anti-A Reagents Research Articles

ABO Blood System: Biosynthesis of Agglutinogenic Alkaline and Non-Agglutinogenic Acid Glycotopes of A and B Antigens at Different pHs of the Culture Medium.

The biosynthesis of agglutinogenic and adsorbing groups A and B glycotopes of the erythrocyte's membrane is mediated by the activity of specific glycosyltransferases. This study aimed to assess the nature of the biosynthesis of A and B antigenic glycotopes, depending on the pH of the medium during the cultivation of erythrocytes, and the antigenic (transferase) characteristics of the donor serum of the other group. Monoclonal antibodies (Mabs) were obtained from IGBRL under Program IV of the International Workshop on Monoclonal Antibodies and Red Blood Cell Antigens. Biosynthesis was performed using erythrocytes, fresh serum, medium 199, and an antibiotic solution. The agglutinogenic characteristics of 11 out of 33 samples changed by the end of the cultivation period due to the acquisition of additional agglutinogen corresponding to the donor serum. None of the samples lost their inherent agglutinogen due to its absence in the donor serum. Four of six samples of O(I) erythrocytes acquired the ability to be agglutinated by anti-A reagents, especially by the polyclonal anti-A, and the manifestation of agglutination depended on the reaction time. Two of the three samples with initial A(II) agglutinogenic specificity added to the donor serum with Bc'+ characteristic of the erythrocytes acquired this characteristic. However, none of the five A(II)Ac'+ samples cultured in the serum of Ac'-O(I)Ac'-Bc'+ and O(I)Ac'-Bc'- donors lost their inherent earlier Ac'+ characteristic. The investigation of the inhibitory ability of alkaline and acidic glycoconjugates isolated from membranes revealed that alkaline Alp-00 and Alp-1 glycotopes isolated from glycolipids had the highest inhibitory activity, and the degree of inhibition of polyclonal anti-A antibodies was even higher than that of monovalent BRIC-131. This study showed the possibility of the biosynthesis of specific non-agglutinogenic A and B glycotopes under the influence of a different group's serum as a source of the corresponding transferase.

Serological and molecular analysis of the B(A) subtype in China-A systematic review.

To study the serological and molecular biological characteristics of the B(A) subtype and its geographical distribution in China through case discussion and systematic review. A case of the B(A)02 subtype previously found in our laboratory was retrospectively analysed. The distribution characteristics and specific serological and genotypic characteristics of the B(A) subtype in China were systematically evaluated by searching four major Chinese databases. In a previous case of an abnormal blood group, both the proband and her father were found to be genotype B(A)02/O02, while the mother was normal type B. After a systematic search, irrelevant studies were screened out, and 88 studies were included for analysis. The results showed that the B(A)04 subtype was significantly more frequently reported in the north than in the south, while the B(A)02 subtype was predominant in the southwest. The A antigen of the B(A)02 subtype reacts with monoclonal anti-A reagents in a wide range, while the A antigen of the B(A)04 subtype has a weak agglutination intensity of less than or equal to 2+. The results showed that the B(A) subtype has specific characteristics in the Chinese population, and this study further enriched the serological and molecular biological characteristics of the B(A) subtype.

Comparison of Conventional Tube and Gel-Based Agglutination Tests for AB System Blood Typing in Cat.

