The Fy(x) phenotype is associated with a missense mutation in the Fy(b) allele predicting Arg89Cys in the Duffy glycoprotein

Duffy antigen is expressed during erythropoiesis in Duffy-negative individuals

The erythrocyte silent Duffy blood group phenotype in Africans is thought to confer resistance to Plasmodium vivax blood-stage infection. However, recent studies report P. vivax infections across Africa in Fy-negative individuals. This suggests that the globin transcription factor 1 (GATA-1) SNP underlying Fy negativity does not entirely abolish Fy expression or that P. vivax has developed a Fy-independent red blood cell (RBC) invasion pathway. We show that RBCs and erythroid progenitors from in vitro differentiated CD34 cells and from bone marrow aspirates from Fy-negative samples express a functional Fy on their surface. This suggests that the GATA-1 SNP does not entirely abolish Fy expression. Given these results, we developed an in vitro culture system for P. vivax and show P. vivax can invade erythrocytes from Duffy-negative individuals. This study provides evidence that Fy is expressed in Fy-negative individuals and explains their susceptibility to P. vivax with major implications and challenges for P. vivax malaria eradication.

Genome-wide meta-analysis of 92 cardiometabolic protein serum levels

OBJECTIVES

Global cardiometabolic disease prevalence has grown rapidly over the years, making it the leading cause of death worldwide. Proteins are crucial components in biological pathways dysregulated in disease states. Identifying genetic components that influence circulating protein levels may lead to the discovery of biomarkers for early stages of disease or offer opportunities as therapeutic targets.

METHODS

Here, we carry out a genome-wide association study (GWAS) utilising whole genome sequencing data in 3,005 individuals from the HELIC founder populations cohort, across 92 proteins of cardiometabolic relevance.

RESULTS

We report 322 protein quantitative trait loci (pQTL) signals across 92 proteins, of which 76 are located in or near the coding gene (cis-pQTL). We link those association signals with changes in protein expression and cardiometabolic disease risk using colocalisation and Mendelian randomisation (MR) analyses.

CONCLUSIONS

The majority of previously unknown signals we describe point to proteins or protein interactions involved in inflammation and immune response, providing genetic evidence for the contributing role of inflammation in cardiometabolic disease processes.

The highest Duffy (FYX) allele frequency ever reported for Scottish population: A cross-sectional study

Background and Aim

The Duffy (FY) blood group system has six known antigens among which the Fy^a and Fy^b are known as major antigens. Fy^x phenotype forms as a result of two point mutations in the FYB allele leading to instability of Duffy protein and so reduction of Duffy antigen expression in the cells. This study aimed to investigate the FYX allele frequency in the Scottish population.

Methods

The Duffy blood group system was serologically and molecularly investigated in 222 samples collected from donors of Aberdeen Regional Blood Transfusion Center (BTC). The haemagglutination and BeadChip microarray chemistry methods were used for phenotyping and genotyping. Confirmatory tests were also used to check the discrepant results.

Results

In this study, the frequency of Duffy blood group phenotypes including Fy^a+, Fy^a+b+, and Fy^b+ were 17.57%, 42.79%, and 39.64%, respectively. Furthermore, the frequency of FYA/FYA, FYA/FYB, and FYB/FYB genotypes was estimated to be 14.41%, 45.95%, and 39.64%, respectively, using the Bioarray method. In the present study, based on Duffy DNA sequencing results, 12 samples (5.41%) had just one FYX allele.

Conclusion

The frequency of the FYX allele in this study was estimated to be 0.0270% which is more than the results reported so far.

Diversity of variant alleles encoding Kidd, Duffy, and Kell antigens in individuals with sickle cell disease using whole genome sequencing data from the NHLBI TOPMed Program

BACKGROUND

Genetic variants in the SLC14A1, ACKR1, and KEL genes, which encode Kidd, Duffy, and Kell red blood cell antigens, respectively, may result in weakened expression of antigens or a null phenotype. These variants are of particular interest to individuals with sickle cell disease (SCD), who frequently undergo chronic transfusion therapy with antigen-matched units. The goal was to describe the diversity and the frequency of variants in SLC14A1, ACKR1, and KEL genes among individuals with SCD using whole genome sequencing (WGS) data.

STUDY DESIGN AND METHODS

Two large SCD cohorts were studied: the Recipient Epidemiology and Donor Evaluation Study III (REDS-III) (n = 2634) and the Outcome Modifying Gene in SCD (OMG) (n = 640). Most of the studied individuals were of mixed origin. WGS was performed as part of the National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine (TOPMed) program.

RESULTS

In SLC14A1, variants included four encoding a weak Jka phenotype and five null alleles (JKnull ). JKA*01N.09 was the most common JKnull . One possible JKnull mutation was novel: c.812G>T. In ACKR1, identified variants included two that predicted Fyx (FY*X) and one corresponding to the c.-67T>C GATA mutation. The c.-67T>C mutation was associated with FY*A (FY*01N.01) in four participants. FY*X was identified in 49 individuals. In KEL, identified variants included three null alleles (KEL*02N.17, KEL*02N.26, and KEL*02N.04) and one allele predicting Kmod phenotype, all in heterozygosity.

CONCLUSIONS

We described the diversity and distribution of SLC14A1, ACKR1, and KEL variants in two large SCD cohorts, comprising mostly individuals of mixed ancestry. This information may be useful for planning the transfusion support of patients with SCD.

Blood group typing from whole-genome sequencing data

Many questions can be explored thanks to whole-genome data. The aim of this study was to overcome their main limits, software availability and database accuracy, and estimate the feasibility of red blood cell (RBC) antigen typing from whole-genome sequencing (WGS) data. We analyzed whole-genome data from 79 individuals for HLA-DRB1 and 9 RBC antigens. Whole-genome sequencing data was analyzed with software allowing phasing of variable positions to define alleles or haplotypes and validated for HLA typing from next-generation sequencing data. A dedicated database was set up with 1648 variable positions analyzed in KEL (KEL), ACKR1 (FY), SLC14A1 (JK), ACHE (YT), ART4 (DO), AQP1 (CO), CD44 (IN), SLC4A1 (DI) and ICAM4 (LW). Whole-genome sequencing typing was compared to that previously obtained by amplicon-based monoallelic sequencing and by SNaPshot analysis. Whole-genome sequencing data were also explored for other alleles. Our results showed 93% of concordance for blood group polymorphisms and 91% for HLA-DRB1. Incorrect typing and unresolved results confirm that WGS should be considered reliable with read depths strictly above 15x. Our results supported that RBC antigen typing from WGS is feasible but requires improvements in read depth for SNV polymorphisms typing accuracy. We also showed the potential for WGS in screening donors with rare blood antigens, such as weak JK alleles. The development of WGS analysis in immunogenetics laboratories would offer personalized care in the management of RBC disorders.

