Further improvement of the enzyme-linked antiglobulin test (ELAT) for erythrocyte antibodies

An enzyme-linked immunosorbent assay for the quantitative determination of anti-D in plasma samples and immunoglobulin preparations

Here we present an enzyme-linked immunosorbent assay (ELISA) on microtiter plates for the quantitative determination of anti-D. This method is based on the solubilization of red blood cells sensitized with anti-D and the subsequent measurement of immunoglobulin G by ELISA. The measuring range of the assay is 40-5,000 IU/ml and the lowest quantifiable concentration in plasma is 0.5 IU/ml. The interassay relative standard deviation for concentrations above 130 IU/ml ranges from 3.2 to 8.1% and below 50 IU/ml from 10.5 to 19.7%. Comparison of ELISA with automated hemagglutination shows that the results of the two assays correlate well: r = 0.992, n = 26. The assay was validated for donor plasma samples and anti-D immunoglobulin preparations and it can also be used in assessing the severity of Rh (D) hemolytic disease during pregnancy.

An enzyme-linked antiglobulin test to detect red cell globulins after glutaraldehyde fixation

The purpose of this study was to develop an enzyme-linked antiglobulin test (ELAT) for IgG on RBC without the hemolysis caused by the high pH of the alkaline phosphatase reaction. This was achieved by fixing the RBC with 0.05% glutaraldehyde after attachment of the antibodies. Assays using anti-D reference standards demonstrated the sensitivity to be 1-2 ng of antibody as compared to 7.5 ng for the manual indirect antiglobulin test. The coefficients of variation of these assays ranged from 10.4 to 20.1%. The mean background absorbance at 405 nm of 105 normal RBC samples was 0.08 +/- 0.03 SD. There was an increase in sensitivity of the test after the fixed RBC were stored. Dilute glutaraldehyde stabilizes the RBC membrane and the antigen-antibody linkage resulting in a more sensitive ELAT.

An enzyme-linked antiglobulin test for assessing anti-D immunoglobulin preparations

Two enzyme-linked antiglobulin tests (ELAT) for assessing anti-D IgG preparations are described; one is performed in tubes and the other in microtitre plates. An anti-human IgG alkaline phosphatase conjugate and the substrate p-nitrophenyl phosphate are used. Both methods were sensitive and reproducible, with variations coefficients of 7.8 and 8.6% for enzyme immunoassay in tubes and microplates, respectively. The linear relationship between the amount of red cell-bound anti-D and the optical density shows that the method is suitable for quantitative studies. Results obtained by the two methods show a very good correlation (r = 0.99) in 12 of the 14 samples assayed, and both give good agreement with results obtained in automated haemagglutination. Since microtitre plate ELAT has numerous advantages over the tube method, it could provide an alternative method for assessing anti-D activity of specific IgG preparations in control laboratories.

Incomplete warm hemolysins. I. Case reports, serology, and immunoglobulin classes

Incomplete warm hemolysins (IWHs) form an independent class of red blood cell (RBC) autoantibodies. We studied eight sera in which autoantibodies with the characteristic features of IWHs were demonstrated. The case reports of those patients revealed that IWHs were predominantly associated with a serious course of autoimmune hemolytic disease. In four sera we found a combination of IWHs and cold agglutinins with the specificity anti-I. The cold agglutinins could be separated from the IWHs by affinity chromatography with immobilized I-active RBC material. The binding of IWHs to RBCs was demonstrated on the RBC surface with a modified enzyme-linked immunoassay (APAAP-EIA: monoclonal anti-immunoglobulin antibodies + bridging antibody + alkaline phosphatase/anti-alkaline phosphatase complexes). With the APAAP-EIA technique and different primary anti-immunoglobulin antibodies we found that seven sera contained IgM-IWHs and one contained IgG-IWHs. In three sera, IgM-IWHs with monotypical kappa light chains were detected.

Immunoaffinity isolation of the Lewis blood group antigens

Extraction, followed by immunoaffinity chromatography on a column of immobilized antibodies is described for the isolation of the Lewis blood group antigens. These affinity-isolated antigens are suitable in organ transplant immunology laboratories for screening potential donors and recipients for mismatch at the Lewis antigen loci.

Direct enzyme linked antiglobulin tests (ELAT) for detecting in-vivo sensitized erythrocytes: evaluation of screening for ABO incompatibility of newborn

ABO incompatibility of the newborn is one instance where immune hemolysis may present with a negative direct antiglobulin test (DAT) and therefore a simple sensitive test for detecting sensitization would be useful in this clinical situation. To evaluate the usefulness of ELAT in detecting in-vivo sensitized red cells, 1608 maternal-baby pairs were screened for ABO incompatibility over a period of 10 mth. Of 251 ABO-incompatible babies, there were 49 (19.5%) with positive DAT, but an additional 67 (26.7%) were ELAT positive. These were eluate positive as well, indicating that the increased number with sensitized cells as shown by ELAT is due to detection of in-vivo sensitized cells. The positive predictive value for ABO hemolytic disease of the newborn (HDN) is 48%, which is two times that of DAT. Calculating the difference of the absorbance from baseline (delta OD) may give an indication of degree of sensitization which together with the maternal antibody titre would aid us in the estimation of antigen dosage on the baby's red cells and in the appraisal of the role of antigen dosage in HDN.

