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

Effects of RHD gene polymorphisms on distinguishing weak D or DEL from RhD- in blood donation in a Chinese population

BACKGROUND

Weak D or DEL red blood cell units may be mistyped as RhD- by current serology assays, which can lead to incompatible transfusion to RhD- recipients and further cause anti-D immunization. Molecular RHD blood group typing is a very effective method for overcoming current technical limits. The purpose of this study was to identify RHD single-nucleotide polymorphisms (SNPs) and compare the genotype prevalence among confirmed RhD- individuals in a Chinese population as well as explore effective biomarkers for current weak D or DEL detection before blood transfusion.

METHODS

In the present study, 125 weak D (1, 2, 3, and 4.1) or DEL and 185 RhD- blood samples from donors detected by current standard serology were collected. Genotyping system was used to analyze the SNPs of RHD in each sample.

RESULTS

Seven SNPs (rs592372, rs11485789, rs6669352, rs3118454, rs1053359, rs590787, and rs3927482) were detected in the RHD region. Rs3118454, rs1053359, rs590787, and rs3927482 showed significant differences between the weak D (1, 2, 3 and 4.1) or DEL and RhD- groups. Further combined analysis of the allelic distribution of these four SNPs revealed their higher frequencies in the RhD- group.

CONCLUSION

The SNPs rs3118454, rs1053359, rs590787, and rs3927482 in RHD showed a significantly higher frequency among an RhD- Chinese population and are potential biomarkers.

Two large deletions extending beyond either end of the RHD gene and their red cell phenotypes

Only two partial deletions longer than 655 nucleotides had been reported for the RHD gene, constrained within the gene and causing DEL phenotypes. Using a combination of quantitative PCR and long-range PCR, we examined three distinct deletions affecting parts of the RHD gene in three blood donors. Their RHD nucleotide sequences and exact boundaries of the breakpoint regions were determined. DEL phenotypes were caused by a novel 18.4 kb deletion and a previously published 5.4 kb deletion of the RHD gene; a D-negative phenotype was caused by a novel 7.6 kb deletion. Examination of the deletion-flanking regions suggested microhomology-mediated end-joining, replication slippage, and non-homologous end-joining, respectively, as the most likely mechanisms for the three distinct deletions. We described two new deletions affecting parts of the RHD gene, much longer than any previously reported partial deletion: one was the first deletion observed at the 5' end of the RHD gene extending into the intergenic region, and the other the second deletion observed at its 3' end. Large deletions present at either end are a mechanism for a much reduced RhD protein expression or its complete loss. Exact molecular characterization of such deletions is instrumental for accurate RHD genotyping.

Red cell genotyping precision medicine: a conference summary

This review summarizes the salient points of the symposium 'Red Cell Genotyping 2015: Precision Medicine' held on 10 September 2015 in the Masur Auditorium of the National Institutes of Health. The specific aims of this 6th annual symposium were to: (1) discuss how advances in molecular immunohematology are changing patient care; (2) exemplify patient care strategies by case reports (clinical vignettes); (3) review the basic molecular studies and their current implications in clinical practice; (4) identify red cell genotyping strategies to prevent alloimmunization; and (5) compare and contrast future options of red cell genotyping in precision transfusion medicine. This symposium summary captured the state of the art of red cell genotyping and its contribution to the practice of precision medicine.

Interlocus gene conversion explains at least 2.7% of single nucleotide variants in human segmental duplications

Background

Interlocus gene conversion (IGC) is a recombination-based mechanism that results in the unidirectional transfer of short stretches of sequence between paralogous loci. Although IGC is a well-established mechanism of human disease, the extent to which this mutagenic process has shaped overall patterns of segregating variation in multi-copy regions of the human genome remains unknown. One expected manifestation of IGC in population genomic data is the presence of one-to-one paralogous SNPs that segregate identical alleles.