Identification of ACKR1 variants associated with altered Duffy phenotype expression in blood donors from southern Brazil

The atypical chemokine receptor 1 gene (ACKR1) is responsible for the clinically significant Duffy blood group. The main antigens of this system, Fya and Fyb, can be related to a null or weak expression of the DARC protein. In the present work, we aimed to identify ACKR1 gene variants in blood donors from southern Brazil based on discrepancies between their serological and molecular typing results. Then, we analyzed the association of these variants with the expression of the Duffy phenotype. The Fy antigen types were determined via hemagglutination and real-time PCR (c.125 G > A, c.265C > T and c.-67T > C SNPs) tests in a sample composed of 382 regular repetitive voluntary blood donors to the Blood Bank of Hospital de Clínicas de Porto Alegre. An inconclusive correlation between phenotype-genotype analyses was found in 11 (2.88 %) donors, and the entire ACKR1 gene was sequenced in these samples. Our investigation found 11 genetic variants, four of which (c.-541C > T, c.21 + 150C > T, c.22-58A > G, and c.298 G > A SNPs) seem to have putative functional effects on the structure and expression of DARC undertaken for in silico analysis (SIFT, PolyPhen-2 and RegulomeDB). Molecular events can result in apparent discrepancies between red cell genotypes and phenotypes. Our findings provided insight into the molecular background of FY antigens to improve technical approaches for red cell genotyping.

Defining Blood Group Gene Reference Alleles by Long-Read Sequencing: Proof of Concept in the ACKR1 Gene Encoding the Duffy Antigens

Background

In the novel era of blood group genomics, (re-)defining reference gene/allele sequences of blood group genes has become an important goal to achieve, both for diagnostic and research purposes. As novel potent sequencing technologies are available, we thought to investigate the variability encountered in the three most common alleles of ACKR1, the gene encoding the clinically relevant Duffy antigens, at the haplotype level by a long-read sequencing approach.

Materials and Methods

After long-range PCR amplification spanning the whole ACKR1 gene locus (∼2.5 kilobases), amplicons generated from 81 samples with known genotypes were sequenced in a single read by using the Pacific Biosciences (PacBio) single molecule, real-time (SMRT) sequencing technology.

Results

High-quality sequencing reads were obtained for the 162 alleles (accuracy >0.999). Twenty-two nucleotide variations reported in databases were identified, defining 19 haplotypes: four, eight, and seven haplotypes in 46 ACKR1*01, 63 ACKR1*02, and 53 ACKR1*02N.01 alleles, respectively.

Discussion

Overall, we have defined a subset of reference alleles by third-generation (long-read) sequencing. This technology, which provides a "longitudinal" overview of the loci of interest (several thousand base pairs) and is complementary to the second-generation (short-read) next-generation sequencing technology, is of critical interest for resolving novel, rare, and null alleles.

Impact of Duffy polymorphisms on parasite density in Brazilian Amazonian patients infected by Plasmodium vivax

Background

The Duffy glycoprotein acts as the entry point for merozoites of Plasmodium vivax in the invasion of red blood cells. The host–parasite relationship has revealed new perspectives regarding the association between Duffy polymorphisms that can impact both the parasite density of this Plasmodium and the symptoms of this type of malaria. This study investigates the impact of Duffy polymorphisms on parasite density in patients infected with P. vivax in the Brazilian Amazon region.

Methods

Genotypes and Duffy polymorphism allele frequencies were compared in 287 patients with malaria, presenting low, medium and high density of P. vivax. The diagnosis of malaria was performed using a specialized team with a standardized clinical-laboratory method, while the Duffy genotyping was performed through the Bead Chip BioArray system. Both teams are reference services in Brazil.

Results

The FY*01 and FY*02 alleles were found in all three parasite density classes: low, medium and high, but when these alleles form genotypes with FY*02N.01 and FY*02W.01 alleles, they are found only in patients with low parasite density and low symptomatology. Another interesting finding found in this study is the presence of the genotype FY*02N.01/FY*02W.01 in one of the patients, presenting a very low parasite density and malaria considered subclinical, a genotype which had not been previously described in the literature.

Conclusion

The presence of FY*02N.01 and FY*02W.01 alleles may have an impact on the reduction of clinical manifestations in malaria, leading to the development of subclinical malaria, making the infected individual an undetected natural reservoir, which may hinder the eradication of malaria in the Amazon.

Duffy blood group system - the frequency of Duffy antigen polymorphisms and novel mutations in the Polish population

Duffy blood group genes are highly polymorphic with the distribution of alleles varying between different populations and ethnic groups. The aim of this study was to genotype Duffy blood group antigens and to establish FY alleles frequency in the Polish population and screen for novel FY gene mutations. Duffy phenotype and genotype frequencies analysis was based on studies of 596 persons. All these subjects were genotyped by high-resolution melting (HRM) method. It was shown that phenotype Fy(a+b+), defined by genotypes FY*A/FY*B (33%), FY*A/FY*B298A (13%), and FY*A/FY*02W.01 (2.8%) was the most common in Polish population (˜49%), followed by Fy(a-b+), ˜29%, determined by genotypes arising from FY*B allele and all its variants. Fy(a+b-) phenotype occurred with a frequency of 21.3% and was defined by the following genotypes: FY*A/A (21%), and FY*A/02N.01 (0.3%). Among the Polish population the frequencies of FY*A, FY*B, and FY*B298A alleles were 45.7%, 36% and 15.5%, respectively. The alleles FY*B298A and FY*B combined together, represented higher frequency (51%) than FY*A. Alleles FY*02W.01 and FY*02N.01 had frequencies 2.51% and 0.25%, respectively. The distribution of Duffy genotypes in the Polish population was in accordance with Hardy-Weinberg equilibrium (p = 0.9682). Alleles in the genotypes are independent from each other (r = 0.0278, R² = 0.00077). New mutations identified in the promoter region (c.-79T > C) and the coding region of the FY gene (c.147C > A and c.175 G > A) did not affect the Duffy antigen expression on erythrocyte. Although FY alleles frequency is known in different populations, no data for Polish population is available.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of 36 blood group alleles among 396 Thai samples reveals region-specific variants

BACKGROUND

Blood group phenotype variation has been attributed to potential resistance to pathogen invasion. Variation was mapped in blood donors from Lampang (northern region) and Saraburi (central region), Thailand, where malaria is endemic. The previously unknown blood group allele profiles were characterized and the data were correlated with phenotypes. The high incidence of the Vel-negative phenotype previously reported in Thais was investigated.

STUDY DESIGN AND METHODS

DNA from 396 blood donors was analyzed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. Outliers were investigated by serology and DNA sequencing. Allele discrimination assays for SMIM1 rs1175550A/G and ACKR1 rs118062001C/T were performed and correlated with antigen expression.

