Murine monoclonal anti-s and other anti-glycophorin B antibodies resulting from immunizations with a GPB.s peptide

The study of variant s antigen expression revealing a novel c.160C>T (p.Arg54Cys) variant on GYPB*s allele associated with partial s phenotype

BACKGROUND

Little s antigen is mainly defined by a single nucleotide polymorphism at c.143C (p.Thr48) on the GYPB gene. Several variants on GYPB can alter the expression of s antigen. The aim of this study was to investigate the molecular basis of variant s antigen expression in the Chinese population.

STUDY DESIGN AND METHODS

A total of 4983 whole blood samples were collected to screen the individuals with discrepant s typing results using two different monoclonal anti-s. Then, the sequence of GYPB exon 4 was analyzed by Sanger sequencing. Flow cytometry analysis was performed to quantify s antigen expression on red blood cells (RBCs). In vitro expression study was performed to verify the effect of the GYPB variants identified on the expression of s antigen.

RESULTS

Four donors were identified to have discrepant s typing results. Sanger sequencing showed that three donors carried the c.173C > G variant (p.Pro58Arg) specific for sD antigen, the other one carried a novel GYPB (c.160C > T, p.Arg54Cys) variant. Flow cytometry identified a partial and weak expression of s antigen on the RBCs of the four donors. Furthermore, in vitro expression study confirmed the effect of the two variants on the s antigen expression.

CONCLUSION

The results demonstrated that in addition to p.Thr48, the two extra amino acids p.Arg54 and p.Pro58 are also important for full expression of s antigen. Since the individuals with partial s antigen are at risk for the development of alloanti-s, it is important to select at least two different monoclonal anti-s for correct s typing.

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

BACKGROUND

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

STUDY DESIGN AND METHODS

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

RESULTS

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

DISCUSSION

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

Universal Detection of Mia Antigen and Frequencies of Glycophorin Hybrids among Blood Donors in Taiwan by Human Monoclonal Antibodies against Mia (MNS7), Mur (MNS10), and MUT (MNS35) Antigens

Glycophorin hybrids such as GP.Mur are common in Southeast Asians. In Taiwan, clinically significant alloantibodies to the GP.Mur phenotype are the most important issue in blood banks. A large-scale screening of glycophorin hybrids in the Taiwanese population is urgently needed to ensure transfusion safety. Four clones of human hybridomas that secrete anti-Mi^a, anti-MUT, and anti-Mur were established by fusing human B-lymphocytes and myeloma cells (JMS-3). The specificity of each monoclonal antibody (MoAb) was characterized. Three MoAbs were applied on an Automated Pretransfusion Blood Testing Analyzer (PK7300/PK7400) for donor screening. Genotyping was performed to determine the detailed subgrouping of glycophorin hybrids. Four MoAbs are IgM antibodies. Anti-Mi^a (377T) binds to ⁴⁶DXHKRDTYA⁵⁴, ⁴⁸HKRDTYAAHT⁵⁷ peptides, and anti-Mi^a (367T) binds to ⁴³QTNDXHKRD⁵¹ peptides (X indicates T, M, or K). Anti-Mur is reactive with ⁴⁹KRDTYPAHTA⁵⁸ peptides. Anti-MUT is reactive with ⁴⁷KHKRDTYA⁵⁴. A total of 78,327 donors were screened using three MoAbs, and 3690 (4.71%) were GP.Mur, 20 (0.025%) were GP.Hut, and 18 (0.022%) were GP.Vw. When the Mi^a antigen was introduced as routine screening, the frequency of Mi(a+) among blood donors in Taiwan was 4.66% (67,348/1,444,541). Mi^a antigen was implemented as a routine blood testing, and the results were labeled on all red blood cell (RBC) units.