Results

Here, I use SNP genotype calls from the low-coverage phase 3 release of the 1000 Genomes Project to identify 15,790 parallel, shared SNPs in duplicated regions of the human genome. My approach for identifying these sites accounts for the potential redundancy of short read mapping in multi-copy genomic regions, thereby effectively eliminating false positive SNP calls arising from paralogous sequence variation. I demonstrate that independent mutation events to identical nucleotides at paralogous sites are not a significant source of shared polymorphisms in the human genome, consistent with the interpretation that these sites are the outcome of historical IGC events. These putative signals of IGC are enriched in genomic contexts previously associated with non-allelic homologous recombination, including clear signals in gene families that form tandem intra-chromosomal clusters.

Conclusions

Taken together, my analyses implicate IGC, not point mutation, as the mechanism generating at least 2.7 % of single nucleotide variants in duplicated regions of the human genome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1681-3) contains supplementary material, which is available to authorized users.

Signals of historical interlocus gene conversion in human segmental duplications

Standard methods of DNA sequence analysis assume that sequences evolve independently, yet this assumption may not be appropriate for segmental duplications that exchange variants via interlocus gene conversion (IGC). Here, we use high quality multiple sequence alignments from well-annotated segmental duplications to systematically identify IGC signals in the human reference genome. Our analysis combines two complementary methods: (i) a paralog quartet method that uses DNA sequence simulations to identify a statistical excess of sites consistent with inter-paralog exchange, and (ii) the alignment-based method implemented in the GENECONV program. One-quarter (25.4%) of the paralog families in our analysis harbor clear IGC signals by the quartet approach. Using GENECONV, we identify 1477 gene conversion tracks that cumulatively span 1.54 Mb of the genome. Our analyses confirm the previously reported high rates of IGC in subtelomeric regions and Y-chromosome palindromes, and identify multiple novel IGC hotspots, including the pregnancy specific glycoproteins and the neuroblastoma breakpoint gene families. Although the duplication history of a paralog family is described by a single tree, we show that IGC has introduced incredible site-to-site variation in the evolutionary relationships among paralogs in the human genome. Our findings indicate that IGC has left significant footprints in patterns of sequence diversity across segmental duplications in the human genome, out-pacing the contributions of single base mutation by orders of magnitude. Collectively, the IGC signals we report comprise a catalog that will provide a critical reference for interpreting observed patterns of DNA sequence variation across duplicated genomic regions, including targets of recent adaptive evolution in humans.

Large-scale blood group genotyping: clinical implications

The molecular background of blood group antigen expression of the major clinically significant blood group antigens has been largely accomplished. Despite this large body of work, blood group phenotype prediction by genotyping has a marginal supporting role in the routine blood bank. It has however had a major impact in the prenatal determination of fetal blood group status in the management of haemolytic disease of the fetus and newborn. In the past few years several high throughput systems have been in development that have the potential capacity to perform genotyping on a mass scale. Such systems have been designed for use on donor- and patient-derived DNA and provide much more comprehensive information regarding an individuals blood group than is possible by using serological methods alone. DNA-based typing methodology is easier to standardize than serology and has the potential to replace it as a front line diagnostic in blood banks. This review overviews the current situation in this area and attempts to predict how blood group genotyping will evolve in the future.

Large scale blood group genotyping

Determination of predicted blood group phenotype by determination of genotype has been performed since the 1990s. This evolved due to the rapid accrual of information surrounding the molecular basis of blood group antigen expression, which started in 1990 with ABO and RH systems and has now resulted in the molecular description of 28 of the 29 blood groups. Blood group genotyping is currently performed mostly for fetal blood group incompatibility and for assessment of multi-transfused patients. Both of these clinical scenarios are either dangerous or technically difficult, respectively to define serologically. With the simultaneous development of mass scale genotyping platforms it has now permitted the application of them to blood group genotype determination. In this paper, I describe some recently published work that has demonstrated that mass scale genotyping approaches are feasible. These approaches may lead to more effective management of blood stocks and patient cross-matching by reducing the dependence on serology during the time critical pre-transfusion phase. It is most probable that large scale studies, perhaps involving many European Union and North American based blood suppliers, may drive the introduction of this technology and convince red cell serologists that this approach may allow their work to be more focussed.