RESULTS

All samples were phenotyped for Rh, MNS, and K. Genotyping/phenotyping for RhD, K, and S/s showed 100% concordance. Investigation of three RHCE outliers revealed an e-variant antigen encoded by RHCE*02.22. Screening for rs147357308 (RHCE c.667T) revealed a frequency of 3.3%. MN typing discrepancies in 41 samples revealed glycophorin variants, of which 40 of 41 were due to Mi^a . Nine samples (2.3%) were heterozygous for FY*01W.01 (c.265C > T), and six samples (1.5%) were heterozygous for JK*02N.01. All samples were wildtype SMIM1 homozygotes with 97% homozygosity for rs1175550A.

CONCLUSIONS

Matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry is an efficient method for rapid routine genotyping and investigation of outliers identified novel variation among our samples. The expected high prevalence of the Mi(a+) phenotype was observed from both regions. Of potential clinical relevance in a region where transfusion-dependent thalassemia is common, we identified two RHCE*02 alleles known to encode an e-variant antigen.

Genetic variants related to disease susceptibility and immunotolerance in the Duffy antigen receptor for chemokines (DARC, Fy) gene in the black lion tamarin (Leontopithecus chrysopygus, primates)

The DARC (Duffy antigen receptor for chemokines) gene encodes the DARC protein, which serves multiple roles in the immune system, as a binding site for the malarial parasites Plasmodium vivax and Plasmodium knowlesi, a promiscuous chemokine receptor and a blood group antigen. Variation in DARC may play particularly significant roles in innate immunity, immunotolerance and pathogen entry in callitrichines, such as the black lion tamarin (Leontopithecus chrysopygus). We compared amino acid sequences of DARC in the black lion tamarin (BLT) to non-human Haplorhine primates and Homo sapiens. Consistent with prior studies in other Haplorhines, we observed that the chemokine receptor experiences two opposing selection forces: (1) positive selection on the Plasmodium binding site and (2) purifying selection. We observed also that D21N, F22L, and V25L differentiated BLT from humans at a critical site for P. vivax and P. knowlesi binding. One amino acid residue, F22L, was subject to both positive selection and fixation in New World monkeys, suggesting a beneficial role as an adaptive barrier to Plasmodium entry. Unlike in humans, we observed no variation in DARC among BLTs, suggesting that the protein does not play a role in immunotolerance. In addition, lion tamarins differed from humans at the blood compatibility Fy^a /Fy^b antigen-binding site 44, as well as at the putative destabilizing residues A61, T68, A187, and L215, further supporting a difference in the functional role of DARC in these primates compared with humans. Further research is needed to determine whether changes in the Plasmodium and Fy^a /Fy^b antigen-binding sites disrupt DARC function in callitrichines.

Molecular basis of the Duffy blood group system

ACKR1, located on chromosome 1q23.2, is the gene that encodes a glycoprotein expressing the Duffy blood group antigens. This gene is transcribed in two mRNA variants yielding two isoforms, encoding proteins with 338 and 336 amino acids. This review provides a general overview of the Duffy blood group to characterise and elucidate the genetic basis of this system. The Fy^a and Fy^b antigens are encoded by co-dominant FY*A (FY*01) and FY*B (FY*02) alleles, which differ by c.125G>A (rs12075), defining the Fy(a+b-), Fy(a-b+) and Fy(a+b+) phenotypes. The Fy(a-b-) phenotype that occurs in Africans provides an explanation for the apparent absence of Plasmodium vivax in this region: this phenotype arises from homozygosity for the FY*B allele carrying a point mutation c.1-67T>C (rs2814778), which prevents Fy^b antigen expression only in red blood cells. The same mutation has also been found on the FY*A allele, but it is very rare. The Fy(a-b-) phenotype in Europeans and Asians arises from mutations in the coding region of the FY*A or FY*B allele, preventing Duffy antigen expression on any cell in the body and thus are true Duffy null phenotypes. According to the International Society for Blood Transfusion, ten alleles are associated with the null expression of the Fy antigens. Furthermore, different allelic forms of FY*B modify Fy^b antigen expression, which may result in very weak or equivocal serology results. The mostly common found variants, c.265C>T (rs34599082) and c.298G>A (rs13962) -previously defined in combination only with the FY*B allele - have already been observed in the FY*A allele. Thus, six alleles have been recognised and associated with weak expression of the Fy antigens. Considering the importance of the Duffy blood group system in clinical medicine, additional studies via molecular biology approaches must be performed to resolve and clarify the discrepant results that are present in the erythrocyte phenotyping.

FY*A silencing by the GATA-motif variant FY*A(-69C) in a Caucasian family

BACKGROUND

The c.1-67C variant polymorphism in a GATA motif of the FY promoter is known to result in erythroid-specific FY silencing, that is, in Fy(a-) and Fy(b-) phenotypes. A Caucasian donor presented with the very rare Fy(a-b-) phenotype and was further investigated.

STUDY DESIGN AND METHODS

Genomic DNA was analyzed by sequencing to identify the cause of the Fy(a-b-) phenotype. Samples were collected from some of his relatives to establish a correlation between the serology and genotyping results. Red blood cells were analyzed by gel column agglutination and flow cytometry. Genomic DNA was analyzed on genotyping microarrays, by DNA sequencing and by allele-specific PCR.

RESULTS

In the donor, a single-nucleotide polymorphism T>C within the GATA motif was found at Position c.1-69 of the FY promoter and shown to occur in the FY*A allele. His genotype was found to be FY*A(-69C), FY*BW.01. In six FY*A/FY*B heterozygous members of the family, a perfect correlation was found between the presence vs. absence of the FY*A(-69C) variant allele and a Fy(a-) vs. Fy(a+) phenotype.

CONCLUSION

The location of the c.1-69C polymorphism in a GATA motif whose disruption is known to result in a Fy null phenotype, together with the perfect correlation between the presence of the FY*A(-69C) allele and the Fy(a-) phenotype support a cause-effect relationship between the two.

The Duffy blood group system in the Tunisian population

BACKGROUND

Tunisia was described to as genetically heterogenous. Besides the 1% native Berber, the genetically influence of the Europeans seems much larger than that of sub-Saharan populations. Due to their ethnic variability, blood group variants have the potential to support population analyses. The aim of this study was to estimate the Duffy blood group system in this mixed population with enhanced characterization of samples with aberrant expression.

MATERIALS AND METHODS

Standard serological testing for the Duffy antigen was done for 105 Tunisian blood donors. Samples with altered Fy expression underwent DNA sequencing of the DARC, RHD and RHCE genes.

