Demonstration of seven epitopes on the Rh antigen D using human monoclonal anti-D antibodies and red cells from D categories

Relationship between B-cell epitope structural properties and the immunogenicity of blood group antigens: Outlier properties of the Kell K1 antigen

BACKGROUND

The immunogenicities of polypeptide blood group antigens vary, despite most being created by single amino acid (AA) substitutions. To study the basis of these differences, we employed an immunoinformatics approach to determine whether AA substitution sites of blood group antigens have structural features typical of B-cell epitopes and whether the extent of B-cell epitope properties is positively related to immunogenicity.

STUDY DESIGN AND METHODS

Fifteen structural property prediction programs were used to determine the likelihood of β-turns, surface accessibility, flexibility, hydrophilicity, particular AA composition and AA pairs, and other B-cell epitope properties at AA substitution sites of polypeptide blood group antigens.

RESULTS

AA substitution sites of Lu^a , Jk^a , E, c, M, Fy^a , C, and S were each located in regions with at least two structural features typical of B-cell epitopes. The substitution site of K, the most immunogenic non-ABO/D antigen, scored the lowest for most B-cell epitope properties and was the only one not predicted to be part of a linear B-cell epitope. The most immunogenic antigens studied (K, Jk^a , Lu^a , E) had B-cell epitope structural properties determined by the fewest programs; the least immunogenic antigens (e.g., Fy^a , S, C, c) had B-cell epitope properties according to the most programs.

DISCUSSION

Counter to prediction, the immunogenicity of polypeptide blood group antigens was not positively related to B-cell epitope structural features present at their AA-substitution sites. Instead, it tended to be negatively related. The AA-substitution site of the most immunogenic non-ABO/D antigen, K, had the least B-cell epitope features.

Structural and functional impacts of amino acid substitutions that create blood group antigens: implications for immunogenicity

BACKGROUND

The immunogenicities of polypeptide blood group antigens vary widely. One possible determinant of immunogenicity is antigenic foreignness. The goal was to employ alternative ways of assessing foreignness and determine whether foreignness was related to immunogenicity.

STUDY DESIGN AND METHODS

Foreignness was assessed as the extent of protein functional disruption caused by the exofacial amino acid (AA) substitutions that create blood group antigens, using AA substitution prediction algorithms such as Meta-SNP and according to whether those substitutions were radical or conservative.

RESULTS

AA substitutions that create the most immunogenic antigens had the highest Meta-SNP scores, predictive of greater protein structure and function changes. Four of the 11 exofacial AAs that distinguish the most immunogenic antigen, RhD, from RhCE, and substitutions creating four of the five next most immunogenic antigens had the highest Meta-SNP scores (0.293-0.649). Excluding the outlier Jk^a , the mean Meta-SNP score of the four most immunogenic non-RhD antigens (K, Lu^a , E, c) was 3.7-fold higher than the mean of the four least immunogenic (M, Fy^a , C, S), 0.459 versus 0.123 (p = 0.0026). Regression analysis revealed a relationship between immunogenicity and Meta-SNP score (R²  = 0.953). Actual protein functional disruption was predicted for the AA substitution creating the E antigen. An AA cluster at Positions 350, 353, and 354 of RhD was unique, containing radical substitutions according to two classification schemes and relatively high Meta-SNP scores (0.351-0.432).

CONCLUSION

The immunogenicity of blood group antigens was related to the functional disruption caused by the AA substitutions that create the antigens, as measured by Meta-SNP score.

Testing for Partial RhD with a D-Screen Diagast Kit in Moroccan Blood Donors with Weak D Expression

The aim of this study was to search for the partial D phenotype in Moroccan blood donors with weak D expression. The study included 32 samples with weak D phenotype, and partial D category red blood cells were detected with the D-Screen Diagast kit, which consists in 9 monoclonal anti-D antibodies specific for the most common categories of partial D. Among the 32 samples studied, we identified 13 specific reactions to a partial D antigen (3 DVI, 2 DVa, 2 DIII^(a,b,c), and 6 DVII), with 8 reactions suggesting a weak D and 11 reactions providing no formal argument in favor of a partial D antigen. This work can be used to validate the performance of the anti-D reagent and to improve the safety of transfusion of red blood cells from donors expressing the partial D antigen by integrating the finding into the recipient file with a recommendation concerning the appropriate care.

