Defining the Rh blood group antigens. Biochemistry and molecular genetics

The Expression of Human Blood Group Antigens During Erythropoiesis in a Cell Culture System

Phenotypic analysis of hematopoietic stem and progenitor cells has been an invaluable tool in defining the biology of stem cell populations. We use here flow cytometry to examine the expression of human erythroid-specific surface markers during the maturation of early committed erythroid cells derived from cord blood in vitro. The temporal order of the expression of erythroid specific markers was as follows: Kell glycoprotein (gp), Rh gp, Landsteiner Wiener (LW) gp, glycophorin A (GPA), Band 3, Lutheran (Lu) gp, and Duffy (Fy) gp. The time at which some of these markers appeared suggests possible roles for some of these erythroid-specific polypeptides during the differentiation of these committed progenitors. The early appearance of Kell gp raises the possibility that it may have an important role in the early stages of hematopoiesis or cell lineage determination. Kell gp may also be a useful marker for the diagnosis of erythroleukemia. The late expression of Lu gp suggests it may be involved in the migration of erythroid precursors from the marrow. Fy gp is also expressed late consistent with a role as a scavenger receptor for cytokines in the bone marrow and circulation. Rh c antigen appeared before Rh D antigen, and it is suggested that this may reflect a reorganization of the developing erythroid cell membrane involving the Rh polypeptides and other components, including GPA and Band 3.

Synthesis of Rh Fv phage-antibodies using VH and VL germline genes

Antibodies to the D antigen of the Rh system use a restricted set of immunoglobulin V and J gene segments, especially VH DP50 and DP63, JH6, Vlambda DPL16 and Jlambda 2/3. These gene segments may confer a natural affinity on the antibodies for the D antigen and this hypothesis has been tested by constructing two single-chain Fv phage-antibody libraries based on the germline gene segments DP50 and DP63; structural variability was obtained by insertion of 11 amino acids in random sequence in the VHCDR3. 10 anti-D antibodies were selected from these libraries, each with a unique VHCDR3. In contrast, selections with the CcEe antigens produced antibodies reacting with the Rh polypeptide molecules but without strict blood group specificity. One of these latter DP50-based antibodies was converted into 12 different antibodies with specificity for E by replacing the original germline light chain with chains from a rearranged L chain library. The CDR1 and CDR2 sequences of the DP50-based antibodies were common to both anti-D and anti-E molecules; differentiation between D and E specificity was dependent on VHCDR3 sequences and their correct pairing with an appropriate L chain.

Antibody mimicking an anti-E antibody that binds to patient's E negative red cells

We have reported a rare case of auto anti-E antibody with specificity mimicking alloantibody with E specificity. A patient whose red cells typed as R1R1 and who had a positive direct antiglobulin test was admitted to our hospital. After standard serologic testing was performed, flow cytometry, Western blot analysis and differential allogenic adsorption test were used to verify whether antibody binds to the patient's red cells and normal red cells. A high titer anti-E antibody was detected transiently from the patient's serum and eluate. An indirect antiglobulin test using red cells treated by cysteine-activated papain and dithiothreitol (ZZAP) and chloroquine showed that both the patient's serum and eluate bound an apparent anti-E antibody to E negative patient's red cells. Fluorescence activated cells sorter (FACS) and Western blot analysis verified that the patient's red cells lacked E antigen. Further, it was clarified that the antibody does not bind to any E negative normal red cells by differential allogenic adsorption test. These results provide evidence that an antibody mimicking an E alloantibody can bind to patient's own E negative red cells but not to allogenic E negative red cells.

The genomic organization of the partial D category DVa: the presence of a new partial D associated with the DVa phenotype

Within the Rh blood group, the partial D phenotype is a well known RhD variant, that induces Rh-incompatible blood transfusion and hemolytic diseases in the newborn. The partial D category DVa phenotype (DVa Kou.) results from a hybrid of RhD-CE-D transcript. We demonstrated a genomic organization of the hybrid RHD-CE-D gene leading to the DVa phenotype, and showed that the DVa gene were generated from gene conversion between the RHD and the RHCE genes in relatively small regions. This study also revealed that the presence of a new partial D associated with the DVa phenotype, which we termed the DVa-like phenotype. In this phenotype, five RHD-specific nucleotides were replaced with the corresponding RHCE-derived nucleotides on the exon 5 of the RHD gene. In addition, two variants of the mutated RHD genes at nucleotide 697 were revealed in the RhD variant samples. These results will provide useful information for future research into the diversification of the Rh polypeptides.

Functional Cell Surface Expression of Band 3, the Human Red Blood Cell Anion Exchange Protein (AE1), in K562 Erythroleukemia Cells: Band 3 Enhances the Cell Surface Reactivity of Rh Antigens

Human K562 erythroleukemia cells were transfected with human band 3 (anion exchanger 1 [AE1]) cDNA, using the pBabe retroviral vector. Stable K562 clones expressing band 3 were isolated by flow cytometry, and surface expression was quantified by immunoblotting. The function of band 3 expressed at the cell surface was demonstrated in chloride transport assays. K562 cells expressing band 3 also displayed high levels of the Wrb blood group antigen, confirming the role of band 3 in Wrb expression, and an increase in the low levels of endogenous Rh antigen activity. We also performed coexpression experiments with K562 clones that had previously been transduced with cDNAs encoding RhD or RhcE polypeptides. The transfection and expression of band 3 in these clones substantially increased the levels of RhD and cE antigen activity expressed on the cells and also increased the reactivity of the cells with antibody to the endogenous Rh glycoprotein (RhGP, Rh50). The increased reactivity of Rh antigens may result from cell surface or intracellular interactions of band 3 with the protein complex which contains the Rh polypeptides and RhGP, or from indirect effects of band 3 on the membrane environment. This work establishes a system for cell surface expression of band 3 in a mammalian cell line, which will enable further studies of the protein and its interactions with other membrane components.

Rh phenotype prediction by DNA typing and its application to practice

The complexity of the RHD and RHCE genes, which is the greatest of all blood group systems, confounds analysis at the molecular level. RH DNA typing was introduced in 1993 and has been applied to prenatal testing. PCR-SSP analysis covering multiple polymorphisms was recently introduced for the screening and initial characterization of partial D. Our objective is to summarize the accrued knowledge relevant to the approaches to Rh phenotype prediction by DNA typing, their possible applications beyond research laboratories and their limitations. The procedures, results and problems encountered are highly detailed. It is recommended that DNA typing comprises an analysis of more than one polymorphism. We discuss future directions and propose a piecemeal approach to improve reliability and cost-efficiency of blood group genotyping that may eventually replace the prevalent serology-based techniques even for many routine tasks. Transfusion medicine is in the unique position of being able to utilize the most extensive phenotype databases available to check and develop genotyping strategies.

