Evidence that CD36 is expressed on red blood cells and constitutes a novel blood group system of clinical importance

BACKGROUND AND OBJECTIVES

Polymorphic molecules expressed on the surface of certain blood cells are traditionally categorized as blood groups and human platelet or neutrophil antigens. CD36 is widely considered a platelet antigen (Naka) and anti-CD36 can cause foetal/neonatal alloimmune thrombocytopenia (FNAIT) in CD36-negative pregnant women. CD36 is used as a marker of differentiation in early erythroid culture. During the experimental culture of CD34+ cells from random blood donors, we observed that one individual lacked CD36. We sought to investigate this observation further and determine if CD36 fulfils the International Society of Blood Transfusion criteria for becoming a blood group.

MATERIALS AND METHODS

Surface markers were monitored by flow cytometry on developing cells during the erythroid culture of CD34+ cells. Genetic and flow cytometric analyses on peripheral blood cells were performed. Proteomic datasets were analysed, and clinical case reports involving anti-CD36 and foetal anaemia were scrutinized.

RESULTS

Sequencing of CD36-cDNA identified homozygosity for c.1133G>T/p.Gly378Val in the CD36-negative donor. The minor allele frequency of rs146027667:T is 0.1% globally and results in abolished CD36 expression. CD36 has been considered absent from mature red blood cells (RBCs); however, we detected CD36 expression on RBCs and reticulocytes from 20 blood donors. By mining reticulocyte and RBC datasets, we found evidence for CD36-derived peptides enriched in the membrane fractions. Finally, our literature review revealed severe cases of foetal anaemia attributed to anti-CD36.

CONCLUSIONS

Based on these findings, we conclude that CD36 fulfils the criteria for becoming a new blood group system and that anti-CD36 is implicated not only in FNAIT but also foetal anaemia.

Genetic prediction of 33 blood group phenotypes using an existing genotype dataset

BACKGROUND

Accurate blood type data are essential for blood bank management, but due to costs, few of 43 blood group systems are routinely determined in Danish blood banks. However, a more comprehensive dataset of blood types is useful in scenarios such as rare blood type allocation. We aimed to investigate the viability and accuracy of predicting blood types by leveraging an existing dataset of imputed genotypes for two cohorts of approximately 90,000 each (Danish Blood Donor Study and Copenhagen Biobank) and present a more comprehensive overview of blood types for our Danish donor cohort.

STUDY DESIGN AND METHODS

Blood types were predicted from genome array data using known variant determinants. Prediction accuracy was confirmed by comparing with preexisting serological blood types. The Vel blood group was used to test the viability of using genetic prediction to narrow down the list of candidate donors with rare blood types.

RESULTS

Predicted phenotypes showed a high balanced accuracy >99.5% in most cases: A, B, C/c, Coa /Cob , Doa /Dob , E/e, Jka /Jkb , Kna /Knb , Kpa /Kpb , M/N, S/s, Sda , Se, and Yta /Ytb , while some performed slightly worse: Fya /Fyb , K/k, Lua /Lub , and Vel ~99%-98% and CW and P1 ~96%. Genetic prediction identified 70 potential Vel negatives in our cohort, 64 of whom were confirmed correct using polymerase chain reaction (negative predictive value: 91.5%).

DISCUSSION

High genetic prediction accuracy in most blood groups demonstrated the viability of generating blood types using preexisting genotype data at no cost and successfully narrowed the pool of potential individuals with the rare Vel-negative phenotype from 180,000 to 70.

Elucidation of the low-expressing erythroid CR1 phenotype by bioinformatic mining of the GATA1-driven blood-group regulome

Genetic determinants underlying most human blood groups are now clarified but variation in expression levels remains largely unexplored. By developing a bioinformatics pipeline analyzing GATA1/Chromatin immunoprecipitation followed by sequencing (ChIP-seq) datasets, we identify 193 potential regulatory sites in 33 blood-group genes. As proof-of-concept, we aimed to delineate the low-expressing complement receptor 1 (CR1) Helgeson phenotype on erythrocytes, which is correlated with several diseases and protects against severe malaria. We demonstrate that two candidate CR1 enhancer motifs in intron 4 bind GATA1 and drive transcription. Both are functionally abolished by naturally-occurring SNVs. Erythrocyte CR1-mRNA and CR1 levels correlate dose-dependently with genotype of one SNV (rs11117991) in two healthy donor cohorts. Haplotype analysis of rs11117991 with previously proposed markers for Helgeson shows high linkage disequilibrium in Europeans but explains the poor prediction reported for Africans. These data resolve the longstanding debate on the genetic basis of inherited low CR1 and form a systematic starting point to investigate the blood group regulome.