The Rhesus Site

The Rhesus Site is a resource for information of the 'Rhesus' blood group. It is intended for specialists and non-specialists. The website details research in the field relevant for transfusion medicine, immunohematology, and molecular research. Link areas guide to important publications and to methodological resources for Rhesus. Many data originally presented at The Rhesus Site have been formally published later. The 'RhesusBase' section represents the largest database for RHD alleles; the 'RhesusSurveillance' section details the results of the largest prospective observational study on anti-D immunization events in D-positive patients. Visitors to the website are encouraged to explore the intricacies of the most complex blood group gene locus.

Analysis of density and epitopes of D antigen on the surface of erythrocytes from DEL phenotypic individuals carrying the RHD1227A allele

BACKGROUND

The characteristics of the D antigen are important as they influence the immunogenicity of D variant cells. Several studies on antigenic sites have been reported in normal D positive, weak D and partial D cases, including a comprehensive analysis of DEL types in Caucasians. The aim of this study was to assess D antigen density and epitopes on the erythrocyte surface of Asian type DEL phenotypic individuals carrying the RHD1227A allele in the Chinese population.

MATERIALS AND METHODS

A total of 154 DEL phenotypic individuals carrying the RHD1227A allele were identified through adsorption and elution tests and polymerase chain reaction analysis with sequence-specific primers in the Chinese population. D antigen density on the erythrocyte surface of these individuals was detected using a flow cytometric method. An erythrocyte sample with known D antigen density was used as a standard. Blood samples from D-negative and D-positive individuals were used as controls. In addition, D antigen epitopes on the erythrocyte surface of DEL individuals carrying the RHD1227A allele were investigated with 18 monoclonal anti-D antibodies specific for different D antigen epitopes.

RESULTS

The means of the median fluorescence intensity of D antigen on the erythrocyte membrane surface of D-negative, D-positive and DEL individuals were 2.14±0.25, 193.61±11.43 and 2.45±0.82, respectively. The DEL samples were estimated to have approximately 22 D antigens per cell. The samples from all 154 DEL individuals reacted positively with 18 monoclonal anti-D antibodies specific for different D antigen epitopes.

DISCUSSION

In this study, D antigen density on the erythrocyte surface of DEL individuals carrying the RHD1227A allele was extremely low, there being only very few antigenic molecules per cell, but the D antigen epitopes were grossly complete.

[System RH: screening of partials D with RHD/RHCE hybrid gene]

AIM OF THE STUDY

The determination of the RhD phenotype is important in transfusion medicine. However, the complexity of the expression of the D antigen is the cause of the discrepancies observed between two serological determinations and the omission by serology of some variants that can be cause alloimmunization. Therefore, it is important to known in a population the RHD alleles responsible for partial D and weak D phenotype. The aim of the study was the screening of partial D with RHD/RHCE gene hybrid by PCR-multiplex.

MATERIALS AND METHODS

Our study involved 308 blood donors from Tunisian Sahel (269 D positive and 39 D negative). We used the multiplex PCR assay to amplify specific exons of the RHD gene 3, 4, 5, 6, 7, 9 and 10. Further molecular investigations were carried to characterize the RHD variants that were detected by the multiplex.

RESULTS

In the 269 D positive samples, one case showed the absence of amplification of exons 4 and 5 of RHD gene. This variant was identified by PCR-SSP on weak D type 4. None of the RHD exons were amplified from DNA of 39 D negative samples in favor of a total deletion of the RHD gene.

CONCLUSION

We have no found any partial D variant with RHD/RHCE gene hybrid. Results in D negative samples showed that RHD gene deletion is the most frequent mechanism of D negative phenotype in the Tunisian population.

Molecular genetics and clinical applications for RH

Rhesus is the clinically most important protein-based blood group system. It represents the largest number of antigens and the most complex genetics of the 30 known blood group systems. The RHD and RHCE genes are strongly homologous. Some genetic complexity is explained by their close chromosomal proximity and unusual orientation, with their tail ends facing each other. The antigens are expressed by the RhD and the RhCE proteins. Rhesus exemplifies the correlation of genotype and phenotype, facilitating the understanding of general genetic mechanisms. For clinical purposes, genetic diagnostics of Rhesus antigens will improve the cost-effective development of transfusion medicine.