Gel technology is widely used for blood typing in human medicine. It has a number of advantages over routine tube testing, including standardization, stability, smaller sample volume, ease of performance and analysis, and speed. The aim of this study was to evaluate feline blood typing using the gel column technique. TUBE agglutination typing was performed in 143 feline blood samples from blood donors and recipients, healthy and sick patients, and whole-blood units anticoagulated with ethylenediamine tetraacetic acid or citrate phosphate dextrose adenine. Plasma from type B cats was used as anti-A reagent, Triticum vulgaris lectin as anti-B reagent, and the control was saline solution. Agglutination in backtyping of types B and AB samples with type A red blood cells (RBCs) was used to confirm whether the samples were type B (presence of alloantibodies) or type AB (absence of alloantibodies). Blood typing in a neutral gel column technique (GEL) using the same anti-A and anti-B reagents was performed on duplicate samples. Sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, positive predictive value, negative predictive value, overall accuracy, and Cohen κ coefficient (κ) for GEL were calculated, with TUBE considered the gold standard technique. Of 143 samples typed with TUBE, 98 (68.5%) were type A, 25 (17.5%,) type B, and 20 (14.0%) type AB. Backtyping confirmed the categorization of all types B and AB samples. Of these samples, gel testing produced 115 (80.4%) concordant results; a mixed-field agglutination pattern (layers of RBCs at both the top and at the bottom of the gel in either the A or B gel column) was seen in 27 samples, and one type B sample was misidentified as type AB. If the mixed-field pattern was interpreted as a negative result, 141/143 (98.6%) samples showed concordant results with an overall accuracy of the GEL of 100.0% for type A, 98.9% for type B, and 99.1% for type AB. Strength of agreement was very good (κ = 0.97). When the same anti-A and anti-B reagents are used, GEL is a sensitive and specific method for blood typing feline samples. Until additional studies have been performed, mixed-field patterns obtained in GEL testing should be classified as negative results.

DIFFERENTIATION OF THE A1 AND A2 SUBGROUPS OF THE AB0 SYSTEM: BIOLOGICAL BACKGROUND AND SEROLOGICAL STRATEGY

Introduction. The identification of weak variants of the A antigen, as well as their differentiation, is necessary for the proper selection of erythrocyte-containing media for blood transfusions. To this end, selective anti-A1 reagents that react only with the A1 antigen are used in combination with anti-A reagents reacting equally with the A1 and A2 antigens. Given that the expression of the A antigen varies within the subgroups and there is no established standard for reagents and procedures, the interpretation of the obtained results presents difficulties.Aim. To develop a strategy for identifying the variants of the A antigen using available reagents in an agglutination reaction.Methods. We compared the effectiveness of four anti-A1 and two anti-H reagents using 23 blood samples (groups A2 and A2B) and control samples (groups A1 and A1 B). Two types of anti-A1 reagents were employed: Dolychos biflorus lectin and monoclonal antibodies. All of the reagents were designed for direct agglutination reactions. Belonging of the erythrocytes to the A2 subgroup was confirmed using genetic analysis.Results. It is shown that anti-A1 reagents did not interact with A2B red blood cells and often reacted with A2 red blood cells. The strength of the reaction with A2 red blood cells varied greatly and was weaker than with A1 red blood cells; however, it hindered the subgroup identification. Simultaneous tests conducted using an anti-H reagent allowed the authors to draw an unambiguous conclusion about blood belonging to a subgroup: a strong reaction indicated the A2 subgroup, whereas a negative or weak reaction indicated the A1 subgroup. A discrepancy was noted between the results obtained for two donors using serological and molecular methods: the A3 subgroup was identified serologically, whereas genotyping revealed the AB0*A1 allele. In both cases, direct sequencing showed a combination of mutant alleles giving the A3 phenotype. When using commercial kits to perform genotyping analysis through a polymerase chain reaction, it should be taken into consideration that primers are matched to the most common variants and cannot detect all mutations of the AB0 gene.Conclusion. Reliable identification of the A2 subgroup through serological methods is possible when using lectin or monoclonal anti-A1 antibodies in combination with a monoclonal anti-H reagent.Conflict of interest: the authors declare no conflict of interest.Financial disclosure: the study had no sponsorship.

Monoclonal anti-A activity against the FORS1 (Forssman) antigen.