Red Cell Immunohematology Research Conducted in China

ABO subtypes and RhD variants are the most studied blood groups in China. Some of the polymorphisms in these two blood groups have direct clinical relevance. Molecular diagnosis of blood group polymorphisms is underway in China. In addition, research groups have developed methods such as screening for blood group mimetic peptides using phage display technology. New reagents, akin to antibodies directed against RhD and ABO, are being investigated using aptamer-based techniques. Progress is also being made in the development of synthetic exoglycosidases for conversion of group A and/or B antigens to group O. Development of methoxy-polyethylene-glycol modified red cells has been successful in vitro but has not reached clinical application. In this paper, we summarize red cell immunohematology research that has been conducted in China.

'Chameleonic' Serological Findings Leading to Life-Threatening Hemolytic Transfusion Reactions

Background

The phenomena of co-incidence of transfusion-induced allo- and autoantibodies, blockage and/or loss of red blood cell (RBC) antigens are conspicuous and may result in confusion and misdiagnosis.

Case Report

A 67-year-old female was transferred to the intensive care unit due to hemolysis which developed 2 days following transfusion of three Rh(D)-negative RBC units in the presence of strongly reactive autoantibodies. Standard serological testing and genotyping were performed. Upon arrival, the patient was typed as Ccddee. Her hemolysis was decompensated, and an immediate blood transfusion was required. In addition, direct and indirect antiglobulin tests (DAT and IAT) as well as the eluate were strongly positive. Emergency transfusion of Rh(D)-negative RBCs resulted in increased hemolysis and renal failure. An exhaustive testing revealed anti-D, anti-c, CCddee phenotype and CCD.ee genotype. Three units of cryopreserved CCddee RBCs were transfused, and the patient's condition immediately improved. The discrepancy between Rh-D phenotyping and genotyping was likely caused by masking of the D-epitopes by the autoantibodies. In fact, further enquiry revealed that the patient had been phenotyped as Rh(D)-positive 6 months ago and had been transfused at that time following hip surgery.

Conclusion

The phenomena of transfusion-induced autoantibodies, masked alloantibodies, antigen blockage and/or loss are rare but important features which should be considered in patients presenting with autoimmune hemolytic anemia and/or hemolytic transfusion reactions.

Identification of binding domains on red blood cell glycophorins for Babesia divergens

BACKGROUND

Invasion of red blood cells (RBCs) is one of the critical points in the lifecycle of Babesia. The parasite does not invade other host cells. Earlier work has shown that GPA and GPB function as putative receptors during parasite invasion. The primary focus of this study was the delineation of parasite-binding domains on GPA and GPB.

STUDY DESIGN AND METHODS

The assay of choice to validate molecules that participate in invasion is an inhibition of invasion assay, in which changes in parasitemia are assessed relative to a wild-type assay (no inhibitors). Inhibition of invasion can be achieved by modification of different components of the assay or by the addition of competitors of the molecules that participate in invasion. In this study purified antibody fragments to various domains on GPA and GPB were tested for magnitude of inhibition of parasite invasion. Effects on invasion were monitored by assessment of Giemsa-stained smears every 24 hours.

RESULTS

Among 10 selected antibodies directed at various epitopes on GPA and GPB, antibodies directed against GPA(M) epitopes had the most severe effect (up to 35%) on inhibition of invasion, followed by antibodies directed against GPB(S) epitope (up to 24%).

CONCLUSION

This study confirms the role of RBC glycophorins A and B in Babesia divergens invasion and shows that the GPA(M) and GPB(S) epitopes are likely to play an important role in the entry process.

DNA-based methods in the immunohematology reference laboratory

Although hemagglutination serves the immunohematology reference laboratory well, when used alone, it has limited capability to resolve complex problems. This overview discusses how molecular approaches can be used in the immunohematology reference laboratory. In order to apply molecular approaches to immunohematology, knowledge of genes, DNA-based methods, and the molecular bases of blood groups are required. When applied correctly, DNA-based methods can predict blood groups to resolve ABO/Rh discrepancies, identify variant alleles, and screen donors for antigen-negative units. DNA-based testing in immunohematology is a valuable tool used to resolve blood group incompatibilities and to support patients in their transfusion needs.