The D category VI type 4 allele is prevalent in the Spanish population

BACKGROUND

The D category VI (DVI) is one of the clinically most important partial D. Three different molecular structures causing the DVI phenotype have been described.

STUDY DESIGN AND METHODS

To determine the molecular basis of the DVI phenotype in the Spanish population, 20 DVI samples, previously detected in serologic screening, were examined by polymerase chain reaction with RHD exon-specific primers. Unexpected findings were further pursued by cDNA nucleotide sequencing.

RESULTS

A novel pattern of RHD exon amplification was detected, which did not correspond to any of the previously described molecular structures. The cDNA sequence led to the identification of the new hybrid RHD-Ce(3-5)-D allele. The origin of exon 2 is undeterminable, because the 5' breakpoint was located within a region of RHD and RHCE identical sequence, which encompasses this exon. Sequencing of intron 5 allowed the 3' breakpoint to be mapped between the sixth and seventh polymorphic sites. Serologically, the hybrid protein has a D epitope expression pattern identical to the previously described DVI phenotypes and an antigen density slightly lower than DVI type 3. The new DVI variant is linked to the DCe haplotype and expresses the low-incidence BARC antigen.

CONCLUSION

A novel structure causing the DVI phenotype, here named DVI type 4, has been characterized. This novel structure is the most frequent cause of DVI in Spain.

Genetic basis of blood group diversity

In the last 18 years the genes that encode all but one of the 29 blood group systems present on red blood cells (RBCs) have been identified. This body of knowledge has permitted the application of molecular techniques to characterize the common blood group antigens and to elucidate the background for some of the variant phenotypes. Just as the RBC was used as a model for the biochemical characterization of cell membranes, so the genes encoding blood groups provide a readily accessible model for the study of gene expression and diversity. The application of genotyping techniques to identify fetuses at risk of haemolytic disease of the newborn is now the standard of care, and the expansion of nucleic acid testing platforms to include both disease testing and blood typing in the blood centre is on the horizon. This review summarizes the molecular basis of blood groups and illustrates the mechanisms that generate diversity through specific examples.

Prenatal genotyping of RHD and SRY using maternal blood

BACKGROUND AND OBJECTIVES

The aim of the study was to perform fetal RHD genotyping in maternal plasma using a fluorescent polymerase chain reaction (PCR) technique. Duplex PCR, amplifying RHD and SRY in the same tube, was undertaken. The effect of varying storage temperatures on the concentration of fetal DNA was investigated in a separate study involving 10 RhD-negative pregnant women.

MATERIALS AND METHODS

Primers and probes for the RHD gene's exon 7 and the sex-determining region, Y, were designed, and monoplex and duplex PCR were performed. Blood samples from 10 RhD-negative women were split into four and treated in four different ways before measuring the concentration of fetal DNA by quantitative PCR.

RESULTS

DNA extracted from the plasma of 114 RhD-negative pregnant women was tested for the presence of fetal RHD. The discrepancy between genotyping and serological RhD typing of the babies postpartum was 8% when counting one positive replicate as a positive result. Duplex PCR, amplifying RHD and SRY in the same tube, showed a reduced sensitivity for amplification of the SRY gene segment. There was a statistically significant reduction of fetal DNA in blood samples stored at room temperature for 48 h compared with the same sample stored at a temperature of <10 degrees C for the same length of time.

CONCLUSIONS

This method is not suitable for routine analysis because of the lack of a positive control for RHD-negative female fetuses and a decrease in PCR sensitivity when performing duplex PCR. Fetal DNA in maternal plasma is better preserved when the blood sample is kept cool.