'Partial D' women with anti-D alloimmunization in pregnancy

We report five women with Rh 'partial D' who were found to have anti-D during pregnancy. Two patients were category IVa, their red cells typing as Go(a+); one was category VI; and two had a 'partial Du' which could not be categorized. The maternal anti-D concentration increased during four of the eight pregnancies studied, but none reached significant levels. Three of six D-positive cord blood samples had a positive direct antiglobulin test (DAGT). Although one baby became jaundiced, no treatment was required. The policy in the Oxford Region for the management of patients with a weak expression of D is outlined.

Outliers in RhD membrane integration are explained by variant RH haplotypes

BACKGROUND

Variations in a multipass transmembrane protein may affect its membrane integration. To study this effect, the systematic molecular characterization of variant D antigen density is a suitable model. Unlike most other membrane proteins, the expression of the D antigen is often determined by a single allele, because it occurs frequently in hemizygous form.

STUDY DESIGN AND METHODS

The D antigen density distribution of 530 CcDee, 475 ccDEe, and 514 ccDee random samples was established by flow cytometry. The molecular bases of samples with D antigen densities outside a bell-shaped peak was investigated.

RESULTS

The antigen densities of 499 CcDee, 437 ccDEe, and 480 ccDee samples formed bell-shaped peaks. Three, 10, and 12 samples, respectively, had decreased antigen densities and carried variant RHD alleles. Weak D type 19, RHD(I204T); weak D type 20, RHD(F417S); and the partial D DYU (also known as DQC), RHD(R234W) were new RHD alleles. Twenty-eight CcDee, 28 ccDEe, and 22 ccDee samples had increased antigen densities; 53 of them lacked a hybrid Rhesus box and were thus predicted to be RHD homozygous. Eight ccDee samples were predicted to be heterozygous despite a large relative dose of RHD to RHCE alleles in quantitative polymerase chain reaction. One of these samples was further investigated and carried an RHD-CE hybrid transcript characteristic for a -D- haplotype.

CONCLUSIONS

Unusual little and large RhD protein integration into the membrane could be traced to a host of distinct protein variants. Weak expression of D antigen was invariably associated with variant RHD alleles. Larger than normal D antigen density may often be caused by the presence of two D encoding alleles, which may be located in cis, and confounding zygosity testing that is solely based on gene copy number.

Weak D type 1.1 exemplifies another complexity in weak D genotyping

BACKGROUND

Weak D expression is caused by a large number of RHD alleles. Increasingly recommendations for D+ or D- transfusions are based on polymerase chain reaction (PCR) identification of certain RHD alleles. Possible sources of error are rare D variants that are inadvertently carrying known polymorphisms of frequent weak D types.

STUDY DESIGN AND METHODS

Weak D donors were checked by direct column agglutination. In donors with unusually weak expression of D, the molecular weak D type was determined by weak D PCR and nucleotide sequencing. The serologic profile of a weak D type 1 variant was determined by agglutination serology and flow cytometry.

RESULTS

Several donors in whom direct agglutination barely revealed any D expression were shown to carry the new RHD(L18V,V270G) allele dubbed weak D type 1.1. Initially, such donors had been mistyped as weak D type 1 by PCR. In a systematic study, weak D type 1.1 was shown to be present in 7 of 23 donors with very weak D expression who all lived in a restricted area of Northern Germany. Although weak D type 1.1 was typed D- or barely D+ by direct agglutination, it was easily detected by antiglobulin technique and was shown to carry about 600 antigens D per red blood cell.

CONCLUSION

The observation of weak D type 1.1 with its distinct phenotype pinpointed to two general problems of current RHD genotyping strategies: Mistyping of alleles with additional mutations and striking geographic variation of the allele distributions.

Random survey for RHD alleles among D+ European persons

BACKGROUND

RHD alleles are considered more variable in African persons than in European persons. A systematic survey, however, was lacking among D+ European persons at the molecular level, precluding any definite frequency estimate.

STUDY DESIGN AND METHODS

A random survey was performed among 500 ccDee, 250 CcDee, and 250 ccDEe blood donors in southwestern Germany. They were tested by polymerase chain reaction with sequence-specific priming (PCR-SSP) for up to 12 single-nucleotide polymorphisms representative for the most frequent RHD alleles among European persons. The RHD exon 5 nucleotide sequence was also tested in all 1000 samples. The nucleotide sequence of the 10 RHD exons was checked in all samples with aberrant exon 5 or positive PCR-SSP procedures.