Functional Cell Surface Expression of Band 3, the Human Red Blood Cell Anion Exchange Protein (AE1), in K562 Erythroleukemia Cells: Band 3 Enhances the Cell Surface Reactivity of Rh Antigens

Human K562 erythroleukemia cells were transfected with human band 3 (anion exchanger 1 [AE1]) cDNA, using the pBabe retroviral vector. Stable K562 clones expressing band 3 were isolated by flow cytometry, and surface expression was quantified by immunoblotting. The function of band 3 expressed at the cell surface was demonstrated in chloride transport assays. K562 cells expressing band 3 also displayed high levels of the Wrb blood group antigen, confirming the role of band 3 in Wrb expression, and an increase in the low levels of endogenous Rh antigen activity. We also performed coexpression experiments with K562 clones that had previously been transduced with cDNAs encoding RhD or RhcE polypeptides. The transfection and expression of band 3 in these clones substantially increased the levels of RhD and cE antigen activity expressed on the cells and also increased the reactivity of the cells with antibody to the endogenous Rh glycoprotein (RhGP, Rh50). The increased reactivity of Rh antigens may result from cell surface or intracellular interactions of band 3 with the protein complex which contains the Rh polypeptides and RhGP, or from indirect effects of band 3 on the membrane environment. This work establishes a system for cell surface expression of band 3 in a mammalian cell line, which will enable further studies of the protein and its interactions with other membrane components.

Heterogeneity of blood group RhE variants revealed by serological analysis and molecular alteration of the RHCE gene and transcript

After testing red cells from 12 RhE variants with a panel of anti-E monoclonal antibodies (MoAbs), four patterns of reactivity were detected indicating that the MoAbs may recognize four distinct E epitopes designated epE1, epE2, epE3 and epE4. The variants were classified into four categories (cat EI to EIV) which carried epE1 and epE2, epE1 and epE4, epE1, epE3 and epE4, and all four epitopes, respectively. Molecular analysis of the transcripts and genomic DNA of the variants from cat EI, EII and EIII displayed three distinct genetic alterations. Cat EI variants exhibited a point mutation (T500A) in exon 4 of the RHCE gene that resulted in a Met167Lys substitution in the third extracellular loop of the RhcE protein. Cat EII variant carried a hybrid gene structure characterized by replacement of exons 1-3 (or 2-3) of the RHCE gene by their specific counterparts in the RHD gene. This latter variant was also associated with a weak expression of the RhC antigen. In cat EIII variants there was a partial DNA exchange of exon 5 sequences (nt 697 and 712) between the RHCE and the RHD genes, generating a hybrid Rh cE-D-cE protein carrying the Glu233 and Val238 substitutions. The serological and molecular studies of the RhE variants indicated that: (i) the RhE antigen is a mosaic composed of at least four epitopes and proline at position 226 is necessary but not sufficient for the full expression of the E antigen, (ii) the lack of RhE epitope(s) is associated with heterogenous molecular alterations of the RHCE gene, and (iii) amino-acids located on the third and fourth extracellular loops of the RhCE polypeptide are critical for some RhE epitopes expression.

Effect of 1-beta-D-arabino-furanosyl-cytosine (ara-C) induction of K562 cells on expression of Rh and other blood group active proteins

K562 cells undergoing differentiation induced by 1-beta-D-arabino-furanosyl-cytosine (ara-C) were examined as a model for studying the biosynthesis and regulation of Rh and other blood group active membrane proteins. Untreated and ara-C-induced K562 cells were analysed for the expression of these proteins using monoclonal antibodies in combination with flow cytometry. The major membrane proteins glycophorins A and C remained unaltered upon induction by ara-C. The display of LFA-3 (CD58) and DAF (CD55) by uninduced K562 was one order of magnitude lower than that of the glycophorins; following ara-C treatment there was a 50% rise in LFA-3 but a modest decrease in the level of DAF expression. The expression by untreated K562 cells of Rh, Lutheran and Kell proteins as well as the Rh D antigen was low, whereas that of CD44 and band 3 protein was negligible. Following induction by ara-C the levels of Rh and Kell proteins rose up to 7- and 3.5-fold respectively, and there was an increase in RhD-antigen expression. In contrast, ara-C induction of K562 cells failed to augment their display of Lutheran, CD44 and band 3 proteins. Analysis of Rh transcripts following the purification and RT-PCR analysis of K562 mRNA showed that uninduced K562 cells contain two distinct mRNAs corresponding to Rh Ce (1.8 kb) and Rh D (3.5 kb). The apparent concentration of each mRNA increased following induction with ara-C. K562 plasma membranes also contained Rh polypeptides as determined by immunoblot analysis using anti-Rh polypeptide rabbit polyclonal sera raised to Rh synthetic peptides. A novel hybrid Rh transcript corresponding to exons 1-4 of RHD and exons 5-10 of RHCE has been cloned and sequenced from ara-C induced K562 cells, and may have arisen by general recombination between the RHD and RHCE genes.

Rh-Deficiency of the Regulator Type Caused by Splicing Mutations in the Human RH50 Gene

The Rh polypeptides and the glycoproteins Rh50, CD47, LW, and glycophorin B, which interact in the red blood cell membrane to form a multisubunit complex, are lacking or are severely reduced in the Rh-deficiency syndrome. We previously reported that in several Rhnull patients the RH50 gene was altered at the coding sequence level, resulting in either a single amino acid substitution or the synthesis of a truncated polypeptide. In the present report, we have detected two mutations in the intronic region of the RH50 gene that identify a new molecular mechanism involved in Rh-deficiency. The first mutation affected the invariant G residue of the 3′ acceptor splice-site of intron 6, causing the skipping of the downstream exon and the premature termination of translation. The second mutation occurred at the first base of the 5′ donor splice-site of intron 1. Both these mutations were found in homozygote state. RNase protection assays demonstrated that the Rh50 mRNA level was strongly reduced or undetectable in the 3′ and 5′ splice mutants, respectively. The different mutations affecting the RH50 gene are indicative of an heterogeneous mutational pattern, which further supports the hypothesis that the lack of the Rh50 protein may prevent the assembly or transport of the Rh membrane complex to the red blood cell surface.