The DAU allele cluster of the RHD gene

Variant D occurs frequently in Africans. However, considerably less RHD alleles have been described in this population compared with Europeans. We characterized 5 new RHD alleles, dubbed DAU-0 to DAU-4, that shared a T379M substitution and occurred in a cDe haplotype. DAU-1 to DAU-4 were detected in Africans with partial D phenotypes. They harbored one and 2 additional missense mutations, respectively, dispersed throughout the RhD protein. An anti-D immunization was found in DAU-3. DAU-0 carrying T379M only was detected by screening European blood donors and expressed a normal D phenotype. Within the phylogeny of the RHD alleles, DAU formed an independent allele cluster, separate from the DIVa, weak D type 4, and Eurasian D clusters. The characterization of the RH phylogeny provided a framework for future studies on RH alleles. The identification of the DAU alleles increased the number of known partial D alleles in Africans considerably. DAU alleles may be a major cause of antigen D variability and anti-D immunization in patients of African descent.

Isolation, characterization, and family study of DTI, a novel partial D phenotype affecting the fourth external loop of D polypeptides

BACKGROUND

The Rh system is the most polymorphic of the blood group systems and is of major importance in transfusion medicine. The partial D phenotypes lack one or more of the D epitopes. These variants appear to have arisen through hybrid RhD-CE-D or by spontaneous point mutations in RhD. The serologic findings and the molecular characterization of a novel partial D phenotype, termed DTI, are presented here.

STUDY DESIGN AND METHODS

RBCs from the DTI proband and RBCs from individuals with other partial D phenotypes were tested with MoAbs against 16 D epi- topes, according to the recommendations of the 4th ISBT Workshop on MoAbs (Rh Section 1A). A full-length cDNA encoding DTI and introns 4 and 5 of RhD were isolated and analyzed by DNA sequencing. A family study of the DTI allele was carried out using PCR-RFLP and long-range PCR methods.

RESULTS

Analysis of RBCs from the proband revealed that the DTI phenotype lacks epitopes D1, D2.1 (partial), D2.2, D5, D6 (partial), and D8. The DTI polypeptide exhibits seven amino acid substitutions in the D polypeptide: F223V, A226P, E233Q, V238M, V245L, G263R, and K267M. The genomic organization of DTI showed that the replacement of RhD with RhCE was located in intron 4, and the replacement of RhCE with RhD was located in intron 5. Family studies revealed that the DTI allele was inherited maternally, whereas the RhD- allele was inherited paternally in the proband.

CONCLUSION

The serologic data provide the first molecular characterization of DTI, a previously unknown partial D phenotype. This phenotype affected the D polypeptide within the fourth external loop, resulting in a new RhD-CE (entire exon 5)-D hybrid gene. It is worth noting that P226, encoded by exon 5, is derived from E of RhCE in the DTI polypeptide. Family studies demonstrated that DTI was associated with a cDTIE haplotype.

A D(V)-like phenotype is obliterated by A226P in the partial D DBS

BACKGROUND

In D category V types, the RHD exon 5 or parts thereof are replaced by the corresponding RHCE DNA segments. In D category V types I and II, the amino acid at position 226 is alanine, which is typical of the prevalent RHD allele and is observed in all RHCE alleles encoding the antigen e. A proline at position 226 in RHCE encodes the antigen E.

STUDY DESIGN AND METHODS

A blood sample of ccDEe phenotype was referred as suspected D category VI. The RHD nucleotide sequence and the D epitope pattern were determined.

RESULTS

A new partial D, DBS, encoded by an RHD-RHcE(5)-RHD hybrid allele, was found. Although it differed from D(Va) type II by an A226P substitution only, it lacked epitopes epD4, epD12, epD17, epD18, and epD22 that were present in D(Va). The 5' breakpoint region was located between the deletion in RHD intron 4 and the first polymorphic nucleotide of DBS exon 5.