RESULTS

By PCR-SSP, 15 aberrant RHD alleles were found among the 500 ccDee, 2 among the 250 CcDee, and none among the ccDEe samples. One of these was the novel RHD(F223V, E233Q, T379M) allele dubbed DAU-5. Weak D type 4 was detected more frequently than expected, whereas the population frequencies of the other RHD alleles conformed to published estimates. Nucleotide sequencing of RHD exon 5 further revealed three novel alleles RHD(G212G), RHD(R234W), and RHD(V245L), dubbed DUC-1, DQC, and DUC-2.

CONCLUSION

In a limited screen at the molecular level among 1000 random D+ donors in southwestern Germany, 20 donors were found carrying aberrant RHD alleles. Four of these alleles were new and likely sporadic. An estimate was derived of the variety that may be encountered in genotyping approaches, and it was concluded that even within the European population the variety of RHD alleles may be larger than anticipated.

Whole exon 5 and intron 5 replaced by RHCE in DVa(Hus)

The DVa(Hus) was previously investigated through cDNA analysis, which revealed an RHD-CE(5)-D hybrid allele. However, the 5' and 3' breakpoints remain unknown. In this article, gene recombinations between the RHD and RHCE alleles were investigated by a combination approach of a sequence-specific primer PCR (PCR-SSP) and an RHD full-length coding region sequencing method on two Chinese subjects with weak D phenotypes. The hybrid Rhesus box of each individual was also investigated through an established PCR-based method. As a result, two partial D phenotypes, DVa(Hus) and DVI type III, were identified, each carrying one hybrid RHD-CE-D allele. The two samples were also serotyped with Rh phontypes of DccEe and DCcee, respectively. Other sequencing analyses of the DVaHus sample showed that the sequence of intron 4 is identical with RHD, whereas the whole sequence of exon 5 and intron 5 is identical with RHCE except for seven polymorphisms in the intron 5. We may concluded that in the case of this Chinese DVa(Hus), the whole exon 5 and complete intron 5 of a total segment of 1801 nucleotides were replaced by RHCE suggesting that the breakpoints of the replaced region are the 5' end of the exon 5 and the 3' end of the intron 5.

Epitope mapping of four monoclonal antibodies specific for the human RhD antigen

RhD is a highly immunogenic erythrocyte membrane protein, implicated in hemolytic disease of the newborn and other hemolytic disorders. Anti-RhD antibodies are used in the treatment of such disease states. Six mutant forms of recombinant RhD were stably expressed in K562 cells, and these cells were used to investigate epitope specificities of four anti-RhD monoclonal antibodies (mAbs). Amino acid substitutions were made in the exofacial loops of RhD to the corresponding residues found in the related RhCE polypeptide; M169L/M170R and I172F in the third loop, F223V and E233Q in the fourth loop, and D350H and G353W/A354N in the sixth loop. Each mAb was found to have a unique fine specificity and recognized multiple distant sites within RhD. The mAbs also differed in how they recognized individual amino acids in the exofacial loops of RhD.

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.

V(D)J germline gene repertoire analysis of monoclonal D antibodies and the implications for D epitope specificity

BACKGROUND

The D antigen is a highly immunogenic human RBC antigen. Alloimmunization against the D antigen produces high-affinity antibodies that cause hemolytic transfusion reactions and HDN.

STUDY DESIGN AND METHODS

Cloning and subsequent sequence analysis of 11 new samples of monoclonal anti-D was performed in an attempt to identify V(D)J germline gene usage. Sequences were compared and analyzed with 37 previously published samples of anti-D for identification of V(H) and V(L) pairings, canonical structures, and conformation of restricted germline gene usage.

RESULTS

The V(H) and V(L) pairings used by the new D MoAbs resulted in seven canonical combinations, three of which had not been described previously. Preferential usage of gene segments from the VH3 and VH4 families and of D3, D6, JH6, and DPK9 germline gene segments was also determined. Three samples of anti-D from different donors were found to use similar V(H) and V(kappa) germline genes, despite the fact that two of the antibodies recognized epD6/7 and the third recognized epD1. From the cumulative analysis of the anti-D IgG, 24 V(H) and V(L) gene pairings were identified, resulting in only 10 canonical structures.