Rh-Deficiency of the Regulator Type Caused by Splicing Mutations in the Human RH50 Gene

The Rh polypeptides and the glycoproteins Rh50, CD47, LW, and glycophorin B, which interact in the red blood cell membrane to form a multisubunit complex, are lacking or are severely reduced in the Rh-deficiency syndrome. We previously reported that in several Rhnull patients the RH50 gene was altered at the coding sequence level, resulting in either a single amino acid substitution or the synthesis of a truncated polypeptide. In the present report, we have detected two mutations in the intronic region of the RH50 gene that identify a new molecular mechanism involved in Rh-deficiency. The first mutation affected the invariant G residue of the 3′ acceptor splice-site of intron 6, causing the skipping of the downstream exon and the premature termination of translation. The second mutation occurred at the first base of the 5′ donor splice-site of intron 1. Both these mutations were found in homozygote state. RNase protection assays demonstrated that the Rh50 mRNA level was strongly reduced or undetectable in the 3′ and 5′ splice mutants, respectively. The different mutations affecting the RH50 gene are indicative of an heterogeneous mutational pattern, which further supports the hypothesis that the lack of the Rh50 protein may prevent the assembly or transport of the Rh membrane complex to the red blood cell surface.

Rh50 Glycoprotein Gene and Rhnull Disease: A Silent Splice Donor Is trans to a Gly279→Glu Missense Mutation in the Conserved Transmembrane Segment

Rhnull disease includes the amorph and regulator types that are thought to result from homozygous mutations at theRH30 and RH50 loci, respectively. Here we report an unusual regulator Rhnull where two G→A nucleotide (nt) transitions occurred in trans, targeting different regions of the two copies of Rh50 gene. The nt 836 G→A mutation was a missense change located in exon 6; it converted Gly into Glu at position 279, a central amino acid of the transmembrane segment 9 (TM9). While cDNA analysis showed expression of the 836A(Glu279) allele only, genomic studies showed the presence of both 836A(Glu279) and 836G(Gly279) alleles. A detailed analysis of gene organization led to the identification in the Rh50(836G) allele of a defective donor splice site, caused by a G→A mutation in the invariant GT element of intron 1. This is the first known example of such mutations that has apparently abolished the functional splicing of a pre-mRNA encoding a multipass integral membrane protein. With a silent phenotypic copy intrans, the negatively charged Glu279 residue may disrupt TM9 and impair the interaction of the missense protein with Rh30 polypeptides. To evaluate the significance of the mutation, we took a comparative genomic approach and identified Rh50 homologues in different species. We found that Gly279 is a conserved residue and its adjacent amino acid sequence is identical fromCaenorhabditis elegans to human. These findings provide new insight into the diversity of Rhnull disease and suggest that the C-terminal region of Rh50 may also participate in protein-protein interactions involving Rh complex formation.

© 1998 by The American Society of Hematology.

Rh50 Glycoprotein Gene and Rhnull Disease: A Silent Splice Donor Is trans to a Gly279→Glu Missense Mutation in the Conserved Transmembrane Segment

Rhnull disease includes the amorph and regulator types that are thought to result from homozygous mutations at theRH30 and RH50 loci, respectively. Here we report an unusual regulator Rhnull where two G→A nucleotide (nt) transitions occurred in trans, targeting different regions of the two copies of Rh50 gene. The nt 836 G→A mutation was a missense change located in exon 6; it converted Gly into Glu at position 279, a central amino acid of the transmembrane segment 9 (TM9). While cDNA analysis showed expression of the 836A(Glu279) allele only, genomic studies showed the presence of both 836A(Glu279) and 836G(Gly279) alleles. A detailed analysis of gene organization led to the identification in the Rh50(836G) allele of a defective donor splice site, caused by a G→A mutation in the invariant GT element of intron 1. This is the first known example of such mutations that has apparently abolished the functional splicing of a pre-mRNA encoding a multipass integral membrane protein. With a silent phenotypic copy intrans, the negatively charged Glu279 residue may disrupt TM9 and impair the interaction of the missense protein with Rh30 polypeptides. To evaluate the significance of the mutation, we took a comparative genomic approach and identified Rh50 homologues in different species. We found that Gly279 is a conserved residue and its adjacent amino acid sequence is identical fromCaenorhabditis elegans to human. These findings provide new insight into the diversity of Rhnull disease and suggest that the C-terminal region of Rh50 may also participate in protein-protein interactions involving Rh complex formation.

© 1998 by The American Society of Hematology.

Shift from Rh-positive to Rh-negative phenotype caused by a somatic mutation within the RHD gene in a patient with chronic myelocytic leukaemia

We report a female patient whose Rh phenotype shifted from RhD-positive to RhD-negative over a 3-year period (1991-94), during which time she was treated with mastectomy (1992) and local irradiation for a low-grade recurrent breast cancer. She was diagnosed with chronic myeloid leukaemia in 1994, and has since then received chemotherapy. The patient was repeatedly typed as O, RhD-positive between 1965 and 1991 and was repeatedly found RhD-negative after 1994. Bcr-Abl transcripts typical of Ph1 chromosome were detected. Molecular analysis indicated that the patient was heterozygous at the RH locus, carrying one haplotype in which the RHD gene exhibited a single nucleotide deletion (G600) resulting in a frameshift and premature stop codon, and a normal RHCE gene (allele Ce). The second haplotype contained only the RHCE gene (allele ce) and was normal. Further analysis carried out on total leucocytes, purified neutrophils, EBV-lymphoblastoid cell line and cultured erythroblasts indicated that the G600 deletion was restricted to the myeloid lineage. No modification of other blood group antigens could be detected. These findings suggest a somatic mutation which most probably occurred in a stem cell common to the myeloid lineage.

Insights into the structure and function of membrane polypeptides carrying blood group antigens

In recent years, advances in biochemistry and molecular genetics have contributed to establishing the structure of the genes and proteins from most of the 23 blood group systems presently known. Current investigations are focusing on genetic polymorphism analysis, tissue-specific expression, biological properties and structure-function relationships. On the basis of this information, the blood group antigens were tentatively classified into five functional categories: (i) transporters and channels, (ii) receptors for exogenous ligands, viruses, bacteria and parasites, (iii) adhesion molecules, (iv) enzymes and, (v) structural proteins. This review will focus on selected blood groups systems (RH, JK, FY, LU, LW, KEL and XK) which are representative of these classes of molecules, in order to illustrate how these studies may bring new information on common and variant phenotypes and for understanding both the mechanisms of tissue specific expression and the potential function of these antigens, particularly those expressed in nonerythroid lineage.