CONCLUSION

The phenotypes of RHD alleles with gene conversions limited to exon 5 depended critically on the amino acid at position 226. If alanine was present at this position, gene conversions involving E233Q led to a D(Va)-like phenotype. If proline was present, many additional epitopes were lost, and the phenotype became reminiscent of DFR. The 5' breakpoint region is shared by 10 alleles and may represent the most active "hot spot" for gene conversions known in RH.

Molecular biology of the Rh blood group system

Rh molecular biology has made many advances since the first Rh cDNA was cloned in 1990. This review summarizes the current knowledge concerning the molecular basis of Rh antigenicity, D-epitope expression, and the structures of the Rh genes and proteins. Although many recent reviews have appeared regarding these subjects, advances in Rh protein function that have been published within the last 12 months have had a fundamental impact on the future direction of Rh research. In November 2000, an article described the role of Rh proteins in ammonium transport, which has remained undescribed in vertebrates, except for non-specific transport via K+ channels. The recent identification of nonerythroid Rh proteins, their expression in diverse tissues, and notably polarized epithelial and endothelial cells will be of broad functional significance and will greatly increase our understanding of the role of Rh in ammonium transport and the biology of ammonium metabolism as a whole. The advances in Rh molecular genetics have enabled the development of diagnostic tests in the clinic. At present, this is largely confined to the prenatal diagnosis of fetal blood group status in alloimmunized pregnancies, but could be extended to the noninvasive prenatal testing of all D-negative pregnant women and eventually, perhaps, to all patient and donor blood.

CHO expression of a novel human recombinant IgG1 anti-RhD antibody isolated by phage display

Replacement of the hyperimmune anti-Rhesus (Rh) D immunoglobulin, currently used to prevent haemolytic disease of the newborn, by fully recombinant human anti-RhD antibodies would solve the current logistic problems associated with supply and demand. The combination of phage display repertoire cloning with precise selection procedures enables isolation of specific genes that can then be inserted into mammalian expression systems allowing production of large quantities of recombinant human proteins. With the aim of selecting high-affinity anti-RhD antibodies, two human Fab libraries were constructed from a hyperimmune donor. Use of a new phage panning procedure involving bromelin-treated red blood cells enabled the isolation of two high-affinity Fab-expressing phage clones. LD-6-3 and LD-6-33, specific for RhD. These showed a novel reaction pattern by recognizing the D variants D(III), D(IVa), D(IVb), D(Va), D(VI) types I and II. D(VII), Rh33 and DFR. Full-length immunoglobulin molecules were constructed by cloning the variable regions into expression vectors containing genomic DNA encoding the immunoglobulin constant regions. We describe the first, stable, suspension growth-adapted Chinese hamster ovary (CHO) cell line producing a high affinity recombinant human IgG1 anti-RhD antibody adapted to pilot-scale production. Evaluation of the Fc region of this recombinant antibody by either chemiluminescence or antibody-dependent cell cytotoxicity (ADCC) assays demonstrated macrophage activation and lysis of red blood cells by human lymphocytes. A consistent source of recombinant human anti-RhD immunoglobulin produced by CHO cells is expected to meet the stringent safety and regulatory requirements for prophylactic application.

Molecular biology and genetics of the Rh blood group system

The Rh (Rhesus) blood group system is the most complex of the known human blood group polymorphisms. The expression of its antigens is controlled by a two-component genetic system consisting of RH and RHAG loci, which encode Rh30 polypeptides and Rh50 glycoprotein, respectively. Over the past decade, there has been a rapid advance in knowledge of the biochemistry, molecular biology, and genetics of the Rh genes and proteins. The primary structures of D and CcEe antigens have become well understood and the molecular genetic basis of a vast array of phenotype polymorphisms has been delineated. The identification of various molecular defects associated with Rh deficiency syndrome clarifies the nature of the amorph, suppressor, and modifier genes. The observed mutation spectrum defines a basic set of components essential for Rh complex assembly in the erythrocyte membrane. The resulting molecular information, combined with new experimental tools, is helping to dissect the fine structure of Rh antigens in terms of epitope mapping. The discovery of novel Rh homologs in primitive organisms and in nonerythroid tissues opens new avenues of research beyond the scope of erythrocytes and Rh antigens. This review provides an update on the Rh family in antigen expression, phenotype diversity, and disease association.