CONCLUSIONS

Despite the potential for diversity, only a minority of V(H) and V(L) germline genes are used by anti-D. Consequently, V(H) and V(L) pairings and the resulting canonical structures are similarly restricted.

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.

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.

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.

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.

The D antigen characteristic of RoHar is a partial D antigen

The results of testing RoHarr cells with panels of monoclonal anti-D suggest that the D antigen (referred to as DHar) encoded by the haplotype (D)c(e) Rh33 is a partial D antigen. IgM monoclonal anti-D are more efficient than IgG monoclonal anti-D in detecting DHar.DHar expresses some but not all of both epD5 and epD6/7 and appears to lack epD1-epD4, epD8 and epD9.

Reactivity of 62 Rh MAbs with weak and variant antigens

We characterized serologically 5 anti-C (4 IgM and 1 IgG), 3 anti-c (2 IgM and 1 IgG), 4 anti-E (1 IgM and 3 IgG), 4 anti-e (3 IgM and 1 IgG) and 46 anti-D (16 IgM and 30 IgG) monoclonal antibodies, provided by the Rh Section of the Third International Workshop and Symposium on Monoclonal Antibodies against Human Red Blood Cells and Related Antigens (1996) for their ability to detect weak and variant antigens. The agglutination patterns were established using untreated and papain-treated red blood cells in a column agglutination technology system (BioVue, Ortho). Significant differences were found between the IgM and IgG antibodies. The papain treatment seemed to be important for IgM but not for IgG antibodies. Almost all of the IgM anti-D antibodies detected untreated DIV samples and almost all of the IgG anti-D antibodies detected untreated weak D samples. Both IgM and IgG anti-D antibodies showed the highest number of negative reactions with DVI and Rh 33 red blood cells. The CwCw sample was detected by only one of the 4 anti-C IgM MAbs using enzyme-treated red blood cells. All anti-c MAbs were able to detect treated Cx samples. Because of the small number of weakly expressed E and e samples, definitive conclusions cannot be drawn on the ability of these antibodies to detect these antigens.

Frequency of partial D phenotypes in the south western region of France

The aim of this study was to estimate the frequencies of partial D phenotypes among weak D (D14) blood samples. During one year, red blood cell samples with D14 phenotype were tested by the indirect antiglobulin test (IAT) using a panel of six anti-D monoclonal antibodies (Mabs). The panel of Mabs was selected for its capacity to define patterns of reactivity specific to the most frequent categories of partial D phenotypes. Among 475 D14 samples, 16 partial D phenotypes were identified (2 DIIIb, 3 DIVa, 4 DIVb et 7 DVI) corresponding to 3.36% of the D14 population. A strategy for systematic screening of partial D phenotypes is discussed in relation to the results of this study.

The effect of cysteine modification and proteinases on the major antigens (D, C, c, E and e) of the Rh blood group system

We have confirmed and extended previous observations showing that the (Rh) D antigen of erythrocyte membranes is destroyed by various reagents that modify cysteine (Cys) residues (Res.) and by trypsin as well as chymotrypsin, using thirty examples of monoclonal or polyclonal anti-D in heamglutination inhibition assays. We have also shown that most C, c, E, e and BS58 epitopes are inactivated or weakened by most Cys reagents and by these proteinases, using monoclonal and polyclonal antibodies. Inactivation by 5,5-dithiobis-(2-nitrobenzoic acid) was always fully reversible after subsequent dithioerythritol treatment. The essential Cys Res. appear to be buried in the membrane in view of the inability of some reagents to inactivate (iodoacetamide, iodoacetic acid) or reactivate (reduced glutathione) the antigens. Data obtained with N-ethylmaleimide indicate that inactivation of the C and c antigens is, at least in part, attributable to (a) Cys Res. that is (are) different from that (those) involved in the E and e antigens. Data obtained with the Cys reagents and the proteinases suggest that more than one peptide loop of the Rh proteins is involved in the major Rh antigens.

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.