A novel nonsense variant in RHAG underlies a Nordic Rhnull phenotype

BACKGROUND AND OBJECTIVES

The extremely rare Rhnull phenotype is characterized by the absence of all Rh antigens on erythrocytes. It is divided into the regulator and amorph types based on the underlying genetic background. The more common regulator type depends on critical variants silencing RHAG, which encodes RhAG glycoprotein, necessary for RhD/RhCE expression. Rhnull cells have altered expression of glycophorin B and LW glycoprotein.

MATERIALS AND METHODS

Four unrelated Rhnull individuals were investigated. Serological testing was performed according to standard blood bank practice. RHD/RHCE and S/s allele-specific Polymerase chain reaction (PCR) genotyping was done on genomic DNA using in-house PCR assays. RHAG, and in some cases also RHD/RHCE, were sequenced. Initial s phenotyping results triggered additional serological investigation.

RESULTS

Anti-Rh29 was identified in all four individuals. Extended typing with anti-S and anti-s showed that the three samples predicted to type as s+ failed to react with 2 of 5 anti-s. Sequence analysis of all 10 RHAG exons and the immediate intron/exon boundaries revealed a single nucleotide variant in the 3'-end of intron 6, c.946 -2a>g in all samples. RHD/RHCE showed no alterations.

CONCLUSION

A novel Nordic Rhnull allele was identified. In addition, it was shown that s+ Rhnull red blood cells are not only U- but also have qualitative changes in their s antigen expression.

Babesia divergens Shows Equal Predilection for Human ABO Blood Types in an In Vitro Erythrocyte Preference Assay

Babesia is spread to humans via ticks or blood transfusions. Severity of Plasmodium falciparum malaria is strongly correlated to the ABO blood group of the patient. Babesia divergens is an intraerythrocytic parasite with many similarities to malaria, but the impact of ABO on the susceptibility to and progression of the infection in humans is unknown. We have now cultured B. divergens in human group A, B and O erythrocytes in vitro and measured rates of multiplication. The predilection for the different erythrocyte types was also determined using an in vitro erythrocyte preference assay when the parasites were grown in group A, B or O erythrocytes over time and then offered to invade differently stained erythrocytes of all the blood types at the same time. The results showed no difference in multiplication rates for the different blood types, and the parasite exhibited no obvious morphological differences in the different blood types. When cultured first in one blood type and then offered to grow in the others, the preference assay showed that there was no difference between the A, B or O blood groups. In conclusion, this indicates that individuals of the different ABO blood types are likely to be equally susceptible to B. divergens infections.

The LW blood group system: not just "tagging along" with D

This update of the Landsteiner-Wiener (LW) blood group system (Grandstaff Moulds MK. The LW blood group system: a review. Immunohematology 2011;27:136-42. Storry JR. Review: the LW blood group system. Immunohematology 1992;8:87-93) reports new information on the distribution of genetic variants in ICAM4 and reviews the complex serologic identification of the high-prevalence LWEM antigen. The role of ICAM4 in sickle cell disease and malaria susceptibility is discussed.

Autoantibodies against red blood cell antigens are common in a malaria endemic area

Plasmodium falciparum malaria can cause severe anemia. Even after treatment, hematocrit can decrease. The role of autoantibodies against erythrocytes is not clearly elucidated and how common they are, or what they are directed against, is still largely unknown. We have investigated antibodies against erythrocytes in healthy adult men living in a highly malaria endemic area in Uganda. We found antibodies in more than half of the individuals, which is significantly more than in a non-endemic area (Sweden). Some of the Ugandan samples had a broad reactivity where it was not possible to determine the exact target of the autoantibodies, but we also found specific antibodies directed against erythrocyte surface antigens known to be of importance for merozoite invasion such as glycophorin A (anti-En^a, anti-M) and glycophorin B (anti-U, anti-S). In addition, several autoantibodies had partial specificities against glycophorin C and the blood group systems Rh, Diego (located on Band 3), Duffy (located on ACKR1), and Cromer (located on CD55), all of which have been described to be important for malaria and therefore of interest for understanding how autoantibodies could potentially stop parasites from entering the erythrocyte. In conclusion, specific autoantibodies against erythrocytes are common in a malaria endemic area.