RESULTS

The Fy(a-b+) was the most common phenotype identified in the Tunisian population (38.1%). Five samples with Fy(a-b-) phenotype were determined as FY*02N.01/FY*02N.01 by a homozygous occurrence of the FY*B-67C>T alteration. Another three individuals exhibited a Fy(b+(w))Fy(x) expression, confirmed by a FY*A/FY*02M.01 (n = 1) and a FY*02M.01/FY*02M.01 (n = 2) genotype. RHD and RHCE sequencing (n= 8) revealed altered alleles observed in black populations in 5 samples. One individual with FY*02M.01/FY*02M.01 have the silent 165C>T nucleotide substitution each in the RHD and RHCE gene.

DISCUSSION

The composition of blood group variants determined in this study confirms the genetically proximity of Tunisia to Europe. The small sub-Saharan genetic influence was approved by a limited number of variant samples associated with the black population.

Molecular identification of rare FY*Null and FY*X alleles in Caucasian thalassemic family from Sardinia

Molecular genetic studies on Duffy blood group antigens have identified mutations underlying rare FY*Null and FY*X alleles. FY*Null has a high frequency in Blacks, especially from sub-Saharan Africa, while its frequency is not defined in Caucasians. FY*X allele, associated with Fy(a-b+w) phenotype, has a frequency of 2-3.5% in Caucasian people while it is absent in Blacks. During the project of extensive blood group genotyping in patients affected by hemoglobinopathies, we identified FY*X/FY*Null and FY*A/FY*Null genotypes in a Caucasian thalassemic family from Sardinia. We speculate on the frequency of FY*X and FY*Null alleles in Caucasian and Black people; further, we focused on the association of FY*X allele with weak Fyb antigen expression on red blood cells and its identification performing high sensitivity serological typing methods or genotyping.

Duffy blood group phenotype-genotype correlations using high-resolution melting analysis PCR and microarray reveal complex cases including a new null FY*A allele: the role for sequencing in genotyping algorithms

BACKGROUND AND OBJECTIVES

Duffy blood group phenotypes can be predicted by genotyping for single nucleotide polymorphisms (SNPs) responsible for the Fy(a) /Fy(b) polymorphism, for weak Fy(b) antigen, and for the red cell null Fy(a-b-) phenotype. This study correlates Duffy phenotype predictions with serotyping to assess the most reliable procedure for typing.

MATERIALS AND METHODS

Samples, n = 155 (135 donors and 20 patients), were genotyped by high-resolution melt PCR and by microarray. Samples were in three serology groups: 1) Duffy patterns expected n = 79, 2) weak and equivocal Fy(b) patterns n = 29 and 3) Fy(a-b-) n = 47 (one with anti-Fy3 antibody).

RESULTS

Discrepancies were observed for five samples. For two, SNP genotyping predicted weak Fy(b) expression discrepant with Fy(b-) (Group 1 and 3). For three, SNP genotyping predicted Fy(a) , discrepant with Fy(a-b-) (Group 3). DNA sequencing identified silencing mutations in these FY*A alleles. One was a novel FY*A 719delG. One, the sample with the anti-Fy3, was homozygous for a 14-bp deletion (FY*01N.02); a true null.

CONCLUSION

Both the high-resolution melting analysis and SNP microarray assays were concordant and showed genotyping, as well as phenotyping, is essential to ensure 100% accuracy for Duffy blood group assignments. Sequencing is important to resolve phenotype/genotype conflicts which here identified alleles, one novel, that carry silencing mutations. The risk of alloimmunisation may be dependent on this zygosity status.

Approaches to determination of a full profile of blood group genotypes: single nucleotide variant mapping and massively parallel sequencing

The number of blood group systems, currently 35, has increased in the recent years as genetic variations defining red cell antigens continue to be discovered. At present, 44 genes and 1568 alleles have been defined as encoding antigens within the 35 blood group systems. This paper provides a brief overview of two genetic technologies: single nucleotide variant (SNV) mapping by DNA microarray and massively parallel sequencing, with respect to blood group genotyping. The most frequent genetic change associated with blood group antigens are SNVs. To predict blood group antigen phenotypes, SNV mapping which involves highly multiplexed genotyping, can be performed on commercial microarray platforms. Microarrays detect only known SNVs, therefore, to type rare or novel alleles not represented in the array, further Sanger sequencing of the region is often required to resolve genotype. An example discussed in this article is the identification of rare and novel RHD alleles in the Australian population. Massively parallel sequencing, also known as next generation sequencing, has a high-throughput capacity and maps all points of variation from a reference sequence, allowing for identification of novel SNVs. Examples of the application of this technology to resolve the genetic basis of orphan blood group antigens are presented here. Overall, the determination of a full profile of blood group SNVs, in addition to serological phenotyping, provides a basis for provision of compatible blood thus offering improved transfusion safety.

A novel FY*A allele with the 265T and 298A SNPs formerly associated exclusively with the FY*B allele and weak Fy(b) antigen expression: implication for genotyping interpretative algorithms

BACKGROUND AND OBJECTIVES

An Australian Caucasian blood donor consistently presented a serology profile for the Duffy blood group as Fy(a+b+) with Fy(a) antigen expression weaker than other examples of Fy(a+b+) red cells. Molecular typing studies were performed to investigate the reason for the observed serology profile.

MATERIAL AND METHODS

Blood group genotyping was performed using a commercial SNP microarray platform. Sanger sequencing was performed using primer sets to amplify across exons 1 and 2 of the FY gene and using allele-specific primers.

RESULTS

The propositus was genotyped as FY*A/B, FY*X heterozygote that predicted the Fy(a+b+(w) ) phenotype. Sequencing identified the 265T and 298A variants on the FY*A allele. This link between FY*A allele and 265T was confirmed by allele-specific PCR.

CONCLUSION

The reduced Fy(a) antigen reactivity is attributed to a FY*A allele-carrying 265T and 298A variants previously defined in combination only with the FY*B allele and associated with weak Fy(b) antigen expression. This novel allele should be considered in genotyping interpretative algorithms for generating a predicted phenotype.