The Rh blood group system: a review

The Rh blood group system is one of the most polymorphic and immunogenic systems known in humans. In the past decade, intense investigation has yielded considerable knowledge of the molecular background of this system. The genes encoding 2 distinct Rh proteins that carry C or c together with either E or e antigens, and the D antigen, have been cloned, and the molecular bases of many of the antigens and of the phenotypes have been determined. A related protein, the Rh glycoprotein is essential for assembly of the Rh protein complex in the erythrocyte membrane and for expression of Rh antigens. The purpose of this review is to provide an overview of several aspects of the Rh blood group system, including the confusing terminology, progress in molecular understanding, and how this developing knowledge can be used in the clinical setting. Extensive documentation is provided to enable the interested reader to obtain further information.

Surface expression of Rh-associated glycoprotein (RhAG) in nonerythroid COS-1 cells

In the Rh blood system, RhAG (Rh-associated glycoprotein, or Rh50) is thought to be involved in Rh30 (D, CE) expression by forming a protein complex on the red cell surface. To obtain further insight into the Rh complex, we chose nonerythroid COS-1 cells instead of proerythroblast-like K562 cells, which produce endogenous Rh proteins as cell host, for the expression of both RhAG and RhD. The RhAG cDNA was subcloned into a retroviral vector, and a stable COS-1 cell line was then established via retroviral transduction. Surface expression of RhAG on the COS-1 cells was monitored by flow cytometry using mouse monoclonal anti-RhAG(2D10). Under these conditions, we detected significant expression of RhAG on the cell surface, compared to stable COS-1 cells transduced with the vector alone. To confirm the results, we isolated RhAG by immunoprecipitation from the lysate of the COS-1 cells, which were metabolically labeled with [35S]-methionine. A strong band of the 32 kd on SDS-PAGE was obtained, corresponding to the results obtained from other cultured cells (K562 cell and others), which always produce partially glycosylated RhAG with a molecular weight of 32 kd. Thus, RhAG was expressed without Rh30 and other Rh-related glycoproteins (LW, glycophorin B) in nonerythroid cells. Using the same strategy, however, we could not express RhD epitopes on COS-1 cells even in the presence of RhAG cDNA, suggesting that other factors might be required for the surface expression of RhD antigen. (Blood. 2000;95:336-341)

Molecular Configuration of Rh D Epitopes as Defined by Site-Directed Mutagenesis and Expression of Mutant Rh Constructs in K562 Erythroleukemia Cells

The Rh D antigen is the most clinically important protein blood group antigen of the erythrocyte. It is expressed as a collection of at least 37 different epitopes. The external domains of the Rh D protein involved in epitope presentation have been predicted based on the analysis of variant Rh D protein structures inferred from their cDNA sequences and their D epitope expression. This analysis can never be absolute because (1) most partial D phenotypes involve multiple amino acid changes in the Rh D protein and (2) deficiency for 1 or more epitopes may be due to gross structural alteration in the variant Rh D protein structure. We report here the amino acid requirements for the majority of D epitopes. They have been defined by generating a series of novel Rh mutant constructs by mutagenesis using an Rh cE cDNA as template and mutagenic oligonucleotide primers. When transfected into K562 cells, the D epitope expression of the derived mutant clones was then assessed by flow cytometry. The introduction of 9 externally predicted Rh D-specific amino acids on the Rh cE protein was sufficient to express 80% of all tested D epitopes, whereas other clones expressed none. We concluded from our data that the D epitope expression is consistent with at least 6 different epitope clusters localized on external regions of the Rh D protein, most involving overlapping regions within external loops 3, 4, and 6.

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.