Yes, MAM: how the cancer-related EMP3 protein became a regulator of erythropoiesis and the key protein underlying a new blood group system

The MAM blood group system (International Society of Blood Transfusion [ISBT] 041) consists of one high-prevalence antigen to date, first detected in a 31-year-old woman during her third pregnancy. Epithelial membrane protein 3 (EMP3) was recently identified as the gene coding the MAM antigen. Six unique genetic variants have been described in EMP3 in 11 MAM- individuals. EMP3 is an 18-kDa glycoprotein with a large extracellular domain containing at least one N-glycosylation site. The normal function of EMP3 is still unclear, but ex vivo culture of erythropoietic progenitor cells from MAM- individuals shows an increased yield of reticulocytes, suggesting that EMP3 acts as a brake during normal erythropoiesis. EMP3 is abundant on different cell types, including many epithelial tissues and blood cells. Interestingly, EMP3 expression has been suggested as a prognostic marker for a number of cancer types, both for good and poor prognoses. EMP3 may act as a tumor suppressor or an oncogene in different cancer contexts. The protein appears to interact with other cell surface receptors and affects the downstream signaling and function of these proteins. MAM- red blood cells express low levels of CD44 and, consequently, the antigens of the Indian blood group system are only weakly expressed. Clinically, the MAM blood group antigen is important with regard to blood transfusion and pregnancy. Anti-MAM can cause severe hemolytic disease of the fetus and newborn in some pregnancies but have little to no effect in other pregnancies. Cases are typically not detected until problems occur during pregnancy, making the availability of compatible blood a challenge.

International Society of Blood Transfusion Working Party on Red Cell Immunogenetics and Blood Group Terminology Report of Basel and three virtual business meetings: Update on blood group systems

BACKGROUND AND OBJECTIVES

Under the ISBT, the Working Party (WP) for Red Cell Immunogenetics and Blood Group Terminology is charged with ratifying blood group systems, antigens and alleles. This report presents the outcomes from four WP business meetings, one located in Basel in 2019 and three held as virtual meetings during the COVID-19 pandemic in 2020 and 2021.

MATERIALS AND METHODS

As in previous meetings, matters pertaining to blood group antigen nomenclature were discussed. New blood group systems and antigens were approved and named according to the serologic, genetic, biochemical and cell biological evidence presented.

RESULTS

Seven new blood group systems, KANNO (defined numerically as ISBT 037), SID (038), CTL2 (039), PEL (040), MAM (041), EMM (042) and ABCC1 (043) were ratified. Two (039 and 043) were de novo discoveries, and the remainder comprised reported antigens where the causal genes were previously unknown. A further 15 blood group antigens were added to the existing blood group systems: MNS (002), RH (004), LU (005), DI (010), SC (013), GE (020), KN (022), JMH (026) and RHAG (030).

CONCLUSION

The ISBT now recognizes 378 antigens, of which 345 are clustered within 43 blood group systems while 33 still have an unknown genetic basis. The ongoing discovery of new blood group systems and antigens underscores the diverse and complex biology of the red cell membrane. The WP continues to update the blood group antigen tables and the allele nomenclature tables. These can be found on the ISBT website (http://www.isbtweb.org/working-parties/red-cell-immunogenetics-and-blood-group-terminology/).

The Cromer blood group system: an update

This update of the Cromer (CROM) blood group system (Storry JR, Reid ME, Yazer MH. The Cromer blood group system: a review. Immunohematology 2010;26:109-17) includes additional variants to the Cromer system (ISBT021), both new antigens and new molecular bases underlying the null phenotype. The molecule on which the Cromer blood group antigens are carried, CD55 (DAF), is an important receptor for the malaria parasite, Plasmodium falciparum, and the role of CD55 in health and disease continues to expand.

This update of the Cromer (CROM) blood group system (Storry JR, Reid ME, Yazer MH. The Cromer blood group system: a review. Immunohematology 2010;26:109–17) includes additional variants to the Cromer system (ISBT021), both new antigens and new molecular bases underlying the null phenotype. The molecule on which the Cromer blood group antigens are carried, CD55 (DAF), is an important receptor for the malaria parasite, Plasmodium falciparum, and the role of CD55 in health and disease continues to expand.