Red blood cell polymorphism and susceptibility to Plasmodium vivax

Resistance to Plasmodium vivax blood-stage infection has been widely recognised to result from absence of the Duffy (Fy) blood group from the surface of red blood cells (RBCs) in individuals of African descent. Interestingly, recent studies from different malaria-endemic regions have begun to reveal new perspectives on the association between Duffy gene polymorphism and P. vivax malaria. In Papua New Guinea and the Americas, heterozygous carriers of a Duffy-negative allele are less susceptible to P. vivax infection than Duffy-positive homozygotes. In Brazil, studies show that the Fy(a) antigen, compared to Fy(b), is associated with lower binding to the P. vivax Duffy-binding protein and reduced susceptibility to vivax malaria. Additionally, it is interesting that numerous studies have now shown that P. vivax can infect RBCs and cause clinical disease in Duffy-negative people. This suggests that the relationship between P. vivax and the Duffy antigen is more complex than customarily described. Evidence of P. vivax Duffy-independent red cell invasion indicates that the parasite must be evolving alternative red cell invasion pathways. In this chapter, we review the evidence for P. vivax Duffy-dependent and Duffy-independent red cell invasion. We also consider the influence of further host gene polymorphism associated with malaria endemicity on susceptibility to vivax malaria. The interaction between the parasite and the RBC has significant potential to influence the effectiveness of P. vivax-specific vaccines and drug treatments. Ultimately, the relationships between red cell polymorphisms and P. vivax blood-stage infection will influence our estimates on the population at risk and efforts to eliminate vivax malaria.

Duffy antigen receptor for chemokines and its involvement in patterning and control of inflammatory chemokines

Leukocyte functions are linked to their migratory responses, which, in turn, are largely determined by the expression profile of classical chemokine receptors. Upon binding their cognate chemokines, these G-protein-coupled receptors (GPCRs) initiate signaling cascades and downstream molecular and cellular responses, including integrin activation and cell locomotion. Chemokines also bind to an alternative subset of chemokine receptors, which have serpentine structure characteristic for GPCRs but lack DRYLAIV consensus motive required for coupling to G-proteins. Duffy antigen receptor for chemokines (DARC) is a member of this atypical receptor subfamily. DARC binds a broad range of inflammatory CXC and CC chemokines and is expressed by erythrocytes, venular endothelial cells, and cerebellar neurons. Erythrocyte DARC serves as blood reservoir of cognate chemokines but also as a chemokine sink, buffering potential surges in plasma chemokine levels. Endothelial cell DARC internalizes chemokines on the basolateral cell surface resulting in subsequent transcytosis of chemokines and their immobilization on the tips of apical microvilli. These DARC-mediated endothelial cell interactions allow chemokines produced in the extravascular tissues to optimally function as arrest chemokines on the luminal endothelial cell surface.

High-throughput multiplex PCR genotyping for 35 red blood cell antigens in blood donors

BACKGROUND AND OBJECTIVES

One to two per cent of patients in need of red cell transfusion carry irregular antibodies to red blood cell (RBC) antigens and have to be supplied with specially selected blood units. To be able to respond to those requests, blood centres have to screen a significant number of donors for a variety of antigens serologically, which is a costly and through the shortage of reagents, also limited procedure. To make this procedure more efficient, the Austrian Red Cross has developed a genotyping assay as an alternative approach for high throughput RBC typing.

MATERIALS AND METHODS

A multiplex polymerase chain reaction (PCR) assay was designed for typing 35 RBC antigens in six reaction mixes. The assay includes both common as well as high-frequency-alleles: MNS1, MNS2, MNS3 and MNS4; LU1, LU2, LU8 and LU14; KEL1, KEL2, KEL3, KEL4, KEL6, KEL7, KEL11, KEL17 and KEL21; FY1, FY2, FYB(WK) and FY0 (FYB(ES)); JK1 and JK2; DI1, DI2, DI3 and DI4; YT1 and YT2; DO1 and DO2; CO1 and CO2; IN1 and IN2. The assay was validated using 370 selected serologically typed samples. Subsequently 6000 individuals were screened to identify high frequency antigen (HFA)-negative donors and to facilitate the search for compatible blood for alloimmunized patients.

RESULTS

All controls showed complete concordance for the tested markers. The screening of 6000 donors revealed 57 new HFA-negative donors and the blood group database was extended by approximately 210,000 results.

CONCLUSION

The study shows that in practice, this high-throughput genotyping assay is feasible, fast and provides reliable results. Compared to serological testing, this molecular approach is also very cost-efficient.

Vivax malaria in Mauritania includes infection of a Duffy-negative individual

Background

Duffy blood group polymorphisms are important in areas where Plasmodium vivax is present because this surface antigen is thought to act as a key receptor for this parasite. In the present study, Duffy blood group genotyping was performed in febrile uninfected and P. vivax-infected patients living in the city of Nouakchott, Mauritania.

Methods

Plasmodium vivax was identified by real-time PCR. The Duffy blood group genotypes were determined by standard PCR followed by sequencing of the promoter region and exon 2 of the Duffy gene in 277 febrile individuals. Fisher's exact test was performed in order to assess the significance of variables.

Results

In the Moorish population, a high frequency of the FYB^ES/FYB^ES genotype was observed in uninfected individuals (27.8%), whereas no P. vivax-infected patient had this genotype. This was followed by a high level of FYA/FYB, FYB/FYB, FYB/FYB^ES and FYA/FYB^ES genotype frequencies, both in the P. vivax-infected and uninfected patients. In other ethnic groups (Poular, Soninke, Wolof), only the FYB^ES/FYB^ES genotype was found in uninfected patients, whereas the FYA/FYB^ES genotype was observed in two P. vivax-infected patients. In addition, one patient belonging to the Wolof ethnic group presented the FYB^ES/FYB^ES genotype and was infected by P. vivax.

Conclusions

This study presents the Duffy blood group polymorphisms in Nouakchott City and demonstrates that in Mauritania, P. vivax is able to infect Duffy-negative patients. Further studies are necessary to identify the process that enables this Duffy-independent P. vivax invasion of human red blood cells.

4.1R-deficient human red blood cells have altered phosphatidylserine exposure pathways and are deficient in CD44 and CD47 glycoproteins

BACKGROUND

Protein 4.1R is an important component of the red cell membrane skeleton. It imparts structural integrity and has transmembrane signaling roles by direct interactions with transmembrane proteins and other membrane skeletal components, notably p55 and calmodulin.

DESIGN AND METHODS

Spontaneous and ligation-induced phosphatidylserine exposure on erythrocytes from two patients with 4.1R deficiency were studied, using CD47 glycoprotein and glycophorin C as ligands. We also looked for protein abnormalities in the 4.1R-based multiprotein complex.

RESULTS

Phosphatidylserine exposure was significantly increased in 4.1R-deficient erythrocytes obtained from the two different individuals when ligands to CD47 glycoprotein were bound. Spontaneous phosphatidylserine exposure was normal. 4.1R, glycophorin C and p55 were missing or sharply reduced. Furthermore there was an alteration or deficiency of CD47 glycoprotein and a lack of CD44 glycoprotein. Based on a recent study in 4.1R-deficient mice, we found that there are clear functional differences between interactions of human red cell 4.1R and its murine counterpart.

CONCLUSIONS

Glycophorin C is known to bind 4.1R, and we have defined previously that it also binds CD47. From our evidence, we suggest that 4.1R plays a role in the phosphatidylserine exposure signaling pathway that is of fundamental importance in red cell turnover. The linkage of CD44 to 4.1R may be relevant to this process.