An enzyme-linked direct antiglobulin test for assessing erythrocyte bound immunoglobulins

An enzyme-linked direct antiglobulin test (DAGT) for assessing erythrocyte-bound IgG, IgM and IgA is described. The test is carried out in microtitre plates using heavy chain-specific, alkaline phosphatase-linked, goat anti-human globulin reagents with p-nitrophenyl phosphate as substrate. Results are expressed in optical density (OD) units per 3.6 X 10(7) red cells. The method is reproducible, with coefficients of variation of 0.056, 0.093 and 0.087 for IgG, IgM and IgA respectively. The linear relationship between the amount of red cell-bound antibody and the OD reading for each immunoglobulin class shows that the method is suitable for quantitative studies. Healthy individuals were found to have small amounts of immunoglobulin bound to their red cells with mean values of 0.251, 0.087 and 0.128 OD units per 3.6 X 10(7) red cells for IgG, IgM and IgA respectively; there was no difference between male and female subjects. In the clinical situation, the enzyme-linked DAGT was considered to show significantly increased amounts of cell-bound immunoglobulin when the results were more than three standard deviations above the mean and the quantitative results permitted an accurate assessment of the progress and response to treatment of patients with autoimmune haemolysis.

Evaluation of an enzyme-linked antiglobulin test for the detection of red cell antibodies

An enzyme-linked antiglobulin test (ELAT) using low ionic strength saline for the initial red cell sensitisation phase, and alkaline phosphatase conjugated antiglobulin (AP-AHG), has been compared with a conventional low ionic strength antiglobulin test in testing 222 red cell antibodies of various specificities. A wide variation in absorbance values was observed at all levels of haemagglutination strength. Relatively higher absorbance values were obtained with anti-K compared with the agglutination gradings. Haemolysis was eliminated by modifying the substrate buffer used for diluting the AP-AHG, since fixation of red cells prior to sensitisation significantly reduced the sensitivity of the ELAT. Five commercial AP-AHG reagents compared to tests with D, Fya, K and Jka antibodies varied markedly in performance, some being unsatisfactory. The ELAT can be effectively used for antibody detection as well as quantitative determinations but requires automation to realise its full potential.

Improvement of enzyme-linked antiglobulin test by using an antiglobulin linked to glucose oxidase: description of the technique

The classic enzyme-linked antiglobulin test (ELAT) used to detect and quantify the amount of IgG antibodies on red blood cells (RBC) is sensitive to hemolysis and erythrocyte enzymatic activities. We describe a new ELAT by using glucose oxidase (GO) linked to antihuman IgG. The optical density base line of GO-ELAT, alkaline phosphatase-ELAT and peroxidase-ELAT were, respectively, 0.180, 0.350 and 0.550. This very low baseline of GO-ELAT was due to the absence of hemolysis (the pH of the GO substrate is 6.5). This technique is ten times more sensitive than the indirect antiglobulin test and detects up to 1 ng/ml of anti-D alloantibodies. Additional advantages of the technique are (1) there is no intrinsic GO enzyme in RBC, and (2) it is not necessary to fix the RBC.

A new technique in quantitative immunohematology: solid-phase kinetic enzyme-linked immunosorbent assay

A solid-phase kinetic enzyme-linked immunosorbent assay has been developed to measure binding of antibodies to purified or synthetic blood group antigens and tested in the Lewis blood group system. Chemically synthesized Lewis a antigen is used as the target for the binding of serum antibody in this sandwich-type assay. Kinetic, rather than endpoint, determinations are used to calculate the amount of specific antibody. Data are presented showing the assay to be quantitative, sensitive, and specific. It can separately quantitate the amount of IgG or IgM anti-Lewis a present in patient sera. The assay uses commercially available reagents and is semiautomated. Thus, it will be useful for studies in quantitative immunohematology as other blood group antigens become available in purified form.

Radioimmunoassay for immunoglobulin G autoantibody on the surface of mouse erythrocytes

A radioimmunoassay (RIA) for the determination of autoantibody on the surface of erythrocytes from New Zealand Black (NZB) mice is described. This method was adapted to hemagglutination plates in order to facilitate the separation of bound and unbound 125I-labeled rabbit anti-mouse immunoglobulin G with an automated cell harvester. Intra- and interday precision, over the useful quantitative range of the standard curve, was 3.9 and 12.9%, respectively. The RIA was five to ten times more sensitive than the direct antiglobulin test which, unlike the RIA, provided little quantitative information on a group of 20 experimental NZB mice. This is publication number 562 from the Department of Basic and Clinical Immunology and Microbiology, Medical University of South Carolina.