Platelets inhibit erythrocyte invasion by Plasmodium falciparum at physiological platelet:erythrocyte ratios

OBJECTIVE

To evaluate the effect of platelet:erythrocyte (P:E) ratios on Plasmodium falciparum erythrocyte invasion.

BACKGROUND

Recent reports have shown that platelets are directly involved in the immune response towards P. falciparum during erythrocyte invasion. However, the literature both supports and conflicts with a role for platelets in limiting invasion. Also, the effect of platelet numbers on invasion (parasitemia) has not been thoroughly investigated.

METHODS/MATERIALS

The P. falciparum strains FCR3S1.2 and W2mef were cultured with group O erythrocytes. The cultures were synchronised and supplemented with pooled platelets at P:E ratios ranging from 1:100 to 1:2. Parasitemia was measured at 40 h by flow cytometry and by microscopy of blood smears.

RESULTS

A linear relationship was observed between reduced invasion and increased platelet numbers at P:E ratios ranging from 1:100 to 1:20. However, this effect was reversed at lower ratios (1:10-1:2). Microscopic evaluation revealed aggregation and attachment of platelets to erythrocytes, but not specifically to parasitised erythrocytes.

CONCLUSION

We have shown that under physiological P:E ratios (approx. 1:10-1:40), platelets inhibited P. falciparum invasion in a dose-dependent manner. At ratios of 1:10 and below, platelets did not further increase the inhibitory effect and, although the trend was reversed, inhibition was still maintained.

The Ok blood group system: an update

This update of the Ok (OK) blood group system (Smart EA, Storry JR. The OK blood group system: a review. Immunohematology 2010;26:124-6) focuses on new information on the role of basigin (BSG), the carrier molecule of the Ok blood group antigens. No further antigens have been identified since the original review. However, the role of BSG in malaria continues to be explored. Immunohematology 2021;37:18-19. This update of the Ok (OK) blood group system (Smart EA, Storry JR. The OK blood group system: a review. Immunohematology 2010;26:124–6) focuses on new information on the role of basigin (BSG), the carrier molecule of the Ok blood group antigens. No further antigens have been identified since the original review. However, the role of BSG in malaria continues to be explored. Immunohematology 2021;37:18–19.

Human radical scavenger α1-microglobulin protects against hemolysis in vitro and α1-microglobulin knockout mice exhibit a macrocytic anemia phenotype

During red blood cell (RBC) lysis hemoglobin and heme leak out of the cells and cause damage to the endothelium and nearby tissue. Protective mechanisms exist; however, these systems are not sufficient in diseases with increased extravascular hemolysis e.g. hemolytic anemia. α₁-microglobulin (A1M) is a ubiquitous reductase and radical- and heme-binding protein with antioxidation properties. Although present in the circulation in micromolar concentrations, its function in blood is unclear. Here, we show that A1M provides RBC stability. A1M^-/- mice display abnormal RBC morphology, reminiscent of macrocytic anemia conditions, i.e. fewer, larger and more heterogeneous cells. Recombinant human A1M (rA1M) reduced in vitro hemolysis of murine RBC against spontaneous, osmotic and heme-induced stress. Moreover, A1M is taken up by human RBCs both in vitro and in vivo. Similarly, rA1M also protected human RBCs against in vitro spontaneous, osmotic, heme- and radical-induced hemolysis as shown by significantly reduced leakage of hemoglobin and LDH. Addition of rA1M resulted in decreased hemolysis compared to addition of the heme-binding protein hemopexin and the radical-scavenging and reducing agents ascorbic acid and Trolox (vitamin E). Furthermore, rA1M significantly reduced spontaneous and heme-induced fetal RBC cell death. Addition of A1M to human whole blood resulted in a significant reduction of hemolysis, whereas removal of A1M from whole blood resulted in increased hemolysis. We conclude that A1M has a protective function in reducing hemolysis which is neither specific to the origin of hemolytic insult, nor species specific.