A structural model for 30 Rh D epitopes based on serological and DNA sequence data from partial D phenotypes

Both cDNA RHD sequences and reactivity with monoclonal anti-D have been reported in a number of partial D phenotypes, where parts (some epitopes) of the normal D antigen are missing, and anti-D of restricted specificity may be made in response to challenge with normal D positive blood. This paper analyses these reports together and proposes a model for the structure which comprise the epitopes of the Rh D antigen. Some epitopes are proposed to be comprised of continuous peptide sequence within one extracellular loop, whereas others require interactions between two or the extracellular peptide loops.

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.

Development and evaluation of a competitive radioimmunoassay using monoclonal antibodies against Rh D for determining anti-D potency of clinical grade immunoglobulin preparations

A competitive radioimmunoassay using monoclonal anti-D antibodies has been developed for measuring anti-D activity in prophylactic immunoglobulin preparations. The assay is totally specific for anti-D, reproducible and gives potency estimates comparable to those determined using autoanalyzer methodology. The assay also provides a means for comparing different batches of monoclonal anti-D preparations for red-cell binding activity.

Leu110Pro substitution in the RhD polypeptide is responsible for the DVII category blood group phenotype

The nucleotide sequence of the RhD transcripts from the reticulocytes of three unrelated variants with the DVII category blood group phenotype has been determined. Our results indicate that the expression of the low frequency antigen Rh40 and the lack of epD8 at the surface of these variant RhD positive red cells are associated with a single point mutation, T329C, in exon 2 of the RHD gene. This nucleotide polymorphism results in a leucine to proline substitution at amino acid position 110 of the RhD polypeptide.

Defining the Rh blood group antigens. Biochemistry and molecular genetics

The Rh blood group antigens (D, Cc and Ee series) are carried by a family of non glycosylated hydrophobic transmembrane proteins of 30-32 kDa which are missing from the red cells of rare Rhnull individuals that express several membrane defects. The structure of these proteins has been deduced from cDNA cloning and studies have shown that the Rh proteins are erythroid specific and share no sequence homology with any known protein. The RhD and non-D proteins exhibit 92% sequence identity and their predicted membrane topology is similar as most of the molecules appear to reside between the leaflets of the phospholipid bilayer with only short hydrophilic loops connecting the twelve putative transmembrane helices. The RHD and RHCE genes encoding the Rh proteins (D and Cc/Ee, respectively) are organized in tandem on chromosome 1p34-p36 and most likely derived by duplication of a common ancestral gene. This concept is supported by the identification of RH-like genes in non human primates. The human RH locus is best described as a two-gene model in which all RhD-positive and most RhD-negative haplotypes are composed of two (RHD and RHCE) or only one (RHCE) structural genes, respectively. The RHD gene encodes the D protein and the RHCE gene encodes the C/c and E/e proteins presumably by alternative splicing of a pre messenger RNA. The correlation between the blood group D epitopes and the amino acid polymorphism of the Rh proteins is not yet established, but amino acid polymorphisms at positions 103 and 226 determine the molecular basis for the C/c (Ser-->Pro) and E/e (Pro-->Ala) specificities, respectively. Most variants analyzed so far are caused by gene conversion which appears as the principal mechanism responsible for polymorphism and gene diversity in the RH system. However, gene deletions have also been found in some occasions. To date, all Rhnull phenotypes investigated most likely result from transcriptional regulatory mechanisms that are not yet understood. Rhnull individuals suffer a clinical syndrome of varying severity and their red cells are characterized by morphological and functional abnormalities of cation transport and phospholipid asymmetry. In addition, several membrane components including the Rh proteins and other glycoproteins recently characterized (Rh50 glycoprotein, CD47, glycophorin B, Duffy, LW) are absent or severely decreased on these cells. These findings suggest that the Rh proteins are assembled into a multimeric complex with these glycoproteins and further studies should clarify the role in biosynthesis and the potential function of each component in this complex.