The global distribution of the Duffy blood group

Blood group variants are characteristic of population groups, and can show conspicuous geographic patterns. Interest in the global prevalence of the Duffy blood group variants is multidisciplinary, but of particular importance to malariologists due to the resistance generally conferred by the Duffy-negative phenotype against Plasmodium vivax infection. Here we collate an extensive geo-database of surveys, forming the evidence-base for a multi-locus Bayesian geostatistical model to generate global frequency maps of the common Duffy alleles to refine the global cartography of the common Duffy variants. We show that the most prevalent allele globally was FY*A, while across sub-Saharan Africa the predominant allele was the silent FY*B(ES) variant, commonly reaching fixation across stretches of the continent. The maps presented not only represent the first spatially and genetically comprehensive description of variation at this locus, but also constitute an advance towards understanding the transmission patterns of the neglected P. vivax malaria parasite.

Characterization of Jk(a+(weak)): a new blood group phenotype associated with an altered JK*01 allele

BACKGROUND

The clinically important Kidd (JK) blood group system is considered to be relatively uncomplicated, both serologically and genetically. The JK*01 and JK*02 alleles give rise to Jk(a) and Jk(b) antigens, respectively, and silenced alleles result in Jk(a-b-). Other inherited variants analogous to Fy(x) and weak D phenotypes have not been characterized for JK, although recent abstracts indicate their presence.

STUDY DESIGN AND METHODS

Six index samples from individuals whose RBCs reacted variably or weakly with different sources of anti-Jk(a) and 300 controls of the four known JK phenotypes were investigated by standard serology, flow cytometry, Western blotting, and the urea hemolysis test. Molecular analysis, including allele-specific polymerase chain reaction (PCR), DNA sequencing, and transcript analysis by real-time PCR, was performed.

RESULTS

All Jk(a+(w)b-) and Jk(a+(w)b+) index samples were homo- or heterozygous for an altered JK*01 allele carrying 130G>A (Glu44Lys) and the JK*02-associated silent SNPs 588G and Intron 9 -46g. Blood donor screening indicated an allele frequency of 0.042. Titration and flow cytometry with anti-Jk(a) gave lower values in index samples compared to controls, as did anti-Jk3 titers. Donors with 130A also showed significantly decreased Jk(a) density by flow cytometry versus 130G. Western blotting with anti-UT-B demonstrated weaker reactivity with Jk(a+(w)) membranes while JK mRNA levels could not discriminate index samples from controls. The urea hemolysis test was only moderately affected in two Jk(a+(w)b-) samples.

CONCLUSIONS

A new phenotype with weakened Jk(a) expression on RBCs is associated with a JK*01-like allele, which may constitute a risk for hemolytic transfusion reactions if antigen-positive units are missed by routine serology.

High-resolution melting analysis for genotyping Duffy, Kidd and Diego blood group antigens

High-resolution melting (HRM) analysis is a simpler genotyping method than allele-specific PCR, PCR-restriction fragment length polymorphism and multiplex PCR. Duffy, Kidd and Diego are clinically important blood group antigens. We used a novel method to genotype these three blood group antigens. Purified genomic DNA extracts of blood samples (354 Duffy, 347 Kidd and 457 Diego) were amplified using specific amplification primers. HRM curves were obtained by HRM analysis. Results were in complete concordance with those obtained for previous phenotypes and genotypes. Nucleotide substitutions for these blood group antigens were differentiated by the HRM curves. HRM analysis is a simple genotyping method and is an alternative to serological typing. Our results suggest that HRM analysis can also be used for genotyping blood group antigens whose allotype specificity is determined by single nucleotide substitutions.

Plasmodium vivax and the Duffy antigen: a paradigm revisited

The Duffy blood group antigen is the portal of entry of the Plasmodiumvivax malaria parasite into human red blood cells and the receptor for a number of CXC and CC chemokines. We review here epidemiological data and evidence derived from therapeutic or experimental human infections associating P. vivax and the Duffy glycoprotein and laboratory studies indicating that P. vivax uses the Duffy antigen as a receptor to invade the red cell. We then review recent field observations indicating that the conclusion of the absolute dependence on the presence of Duffy on the red cell for P. vivax infection and development into the red cell no longer holds true and that in some parts of the world, P. vivax infects and causes disease in Duffy-negative people.

The relationship between blood groups and disease

The relative contribution of founder effects and natural selection to the observed distribution of human blood groups has been debated since blood group frequencies were shown to differ between populations almost a century ago. Advances in our understanding of the migration patterns of early humans from Africa to populate the rest of the world obtained through the use of Y chromosome and mtDNA markers do much to inform this debate. There are clear examples of protection against infectious diseases from inheritance of polymorphisms in genes encoding and regulating the expression of ABH and Lewis antigens in bodily secretions particularly in respect of Helicobacter pylori, norovirus, and cholera infections. However, available evidence suggests surviving malaria is the most significant selective force affecting the expression of blood groups. Red cells lacking or having altered forms of blood group-active molecules are commonly found in regions of the world in which malaria is endemic, notably the Fy(a-b-) phenotype and the S-s- phenotype in Africa and the Ge- and SAO phenotypes in South East Asia. Founder effects provide a more convincing explanation for the distribution of the D- phenotype and the occurrence of hemolytic disease of the fetus and newborn in Europe and Central Asia.

Plasmodium vivax clinical malaria is commonly observed in Duffy-negative Malagasy people

Malaria therapy, experimental, and epidemiological studies have shown that erythrocyte Duffy blood group-negative people, largely of African ancestry, are resistant to erythrocyte Plasmodium vivax infection. These findings established a paradigm that the Duffy antigen is required for P. vivax erythrocyte invasion. P. vivax is endemic in Madagascar, where admixture of Duffy-negative and Duffy-positive populations of diverse ethnic backgrounds has occurred over 2 millennia. There, we investigated susceptibility to P. vivax blood-stage infection and disease in association with Duffy blood group polymorphism. Duffy blood group genotyping identified 72% Duffy-negative individuals (FY*B(ES)/*B(ES)) in community surveys conducted at eight sentinel sites. Flow cytometry and adsorption-elution results confirmed the absence of Duffy antigen expression on Duffy-negative erythrocytes. P. vivax PCR positivity was observed in 8.8% (42/476) of asymptomatic Duffy-negative people. Clinical vivax malaria was identified in Duffy-negative subjects with nine P. vivax monoinfections and eight mixed Plasmodium species infections that included P. vivax (4.9 and 4.4% of 183 participants, respectively). Microscopy examination of blood smears confirmed blood-stage development of P. vivax, including gametocytes. Genotyping of polymorphic surface and microsatellite markers suggested that multiple P. vivax strains were infecting Duffy-negative people. In Madagascar, P. vivax has broken through its dependence on the Duffy antigen for establishing human blood-stage infection and disease. Further studies are necessary to identify the parasite and host molecules that enable this Duffy-independent P. vivax invasion of human erythrocytes.