The FORS blood group system (originally recognized as the Apae phenotype) was discovered by sporadic activity against polyclonal anti-A reagents and activity against the lectin Helix pomatia. The extent of monoclonal anti-A reagent activity against the FORS1 antigen is serologically and immunochemically incomplete. In the absence of natural FORS1-positive red blood cells (RBCs), kodecytes were created with synthetic disaccharide and pentasaccharide Forssman function-spacer-lipid (FSL) constructs, Fsdi -kodecytes, and FORS1-kodecytes, respectively. FSL constructs were also applied to solid surfaces and used in solid-phase enzyme immunoassays. A range of characterized monoclonal anti-A and anti-B reagents were then serologically and immunochemically characterized against these Forssman antigens. Polyclonal human anti-A, anti-B, the lectin H. pomatia serologic reagents; and canine RBCs were used as serologic controls. None of 19 different monoclonal anti-A reagents were able to detect the pentasaccharide Forssman on FORS1-kodecytes, while three reagents were able to detect disaccharide Forssman on Fsdi -kodecytes. Most anti-A reagents were immunochemically reactive with both the di- and the pentasaccharide Forssman antigens in the solid-phase assays. Historic polyclonal human anti-A and the lectin H. pomatia reacted strongly with the FORS1-kodecytes, correlating with the discovery of the Apae phenotype and supporting the use of FORS1-kodecytes as FORS1 surrogates. Monoclonal anti-A reagents, despite showing reactivity against the FORS1 antigen in solid-phase assays are unlikely to cause the agglutination of FORS1 antigen-positive RBCs.

Mapping the fine specificity of ABO monoclonal reagents with A and B type-specific function-spacer-lipid constructs in kodecytes and inkjet printed on paper.

Monoclonal (MoAb) reagents are routinely used and are usually very reliable for the serologic determination of ABO blood types. However, the fine specificity and cross-reactivity of these reagents are often unknown, particularly against synthetic antigens used in some diagnostic assays. If nonserologic assays or very sensitive techniques other than those specifically prescribed by the manufacturer are used, then there is a risk of incorrect interpretation of results. Forty-seven MoAbs and two polyclonal ABO reagents were tested against red blood cell (RBC) kodecytes prepared with A trisaccharide, A Type 1, A Type 2, A Type 3, A Type 4, B trisaccharide, B Type 1, B Type 2, acquired B trisaccharide, and Le(a) trisaccharide function-spacer-lipid (FSL) constructs. Natural RBCs were tested in parallel. In addition these FSL constructs were printed onto paper with a desktop inkjet printer and used in a novel immunoassay that identifies reactivity through the appearance of alphanumeric characters. Mapping of MoAbs with kodecytes and printed FSL constructs revealed a series of broad recognition patterns. All ABO MoAbs tested were reactive with the RBC dominant Type 2 ABO antigens. Unexpectedly some anti-A reagents were reactive against the B Type 1 antigen, while others were poorly reactive with trisaccharide antigens. All ABO MoAbs detect the RBC dominant Type 2 ABO antigens; however, some reagents may show minor reactivity with inappropriate blood group antigens, which needs to be considered when using these reagents in alternative or highly sensitive analytic systems.

Mosaic Trisomy 9 in an infant with mixed‐field ABO blood grouping

A 44-year-old group A D+ G3P0 woman at 32 weeks' gestation underwent emergent cesarean section delivery of a 1.57-kg singleton male infant due to chorioamnionitis and breech presentation. ABO typing of the infant revealed mixed-field agglutination, with an apparent 50:50 mixture of A+ and O+ cells. There was no evidence of twin gestation, history of intrauterine transfusion, or maternal-fetal hemorrhage. Dextrose column separation of the infant's blood after agglutination with excess anti-A reagent 1 (see figure, left) allowed isolation of the nonreacting cell population. Testing for weak A phenotypes and presence of H antigen confirmed the partial group O phenotype. Serologic testing for D, E, c, e, Fy a , Fy(b), N, S, Jk a , and Jk b antigens disclosed identical expression patterns between the infant's two cell populations. Single-nucleotide polymorphism chromosomal microarray showed a mosaic single-copy genomic gain (trisomy) of Chromosome 9 in approximately 30% of cells. Fluorescence in situ hybridization analysis confirmed the mosaic presence of an additional Chromosome 9 homolog, with a normal (disomic) interphase nucleus (see figure, right, A) adjacent to a metaphase cell with Trisomy 9 (see figure, right, B). ABO mixed-field agglutination is most commonly seen after out-of-group RBC transfusion or hematopoietic stem cell transplantation. Rarely, chimerism resulting from either twin chimerism or tetragametic (dispermic) chimerism may result in dual RBC populations. In this patient, Mosaic Trisomy 9 introduced an extra copy of the ABO gene, located on Chromosome 9q34.2. The observed mixed-field agglutination likely reflects two phenotypically distinct cell lines: a more prevalent disomic line (genotype OO) and a less prevalent trisomic line (genotype AOO). Mosaic Trisomy 9 is a rare finding in liveborn infants resulting in variable outcomes, including cardiac defects. After identification of mosaicism in this infant an echocardiogram was performed, revealing a previously unsuspected atrial septal defect with left-to-right shunt.