Molecular Defects of the RHCE Gene in Rh-Deficient Individuals of the Amorph Type

The deficiency of Rh proteins on the red blood cells from individuals of the Rhnull amorph type may be the result of homozygosity for a silent allele at the RH locus. This phenotype is also associated with the lack or reduced expression of glycoproteins (Rh50, CD47, LW, and glycophorin B), which interact with Rh polypeptides to form the multisubunit Rh membrane complex. In this study, we describe two molecular alterations affecting the RHCEgene in two unrelated Rhnull amorph individuals bearing Rh50 and CD47 normal transcripts. The first type of mutation, located at the donor splice-site in intron 4, induced the activation of two cryptic splice-sites within this intron and one such site in exon 4 that all generated aberrant transcripts. The second type of mutation affected the coding region and introduced a frameshift and a premature stop codon resulting in a shorter predicted protein (398 v 417 residues), including a completely different C-terminus of 76 amino acids. This suggests that protein folding and/or protein-protein interaction mediated by the C-terminal domain of the Rh proteins may play a role in the routing and/or stability of the Rh membrane complex.

Molecular Defects of the RHCE Gene in Rh-Deficient Individuals of the Amorph Type

The deficiency of Rh proteins on the red blood cells from individuals of the Rhnull amorph type may be the result of homozygosity for a silent allele at the RH locus. This phenotype is also associated with the lack or reduced expression of glycoproteins (Rh50, CD47, LW, and glycophorin B), which interact with Rh polypeptides to form the multisubunit Rh membrane complex. In this study, we describe two molecular alterations affecting the RHCEgene in two unrelated Rhnull amorph individuals bearing Rh50 and CD47 normal transcripts. The first type of mutation, located at the donor splice-site in intron 4, induced the activation of two cryptic splice-sites within this intron and one such site in exon 4 that all generated aberrant transcripts. The second type of mutation affected the coding region and introduced a frameshift and a premature stop codon resulting in a shorter predicted protein (398 v 417 residues), including a completely different C-terminus of 76 amino acids. This suggests that protein folding and/or protein-protein interaction mediated by the C-terminal domain of the Rh proteins may play a role in the routing and/or stability of the Rh membrane complex.

Adherence of erythrocytes during exflagellation of Plasmodium falciparum microgametes is dependent on erythrocyte surface sialic acid and glycophorins

Malaria male gametocytes within a newly ingested infected blood meal in the mosquito midgut emerge from erythrocytes and extrude approximately eight flagellar microgametes in a process termed exflagellation. In culture, and in blood removed from infected patients, emerging microgametes avidly adhere to neighboring uninfected and infected erythrocytes, as well as to emerged female macrogametes, creating "exflagellation centers". The mechanism of erythrocyte adherence is not known nor has it been determined for what purpose microgametes may bind to erythrocytes. The proposition of a function underlying erythrocyte adherence is supported by the observation of species-specificity in adhesion: microgametes of the human malaria Plasmodium falciparum can bind human erythrocytes but not chicken erythrocytes, whereas avian host Plasmodium gallinaceum microgametes bind chicken but not human erythrocytes. In this study we developed a binding assay in which normal, enzyme-treated, variant or null erythrocytes are identified by a cell surface fluorescent label and assayed for adherence to exflagellating microgametes. Neuraminidase, trypsin or ficin treatment of human erythrocytes eliminated their ability to adhere to Plasmodium falciparum microgametes, suggesting a role of sialic acid and one or more glycophorins in the binding to a putative gamete receptor. Using nulls lacking glycophorin A [En(a-)], glycophorin B (S-s-U-) or a combination of glycophorin A and B (Mk/Mk) we showed that erythrocytes lacking glycophorin B retain the ability to bind but a lack of glycophorin A reduced adherence by exflagellating microgametes. We propose that either the sialic acid moiety of glycophorins, predominantly glycophorin A, or a more complex interaction involving the glycophorin peptide backbone, is the erythrocyte receptor for adhesion to microgametes.

[Blood groups and structure-activity relations]

In the recent years, advances in biochemistry and molecular genetics have contributed to establish the structure of the genes and proteins from most of the 23 blood group systems presently known. From these findings, five functional classes of molecules can be schematically distinguished: (i) transporters and channels, (ii) receptors for ligands, viruses, bacteria and parasites, (iii) adhesion molecules, (iv) enzymes, and (v) structural proteins. Recent advances on these molecules will be reviewed, particularly by illustrating available structure-function relationships.

A Novel Single Missense Mutation Identified Along the RH50 Gene in a Composite Heterozygous Rhnull Blood Donor of the Regulator Type

Rare individuals who lack all of the Rh blood group antigens are called Rhnull and may be classified as “regulator” or “amorph” types. The suppression of Rh antigen expression for regulator types may be attributed to mutations of the RH50gene, which is independent of the RH locus. The RH50 gene encodes a glycoprotein that interacts with the Rh proteins to form a functional complex within the red blood cell membrane. This report describes an RH50 gene mutation for a previously unclassified Rhnull donor. Sequencing cDNA clones from Rh50 mRNA revealed a single base change (G836A) yielding a missense and nonconservative mutation (Gly279Glu) within a predicted hydrophobic domain for this membrane protein. Genomic DNA studies using polymerase chain reaction (PCR) restriction analysis and sequencing showed that the Rhnull propositus was a composite heterozygote for this mutation, carrying two alleles with the A and G at nucleotide 836, respectively. In contrast, cDNA studies showed that only the A836 sequence was present, suggesting that the second allele with G836 was apparently silent (no transcript detected). Family studies showed that the mutant RH50 allele (836A) was inherited maternally, whereas the silent RH50 allele (836G) was from paternal transmission. These findings provide further evidence that rare but diverse genetic alterations may occur along the RH50 gene where the Rhnull syndrome of the regulator type occurs. The single amino acid change (Gly to Glu) provides insight into the critical value of these residues for assembly of the Rh antigen complex within the membrane.

Absence of expression of RhD by human trophoblast cells

OBJECTIVE

Our purpose was to determine whether the RhD gene is expressed in trophoblast at any stage of gestation.

STUDY DESIGN

Trophoblast and fetal tissue were obtained from 18 pregnancies at 8 to 40 weeks' gestation. Deoxyribonucleic acid and ribonucleic acid were extracted from trophoblast. Complementary deoxyribonucleic acid was synthesized from ribonucleic acid, and reverse transcriptase-polymerase chain reaction was performed using primers specific for the RhD gene. Deoxyribonucleic acid was extracted from fetal tissue to determine the fetal RhD status by means of polymerase chain reaction. Antigen expression was also sought by analytic cytometric analysis (flow cytometry and immunocytochemistry) using a monoclonal anti-D antibody.

RESULTS

Trophoblast was studied from various combinations of RhD-positive and RhD-negative fetuses (on deoxyribonucleic acid) from mothers to find no RhD gene expression in any sample. Flow cytometry and immunocytochemistry confirmed this by demonstrating no RhD antigen sites on trophoblast cells.

CONCLUSION

Contrary to a previous report, we conclude that the RhD gene is not expressed in human trophoblast in any trimester.

