The Dantu erythrocyte phenotype of the NE variety. II. Serology, immunochemistry, genetics, and frequency

Genetic variation of glycophorins and infectious disease

Glycophorins are transmembrane proteins of red blood cells (RBCs), heavily glycosylated on their external-facing surface. In humans, there are four glycophorin proteins, glycophorins A, B, C and D. Glycophorins A and B are encoded by two similar genes GYPA and GYPB, and glycophorin C and glycophorin D are encoded by a single gene, GYPC. The exact function of glycophorins remains unclear. However, given their abundance on the surface of RBCs, it is likely that they serve as a substrate for glycosylation, giving the RBC a negatively charged, complex glycan “coat”. GYPB and GYPE (a closely related pseudogene) were generated from GYPA by two duplication events involving a 120-kb genomic segment between 10 and 15 million years ago. Non-allelic homologous recombination between these 120-kb repeats generates a variety of duplication alleles and deletion alleles, which have been systematically catalogued from genomic sequence data. One allele, called DUP4, encodes the Dantu NE blood type and is strongly protective against malaria as it alters the surface tension of the RBC membrane. Glycophorins interact with other infectious pathogens, including viruses, as well as the malarial parasite Plasmodium falciparum, but the role of glycophorin variation in mediating the effects of these pathogens remains underexplored.

GP.MOT: A novel glycophorin variant identified in a Japanese blood donor

BACKGROUND

In this study, we identified a novel glycophorin variant (GP.MOT) in a Mi^a -positive Japanese blood donor. The proband with this glycophorin variant was discovered by antigen screening of samples from 475,493 Japanese blood donors using monoclonal anti-Mi^a .

STUDY DESIGN AND METHODS

Standard serological techniques and flow cytometry were performed. GP.MOT RBCs were examined by immunoblotting using anti-GPA, anti-MUT or anti-Mur. Genome DNA was extracted from whole blood, and the GYPA/GYPB was analyzed by polymerase chain reactions and Sanger sequencing.

RESULTS

The MNS blood group of the proband was M + N + ^w S-s + with the presence of other low-frequency antigens including Mi^a , Mur, MUT, and KIPP. A 43-kDa molecule, which is almost equivalent in size to glycophorin A (GPA), was identified by immunoblotting using monoclonal anti-MUT and anti-Mur. Sanger sequencing clearly indicated that the proband had two different GYPA*M alleles at SNP rs62334651 (GYPA*M232 + 55A and GYPA*M232 + 55G), as well as a GYP(B-A) hybrid allele (GYP*MOT) with breakpoints located on pseudoexon 3 of GYPB from c.210 to c.219.

DISCUSSION

We identified a hybrid glycophorin GP.MOT with the deduced unique amino acid sequence GPB (20-45)-GPΨB (46-70)-GPA (71-149), which has not been previously reported.

Molecular Detection of Glycophorins A and B Variant Phenotypes and their Clinical Relevance

Crossover or conversion between the homologous regions of glycophorin A (GYPA) and glycophorin B (GYPB) gives rise to several different hybrid glycophorin genes encoding a number of different glycophorin variant phenotypes which bear low prevalence antigens in the MNS blood group system. GP.Mur is the main glycophorin variant phenotype which causes hemolytic transfusion reaction (HTR) and hemolytic disease of the fetus and newborn (HDFN) in East and Southeast Asians. The detection of glycophorin variant phenotypes using serological methods is limited to phenotyping reagents that are not commercially available. Moreover, the red blood cells used for antibody identification are usually of the GP.Mur phenotype. The current Polymerase Chain Reaction (PCR)-based methods and loop-mediated isothermal amplification (LAMP) are available alternatives to phenotyping that allow for the specific detection of glycophorin variant phenotypes. This review highlights the molecular detection method for glycophorins A and B variant phenotypes and their clinical relevance.

Resistance to malaria through structural variation of red blood cell invasion receptors

The malaria parasite Plasmodium falciparum invades human red blood cells by a series of interactions between host and parasite surface proteins. By analyzing genome sequence data from human populations, including 1269 individuals from sub-Saharan Africa, we identify a diverse array of large copy-number variants affecting the host invasion receptor genes GYPA and GYPB We find that a nearby association with severe malaria is explained by a complex structural rearrangement involving the loss of GYPB and gain of two GYPB-A hybrid genes, which encode a serologically distinct blood group antigen known as Dantu. This variant reduces the risk of severe malaria by 40% and has recently increased in frequency in parts of Kenya, yet it appears to be absent from west Africa. These findings link structural variation of red blood cell invasion receptors with natural resistance to severe malaria.

Population genetics of GYPB and association study between GYPB*S/s polymorphism and susceptibility to P. falciparum infection in the Brazilian Amazon

BACKGROUND

Merozoites of Plasmodium falciparum invade through several pathways using different RBC receptors. Field isolates appear to use a greater variability of these receptors than laboratory isolates. Brazilian field isolates were shown to mostly utilize glycophorin A-independent invasion pathways via glycophorin B (GPB) and/or other receptors. The Brazilian population exhibits extensive polymorphism in blood group antigens, however, no studies have been done to relate the prevalence of the antigens that function as receptors for P. falciparum and the ability of the parasite to invade. Our study aimed to establish whether variation in the GYPB*S/s alleles influences susceptibility to infection with P. falciparum in the admixed population of Brazil.