Fiabilité du contrôle ultime prétransfusionnel de compatibilité en présence d’agglutinines froides en chirurgie cardiaque avec circulation extracorporelle

This case report is an example of a bedside pretransfusion compatibility testing issue. An 81-years-old woman was admitted in the operating room for aortic valve replacement under cardiopulmonary bypass. A conflict occurred during the bedside pretransfusion compatibility testing between the results of the patient and the packed red blood cells. Afterwards, the patient was diagnosed with cold agglutinins. It might have produced false positive results with the anti-A and anti-B reagents.

Three Cases of Cis-AB without B Antigen Expression

The cis-AB bood type is a rare phenomenon in which both the A and B blood types are inherited from a single parent. The cis-AB persons are not homogeneous with respect to reactivity of their red cells to anti-A and anti-B reagents, and are split into three groups with on the basis of the strength and characteristics of the serologic reactions； these reactivities are A2B3, A1B3 and A2B. These differences of representative types is the effect of alleles coupled with that of cis-AB allele, and A2B3 , A1B3, and A2B phenotypes can be applicable to cis-AB/O, cis-AB/A1, and cis-AB/B genotypes, respectively.We report three variant cis-AB cases whose genotype were all cis-AB/A1 but B antigen was not expressed and reactions. All these cases were problematic because the paternity among parents and children blood types could not be explained with pedigree analysis through simple serological test. ABO genotyping was the very efficient and unique tool to investigate the inheritance mode of ABO blood type in these cases. Many questions about its mechanism, frequency, etc. raised their heads, which will become interesting subjects of studies.

Serologic and molecular characterization of the B(A) blood group in the Chinese population

Abstract B(A) phenotype individuals have normal B antigen and a small amount of A antigen on the RBCs with anti-A in the plasma. Some highly potent monoclonal anti-A reagents are capable of agglutinating B(A) RBCs, which therefore usually results in a discrepancy between RBC and plasma ABO grouping. To date, five B(A) alleles (ABO*B(A)01, B(A)02, B(A)03, B(A)04, and B(A)05) have been defined by nucleotide sequences. To get a more complete picture of B(A) phenotypes found in the Chinese population and resolve blood donor typing problems caused by B(A) alleles, a serologic and molecular study of nine unrelated Chinese individuals and three families carrying B(A) alleles was conducted. Allele B(A)02 with a 700C>G mutation, allele B(A)04 with a single 640A>G substitution, and allele B(A)05 with a 641T>C mutation were detected in multigenerational families and unrelated blood donors. Neither the B(A)01 nor B(A)03 alleles with 703A>G substitutions were observed in this study. In addition, a polymerase chain reaction with a sequence-specific primer genotyping assay was developed for rapid identification of B(A)02, B(A)04, and B(A)05 alleles using genomic DNA samples. Immunohematology 2007;23:69–74.

Heterozygosity for the Non-Deletional O2 Allele Does Not Cause Discrepancies in Automated Blood Donor ABO Grouping.