The Role of α1-Microglobulin (A1M) in Erythropoiesis and Erythrocyte Homeostasis-Therapeutic Opportunities in Hemolytic Conditions

α₁-microglobulin (A1M) is a small protein present in vertebrates including humans. It has several physiologically relevant properties, including binding of heme and radicals as well as enzymatic reduction, that are used in the protection of cells and tissue. Research has revealed that A1M can ameliorate heme and ROS-induced injuries in cell cultures, organs, explants and animal models. Recently, it was shown that A1M could reduce hemolysis in vitro, observed with several different types of insults and sources of RBCs. In addition, in a recently published study, it was observed that mice lacking A1M (A1M-KO) developed a macrocytic anemia phenotype. Altogether, this suggests that A1M may have a role in RBC development, stability and turnover. This opens up the possibility of utilizing A1M for therapeutic purposes in pathological conditions involving erythropoietic and hemolytic abnormalities. Here, we provide an overview of A1M and its potential therapeutic effect in the context of the following erythropoietic and hemolytic conditions: Diamond-Blackfan anemia (DBA), 5q-minus myelodysplastic syndrome (5q-MDS), blood transfusions (including storage), intraventricular hemorrhage (IVH), preeclampsia (PE) and atherosclerosis.

Association of Maternal Regulatory Single Nucleotide Polymorphic CD99 Genotype with Preeclampsia in Pregnancies Carrying Male Fetuses in Ethiopian Women

Preeclampsia (PE) is a human specific syndrome with unknown etiology causing maternal and fetal morbidities and mortalities. In PE, maternal inflammatory responses are more exaggerated if the fetus is male than female. Other pregnancy complications such as spontaneous abortions are also more common if the fetus is male. Recent transcriptome findings showed an increased expression of CD99 in erythroid cells from male cord blood in PE. The single nucleotide polymorphism (SNP) rs311103, located in a GATA-binding site in a regulatory region on the X/Y chromosomes, governs a coordinated expression of the Xg blood group members CD99 and Xg^a in hematopoietic cells in a sex-dependent fashion. The rs311103C disrupts the GATA-binding site, resulting in decreased CD99 expression. We aimed to investigate the association between PE and the allele frequency of rs311103 in pregnancies in a fetal sex-dependent fashion. In a case-controlled study, we included 241 pregnant women, i.e., 105 PE cases and 136 normotensive controls. A SNP allelic discrimination analysis was performed on DNA from maternal venous blood and fetal cord blood by qPCR. A statistically significant association was observed between rs311103 allele frequency and PE in mothers carrying male fetuses. Therefore, the rs311103 genotype may play a role in the pathogenesis of PE in a fetal sex-specific manner.

Disruption of the tumour-associated EMP3 enhances erythroid proliferation and causes the MAM-negative phenotype

The clinically important MAM blood group antigen is present on haematopoietic cells of all humans except rare MAM-negative individuals. Its molecular basis is unknown. By whole-exome sequencing we identify EMP3, encoding epithelial membrane protein 3 (EMP3), as a candidate gene, then demonstrate inactivating mutations in ten known MAM-negative individuals. We show that EMP3, a purported tumour suppressor in various solid tumours, is expressed in erythroid cells. Disruption of EMP3 by CRISPR/Cas9 gene editing in an immortalised human erythroid cell line (BEL-A2) abolishes MAM expression. We find EMP3 to associate with, and stabilise, CD44 in the plasma membrane. Furthermore, cultured erythroid progenitor cells from MAM-negative individuals show markedly increased proliferation and higher reticulocyte yields, suggesting an important regulatory role for EMP3 in erythropoiesis and control of cell production. Our data establish MAM as a new blood group system and demonstrate an interaction of EMP3 with the cell surface signalling molecule CD44.

Two Prevalent ∼100-kb GYPB Deletions Causative of the GPB-Deficient Blood Group MNS Phenotype S-s-U- in Black Africans

The U antigen (MNS5) is one of 49 antigens belonging to the MNS blood group system (ISBT002) carried on glycophorins A (GPA) and B (GPB). U is present on the red blood cells in almost all Europeans and Asians but absent in approximately 1.0% of Black Africans. U negativity coincides with negativity for S (MNS3) and s (MNS4) on GPB, thus be called S-s-U-, and is thought to arise from homozygous deletion of GYPB. Little is known about the molecular background of these deletions. Bioinformatic analysis of the 1000 Genomes Project data revealed several candidate regions with apparent deletions in GYPB. Highly specific Gap-PCRs, only resulting in positive amplification from DNAs with deletions present, allowed for the exact genetic localization of 3 different breakpoints; 110.24- and 103.26-kb deletions were proven to be the most frequent in Black Americans and Africans. Among 157 CEPH DNAs, deletions in 6 out of 8 African ethnicities were present. Allele frequencies of the deletions within African ethnicities varied greatly and reached a cumulative 23.3% among the Mbuti Pygmy people from the Congo. Similar observations were made for U+var alleles, known to cause strongly reduced GPB expression. The 110- and 103-kb deletional GYPB haplotypes were found to represent the most prevalent hereditary factors causative of the MNS blood group phenotype S-s-U-. Respective GYPB deletions are now accessible by molecular detection of homo- and hemizygous transmission.