The Bloodgen Project of the European Union, 2003-2009

The Bloodgen project was funded by the European Commission between 2003 and 2006, and involved academic blood centres, universities, and Progenika Biopharma S.A., a commercial supplier of genotyping platforms that incorporate glass arrays. The project has led to the development of a commercially available product, BLOODchip, that can be used to comprehensively genotype an individual for all clinically significant blood groups. The intention of making this system available is that blood services and perhaps even hospital blood banks would be able to obtain extended information concerning the blood group of routine blood donors and vulnerable patient groups. This may be of significant use in the current management of multi-transfused patients who become alloimmunised due to incomplete matching of blood groups. In the future it can be envisaged that better matching of donor-patient blood could be achieved by comprehensive genotyping of every blood donor, especially regular ones. This situation could even be extended to genotyping every individual at birth, which may prove to have significant long-term health economic benefits as it may be coupled with detection of inborn errors of metabolism.

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.

Duffy blood group system genotyping in an urban Tunisian population

BACKGROUND

The Duffy blood group system, besides its relevance in transfusion medicine, is of major interest for population genetics. In fact, the Duffy molecule is the only red cell receptor for Plasmodium vivax, thus the fixation of FY*silent allele in western south-Saharan Africa resulted in the absence of this type of malaria in that area (for a review see Kwiatowski, Am J Hum Genet 77:171-192, 2005). For the Duffy functional role see, for example, Daniels (Vox Sanguinis 93:331-340, 2007).

METHODS

Duffy blood group distribution in 115 unrelated Tunisians was determined using the polymerase chain reaction with sequence specific primer (PCR-SSP) method detecting the five allelic versions of the FY gene. The red cell antigenic FY phenotype, for each donor, was deduced through DNA analysis. The blood samples of the positive FY*X alleles were investigated by serological methods, mainly the fixation-elution technique.

RESULTS

The following allele frequencies were found (after having excluded FY*X, which had frequency of 0.0174): FY*1 = 0.291 (expressed 0.260; silent 0.031); FY*2 = 0.709 (expressed 0.427; silent 0.282). The most surprising result in this work is the detection of the FY*1 silent allele, usually quite rare, in four samples (1.74%). For FY*2 silent, the predominant allele in Africans, genotyping results showed a prevalence of 29.57%. The FY locus was in Hardy-Weinberg equilibrium in the present sample.

CONCLUSION

When compared with European and African data, Tunisian samples demonstrated the presence of the common signs of these two ancestries (FY*2 and FY*X for the first population; and FY*2 silent for the last one). These data confirm the mixed roots of this urban Tunisian population already suggested by numerous studies on other haematological markers.

Transfusion-induced autoantibodies and differential immunogenicity of blood group antigens: a novel hypothesis

Blood bank serology has identified hundreds of red blood cell (RBC) antigens contained within numerous blood group systems. Although most blood group antigens are defined by amino acid polymorphisms in the extracellular domain of membrane proteins, it is also possible that additional nonexofacial polymorphisms (NEPs) may exist within cytoplasmic or transmembrane domains. To assess this possibility, we analyzed several blood group molecules by searching the SNPper database for nonsynonymous single-nucleotide polymorphisms. We report the identification of a number of NEPs in the Kell, Kidd, and Duffy molecules. Because the identified NEPs are not exposed on the surface of intact RBCs and are, thus, not accessible to recipient antibodies, they would neither be detected by blood bank serology in vitro, nor would they be recognized targets in hemolytic transfusion reactions in vivo. The presentation of peptides containing NEPs by recipient MHC Class II molecules, however, would nevertheless produce helper T-cell epitopes. In addition to identifying NEPs in human blood group molecules, we explore a novel hypothesis that the presence of NEPs contributes to the immunogenicity of blood group antigens. We further hypothesize that NEPs provide a mechanism by which transfusion can lead to anti-RBC autoantibodies, which are known to occur in humans after transfusion. The scientific basis, existing evidence, approaches to testing, and predicted biology of this hypothesis are presented.

FY*X real-time polymerase chain reaction with melting curve analysis associated with a complete one-step real-time FY genotyping

BACKGROUND AND OBJECTIVES

The Duffy (FY) blood group system is controlled by four major alleles: FY*A and FY*B, the Caucasian common alleles, encoding Fy(a) and Fy(b) antigens; FY*X allele responsible for a poorly expressed Fy(b) antigen, and FY*Fy a silent predominant allele among Black population. Despite the recent development of a real-time fluorescent polymerase chain reaction (PCR) method for FY genotyping FY*X genotyping has not been described by this method. This study focused on the real-time FY*X genotyping development associated with a complete, one-step real-time FY genotyping, based on fluorescence resonance energy transfer (FRET) technology.

MATERIALS AND METHODS

Seventy-two blood samples from Fy(a+b-) Caucasian blood donors were studied by real-time PCR only. Forty-seven Caucasian and Black individual blood samples, referred to our laboratory, were studied by PCR-RFLP and real-time PCR. For each individual, the result of the genotype was compared to the known phenotype.

RESULTS

The FY*X allele frequency calculated in an Fy(a+b-) Caucasian blood donors population was 0.014. With the Caucasian and Black patient samples we found a complete correlation between PCR-RFLP and the real-time PCR method whatever the alleles combination tested. When the known phenotype was not correlated to FY*X genotype, the presence of the Fy(b) antigen was always confirmed by adsorption-elution.

CONCLUSION

The real-time technology method is rapid and accurate for FY genotyping. From now, we are able to detect the FY*X allele in all the alleles combinations studied. Regarding its significant frequency, the detection of the FY*X allele is useful for the correct typing of blood donors and recipients considering the therapeutic use of blood units and the preparation of test red blood cells for antibody screening.

Detection of antibodies reacting with the antithetical duffy blood group antigens Fya and Fyb using recombinant fusion proteins containing the duffy extracellular domain

Detecting blood group-specific antibodies in patient sera is essential to the management of blood transfusions or pregnancies. We produced the antithetical forms of the 65 amino acid extracellular domain (ECD) of the Duffy (Fy) blood group protein fused to glutathione sulfotransferase (GST): GST-Fy(a); and GST-Fy(b), differing only in Gly or Asp at position 44, respectively. The purified recombinant proteins were recognized more effectively by reference polyclonal or monoclonal antibodies than the antithetical Fy specificity by either ELISA or immunoblotting. Combined immunoblot and ELISA tests performed at 1:200 dilutions of sera using the recombinant proteins gave results in agreement with undiluted sera and agglutination for 17/19 alloimmunized patients. At 1:200, agglutination detected anti-Fy(a) or anti-Fy(b) in only three of 12 samples that were positive by ELISA. Recombinant ECD-Fy proteins are suitable and sensitive reagents for the detection of anti-Fy that use technology amenable to automation and/or miniaturization and avoid the need for intact red cells.

