DATs to detect IgG on RBCs. Flow cytometry results were the same as gel microcolumn results in 12 of 15 patient samples and the same as tube agglutination results in 13 of 15. Tube agglutination and both affinity microcolumn assays reacted with RBCs coated with anti-D that was diluted 1-in-100. The gel microcolumn and flow cytometry assays reacted with RBCs coated with anti-D diluted 1-in-400. There was no correlation between tube agglutination and gel microcolumn DATs in detecting bound C3d. CONCLUSION: Detection of IgG bound to RBCs was not consistent with the methods described. Gel microcolumn DATs were more sensitive than tube agglutination and affinity microcolumn DATs. Given the varied results of these assays, reference laboratories should not rely on a single method for DATs. More comprehensive testing should be performed when the tube agglutination DAT is negative in a patient with suspected immune-mediated hemolytic anemia. Further comparisons are necessary to determine the proficiency of flow cytometric assays.

Detection of granulocyte antibodies by flow cytometry without the use of pure granulocyte isolates.

Established methods used to detect serum antibodies to granulocytes require the isolation of granulocytes. Flow cytometric analysis of granulocytes with monoclonal antibodies eliminates the need for granulocyte isolation. The purpose of this study was to develop a method to evaluate reactions of antibodies to granulocytes without separating granulocytes from other leukocytes. Three screening cell samples for granulocyte antibody detection were prepared from whole-blood samples in which the red blood cells (RBCs) were lysed and remaining leukocytes tested against sera at 4 degrees C. Binding of human alloantibodies to the screening cells was determined by flow cytometric analysis using phycoerythrin-conjugated antibody to human immunoglobulin. Forward and side scatter were used to analyze granulocytes separately from other leukocytes. The assay was validated by testing granulocytes with reference alloantibodies directed to NA1, NA2, 5b, and Mart antigens. Samples from 32 patients were tested, and the results of the assays were compared with the results of testing the samples in a granulocyte immunofluorescence (GIF) assay performed by a reference laboratory. In the whole-blood flow cytometric (WBFC) assay the mean fluorescence intensities of reference antisera with antigen-positive cells, expressed in arbitrary units, were anti-NA1 = 48 to 221, anti-NA2 = 24 to 69, anti-5b = 13 to 57, and anti-Mart = 42 to 72. In contrast, the mean fluorescence intensity of type AB-negative control sera ranged from 3 to 11. Of the 32 patient sera tested, 23 were positive (range = 12 to 56) and 9 were negative (range = 3 to 10). When compared with the results obtained by the reference laboratory, 27 sera were concordant between the WBFC and the GIF assays. Four of the samples were positive in WBFC (range = 11 to 31) and negative in GIF and one sample was negative in WBFC (range = 5 to 6) and positive in GIF. Leukocytes prepared from whole blood after lysis of RBCs can be used in flow cytometric analysis to detect granulocyte alloantibodies. The results of testing for granulocyte antibodies with this assay were similar to results of testing sera in GIF. Further comparative studies are indicated to confirm findings and explain the discordant results.

Detection of HLA antibodies by using flow cytometry and latex beads coated with HLA antigens.

BACKGROUND: Detection of HLA class I antibodies in sera is needed in various clinical situations. The standard method for detecting HLA class I antibodies is the complement-dependent lymphocytotoxicity (CDC) assay, but solid-phase assays are now available. STUDY DESIGN AND METHODS: This study assessed the ability of a flow cytometric assay using latex beads coated with HLA class I antigens to detect HLA class I-specific antibodies. The CDC assay was compared with the pooled-bead assay for the detection of HLA class I antibodies. Thirty-one randomly selected serum samples previously tested by CDC assay were tested with pooled beads and analyzed by flow cytometry. Twenty-seven additional serum samples, chosen by clinical criteria and CDC assay results, were tested against the pooled beads. Next, samples from six patients from whom three or more serum samples were drawn on consecutive days were tested with both methods. Finally, serum samples that were proved positive by both methods were tested with selected beads coated with antigens from a single person. RESULTS: Among the randomly selected serum samples, there was 90-percent agreement between the two assays. There was 96-percent agreement between the two assays of the 27 samples that were selected by clinical criteria and CDC assay results. Testing the sera with individual beads suggested that the HLA class I antibodies react with beads expressing the corresponding HLA antigen and beads expressing antigens in the same cross-reactive group. CONCLUSION: The pooled-bead assay can be used as an alternative method for detecting HLA class I antibodies. However, if the specificity of the HLA class I antibody is required, another assay must be used.