Dimerization of small integral membrane protein 1 promotes cell surface presentation of the Vel blood group epitope

The Vel blood group antigen is carried on the short extracellular segment of the 78-amino-acid-long, type II transmembrane protein SMIM1 of unknown function. Here, using biochemical analysis and flow cytometry of cells expressing wild-type and mutant alleles of SMIM1, we demonstrate that dimerization of SMIM1 promotes cell surface display of the Vel epitope. We show that SMIM1 dimerization is mediated both by an extracellular Cys77-dependent, homomeric disulfide linkage and via a GxxxG helix-helix interaction motif in the transmembrane domain. These results provide important context for the observed variability in reactivity patterns of clinically important anti-Vel identified in patient sera.

The Xg blood group system: no longer forgotten

This update of the Xg blood group system (Johnson NC. XG: The forgotten blood group system. Immunohematology 2011;27:68-71) notes the identification of a cis-regulatory element of both XG and CD99 expression, remarkably by two independent groups during 2018, and confirmed by another in 2019. A single nucleotide change at the XG locus (rs311103) abolishes GATA1 binding and suppresses both XG and CD99. The last blood group system to resist elucidation of its genetic basis was thereby resolved. Soon afterwards, it was discovered that the rare anti-Xga response, mainly seen in men, is produced by individuals primarily carrying a large deletion in the X chromosome that truncates XG and leads to the Xgnull phenotype.

International Society of Blood Transfusion Working Party on Red Cell Immunogenetics and Blood Group Terminology: Report of the Dubai, Copenhagen and Toronto meetings

BACKGROUND AND OBJECTIVES

The International Society of Blood Transfusion (ISBT) Working Party for Red Cell Immunogenetics and Blood Group Terminology meets in association with the ISBT congress and has met three times since the last report: at the international meetings held in Dubai, United Arab Emirates, September 2016 and Toronto, Canada, June 2018; and at a regional congress in Copenhagen, Denmark, June 2017 for an interim session.

METHODS

As in previous meetings, matters pertaining to blood group antigen nomenclature and classification were discussed. New blood group antigens were approved and named according to the serologic and molecular evidence presented.

RESULTS AND CONCLUSIONS

Fifteen new blood group antigens were added to eight blood group systems. One antigen was made obsolete based on additional data. Consequently, the current total of blood group antigens recognized by the ISBT is 360, of which 322 are clustered within 36 blood groups systems. The remaining 38 antigens are currently unassigned to a known system. Clinically significant blood group antigens continue to be discovered, through serology/sequencing and/or recombinant or genomic technologies.

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.

The Vel blood group system: a review

The blood group antigen Vel has been one of immunohematology's greatest enigmas: the variation in antigen strength from one individual to another, the property of anti-Vel to readily hemolyze Vel+ red blood cells (RBCs), and the difficulty to screen for sufficient numbers of Vel- blood donors had made Vel a tough nut to crack. In 2013, a small, previously unknown protein called small integral membrane protein 1 (SMIM1) was identified on the RBC by three independent research groups using different approaches, and all three groups demonstrated that Vel- RBCs lacked SMIM1. This discovery correlated with homozygosity for deletion c.64_60del in SMIM1 and meant that for the first time there was a universal method to screen for Vel- blood donors. This finding was not the whole answer, however, and an explanation behind the variability in antigen strength was later shown to be due to polymorphism in SMIM1 intron 2, a region that is responsible for gene transcription. Clinically, anti-Vel is important and has caused severe transfusion reactions, although hemolytic disease of the fetus and newborn caused by anti-Vel is uncommon. However, while screening for Vel- blood donors has become easier, the function of SMIM1 is still unknown, and despite its well-conserved sequence across the animal kingdom, the enigma continues.