The human Rh50 glycoprotein gene. Structural organization and associated splicing defect resulting in Rh(null) disease

The Rh (Rhesus) protein family comprises Rh50 glycoprotein and Rh30 polypeptides, which form a complex essential for Rh antigen expression and erythrocyte membrane integrity. This article describes the structural organization of Rh50 gene and identification of its associated splicing defect causing Rhnull disease. The Rh50 gene, which maps at chromosome 6p11-21.1, has an exon/intron structure nearly identical to Rh30 genes, which map at 1p34-36. Of the 10 exons assigned, conservation of size and sequence is confined mainly to the region from exons 2 to 9, suggesting that RH50 and RH30 were formed as two separate genetic loci from a common ancestor via a transchromosomal insertion event. The available information on the structure of RH50 facilitated search for candidate mutations underlying the Rh deficiency syndrome, an autosomal recessive disorder characterized by mild to moderate chronic hemolytic anemia and spherostomatocytosis. In one patient with the Rhnull disease of regulator type, a shortened Rh50 transcript lacking the sequence of exon 7 was detected, while no abnormality was found in transcripts encoding Rh30 polypeptides and Rh-related CD47 glycoprotein. Amplification and sequencing of the genomic region spanning exon 7 revealed a G-->A transition in the invariant GT motif of the donor splice site in both Rh50 alleles. This splicing mutation caused not only a total skipping of exon 7 but also a frameshift and premature chain termination. Thus, the deduced translation product contained 351 instead of 409 amino acids, with an entirely different C-terminal sequence following Thr315. These results identify the donor splicing defect, for the first time, as a loss-of-function mutation at the RH50 locus and pinpoint the importance of the C-terminal region of Rh50 in Rh complex formation via protein-protein interactions.

Organization of the human RH50A gene (RHAG) and evolution of base composition of the RH gene family

Human Rh (rhesus) antigens are expressed in the red cell membrane as a multi-subunit complex, the central core of which is presumably composed of a tetramer made of two Rh and two Rh50 protein subunits. The interaction between Rh and Rh50 polypeptides is thought to be crucial to the correct assembly and transport of the complex to the cell surface. Here, we show that the human RH50A gene (RHAG) is composed of 10 exons whose size and exon/intron junctions are well conserved compared to those of the RH genes. We have also analyzed the RH50A 5' flanking region where the transcription initiation site has been identified. These results conclusively establish that the RH50A and RH genes do belong to the same gene family. Moreover, we show that the RH50A and RH genes are embedded in different compositional genomic contexts (i.e., different isochores) that are likely to drive the evolution of these genes, the base compositions (G + C content) of which differ drastically. Finally, we propose a scenario in which an RH50-like gene is likely to have played a founding role in the evolution of the RH gene family.

The serological profile and molecular basis of a new partial D phenotype, DHR

BACKGROUND AND OBJECTIVES

The Rh D antigen comprises a mosaic of at least 30 epitopes expressed on a 30-kD non-glycosylated Rh D polypeptide. The equivalent Rh CeEe polypeptide expressing the Rh C/c and E/e antigens differs in only 36 of the 417 amino acid residues. Partial D individuals have been described who fail to express a number of D epitopes.

MATERIALS AND METHODS

Serologic methods were applied with monoclonal anti-D to map epitopes on the red cells of a proposita aberrant D typing. Polymerase chain reaction (PCR) and DNA sequencing were also done.

RESULTS

DNA sequence analysis derived by RT-PCR using total RNA isolated from peripheral blood of this person suggests two mechanisms for the genetic basis of this variants: one here gene conversion events result in the replacement of RHD gene exons with the equivalent RHCE exons; the second where point mutation in the RHD gene generates an amino acid substitution in the Rh D protein.

CONCLUSIONS

We report here a new partial D, DHR, where a single point mutation (G to A at nucleotide 686) in exon 5 of the RHD gene results in a conservative amino acid substitution (Arg229Lys), in the predicted Rh D protein. This residue is localised on the fourth predicted exofacial loop of the Rh D polypeptide as determined by hydropathy analysis. This substitution results in the lack of epD 1, 2, 12 and 20 (30 epitope model) and indicates the involvement of loop 4, and in particular the requirement of Arg229, in the expression of these epitopes.

The RHD gene is highly detectable in RhD-negative Japanese donors

Recent molecular studies on the Rh blood group system have shown that the Rh locus of each haploid RhD-positive chromosome is composed of two structural genes: RHD and RHCE, whereas the locus is made of a single gene (RHCE) on each haploid RhD-negative chromosome. We analyzed the presence or absence of the RHD gene in 130 Japanese RhD-negative donors using the PCR method. The RhD-negative phenotypes consisted of 34 ccEe, 27 ccee, 17 ccEE, 26 Ccee, 19 CcEe, 1 CcEE, and 6 CCee. Among them, 36 (27.7%) donors demonstrated the presence of the RHD gene. Others showed gross or partial deletions of the RHD gene. These results were confirmed by Southern blot analysis. Additionally, the RHD gene detected in the RhD-negative donors seemed to be intact through sequencing of the RhD polypeptide cDNA and the promoter region of RHD gene. The phenotypes of these donors with the RHD gene were CC or Cc, but not cc. It suggested that there is some relationship between the RHD gene and the RhC phenotypes in RhD-negative individuals. In Caucasian RhD-negative individuals, the RHD gene has not been found outside of the report of Hyland et al. (Hyland, C.A., L.C. Wolter, and A. Saul. 1994. Blood. 84:321-324). The discrepant data on the RHD gene in RhD-negative donors between Japanese and Caucasians appear to be derived from the difference of the frequency of RhD-negative and RhC-positive phenotypes. Careful attention is necessary for clinicians in applying RhD genotyping to clinical medicine.

Phosphatidylserine exposure and aminophospholipid translocase activity in Rh-deficient erythrocytes

Endogenous phosphatidylserine (PS) exposure and lipid transport activity have been investigated for seven unrelated cases of Rhnull erythrocytes. Endogenous PS exposure was measured by prothrombinase activity. Out of six cases studied, two Rhnull samples exhibited abnormal aminophospholipid exposure, as suggested by the measurement of a lower Km of factor Xa for prothrombin. Aminophospholipid translocase activity was measured through the transbilayer redistribution of spin-labelled analogues of phospholipids. Provided that incubation conditions allow the maintainance of intracellular ATP level, no difference was observed between Rhnull and control erythrocytes, clearly indicating that the aminophospholipid translocase and Rh polypeptides are different molecular species.