Granulocyte storage and antigen stability.

BACKGROUND: Current methods for the detection of granulocyte antibodies require panels of freshly isolated cells. This makes these assays time-consuming, costly, and technically difficult. STUDY DESIGN AND METHODS: The immunofluorescence method of detecting the binding of antibodies to granulocytes was modified for use with a flow cytometer, and methods were tested to store granulocytes for use in that assay. Granulocytes were stored at 4 degrees C for 7 days under three conditions: 1 -percent formaldehyde-fixed cells were stored in Hanks' balanced salt solution (HBSS); untreated cells were stored in tissue culture medium (RPMI-1640); and cells were fixed and stored with a commercial white cell-storage solution (Cyto-Chex Reagent). Antigen stability was evaluated by using monoclonal antibodies (MoAbs) and alloantibodies. Serologic studies were done by an indirect immunofluorescence assay and assessed by flow cytometric analysis. RESULTS: On Day 2, only 2 to 7 percent of granulocytes stored in RPMI-1640 remained. On Day 7, 67 to 76 percent of granulocytes fixed in formaldehyde and stored in HBSS remained, and 47 to 87 percent of granulocytes stored in a white cell-storage solution remained. All antigens were detectable by the MoAbs and alloantisera on Day 7. However, nonspecific staining by the fluorescein isothiocyanate (FITC)-conjugated secondary antibody hindered interpretation of test results on Day 4. Non-specific staining occurred over time and was associated with increased cell permeability during storage. Two sources of nonspecific staining were identified. The first source was the FITC-conjugated secondary antibody; it was eliminated by switching to a phycoerythrin conjugate. The second source was factors in human serum; it was resolved by examining only viable, impermeable cells identified by using 7-aminoactinomycin-D. CONCLUSION: Granulocytes and their antigens can be preserved for at least 7 days, but evaluation of antibody reactions was possible for only 4 days as a result of non-specific staining due to enhanced membrane permeability of dying cells.

Evaluation of the gel system for ABO grouping and D typing.

BACKGROUND: The gel agglutination assay has been approved by the Food and Drug Administration as an alternative to the tube assay for the detection of red cell antibodies. It has also been approved recently by the Food and Drug Administration for ABO blood grouping and D typing. STUDY DESIGN AND METHODS: Tube and gel agglutination assays were compared for ABO grouping and D typing of 100 donor and 100 patient specimens. ABO grouping of 14 specimens of known ABO groups and D typing of 10 specimens with weak D were also compared. When antigen typing or isohemagglutinin results differed, gel testing was repeated by the use of modified incubation times, reagent or specimen volumes, and red cell concentrations. RESULTS: ABO grouping and D typing in all patient and donor specimens concurred. B isohemagglutinins were not detected in seven group A specimens. Six of seven discrepancies were resolved when gel tests were incubated at room temperature with increased serum or plasma volume. Weak D was detected in all 10 specimens tested by both assays. When weak A and/or B were tested with monoclonal antibody reagents, the correct phenotypes were identified in 9 specimens by gel assay and in 10 by tube assay. Using human antisera, 6 specimens were correctly phenotyped by gel assay and 7 by tube assay. CONCLUSION: The gel assay performed as well as the tube assay in detection of A, B, and D, but the tube assay was slightly better at detecting B isohemagglutinins. The gel assay can be used in place of the tube assay for ABO blood grouping and D typing.

Biotinylation modifies red cell antigens.