METHODS

Two groups of Brazilian Amazonians from Porto Velho were studied: P. falciparum infected individuals (cases); and uninfected individuals who were born and/or have lived in the same endemic region for over ten years, were exposed to infection but have not had malaria over the study period (controls). The GPB Ss phenotype and GYPB*S/s alleles were determined by standard methods. Sixty two Ancestry Informative Markers were genotyped on each individual to estimate admixture and control its potential effect on the association between frequency of GYPB*S and malaria infection.

RESULTS

GYPB*S is associated with host susceptibility to infection with P. falciparum; GYPB*S/GYPB*S and GYPB*S/GYPB*s were significantly more prevalent in the in the P. falciparum infected individuals than in the controls (69.87% vs. 49.75%; P<0.02). Moreover, population genetics tests applied on the GYPB exon sequencing data suggest that natural selection shaped the observed pattern of nucleotide diversity.

CONCLUSION

Epidemiological and evolutionary approaches suggest an important role for the GPB receptor in RBC invasion by P. falciparum in Brazilian Amazons. Moreover, an increased susceptibility to infection by this parasite is associated with the GPB S+ variant in this population.

Impact of malaria on genetic polymorphism and genetic diseases in Africans and African Americans

The high mortality from malaria in sub-Sahara Africa selected multiple genes that give the population a selective advantage. Identification of the genetic basis for resistance may suggest unusual approaches to development of malarial vaccines and antimalarial drugs. Some of these genes may be deleterious, although of selective advantage within the African setting, and need to be identified for counseling for disease prevention.

Human erythrocyte glycophorins: protein and gene structure analyses

Human RBCs glycophorins are integral membrane proteins rich in sialic acids that carry blood group antigenic determinants and serve as ligands for viruses, bacteria, and parasites. These molecules have long been used as a general model of membrane proteins and as markers to study normal and pathological differentiation of the erythroid tissue. The RBC glycophorins known as GPA, GPB, GPC, GPD, and GPE have recently been fully characterized at both the protein and the DNA levels, and these studies have demonstrated conclusively that these molecules can be subdivided into two groups that are distinguished by distinct properties. The first group includes the major proteins GPA and GPB, which carry the MN and Ss blood group antigens, respectively, and a recently characterized protein, GPE, presumably expressed at a low level on RBCs. All three proteins are structurally homologous and are essentially erythroid specific. The respective genes are also strikingly homologous up to a transition site defined by an Alu repeat sequence located about 1 Kb downstream from the exon encoding the transmembrane regions. Downstream of the transition site, the GPB and GPE sequences are still homologous, but diverge completely from those of GPA. The three glycophorin genes are organized in tandem on chromosome 4q28-q31, and define a small gene cluster that presumably evolved by duplication from a common ancestral gene. Most likely two sequential duplications occurred, the first, about 9 to 35 million years ago, generated a direct precursor of the GPA gene, and the second, about 5 to 21 million years ago, generated the GPB and GPE genes and that involved a gene that acquired its specific 3' end by homologous recombination through Alu repeats. Numerous variants of GPA and GPB usually detected by abnormal expression of the blood group MNSs antigens are known. An increasing number of these variants have been structurally defined by protein and molecular genetic analyses, and have been shown to result from point mutations, gene deletions, hybrid gene fusion products generated by unequal crossing-over (not at Alu repeats), and microconversion events. The second group of RBC membrane glycophorins includes the minor proteins GPC and GPD both of which carry blood group Gerbich antigens. Protein and nucleic acid analysis indicated that GPD is a truncated form of GPC in its N-terminal region, and that both proteins are produced by a unique gene called GE (Gerbich), which is present as a single copy per haploid genome and is located on chromosome 2q14-q21.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood group-active surface molecules of the human red blood cell

The surface of the human red blood cell is dominated by a small number of abundant blood group active proteins. The major proteins are the anion transport protein (band 3) which has AB(H) activity, and Glycophorin A which has MN activity. Band 3 and Glycophorin A are of equal abundance in the normal red cell membrane (approximately 10(6) copies of each) and the two proteins may associate together as a complex. The glucose transporter (band 4.5) had AB(H) activity and there are about 5 x 10(5) copies/red cell. Several polypeptides associate together to form the Rh complex. The major components of this complex (abundance 1-2 x 10(5) copies/red cell) are polypeptides of Mr 30,000, polypeptides of Mr 45,000-100,000 and Glycophorin B. The antigens of the Rh blood group system appear to be associated with the polypeptides of Mr 30,000 and those of Mr 45,000-100,000 (the latter also express AB(H) activity). Glycophorin B expresses the blood group 'N' antigen and the Ss antigens. Glycophorins C and D carry the Gerbich antigens and, together, these polypeptides comprise approximately 10(5) copies/red cell. The complete protein sequence of all the above-mentioned proteins is known, except for the Mr 30,000 and Mr 45,000-100,000 polypeptides of the Rh complex for which only partial sequences are available, and Glycophorin D, the sequence of which can be inferred from that of Glycophorin C. Several of the minor blood group active proteins at the red cell surface (abundance less than 1.2 x 10(4)/red cell) have been the subject of recent studies. The polypeptide expressing Cromer-related blood group antigens has been identified as decay-accelerating factor and that carrying the Ina/Inb antigens as CD44. The protein sequence of both of these proteins has been deduced form nucleotide sequencing. The polypeptides expressing Kell antigens, Lutheran antigens, Fy antigens, and LW antigens have also been identified and partially characterised.