Restricted Use of Cationic Germline VH Gene Segments in Human Rh(D) Red Cell Antibodies

The human red cell Rh(D) antigen elicits the production of high-affinity IgG antibodies, which can prevent blood transfusion and cause hemolytic disease of the newborn. It has been known for 20 years that Rh(D) antibodies are among the most positively charged human serum IgGs. Analysis by IEF of 9 human anti-Rh(D) monoclonal antibodies showed that their isoelectric points (pI) (8.3 to 8.6) were also significantly higher than the average pI of serum IgGs (7.0 to 8.5). Sequencing of the anti-Rh(D) H and L chains cDNAs showed a preferential use of VH1 , VH3, JH6, and Vκ1 gene segments. The high pIs in IEF were correlated with a higher number of cationic amino acid residues in the H chain V regions without clustering in the complementary determining region. Computer analysis indicated that the germline VH used in anti-Rh(D) was selected among the most cationic segments available in the human VH repertoire or expressed in normal B cells. These results indicate that the selection of cationic VH segments may be an important early step in the formation of clinically relevant anti-Rh(D) and other red cell antibodies, possibly to facilitate epitope binding in the negatively charged red cell membrane environment.

Evidence of Genetic Diversity Underlying Rh D−, Weak D (Du), and Partial D Phenotypes as Determined by Multiplex Polymerase Chain Reaction Analysis of the RHD Gene

The human blood group Rh antigens are expressed by proteins encoded by a pair of highly homologous genes located at chromosome 1p34-36. One of the genes (RHCE ) encodes Rh CcEe antigens, while the other (RHD) the D antigen. Point mutations in the RHCE gene generate the C/c and E/e polymorphisms, while it has been shown that an RHD gene deletion can generate the D-negative phenotype. We have analyzed intron 4 of the RHCE and RHD genes and have defined the site of an RHD-specific deletion located in this intron. Using a multiplex RHD typing assay, which combines a reverse polymerase chain reaction (PCR) primer, which straddles this RHD-specific sequence, and a pair of primers located in exon 10 of the RHD gene, we have analyzed 357 different genomic DNA samples derived from individuals expressing D+, D−, weak D, and partial D phenotypes. Of these, we have noted a significant discordance with our multiplex PCR assay in the D− phenotypes dCcee and dccEe (which have been previously described) and weak D phenotypes. Our results suggest that in five serologically D− individuals we have identified an apparently intact RHD gene. Sequence analysis of transcripts obtained from one of these individuals (of phenotype dCCee) illustrates the presence of full-length RHD transcripts, which have a point mutation at nucleotide 121 (C → T), which generates an in-frame stop codon (Gln41Stop). Thus, we describe a different molecular basis for generating the D− phenotype to the complete RHD gene deletion described previously. We also show that there are discordances with serotype and the multiplex assay in weak D and partial D phenotypes, indicating that the underlying molecular basis can be heterogeneous. Existing Rh D PCR assays assume the complete absence of the RHD gene in D− phenotypes. We describe a different molecular basis for generating the D− phenotype to the complete RHD gene deletion described previously.

Molecular Analysis of Rh Transcripts and Polypeptides From Individuals Expressing the DVI Variant Phenotype: An RHD Gene Deletion Event Does Not Generate All DVIccEe Phenotypes

The D antigen is a mosaic comprising at least 30 epitopes. Partial Rh D phenotypes occur when there is absence of one or more of these epitopes, with the remainder expressed. The DVI phenotype is the most common of the partial D phenotypes, lacking most D antigen epitopes (ep D) (epD1, 2, 5-8 using the 9-epitope model or epD 1-4,7-22, 26-29 using the 30-epitope model). DVI mothers may become immunized by transfusion with D-positive blood (if typed as D-positive using polyclonal typing reagents) or by fetuses which have all of the D antigen. This situation can give rise to severe hemolytic disease of the newborn (HDN). The molecular basis of the DVI phenotype has previously been proposed to occur by two different genetic mechanisms, one (in individuals of DVICcee phenotype) where a gene conversion event generates a hybrid RHD-RHCE-RHD gene; the second (in individuals of DVIccEe phenotype) was proposed to be caused by a partial RHD gene deletion. We present evidence that in four DVICcee phenotypes studied, this phenotype is not generated by a partial RHD gene deletion, but occurs by a similar mechanism to the DVICcee phenotypes. In two individuals we have found hybrid RHD-RHCE-RHD transcripts in both DVICe and DVIcE haplotypes. These differ in that the DVICe transcripts are derived from an RHD gene where exons 4-6 have been replaced with RHCE equivalents (encoding Ala226 ); the DVIcE transcripts are derived from an RHD gene where exons 4 and 5 are replaced by RHCE equivalents (encoding Pro226 ). We provide direct evidence that Rh DVI polypeptides are expressed at the erythrocyte surface as full-length polypeptide products. We have used immunoprecipitation experiments using anti-D reactive with DVI erythrocytes followed by immunoblotting the immune complexes with rabbit sera immunoreactive to the fourth external and C-terminal domains of all Rh polypeptides. Our results illustrate that these domains are present on all Rh DVI proteins studied, and suggest that Rh DVI polypeptide species studied here exist as full-length Rh proteins.

Molecular Analysis of Rh Transcripts and Polypeptides From Individuals Expressing the DVI Variant Phenotype: An RHD Gene Deletion Event Does Not Generate All DVIccEe Phenotypes

The D antigen is a mosaic comprising at least 30 epitopes. Partial Rh D phenotypes occur when there is absence of one or more of these epitopes, with the remainder expressed. The DVI phenotype is the most common of the partial D phenotypes, lacking most D antigen epitopes (ep D) (epD1, 2, 5-8 using the 9-epitope model or epD 1-4,7-22, 26-29 using the 30-epitope model). DVI mothers may become immunized by transfusion with D-positive blood (if typed as D-positive using polyclonal typing reagents) or by fetuses which have all of the D antigen. This situation can give rise to severe hemolytic disease of the newborn (HDN). The molecular basis of the DVI phenotype has previously been proposed to occur by two different genetic mechanisms, one (in individuals of DVICcee phenotype) where a gene conversion event generates a hybrid RHD-RHCE-RHD gene; the second (in individuals of DVIccEe phenotype) was proposed to be caused by a partial RHD gene deletion. We present evidence that in four DVICcee phenotypes studied, this phenotype is not generated by a partial RHD gene deletion, but occurs by a similar mechanism to the DVICcee phenotypes. In two individuals we have found hybrid RHD-RHCE-RHD transcripts in both DVICe and DVIcE haplotypes. These differ in that the DVICe transcripts are derived from an RHD gene where exons 4-6 have been replaced with RHCE equivalents (encoding Ala226 ); the DVIcE transcripts are derived from an RHD gene where exons 4 and 5 are replaced by RHCE equivalents (encoding Pro226 ). We provide direct evidence that Rh DVI polypeptides are expressed at the erythrocyte surface as full-length polypeptide products. We have used immunoprecipitation experiments using anti-D reactive with DVI erythrocytes followed by immunoblotting the immune complexes with rabbit sera immunoreactive to the fourth external and C-terminal domains of all Rh polypeptides. Our results illustrate that these domains are present on all Rh DVI proteins studied, and suggest that Rh DVI polypeptide species studied here exist as full-length Rh proteins.