Site-directed mutagenesis of the human D antigen: definition of D epitopes on the sixth external domain of the D protein expressed on K562 cells

BACKGROUND

The antigens of the human Rh system are of great clinical significance in transfusion medicine and pregnancy. Of the Rh system antigens, D is clinically the most important, being one of the most immunogenic structures arising from human cells. The human D antigen represents a collection of epitopes expressed on a red cell membrane protein that is predicted to have 12 membrane-spanning segments giving rise to six exofacial domains.

STUDY DESIGN AND METHODS

By site-directed mutagenesis using the method of inverse polymerase chain reaction, cE and D cDNA mutant constructs were generated with changes to the RHD-specific residues 350, 353, and 354 in the predicted sixth exofacial loop. Each mutant cDNA was subcloned into the pBabe puromycin retroviral vector, and supernatants were used to transduce K562 cells. Puromycin-resistant K562 clones were screened by flow cytometric analysis using a panel of monoclonal antibodies with specificities to ep (epitope) D1 through epD9.

RESULTS

De novo expression of epD3 and epD9 was generated in the K562 cell lines expressing the mutated cE polypeptide (cE-Asp350His, Gly353Trp, Ala354Asn). Expression of c and E was unaffected. Conversely, the cells expressing the mutated D polypeptide demonstrated loss of expression of epD1, epD2, epD3, epD4, and epD9.

CONCLUSION

The data provide strong evidence for the critical involvement of three amino acids, Asp350, Gly353, and Ala354, in the expression of epD3 and epD9 on the predicted sixth external domain of the D protein. This domain also appears to be essential for the expression of epD1, epD2, and epD4, as a loss of expression of these epitopes was observed in K562 cells transduced with the Dmut construct (encoding His350, Trp353, and Asn354). The K562/Dmut cell line has an identical molecular and serologic profile as the red cell D(IVb) phenotype, which confirms that retroviral gene transfer of Rh cDNA into K562 cells provides us with a powerful means by which to further map epitopes of D.

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.

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.

The VS and V blood group polymorphisms in Africans: a serologic and molecular analysis

BACKGROUND

VS and V are common red cell antigens in persons of African origin. The molecular background of these Rh system antigens is poorly understood.

STUDY DESIGN AND METHODS

Red cells from 100 black South Africans and 43 black persons from Amsterdam, the Netherlands, were typed serologically for various Rh system antigens. Allele-specific polymerase chain reaction and sequencing of polymerase chain reaction products were used to analyze C733G (Leu245Val) and G1006T (Gly336Cys) polymorphisms in exons 5 and 7 of RHCE and the presence of a D-CE hybrid exon 3.

RESULTS

The respective frequencies of all VS+ and of VS+ V-(r's) phenotypes were 43 percent and 9 percent in the South Africans and 49 percent and 12 percent in the Dutch donors. All VS+ donors had G733 (Val245), but six with G733 were VS- (4 V+w, 2 V-). The four VS- V+w donors with G733 appeared to have a CE-D hybrid exon 5. T1006 (Cys336) was present in 12 percent and 16 percent of donors from the two populations. With only a few exceptions, T1006, a D-CE hybrid exon 3, and a C410T (Ala137Val) substitution were associated with a VS+ V-phenotype ((C)ces or r's haplotype). Two VS+ V-individuals, with the probable genotype, (C)ces/(C)ces), were homozygous for G733 and for T1006.

CONCLUSIONS

It is likely that anti-VS and anti-V recognize the conformational changes created by Val245, but that anti-V is sensitive to additional conformational changes created by Cys336.