High-throughput molecular profiling of blood donors for minor red blood cell and platelet antigens

BACKGROUND

ABO and D phenotyping of both blood donors and patients receiving transfusions is routinely performed by blood banks to ensure compatibility. These analyses are performed by antibody-based agglutination assays. Blood is not tested for minor blood group antigens on a regular basis, however, because of cost and time constraints. This can result in alloimmunization of the patient against one to several minor antigens and may complicate future transfusions.

STUDY DESIGN AND METHODS

To address this problem, an assay has been generated on the GenomeLab SNPstream genotyping system to test simultaneously polymorphisms linked to 22 different blood antigens with donor's DNA isolated from minute amounts of white blood cells.

RESULTS

The results showed that both the error rate of the assay, as measured by the strand concordance rate, and the no-call rate were very low (0.1%). The concordance rate with the actual red blood cell (RBC) and platelet (PLT) serology data varied from 97 to 100 percent. Experimental or database errors as well as rare polymorphisms contributing to antigen conformation could explain the observed differences. These rates, however, are well above requirements because phenotyping and cross-matching will always be performed before transfusion.

CONCLUSION

Molecular profiling of blood donors for minor RBC and PLT antigens will give blood banks instant access to many different matched donors through the setup of a centralized data storage system.

Blood group genotype analysis for the quality improvement of reagent test red blood cells

BACKGROUND AND OBJECTIVES

Reagent red blood cells (RBCs) for antibody detection should express certain important antigens as a double dose, that is, the donors must be homozygous for the corresponding alleles. Traditionally, dose is determined by serological typing and known allele frequencies. However, RHD zygosity cannot be predicted serologically owing to the absence of an antithetical antigen, and FY zygosity is confounded by two variant haplotypes, FY*0 and FY*X. Furthermore, lack of reagents hampers our ability to type for some clinically important antigen pairs such as Do(a)/Do(b).

MATERIALS AND METHODS

Genomic DNA was isolated from reagent RBC samples. Established, validated methods were used to determine the RHD, FY, and DO genotypes.

RESULTS

Three of 52 D+ samples gave results that differed from the predicted genotype: two presumed R(1)R(1) samples and an R(2)R(2) sample were shown to be R(1)r' and R(2)r'', respectively. Five of 59 samples that were from presumed homozygotes for either FY*A or FY*B were heterozygous, together with either FY*X (three samples) or FY*0 (two samples). Seventy-five samples tested for DO were DO*A/A (n = 14), DO*A/B (n = 39), or DO*B/B (n = 22).

CONCLUSIONS

The results show that serologically determined RhD and Duffy phenotypes of reagent RBCs are unreliable and that antigens we thought were represented as a double dose were single dose. The addition of Dombrock genotyping provides information which is useful in antibody identification. We conclude that selected genotype analyses are a valuable quality assurance measure to ensure that reagent RBCs comply with national and international recommendations for test sensitivity.

A novel FY allele in Brazilians

The GATA box single nucleotide polymorphism (SNP) at position -33 (T>C) in Blacks silences the expression of FY*B in erythrocytes, and the substitution 265 C>T, together with 298 G>A, weakens the Fy(b) antigen (Fy(x)). Individuals with these phenotypes/genotypes who receive Fy(b+) blood are unlikely to be alloimmunized to Fy(b) because, in the presence of 265 T, the Fy(b) antigen is expressed, and in the case of -33 C, other tissues express Duffy protein and probably the Fy(b) antigen. We studied samples from 361 blood donors (182 of African ancestry and 179 of Caucasian ancestry) by haemagglutination and polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP). Forty Caucasian and 130 donors of African ancestry were serologically Fy(b-); among these, the majority of the donors of African ancestry had FY*B with the GATA SNP, while the majority of Caucasians typing Fy(b-) had FY*B with 265 T/298 A SNPs. Six of the Fy(b-) donors (three Africans and three Caucasians) had both GATA and 265/298 SNPs, and six donors of Caucasian ancestry apparently had a GATA SNP. Samples from two donors - one African and one Caucasian with an unusual MspA1I-RFLP pattern - were sequenced and found to have a novel SNP (145 G>T) co-existent with 265 C>T and 298 G>A SNPs. These findings highlight the importance of establishing the incidence and nature of molecular events that impact on Duffy expression in different populations.

Red blood cell blood group antigens: structure and function

Red blood cell (RBC) blood group antigens are polymorphic, inherited, carbohydrate or protein structures located on the extracellular surface of the RBC membrane. They contribute to the architecture of the RBC membrane, and their individual function(s) are being slowly revealed. The biological qualities assigned to these RBC membrane structures are based on observed physiological alteration in RBCs that lack the component, by documenting similarities in its protein sequence (predicted from the nucleotide sequence of the gene) to proteins of known function and by extrapolation to identified functional homologues in other cells. The varied roles of RBC antigens include membrane structural integrity, the transport of molecules through the membrane, as receptors for extracellular ligands, adhesion molecules, enzymes, complement components and regulators, and in glycocalyx formation.

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.

Extended blood grouping of blood donors with automatable PCR-ELISA genotyping

BACKGROUND

In the past 10 years, PCR-based methods have been described to allow the detection of gene polymorphisms responsible for many blood group antigens. These methods are routinely used to test samples of fetal origin and to resolve serologic discrepancies. Another interesting application of blood group genotyping could be the extended typing of blood donors for minor antigens to facilitate the procurement of compatible blood for alloimmunized patients.

STUDY DESIGN AND METHODS

PCR-based tests have been modified to allow multiplex amplification of specific fragments of blood group genes and the convenient detection of hybridized amplicons by ELISA in a microplate format.

RESULTS

The results obtained show that fragments of the Rh (D, c, C, e, E), Kell (K, k), Duffy (Fya, Fyb), and Kidd (Jka, Jkb) genes could be amplified along with controls in multiplex PCR reactions. Labeling of amplicons with digoxigenin allowed their solid-phase detection in microplate wells previously coated with individual blood group-specific oligonucleotides. A comparative study performed with 100 individuals showed a 99.7 percent concordance between genotypes and phenotypes for the 11 antigens assayed, with only three discrepant Fyb genotypes.

CONCLUSION

Extended genotyping could be performed once on regular donors and confirmed when needed by standard serologic RBC assays. The format of these tests will allow easy automation of the procedure including the interpretation and downloading of the results with existing ELISA software.