Human monoclonal antibodies against the rhesus D antigen from women with severe Rh immunization submitted to high-dose intravenous immunoglobulin treatment

The pre- and postpartum maternal serum anti-D concentrations of 28 women with severe Rh(D) immunization who received high-dose intravenous immunoglobulin treatment has been determined. In all cases, including 1 in which the newborn was D negative, a sharp increment in the anti-D titer was observed after delivery. The specific immunoglobulin concentration rose to levels ranging from 4.7 to 204.0 micrograms/ml and, in 20% of the patients, increments of fifty times or greater were observed. Human monoclonal antibodies (hmAb) have been produced from Epstein-Barr virus-transformed lymphoblastoid B cell lines derived from 1 of these naturally hyperimmunized patients whose serum contained an anti-D-category DVI antibody. Four anti-D-secreting cell lines (97.E3.39.214, 44.E4.R1.257, E7.R1.126.83.115 and E11V.117.63; hereafter referred to as 214, 257, 115 and 63) have been established and maintained in continuous culture for periods ranging from several months to 3 years, without loss of antibody production capacity. Antibodies 115 and 214 recognize all Du samples tested at the same level as the polyclonal positive control. Antibodies 63 and 257 show a significantly lower reaction strength with some of the Du samples. Studies with D category cells showed that the DVI category was recognized only by hmAb 214. The reactivity pattern of this antibody is that of an anti-epD4, although the reaction strength varied greatly with different DIVa cell samples. Results obtained with hmAb 257 and 115 using papain-treated D category cells suggest that booth react as anti-epD6/7.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of D sites on selected 'weak D' and 'partial D' red cells

Measurements have been made of the number of available sites on 10 examples of red cells in which the only abnormality appeared to be a quantitative reduction in the expression of D (weak D cells); these estimates were carried out using three monoclonal anti-D antibodies, Fog-1, Brad-3 and Los-2. The values varied with the monoclonal antibody that was used and fell within the range of 170-1,870 sites/cell. A further 3 examples of weak D cells which had brought about immunisation following transfusion were found to have between 390 and 1,470 sites per red cell. The implications of the D site density on the immunogenicity of weak D cells are discussed. The number of sites on red cells with structurally abnormal D (partial D cells) were also estimated, using the antibody Fog-1. Four of the 5 examples of cells of category IVa (probable phenotype Ror) were found to have a high expression of D (range 29,300-41,300), but the available D sites of categories DVa, DVIa, and DVII were considerably reduced (< 500, < 500 and 2,400-7,500 sites/cell, respectively). As a working hypothesis, it is suggested that there are two types of genetic abnormality leading to an abnormal expression of D. First, a defect in genomic DNA leading only to a quantitative reduction in the number of available D sites; this genomic lesion should be termed 'weak D'. Secondly, genomic defects leading to amino acid sequence abnormalities and structural change in the D polypeptide; these lesions should be collectively known as 'partial D'.

The role of Rh antibodies in haemolytic disease of the newborn

Recent insights into the structure-function relationship of IgG, the nature of Fc receptors and their interactions with antibodies, and the cellular mechanisms involved in the immune destruction of IgG-sensitized cells have all contributed to a fuller understanding of the role of Rh antibodies in HDN. As this understanding has increased, so different diagnostic and therapeutic approaches have been developed and evaluated in order either to predict or ameliorate disease severity. The role of Rh antibodies in HDN can be considered in three contexts: maternal anti-D, monoclonal anti-D and prophylactic anti-D. Anti-D formed after maternal alloimmunization may be transported across the placenta, resulting in destruction of sensitized red cells by mononuclear phagocytes in the fetus and infant. The use of monoclonal anti-D has given an insight into the cellular and molecular mechanisms involved in red cell destruction, and has facilitated the development and evaluation of assays which use maternal anti-D to predict the severity of HDN. Polyclonal anti-D, given prophylactically, can prevent maternal alloimmunization to D-positive fetal red cells. Future developments are likely in several areas. Prophylactic polyclonal anti-D may be replaced, wholly or partially, with monoclonal anti-D. The development and introduction of cellular assays as non-invasive tests for predicting disease severity is likely to continue as preliminary results are encouraging. Finally, new strategies for ameliorating disease severity may be assessed including the role of ivIgG and Fc gamma R-blocking antibodies.

Production of stable human-mouse hybridomas secreting monoclonal antibodies against Rh D and c antigens

Peripheral blood lymphocytes from donors immunized against Rh antigens were fused with mouse myelomas and heteromyelomas in order to obtain human-mouse hybridomas secreting antibodies specific for these antigens. Three cell lines secreting anti-D IgG and two secreting anti-c IgM were stabilized and produced immunoglobulins for several months. These human monoclonal antibodies were evaluated as reagents for Rh phenotyping. Their complementary activity towards weak D and partial D antigens is examined.