Anti-Di(b) as a red cell autoantibody

BACKGROUND

It is known that some "warm"-reactive autoantibodies are directed against epitopes on the red cell anion exchanger, protein band 3. Some such antibodies (but not all) recognize Wrb. It is also known that Dia and Dib represent an amino acid polymorphism of band 3.

STUDY DESIGN AND METHODS

Autoantibodies from 119 patients were tested against Di(b-) red cells. Seventy-four of these autoantibodies were subsequently absorbed with Di(b-) red cells.

RESULTS

All 119 autoantibodies initially reacted with the Di(b-) red cells, which showed that none contained only anti-Dib. Among the 74 adsorbed with Di(b-) red cells, two were found to contain an unadsorbed anti-Dib component.

CONCLUSION

No example of autoanti-Dib as the only autoantibody present was found among the 119 samples tested. However, 2 (2.7%) of 74 autoantibodies subjected to adsorption with Di(b-) red cells were seen to contain an anti-Dib component. This low incidence of autoanti-Dib is in marked contrast to the high incidence of autoanti-Wrb, although both antibodies define epitopes associated with the red cell anion exchanger, band 3.

Immunochemical analysis of the human erythrocyte Rh polypeptides

We have used rabbit polyclonal antisera raised against synthetic peptides complementary to different domains of the Rh polypeptides and Rh glycoprotein to examine the topography and organization of these proteins in the human erythrocyte membrane. Previously unrecognized exofacial protease sites have been identified on Rh CcEe, D proteins, and Rh glycoprotein. The Rh D protein has two specific bromelain cleavage sites located within the first and sixth predicted external domains, with the site of cleavage localized in the sixth domain to lie between residues 353 and 354. All Rh polypeptide species were found to be susceptible to cleavage with trypsin and subtilisin within the first external domain of these proteins. The Rh glycoprotein has two bromelain cleavage sites within the first external domain. These flank the single N-glycosylation site (Asn37), with the cleavage site toward the C-terminal side of this residue being between residues 39 and 40. Bromelain treatment was found to deglycosylate the Rh glycoprotein. Immunoprecipitation experiments have revealed that anti-C, -c,E, -e, and -D immune complexes are reactive with antisera raised against the fourth predicted external loop of the Rh proteins and the C-terminal domain. These data indicate that the hypothesis that suggests Rh C/c antigens are expressed on truncated Rh polypeptides by a mechanism of alternate splicing is incorrect and support the hypothesis that Rh Cc and Ee antigens are expressed on a single polypeptide chain.

Selection of monoclonal antibodies for the identification of D variants: ability to detect weak D and to split epD2, epD5 and epD6/7

Red cells from known D variant donors were tested with 41 monoclonal anti-D reagents, 26 IgG and 15 IgM, with the view to selecting a panel to aid the identification of unusual D types. These antibodies gave reaction patterns which allowed the identification of most of the known D category cells, recognizing epD2, epD5, epD6/7, epD8 and epD9, but were unable to distinguish category III from normal D-positive cells. Reactivity with HMi, HMii, DFR, DBT and RoHar cells split epD2, epD5 and epD6/7 into two, three and eight groups, respectively. A panel comprising 15 monoclonal anti-D, 11 IgG and four IgM, was selected as representative of the antibodies tested. Reactivity of monoclonal anti-D was dependent on antibody concentration and antibody avidity. An antibody concentration of at least 12 micrograms/ml was required for optimum reactivity of the two monoclonal antibodies tested. A simple calculation of division of the titre by the antibody concentration provided a relatively simple means of establishing the reactivity performance of the antibody and correlated well with ability to detect weak D (Du) cells. A characteristic variable reduction in reaction strength with all the IgG anti-D was observed with weak D cells. The IgM antibodies, except the high avidity RUM-1, T3D2T6, D9A4 and BS226, performed poorly in detecting weak D. The majority of the IgM antibodies tested reacted with RoHarr cells, while only one IgG antibody was positive.

The Rh antigen D: partial D antigens and associated low incidence antigens

The expression of the Rh antigen D varies quantitatively and qualitatively (partial D); published information and 15 years' work studying D variants are discussed in this review. D epitopes correspond to the reaction patterns of monoclonal anti-D with partial D antigens. Partial D antigens can be reported in terms of their D epitopes but the epitope profile of cells with a quantitative variant of D (weak D) is difficult to determine reliably by haemagglutination tests. Nine partial D antigens, categories II-VII, DFR and two not previously reported, are identified by their epitope profiles and by association with low incidence antigens. Monoclonal anti-D recognize 16 D epitopes and more epitopes are anticipated. The specificities of polyclonal anti-D made by people with partial D antigens are considered in terms of possible D epitope specificities: recognized epitope specificities, or combination thereof, were not able to account for all observed reaction patterns of anti-D made by immunized individuals with partial D phenotypes. An attempt is made to understand partial D antigens and their associated low incidence antigens in terms of the molecular genetic information available.

Candidate gene acting as a suppressor of the RH locus in most cases of Rh-deficiency

The Rh antigen is a multi-subunit complex composed of Rh polypeptides and associated glycoproteins (Rh50, CD47, LW and glycophorin B); these interact in the red cell membrane and are lacking or severely reduced in Rhnull cells. As a result, individuals with Rhnull suffer chronic haemolytic anaemia known as the Rh-deficiency syndrome. Most frequently, Rhnull phenotypes are caused by homozygosity of an autosomal suppressor gene unlinked to the RH locus (Rhnull regulator or Rhmod types). We have analysed the genes and transcripts encoding Rh, CD47 and Rh50 proteins in five such unrelated Rhnull cases. In all patients, we identified alteration of Rh50--frameshift, nucleotide mutations, or failure of amplification--which correlated with Rhnull phenotype. We propose that mutant alleles of Rh50, which map to chromosome 6p11-21.1, are likely candidates for suppressors of the RH locus accounting for most cases of Rh-deficiency.