In the ABO blood group system any allele which does not give rise to A or B antigen expression is an O allele. The most common O alleles, O1 (O01) and O1v (O02) encode enzymatically inactive truncated proteins due to a single nucleotide polymorphism (SNP) compared to the consensus A1 allele, 261delG. Other O alleles containing the consensus nucleotide at residue 261 have been identified. The most common of these non-deletional O alleles is O2 (O03). It contains other SNPs which render the resulting protein non-functional. The most significant SNP is 802G>A (G268R); the arginine residue blocks the donor sugar's access to the active site preventing its transfer. Recently O2 alleles were proposed to be the most common cause of ABO discrepancies (anti-A lacking or weakened in plasma despite apparent group O phenotype) in automated blood grouping (Transfusion 2005; 45:1331). Other clinical or biochemical reports have suggested that O2 may produce small amounts of A antigen on the RBC surface (Transfusion 2005; 45:70, 2005;45:359, J Biol Chem 2005; 280:525). To establish the effect of the O2 allele on automated ABO typing we extracted DNA from 562 randomly selected group O RBC units that were available for transfusion. Automated forward and reverse ABO grouping was performed on an Olympus PK7231 using A1 and B cells for reverse typing (Pittsburgh) and the IBG Multisampler Plato 3000 SI system using A1, A2 and B cells (Lund). A PCR-RFLP assay (Vox Sang 1995; 69:242) involving amplification of exon 6 of the ABO gene followed by cleavage with KpnI to detect the presence of the 261delG SNP was performed and 34/562 (6%) of these units were heterozygous for a deletional and a non-deletional O allele. All 34 of these donors demonstrated an identical digestion pattern with BstEII which cleaves exon 6 in the presence of the consensus sequence at residue 261, confirming their heterozygosity for a non-deletional O allele. Allele-specific PCR to detect the O2-specific 802G>A polymorphism was performed on 32 of these donors for which additional DNA was available; the O2 allele was uniformly detected along with either an O1 or O1v allele. No homozygous O2O2 donors were identified. A sensitive flow cytometric analysis of the RBCs from 7 donors with the O2 allele was performed using monoclonal anti-A (ES-15) and a PE-labelled rat-anti-mouse kappa Ig secondary antibody. None of these RBCs demonstrated fluorescence levels in significant excess of the control O (O1O1) cells whilst A antigen on group B cells was demonstrable. Manual immediate spin and gel card forward typing was performed on these donors using a variety of murine monoclonal, polyclonal and experimental anti-A reagents; no A antigen was detected on their RBCs. Adsorption-elution studies were performed on the RBCs of 3 donors heterozygous for O2 using human-source polyclonal anti-A but no A antigen was detected. All 34 group O RBC units were transfused to group O recipients without reported hemolytic reactions. Our results suggest that in its heterozygous state the O2 allele does not necessarily induce ABO discrepancies in automated testing. Transfusing group O RBCs from donors with an O2 allele to recipients with anti-A did not result in reports of symptoms associated with hemolytic events in the recipients.

International standards for minimum potency of anti‐A and anti‐B blood grouping reagents: evaluation of candidate preparations in an international collaborative study

The aim of the study was to evaluate lyophilized monoclonal IgM anti-A and anti-B preparations for use as international standards (IS) to specify recommended minimum potencies of anti-A and anti-B blood grouping reagents in tube tests. The candidate IS for minimum potency of anti-A and anti-B blood grouping reagents, codes 03/188 and 03/164, respectively, were evaluated against a wide range of commercial anti-A and anti-B blood grouping reagents in an international collaborative study involving 16 laboratories in nine countries. Laboratories titrated 03/188 and 03/164 in parallel with as many commercial anti-A and anti-B blood grouping reagents, respectively, as were available to them, in tube tests according to specified haemagglutination methodology. Three of these laboratories and a further laboratory also titrated 03/188 and 03/164 in parallel with currently available reference preparations for anti-A and anti-B. The ratios of the mean endpoint titres of the anti-A and anti-B reagents to those of 03/188 and 03/164, respectively, within each laboratory were calculated. The ratios of the mean titres of the anti-A reagents to the mean titre of 03/188 within a laboratory fell within 0.062 and 4, i.e. the potencies of the anti-A reagents were between a sixteenth to four times as strong as 03/188. The ratios of the mean titres of the anti-B reagents to the mean titre of 03/164 within a laboratory also fell within 0.062 and 4, with one outlier. By international consensus, a 1 in 8 dilution of the candidate IS for anti-A, 03/188, and a 1 in 4 dilution of the candidate IS for anti-B, 03/164, were considered appropriate to define the recommended minimum potencies of anti-A and anti-B blood grouping reagents, respectively, in tube tests. On the basis of these results, preparations 03/188 and 03/164 were established by the World Health Organization as International Standards for Minimum Potency of Anti-A and Anti-B Blood Grouping Reagents respectively, and by the US Food and Drug Administration Center for Biologics Evaluation and Research as Minimum Potency Reference Reagents.