Antenatal genotyping of the blood groups of the fetus

Antenatal genotyping of the fetus is now in widespread use as an aid to the clinical management in cases where there is the potential of haemolytic disease of the newborn occurring. The rapid diagnosis of an antigen-negative fetus will preclude the requirement for further, potentially risky invasive procedures being performed, whilst the determination of an antigen-positive fetus allows the potential of intensifying obstetric care for this pregnancy. Molecular genotyping is a major clinical application which has led from the determination of the molecular bases of blood group antigens expressed, most of which have been defined at the level of the gene. All assays used are dependent on the Polymerase Chain Reaction amplification of fetal DNA derived from either amniotic fluid or chorionic villi. Recent work has explored the potential of utilising fetal cells found to be present in maternal peripheral blood as a source of nucleic acid for prenatal diagnosis. Using non-invasive methods will preclude exposing mother and fetus to the potential hazards of invasive methods (amniocentesis, chorionic villus sampling and cordocentesis) which include miscarriage, fetal malformations and further maternal alloimmunisation.

Three Molecular Structures Cause Rhesus D Category VI Phenotypes With Distinct Immunohematologic Features

Rhesus D category VI (DVI) is the clinically most important partial D. DVI red blood cells were assumed to possess very low RhD antigen density and to be caused by twoRHD-CE-D hybrid alleles. Because there was no population-based work-up, we screened three populations in central Europe for DVI. Twenty-six DVI samples were detected and examined by exon-specific RHD polymerase chain reaction with sequence-specific primers (PCR-SSP). A new genotype, hereby designated D category VI type III, was characterized as a RHD-Ce(3-6)-D hybrid allele by sequencing of the cDNA, parts of intron 1, and by PCR-restriction fragment length polymorphism (PCR-RFLP) of intron 2. Rhesus introns 5 and 6 were sequenced and the 3′ breakpoints of all knownDVItypes shown to be distinct. We differentiated the 5′ breakpoints of DVItypeI andDVItype II by a newly devised RHD-PCR. Thus, the DVI phenotype originated in at least three independent molecular events. Each DVI type showed distinct immunohematologic features in flow cytometry. The number of RhD proteins accessible on the red blood cells' surface ofDVItype III was normal (about 12,000 antigens/cell; DVItypeI, 500;DVItype II, 2,400) based on the determination of an RhD epitope density profile. DVItype II and DVItype III occurred as CDe haplotypes, and DVItype I as a cDE haplotype.The distribution of the DVItypes varied significantly in three German-speaking populations. Genotyping strategies should take account of allelic variations in partial RhD. The reconsideration of previous serologic and clinical data for partial D in view of the underlying molecular structures may be worthwhile.

Three Molecular Structures Cause Rhesus D Category VI Phenotypes With Distinct Immunohematologic Features

Rhesus D category VI (DVI) is the clinically most important partial D. DVI red blood cells were assumed to possess very low RhD antigen density and to be caused by twoRHD-CE-D hybrid alleles. Because there was no population-based work-up, we screened three populations in central Europe for DVI. Twenty-six DVI samples were detected and examined by exon-specific RHD polymerase chain reaction with sequence-specific primers (PCR-SSP). A new genotype, hereby designated D category VI type III, was characterized as a RHD-Ce(3-6)-D hybrid allele by sequencing of the cDNA, parts of intron 1, and by PCR-restriction fragment length polymorphism (PCR-RFLP) of intron 2. Rhesus introns 5 and 6 were sequenced and the 3′ breakpoints of all knownDVItypes shown to be distinct. We differentiated the 5′ breakpoints of DVItypeI andDVItype II by a newly devised RHD-PCR. Thus, the DVI phenotype originated in at least three independent molecular events. Each DVI type showed distinct immunohematologic features in flow cytometry. The number of RhD proteins accessible on the red blood cells' surface ofDVItype III was normal (about 12,000 antigens/cell; DVItypeI, 500;DVItype II, 2,400) based on the determination of an RhD epitope density profile. DVItype II and DVItype III occurred as CDe haplotypes, and DVItype I as a cDE haplotype.The distribution of the DVItypes varied significantly in three German-speaking populations. Genotyping strategies should take account of allelic variations in partial RhD. The reconsideration of previous serologic and clinical data for partial D in view of the underlying molecular structures may be worthwhile.