Tentative model for the mapping of D epitopes on the RhD polypeptide

The partial D phenotypes correspond to D-positive individuals that may develop anti-D antibodies following immunization by transfusion or pregnancy, since they lack some of the D epitopes that compose the D antigen. When these red cells are tested with a panel of human monoclonal anti-D, different patterns of reactivity are observed and at least nine distinct epitopes termed epD1 to epD9 can be identified. Molecular analysis of partial D variants have shown that the loss of some D epitopes is associated either with intergenic recombination events between the D and CE genes generating hybrid gene structures D-CE-D or CE-D-CE, or with point mutations of the D gene. Based on these findings, a tentative model that correlates critical amino acid positions and D epitope expression on the D protein was proposed. Although recent studies suggest that the D antigen may be composed of as many as 30 epitopes, the relatively simple model presented here may be useful to serologists as a preliminary approach to understanding the basis of D antigenic variation in terms of structure-activity relationship.

Rh DNA--coordinator's report

Four laboratories contributed to molecular analysis of 66 Rh variant samples originating from 12 countries. Most studies were carried out on genomic DNA using allele-specific-PCR, PCR-RFLP or nucleotide exon sequencing. In some cases, the molecular basis of some new phenotypes was established by DNA sequence analysis and the basis for the DVIE haplotypes was revisited.

[A molecular approach to the structure, polymorphism and function of blood groups]

Biochemical and molecular genetic studies have contributed to our molecular knowledge of blood group-associated molecules in the past few years. Among the 23 blood group systems presently identified, almost all have a molecular basis and present investigations are oriented towards the analysis of genetic polymorphisms, tissue-specific expression and structure-function relationships. Antigens defined by carbohydrate structures, among which ABO, Hh, Lewis and Secretor are the main representative species, are indirect gene products. They are synthesized by Golgi-resident glycosyltransferases, which are the direct products of the blood group genes. Many of these enzymes have been cloned and the molecular basis of the silent phenotypes, for instance 0, Bombay/paraBombay, Le(a-b-) and non-secretor, has been elucidated. However, the glycosyltransferases involved in the biosynthesis of Pk, P and P1 antigens are not yet characterized. A large number of blood group antigens carried by red cell polypeptides expressed at the cell surface are not related to a carbohydrate structure, and these proteins are direct blood group gene products. Most have been cloned and characterized recently, for instance MN antigens (glycophorin A), Ss antigens (glycophorin B), Gerbich antigens (glycophorins C and D) and antigens encoded by the RH, LW, KEL, FY, JK, XG, LU and XK loci. Other antigens have been located on proteins already identified, for instance the Cromer antigens on DAF, Knops antigens on CR1, Indian and AnWj antigens on CD44, Yt antigens on AChE, Diego, Wr, Rga and Warr on Band 3, Colton antigens on AQP-1 (water channel). The SC (Scianna) et DO (Dombrock) systems, however, still resist to molecular cloning. On the basis of this information, a tentative classification of blood group antigens into five functional categories is emerging: - Transporters and channels, - Receptors and ligands, - Adhesion molecules, - Enzymes, - Structural proteins. This review will focus on these recent findings and will illustrate how these studies may bring new information for analysis of normal and abnormal phenotypes and for understanding both the mechanisms of tissue specific expression and the potential function of these antigens, particularly those expressed in non-erythroid lineage. In addition, since our knowledge of the molecular basis of blood group polymorphisms has significantly increased, new genotyping techniques potentially useful in clinical applications will become available.

Molecular biology of partial D phenotypes

We have examined all DVI variant phenotypes submitted to the workshop by a combination of RT-PCR, multiplex RHD PCR and immunoblotting with Rh antipeptide sera. Our findings suggest that all DVI phenotypes arise through hybrid RHD-RHCE-RHD genes. Genomic DNA derived from all DVI samples were shown to be RHD intron 4 negative when analysed with an RHD intron 4/exon 10 multiplex assay. We assume therefore that all DVI phenotypes involve gene conversion events involving at least exons 4 and 5 of the RHD gene. Analysis of a novel D and E variant phenotype individual (ISBT49) by RT-PCR has allowed the identification of a hybrid Rh gene composed of exons 1-4 RHD: 5 RHCE/D and 6-10 RHD. We propose that the partial D & E phenotype observed arises through D & E expression on the hybrid RHD-RHCE-RHD protein: as no transcripts encoding Rh E could be found.

Monoclonal anti-D specificity and Rh D structure: criteria for selection of monoclonal anti-D reagents for routine typing of patients and donors

The Rh blood group system is the next most important to the ABO system in terms of its clinical significance in blood transfusion. It is vital to the safe, efficient practice of transfusion medicine that Rh D phenotyping tests are selected, executed and interpreted correctly. However, the Rh D blood group antigen has been shown to be subject to many phenotypic variations, and different reagents and typing techniques vary in their ability to detect these variants. The range of D-positive phenotypes are reviewed in terms of their reactivity with monoclonal antibody reagents and their clinical significance. In view of the available evidence, it is suggested that patient typing can be safely achieved by the duplicate use of one high-avidity or two very similar IgM monoclonal anti-D reagents that detect most variants except category DVI in simple tube or microplate saline tests. Antiglobulin testing for weak D should not be carried out on patient samples. Donor typing can be safely achieved by the use of the same monoclonal, used in parallel with a polyclonal anti-D reagent that detects DVI on sensitive automated equipment.

Kidd blood group and urea transport function of human erythrocytes are carried by the same protein

The gene encoding the urea transporter of human erythrocytes (HUT11 clone) has been cloned recently (Olives, B., Neau, P., Bailly, P., Hediger, M. A., Rousselet, G., Cartron, J. P., and Ripoche, P. (1994) J. Biol. Chem. 269, 31649-31652). Now, this gene has been assigned to chromosome 18q12-q21 by in situ hybridization, as also found for the Kidd (Jk) blood group locus. In coupled transcription-translation assays, the HUT11 cDNA directed the synthesis of a 36-kDa protein which was immunoprecipitated by a human anti-Jk3 antibody produced by immunized Jk(a-b-) donors whose red cells lack Kidd antigens. The anti-Jk3 antibody also immunoprecipitated a protein material of 46-60 kDa from all red cell membranes, except those from Jk(a-b-) cells. After N-glycanase digestion the 46-60-kDa component was reduced to 36 kDa. A rabbit antibody raised against the predicted NH2-terminal amino-acids of the HUT11 protein reacted on immunoblots with a 46-60-kDa component present in all human erythrocytes except those from Jk(a-b-) individuals. Jk(a-b-) red cells lack the Kidd/urea transport protein and have a selective defect of the urea transport capacity, but a normal water permeability and aquaporin-associated Colton blood group antigens. These findings indicate that the erythrocyte urea transporter is encoded by the Kidd locus and may have implications for the biology of urea transporters and their tissue-specific regulation.