Dispermic chimerism identified during blood group determination and HLA typing

Chimerism is the presence of two or more genetically distinct cell populations in one organism. We report the identification of dispermic chimerism in a 19-year-old female volunteer blood donor. During routine ABO blood grouping strong reactions of the blood donors red blood cells (RBCs) with anti-A reagents and mixed-field reactions with anti-B reagents were observed, while serum-testing showed the absence of anti-A and anti-B antibodies. AB0 blood group genotyping, HLA-typing and microsatellite analysis were performed using blood-samples, buccal mucosa and fibroblasts of the blood-donor and blood-samples of her parents. AB0 blood group genotyping showed three ABO blood group alleles (0(1), A(2) and B) in the DNA-samples of the blood-donor. The evidence of chimerism was supported by the detection of three alleles for the HLA-A and HLA-DRB1 loci. Microsatellite analysis with ten markers revealed three alleles for loci D7S821 and D19S412. All studies carried out, the third allele was always of paternal origin. CONCLISION: The results suggested a case of a human dispermic chimerism. Our proposed explanation for the development of chimerism in the reported case is the fertilization of an oocyte and the corresponding second polar body by two different sperms.

Chimerism and mosaicism are important causes of ABO phenotype and genotype discrepancies

Abstract Discrepancies between blood group genotype and RBC phenotype are important to recognize when implementing DNA-based blood grouping techniques. This report describes two such cases involving the ABO blood group in the Korean population. Propositus #1 was a 22-year-old healthy man undergoing pretransfusion testing for minor surgery. Propositus #2 was a 23-year-old male blood donor. RBCs from both propositi were determined to be group AB and demonstrated unusual agglutination patterns on forward typing, which were inconsistent with their ABO genotype determined by allele-specific (AS) PCR. RBCs from propositus #1 demonstrated mixed field agglutination with both anti-A and -B, while RBCs from propositus #2 demonstrated mixed field only with anti-A reagents. Both had B/O genotypes by AS-PCR. Cloning and sequencing of ABO exons 6 and 7 revealed three alleles in both propositi: propositus #1: A102/B101/O04; propositus #2: A102/B101/O01. A panel of nine short-tandem repeat (STR) loci was tested on DNA extracted from blood, buccal mucosal cells, and hair from the propositi and on DNA isolated from their parents’ blood. In all tissues tested from propositus #1, three loci demonstrated a double paternal and a single maternal DNA contribution, indicating that he was a chimera or a mosaic; in those from propositus # 2, one STR locus demonstrated a double paternal DNA contribution, indicating that he was a tetragametic chimera. Chimerism and mosaicism are uncommon but important causes of ABO genotype and phenotype discrepancies. The evaluation of patients and donors with unusual or unexpected serology in pretransfusion testing and consensus ABO alleles may include the evaluation of STR loci to detect these phenomena. Immunohematology 2006;22:183–187.

ABO and Rh(D) blood typing on the PK 7200 with ready-to-use kits

Abstract The performance of ready-to-use kits was evaluated on the PK 7200 blood grouping system. The Olymp Group (kit 1) and Olymp Group II (kit 2) containing anti-A, -B, -AB, and -D reagents were tested for first and second determinations of A, B, and D antigens. More than 500 RBC samples, including several variant ABO and D phenotypes, were evaluated for specificity, repeatability, reproducibility, and sensitivity. Specificity was tested with well-characterized reagent RBCs. Repeatability was established by at least 12 assays per run with three reagent RBCs, and reproducibility was established on one run per day for 5 days. No discrepancy was observed in ABO and D determinations with either kit. In repeatability, three discrepancies were found with group A and B RBCs with kit 1. In reproducibility, no discrepancies were observed. The kit 1 anti-A reagent detected A3 but not Ax RBCs and anti-AB detected both. A B3 RBC was detected by both kits. Among eight weak D phenotypes, six were positive with kit 1. With kit 2, only one of five weak D phenotypes was detected. Immunohematology 2003;19:54–56.