A novel variety of the Dantu gene complex (DantuMD) detected in a Caucasian

The first Caucasian (MD) shown to exhibit the low-frequency MNSs system antigen, Dantu was detected due to an increased tendency of erythrocytes to be aggregated by substances that promote red cell agglutination. The donor was found to exhibit a novel variety of the Dantu gene complex (DantuMD), as judged from biochemical, immunochemical, and serological studies. The glycophorin (GP) A level of MD's erythrocyte membranes were slightly decreased (about 17%) but GP B was not significantly different from normal. GP A and GP B of MD's cells were shown to carry M and N or S and s antigens, respectively, indicating that MD exhibits two genes encoding GP A and two genes encoding GP B. MD's cells contain a Dantu-, N- and s-specific GP B-GP A hybrid GP (molar ratio to GP A approx. 0.6:1.0). Partial amino-acid sequence analysis indicates that the structure of this molecule is rather similar to, or completely identical with, that of the hybrid GP in DantuNE erythrocytes. The residues 1-39 or 40-99 of the latter molecule correspond to the residues 1-39 of s-specific GP B and the residues 72-131 of GP A, respectively. Statistical evidence suggests that MD exhibits a single gene encoding the hybrid GP. Thus, MD appears to be heterozygous for a typical anti-Lepore type gene complex that seems to comprise genes for GP A, GP B, and the GP B-GP A hybrid. The diminished GP A level and a decreased galactose-oxidase labelling of the major membrane protein (anion channel protein, band 3) in MD's cells is in accordance with previous data suggesting that band 3 might form a complex with GP A and the Dantu-specific hybrid GP. This complex formation may be necessary for optimum incorporation of the latter molecules into the membrane.

A family study of multiple mutations of alpha and delta glycophorins (glycophorins A and B)

Glycophorins alpha and delta are the carriers of the antigens of the MNSs blood system; this report documents the presence of three glycophorin mutations in two individuals of a 16 member family. Erythrocytes were examined by serology, sodium dodecyl sulfate electrophoresis, and immunoblotting. The inheritance pattern and immunoblot profile revealed: (1) A variant Dantu glycophorin showed properties consistent with a delta-alpha glycophorin hybrid structure, previously noted in other individuals. The gene responsible for the Dantu glycophorin in this family is linked to a gene coding for an M-specific alpha glycophorin. (2) Another variant glycophorin, Mi-III glycophorin, was first revealed by immunoblotting and subsequently confirmed by erythrocyte antigen typing. This autosomal dominant trait is associated with N blood group activity and the inheritance pattern indicates that it could be a variant of delta glycophorin. (3) In the individuals with both Dantu and Mi-III glycophorins a delta glycophorin deficiency was observed suggesting that a deletion or alteration of delta gene may exist cis to the Dantu gene. Our findings that document clustering of multiple mutations in MNSs gene loci in the propositus family are very unusual as such variants are relatively rare.

The Dantu erythrocyte phenotype of the NE variety. I. Dodecylsulfate polyacrylamide gel electrophoretic studies

Red cell membranes from patient NE, Mr. Dantu and 16 additional Black individuals, positive for the low-frequency MNSs-system antigen Dantu, were studied by dodecylsulfate polyacrylamide gel electrophoretic techniques. The content of the major, blood group M- or N-active sialoglycoprotein (glycophorin A, GP A) was found to be decreased by about 57%. The blood group S- or s-active sialoglycoprotein (GP B) was decreased by about 51% in membranes from proven Dantu/U heterozygotes and not detectable in those from patient NE and other Dantu+U- individuals. Donor NE was shown to exhibit the genotype Dantu/u. Dantu-positive cells exhibit a proteinase-resistant GP B-GP A hybrid with an apparent molecular mass of 29 KDa whose intramembraneous and cytoplasmic domains were shown to be similar to those of GP A. The molar hybrid: GP A ratio in all cells was found to be about 2.4: 1, indicating that the NE variety of the Dantu phenotype is much more frequent than the Ph or MD types. The significance of an additional minor 'new' component (molecular mass 21 KDa) in Dantu+ membranes and the minor component J (molecular mass 22 KDa) occurring in normal and Dantu+U+ GP preparations, but not in those from Dantu+U- cells, has not been resolved. The apparent molecular mass of the anion channel protein (band 3) in all cells of the NE variety was shown to be decreased by about 3 KDa, due to a shortening of carbohydrate chains. This suggests that the hybrid, just like GP A, might form a complex with band 3.