BACKGROUND: Chemical biotinylation of red cell membranes may be useful for several clinical applications, including red cell survival studies. STUDY DESIGN AND METHODS: To examine the possible effects of biotinylation on red cell antigens, standard hemagglutination assays were performed on matched sets of control and biotinylated red cells. The red cells were biotinylated at a final concentration of 2.0 pg of sulfo-N-hydroxysuccinimide-biotin per cell, and antigen-negative cells were directly compared to antigen-positive cells when possible. The hemagglutination assays were graded in a blinded fashion. Forty-one red cell antigens from 21 of the 23 established blood group systems were tested. RESULTS: Hemagglutination based upon antibody binding to A, A1, M, N, S, s, P1, D, C, E, c, e, C(w), Lu(b), K, k, Kp(b), Le(a), Le(b), Fy(a), Fy(b), Jk(a), Jk(b), Di(a), Wr(a), Wr(b), Yt(a), Xg(a), Sc1, Do(b), Co(a), Ch, H, Ge2, Cr(a), Kn(a), I, and P was not affected by biotinylation. Unexpectedly, the hemagglutination of Di(b+) and LW(a+) red cells was blocked after biotinylation. Conversely, MH04 monoclonal anti-A agglutinated red cells expressing B only after biotinylation. BIRMA-1 monoclonal anti-A and polyclonal anti-A from sera did not agglutinate the biotinylated B red cells. CONCLUSION: Biotinylation of human red cells specifically modified their antigenicity, as measured by standard hemagglutination assays.

Comparison of tube and gel red blood cell agglutination techniques in detecting chimeras after major ABO-mismatched allogeneic hematopoietic stem cell transplantation.

We compared the ability of tube and gel red blood cell (RBC) agglutination techniques to follow erythroid engraftment in a patient who received a major ABO-mismatched peripheral blood stem cell transplant and bone marrow transplant. Tube and gel RBC agglutination techniques were used to detect mixed-field reactivity in cell mixtures containing A/O and c+/c- RBCs and the ability of these two technologies to detect RBC chimeras were compared. We detected c+ RBCs in c+/c- RBC populations microscopically at 1% by the tube RBC agglutination technique, but not until 10% by the gel technique. Group A RBCs in A/O RBC populations were detected at 10% by both techniques. In the patient studied, group A RBCs and c+ RBCs were detected on Days 20 and 14, respectively, with the tube RBC agglutination technique, but neither marker was detected until Day 26 with the gel technique. Tube and gel RBC agglutination techniques comparably identified ABO mixed fields. Although the tube RBC agglutination technique showed greater sensitivity than the gel technique in detecting the c antigen, the gel technique was easier to use and allowed more reliable interpretation of mixed fields by the technologist.

Positive selection of CD34+ hematopoietic cells using an immunoaffinity column results in T cell-depletion equivalent to elutriation.

Acute graft-vs.-host disease (GVHD) continues to present a barrier to successful allogeneic marrow transplantation. T cell-depletion may prevent severe GVHD but carries an increased risk of graft rejection and relapse posttransplant. Clinical trials have defined the number of lymphocytes associated with sustained engraftment but low risk of significant GVHD (greater than grade I or II skin only) as < or = 10(5)/kg. We examined T cell-depletion resulting from positive selection of CD34+ hematopoietic cells with a biotinylated monoclonal anti-CD34 antibody and an immunoaffinity column. Eleven patients (six myeloma and five breast cancer) underwent both peripheral blood stem cell (PBSC) collection and marrow harvest prior to autologous transplantation. One PBSC collection and one-third of each marrow underwent column separation. PBSCs were enriched for CD34+ cells from an initial mean of 1.5 to 53.3%, while marrow went from an initial mean of 2.8 to 65.4%. PBSC were depleted of CD3+ cells from an initial mean of 9.6 x 10(9) to 8.6 x 10(6). Marrow CD3+ lymphocyte content was reduced from an initial mean of 5.6 x 10(9) to 8 x 10(5). Since the column permits quantification and salvage of depleted T cells, its use should allow re-addition of T cell-aliquots associated with minimal risk for GVHD and rejection. In addition, since PBSCs were as readily depleted as marrow, allogeneic PBSC transplant may be feasible using this method.