HOSAICISM OF BLOOD GROUP SPECIFICITY OF BRUSH BORDER OF HUMAN ENTEROCYTES

The pattern of differentiation of the enterocyte along the villus is considered to be dependent on the age of the cell and uniform in cells occupying comparable location on the villus. Using a polyclonal antibody against A blood group specific components of enterocyte brush border and three monoclonal antibodies we have demonstrated the expression of the A and B antigens in the brush border and Golgi apparatus of enterocytes of individuals of the expected blood groups, by light and electron microscopy, with the immunogold technique. The polyclonal anti-A serum was specific for the brush border whereas the monoclonal reagents also bound the endothelial cells and erytrocytes in the sections. Four of 16 blood group A individuals showed a mosaic pattern of expression of the A antigen, both with the polyclonal serum and the monoclonal anti-A reagent. Some enterocytes showed a normal staining and some other enterocytes at similar position on the villus showed no staining at all. An anti-Le a antibody showed that all the 4 individuals with the mosaic pattern were non secretor. Abnormalities of blood group antigens may reflect abnormal expression of glucosyl-transferase genes or disturbances of their acceptors. Enterocytes may therefore display a non homogeneous pattern of differentiation in morphologically similar cells occupying comparable location on the villus.

Group A variants defined with a monoclonal anti‐A reagent

Unusual serologic findings mimicking the B(A) phenomenon were noted in two group B blood donors using blended murine monoclonal anti-A reagent. With additional studies, including a binding experiment using affinity chromatography, the presence of aberrant group A activities was confirmed. This observation suggests that persons with atypical B(A) phenotype may warrant further investigation to delineate the ABO blood group.

Identification of a Subset of Group B Donors Reactive with Monoclonal Anti-A Reagent

Two red blood cell (RBC) units labeled group B were returned to the source blood center after they had been retyped as AB by a transfusion service. The discrepancy could be reproduced, but only with the use of the transfusion service's reagent, Ortho Diagnostic's anti-A Bioclone (a licensed, blended, murine monoclonal anti-A reagent). RBCs from 35 of 3,458 random group B donors (1%) reacted with the monoclonal anti-A after immediate centrifugation. Reactivity was associated with high serum levels of B-gene-specified transferase and was caused by the MH04 component, a potent anti-A capable of detecting some examples of Ax RBCs. It is probable that the potency of MH04 permitted detection of low levels of A determinants synthesized by the donors' unusually strong B-gene-specified transferase. Transfer of N-acetylgalactosamine by B-gene-specified transferases, reported in vitro, has not been detected previously in vivo. Use of highly sensitive monoclonal reagents may result in clinically ambiguous blood grouping results.

Evaluation of monoclonal anti-A reagents by salivary inhibition studies

Ten commercially available monoclonal and polyclonal anti-A reagents were evaluated for use in the test for ABH secretor status after finding unexpected inhibition with a monoclonal anti-A (reagent Z). Two of the available monoclonal reagents were from different batches from the same clone as reagent Z. Those two reagents, as well as reagent Z, appeared to be partially neutralized by salivary substances from group A nonsecretor individuals. This finding suggests that when a saliva inhibition test is done, a nonsecretor control saliva of the same ABO group as the saliva to he tested should be used.

Heterogeneity of Anti‐A and Anti‐B Monoclonal Reagents

Eight anti-A and seven anti-B monoclonal reagents were tested in parallel, with normal and weak ABH red cell phenotypes. A whole range of different reactivity patterns was found, but by making a comparison with the results obtained using polyclonal standard reagents, two major categories of reagents were distinguished: (a) stronger and more specific reagents, and (b) reagents similar to, or weaker than, the standard polyclonal controls. The analysis of the specificity of the reagents by tissue fluorescence staining and reactivity with synthetic oligosaccharides and purified glycolipids confirmed the existence of broad and restricted specificities. Two kinds of anti-A1 reagents are described. One related to type 3/4 structures, which stains the Golgi apparatus, and another with broad anti-A specificity which cross-reacts with 'A-like' structures. The inhibition of anti-A reagents with salivas and synthetic oligosaccharide antigens gave parallel results for the secretor salivas and the difucosylated A antigens.