SMIM1 variants rs1175550 and rs143702418 independently modulate Vel blood group antigen expression

The Vel blood group antigen is expressed on the red blood cells of most individuals. Recently, we described that homozygosity for inactivating mutations in SMIM1 defines the rare Vel-negative phenotype. Still, Vel-positive individuals show great variability in Vel antigen expression, creating a risk for Vel blood typing errors and transfusion reactions. We fine-mapped the regulatory region located in SMIM1 intron 2 in Swedish blood donors, and observed a strong correlation between expression and rs1175550 as well as with a previously unreported tri-nucleotide insertion (rs143702418; C > CGCA). While the two variants are tightly linked in Caucasians, we separated their effects in African Americans, and found that rs1175550G and to a lesser extent rs143702418C independently increase SMIM1 and Vel antigen expression. Gel shift and luciferase assays indicate that both variants are transcriptionally active, and we identified binding of the transcription factor TAL1 as a potential mediator of the increased expression associated with rs1175550G. Our results provide insight into the regulatory logic of Vel antigen expression, and extend the set of markers for genetic Vel blood group typing.

International society of blood transfusion working party on red cell immunogenetics and terminology: report of the Seoul and London meetings

The Working Party has met twice since the last report: in Seoul, South Korea 2014, and in London, UK 2015, both in association with the International Society of Blood Transfusion (ISBT) Congress. As in previous meetings, matters pertaining to blood group antigen nomenclature were discussed. Eleven new blood group antigens were added to seven blood group systems. This brings the current total of blood group antigens recognized by the ISBT to 346, of which 308 are clustered within 36 blood groups systems. The remaining 38 antigens are currently unassigned to a known blood group system.

A novel RHCE*02 allele, containing the single-nucleotide change c.460A>G, encodes weakened expression of C and e antigens

We report a novel RHCE*02 allele in a Swedish blood donor that is characterized by the change c.460A>G (Arg154Gly). The blood donor's red blood cells showed variable reactivity with different monoclonal anti-C and anti-e and antigen strength was markedly weakened. We believe that these changes represent both a quantitative and qualitative alteration of the antigens encoded by this allele.

[Security laboratory facilitates the management of infections like Ebola]

Ebola and MERS are contagious diseases with high mortality, and separate handling of blood samples in the laboratory is necessary. Most people who arrive in Sweden with suspicious symptoms will likely have other diseases than Ebola/MERS, for example malaria or pneumococci, but we still need to take care of these patients and be able to provide optimal treatment of electrolyte disturbances, kidney failure, bleedings etc. In this report, we describe how we solved the problem in Skåne, where we built a security laboratory within the facilities of Clinical Chemistry in Malmö. Here we can now analyze malaria, blood gases, cell counts, PK-value, liver status, pneumococci and legionella as well as perform routine pre-transfusion testing. We describe the different point-of-care instruments that are used in the laboratory and the reasoning behind our choices, as well as challenges that we encountered on the way.

Identification of the Molecular and Genetic Basis of PX2, a Glycosphingolipid Blood Group Antigen Lacking on Globoside-deficient Erythrocytes

The x2 glycosphingolipid is expressed on erythrocytes from individuals of all common blood group phenotypes and elevated on cells of the rare P/P1/P(k)-negative p blood group phenotype. Globoside or P antigen is synthesized by UDP-N-acetylgalactosamine:globotriaosyl-ceramide 3-β-N-acetylgalactosaminyltransferase encoded by B3GALNT1. It is the most abundant non-acid glycosphingolipid on erythrocytes and displays the same terminal disaccharide, GalNAcβ3Gal, as x2. We encountered a patient with mutations in B3GALNT1 causing the rare P-deficient P1 (k) phenotype and whose pretransfusion plasma was unexpectedly incompatible with p erythrocytes. The same phenomenon was also noted in seven other unrelated P-deficient individuals. Thin-layer chromatography, mass spectrometry, and flow cytometry were used to show that the naturally occurring antibodies made by p individuals recognize x2 and sialylated forms of x2, whereas x2 is lacking on P-deficient erythrocytes. Overexpression of B3GALNT1 resulted in synthesis of both P and x2. Knockdown experiments with siRNA against B3GALNT1 diminished x2 levels. We conclude that x2 fulfills blood group criteria and is synthesized by UDP-N-acetylgalactosamine: globotriaosylceramide 3-β-N-acetylgalactosaminyltransferase. Based on this linkage, we proposed that x2 joins P in the GLOB blood group system (ISBT 028) and is renamed PX2 (GLOB2). Thus, in the absence of a functional P synthase, neither P nor PX2 are formed. As a consequence, naturally occurring anti-P and anti-PX2 can be made. Until the clinical significance of anti-PX2 is known, we also recommend that rare P1 (k) or P2 (k) erythrocyte units are preferentially selected for transfusion to P(k) patients because p erythrocytes may pose a risk for hemolytic transfusion reactions due to their elevated PX2 levels.