Further complexities of the Rh antigen D disclosed by testing category DII cells with monoclonal anti-D

The reaction pattern of monoclonal anti-D with category DII cells differed from those of other category D cells. DII cells express epD1, epD2, epD3, epD5, epD6/7 and epD8 but lack epD4 and a new epitope epD9. The new epitope, epD9, is proposed to explain the failure of some monoclonal anti-D (previously considered to be anti-epD3) to react with DII cells.

Molecular cloning and primary structure of the human blood group RhD polypeptide

The RH (rhesus) blood group locus from RhD-positive donors is composed of two homologous structural genes, one of which encodes the Cc and Ee polypeptides, whereas the other, which is missing in the RhD-negative condition, encodes the D protein that carries the major antigen of the RH system. Recently, different splicing isoforms transcribed from the CcEe gene were isolated. We report now the characterization of two other Rh clones, RhII and RhXIII, generated by alternative choices for poly(A) addition sites that were identified as the RhD gene transcripts. That these cDNAs represented the RhD messenger and that the previously described Rh clones were derived from the CcEe gene was demonstrated by amplification of RhII/XIII sequences only from D-positive genomes and by cloning and sequencing of D- and CcEe-specific gene fragments. The predicted translation product of the RhD mRNA is a 417-amino acid protein (M(r) = 45,500) that exhibited a similar membrane organization with 13 bilayer-spanning domains compared with the polypeptide encoded by the CcEe gene. The D and Cc/Ee polypeptides differ by 36 amino acid substitutions (8.4% divergence), but the NH2- and COOH-terminal regions of the two proteins are well conserved. Similarly, five of the six cysteine residues of the Cc/Ee proteins were conserved in the D protein, including the unique exofacial cysteine, which is critical for antigenic reactivity. The sequence homology between the Cc/Ee and D proteins supports the concept that the genes encoding these polypeptides have evolved by duplication of a common ancestor gene.

Molecular characterization of a human anti-Rh(D) antibody with a DH segment encoded by a germ-line sequence

The lambda-light-chain and lambda-heavy-chain variable-region genes of an anti-Rh(D) (Rh, Rhesus; D, heavy-chain diversity region) human monoclonal antibody secreted by lymphocytes transformed by the Epstein-Barr virus have been cloned and sequenced. Sequence comparison of the anti-Rh(D)mAb lambda-chain variable region with those of the other available human lambda chains revealed that it belonged to the human V lambda I (V lambda, variable region of lambda chain) subgroup. The greatest sequence similarity (80%) was observed with that of another anti-Rh antibody lambda-chain directed against the Rh(c) antigen. For the VH (VH, variable region of heavy chain) sequence, the highest similarity (86%) was observed with the germline VHG3 gene which belongs to the VHI subgroup. The expressed DH sequence of the anti-Rh(D) antibody is also of germline origin and complementarity-determining region 3 is thus produced by VH-DH and DH-JH (J, joining region) joining without recombination of multiple DH gene segments.

Human monoclonal antibodies against blood group antigens preferentially express a VH4-21 variable region gene-associated epitope

An anti-idiotypic antibody has been raised which recognizes human immunoglobulins with cold agglutinin activity of anti-I/i specificity. The pattern of reactivity of the antibody indicates that the structural basis for the epitope is located in the VH4-21 gene segment of the VHIV family, which is preferentially utilized by these cold reactive antibodies. Using this antibody, epitope expression was investigated in a panel of 72 human monoclonal allo-antibodies specific for human blood group antigens, as compared with a control panel of 39 randomly selected human monoclonal IgM antibodies of unknown specificities. The anti-blood group panel included 44 IgM and 28 IgG monoclonal antibodies against a variety of blood group antigens including the A antigen, Rh C, c, D, E, e, G antigens, and the Kidd antigens Jka and Jkb. The epitope was expressed by 64% (28/44) of the IgM anti-blood group antibodies and by 21% (6/28) of the IgG antibodies, but by only 7.7% (3/39) of the control IgM antibodies. These data indicate that the human alloimmune response to blood group antigens is biased in the use of VH gene families, with a preference for the VH4-21 gene segment of the VHIV family, or closely related gene segments. The fact that this mirrors the findings for the autoimmune cold agglutinins suggests a link in immunoglobulin gene usage between antibodies against structurally diverse antigens on the red cell surface.