RIFINs are adhesins implicated in severe Plasmodium falciparum malaria

Rosetting is a virulent Plasmodium falciparum phenomenon associated with severe malaria. Here we demonstrate that P. falciparum-encoded repetitive interspersed families of polypeptides (RIFINs) are expressed on the surface of infected red blood cells (iRBCs), where they bind to RBCs--preferentially of blood group A--to form large rosettes and mediate microvascular binding of iRBCs. We suggest that RIFINs have a fundamental role in the development of severe malaria and thereby contribute to the varying global distribution of ABO blood groups in the human population.

Shiga toxin-induced complement-mediated hemolysis and release of complement-coated red blood cell-derived microvesicles in hemolytic uremic syndrome

Shiga toxin (Stx)-producing Escherichia coli (STEC) cause hemolytic uremic syndrome (HUS). This study investigated whether Stx2 induces hemolysis and whether complement is involved in the hemolytic process. RBCs and/or RBC-derived microvesicles from patients with STEC-HUS (n = 25) were investigated for the presence of C3 and C9 by flow cytometry. Patients exhibited increased C3 deposition on RBCs compared with controls (p < 0.001), as well as high levels of C3- and C9-bearing RBC-derived microvesicles during the acute phase, which decreased after recovery. Stx2 bound to P1 (k) and P2 (k) phenotype RBCs, expressing high levels of the P(k) Ag (globotriaosylceramide), the known Stx receptor. Stx2 induced the release of hemoglobin and lactate dehydrogenase in whole blood, indicating hemolysis. Stx2-induced hemolysis was not demonstrated in the absence of plasma and was inhibited by heat inactivation, as well as by the terminal complement pathway Ab eculizumab, the purinergic P2 receptor antagonist suramin, and EDTA. In the presence of whole blood or plasma/serum, Stx2 induced the release of RBC-derived microvesicles coated with C5b-9, a process that was inhibited by EDTA, in the absence of factor B, and by purinergic P2 receptor antagonists. Thus, complement-coated RBC-derived microvesicles are elevated in HUS patients and induced in vitro by incubation of RBCs with Stx2, which also induced hemolysis. The role of complement in Stx2-mediated hemolysis was demonstrated by its occurrence only in the presence of plasma and its abrogation by heat inactivation, EDTA, and eculizumab. Complement activation on RBCs could play a role in the hemolytic process occurring during STEC-HUS.

International Society of Blood Transfusion Working Party on red cell immunogenetics and blood group terminology: Cancun report (2012)

The International Society of Blood Transfusion Working Party on red cell immunogenetics and blood group terminology convened during the International congress in Cancun, July 2012. This report details the newly identified antigens in existing blood group systems and presents three new blood group systems.

Homozygosity for a null allele of SMIM1 defines the Vel-negative blood group phenotype

The Vel antigen is present on red blood cells (RBCs) from all humans except rare Vel-negative individuals who can form antibodies to Vel in response to transfusion or pregnancy. These antibodies may cause severe hemolytic reactions in blood recipients. We combined SNP profiling and transcriptional network modeling to link the Vel-negative phenotype to SMIM1, located in a 97-kb haplotype block on chromosome 1p36. This gene encodes a previously undiscovered, evolutionarily conserved transmembrane protein expressed on RBCs. Notably, 35 of 35 Vel-negative individuals were homozygous for a frameshift deletion of 17 bp in exon 3. Functional studies using antibodies raised against SMIM1 peptides confirmed a null phenotype in RBC membranes, and SMIM1 overexpression induced Vel expression. Genotype screening estimated that ~1 of 17 Swedish blood donors is a heterozygous deletion carrier and ~1 of 1,200 is a homozygous deletion knockout and enabled identification of Vel-negative donors. Our results establish SMIM1 as a new erythroid gene and Vel as a new blood group system.

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.