Allo-anti-M: Detection peaks around 2 years of age, but may be attenuated by red blood cell transfusion.

BACKGROUND: Anti-M is frequently observed as a naturally occurring antibody of little clinical significance. Naturally occurring anti-M is often found in children although the specific triggers of production, persistence, and evanescence of anti-M have yet to be elucidated. METHODS: In a retrospective, multicenter, nationwide cohort survey conducted from 2001 to 2015, alloantibody screening was performed before and after transfusion in 18,944 recipients younger than 20 years. Recipients were categorized into six cohorts based on their age at transfusion; within and among these cohorts, allo-anti-M was analyzed in regard to its production, persistence, and evanescence. RESULTS: In 44 patients, anti-M detected before and/or after transfusion was an age-related phenomenon, with a median age of 2 years and an interquartile range of 1-3 years; anti-M was most frequently detected in a cohort of children 1 to <5 years (0.77%, 31 of 4035). At least five patients were presumed to have concurrent infections. Among 1575 adolescents/young adults (15 to <20 years), no anti-M was detected. Of 29 patients with anti-M prior to transfusion, the antibody fell to undetectable levels in 17 recipients (89.5%, of whom at least 13 received only M-negative red cells) after anywhere from 5 days to 5.8 years; anti-M persisted in 2, and was not tested in 10. Only 15 recipients (0.08%) produced new anti-M after transfusion. CONCLUSION: Naturally occurring anti-M is a phenomenon of younger ages, predominantly between 1 and 3 years. After transfusion, it often falls to undetectable levels.

A Jordanian family with three sisters apparently homozygous for Mk and evidence for clinical significance of antibodies produced by Mk Mk individuals.

BACKGROUND: The rare Mk Mk phenotype is the result of a deletion of the coding regions of both GYPA and GYPB. Red blood cells (RBCs) of individuals homozygous for the rare Mk gene lack all MNS blood group antigens and have no glycophorin A or glycophorin B. This phenotype is extremely rare and only four families have been reported. CASE REPORT: A 28-year-old woman was referred for assessment of recurrent early neonatal deaths. She was found to be apparently homozygous for Mk . With the presence of two Mk Mk sisters as matched donors, an intrauterine transfusion was performed to treat fetal anemia due to a strong maternal atypical antibody. Twins were delivered and subsequently transfused with RBCs from the proposita and her Mk Mk sisters. CONCLUSION: This case reports the fifth family with members apparently homozygous for Mk and the second example of severe hemolytic disease of the fetus and newborn (HDFN) due to maternal antibodies produced by Mk Mk individuals. It also shows the importance of intensive monitoring and management of HDFN caused by alloantibodies to RBC antigens.

Frequency of Mi(a) antigen: A pilot study among blood donors.

The Miltenberger (Mi) classes represent a group of phenotypes for red cells that carry low frequency antigens associated with the MNSs blood group system. This pilot study was aimed at determining the Mia antigen positivity in the blood donor population in a tertiary care hospital in New Delhi, India. The study was performed between June to August 2014 on eligible blood donors willing to participate. Antigen typing was performed using monoclonal anti-Mia antiserum by tube technique. Only one of the 1000 blood donors (0.1%) tested was found to be Mia antigen positive. the Mia antigen can, therefore, be considered as being rare in the Indian blood donor population.

Gene conversion events between GYPB and GYPE abolish expression of the S and s blood group antigens.

BACKGROUND AND OBJECTIVE: The locus specifying the MNS blood group system is composed of three highly homologous genes, glycophorin A (GYPA), B (GYPB) and E (GYPE). While more than 20 hybrid genes between GYPA and GYPB have been identified, no hybrid genes between GYPB and GYPE have been reported so far. We serendipitously identified GYPB-E-B hybrid genes by studying three individuals whose rare S-s- blood phenotype failed to be predicted by our genotyping platform. MATERIALS AND METHODS: Long-range PCR amplification and extended Sanger sequencing were required to identify and characterize these GYPB-E-B hybrid genes. A PCR assay was developed to detect them in individual or pooled gDNA samples. RESULTS: The first S-s- proband appeared to have two silenced GYPB alleles, one harbouring the so-called P2 mutation and one harbouring GYPE Pseudoexon E4 in place of GYPB Exon B4 (GYPB-E-B hybrid). The two other S-s- probands were homozygous or hemizygous for other GYPB-E-B hybrid alleles, which also lack GYPB Exon B4 and thus do not carry the S/s polymorphism. CONCLUSION: The three GYPB-E-B hybrid genes reported here constitute the first evidence of recombination events between GYPB and GYPE. As these GYPB-E-B hybrid genes drive the S-s- blood phenotype, it is important to know they are a limitation for the current blood group genotyping methods, including those performed by commercial platforms.

MNSs blood group glycophorin variants in Taiwan: a genotype-serotype correlation study of 'Mi(a)' and St(a) with report of two new alleles for St(a).

BACKGROUND: Glycophorin variants of the MNSs blood group are important in Taiwan. For more than 20 years, screening for the most frequent irregular antibody, anti-''Mi(a)', has been conducted by using 'Mi(a)'(+) RBCs, with a significant success. However, the sensitivity and the specificity of this screening strategy have never been validated, and the true incidences of different glycophorin variants in Taiwan have been in controversy. Also, the significance of another less frequent and usually separately reported variant, St(a), has never been evaluated. METHODOLOGY/PRINCIPAL FINDINGS: We ran a population-based screening (from unselected patients in our hospital) for MNSs blood group glycophorin variants by PCR-sequencing method. GP.Mur (Mil.III) was confirmed by sequence from 57 out of 1027 samples (5.6%), and there was no other Miltenberger subtype glycophorin variant found. Glycophorin variant St(a) was found from 35 out of 1027 samples (3.4%). In contrast to anti-'Mi(a)', which is the most frequently identified irregular antibody in Taiwan, the prevalence of anti-St(a) was only 0.13% as determined by serologic method. In addition, two new alleles for St(a) were found and reported. CONCLUSION/SIGNIFICANCE: We confirm the long-standing assumption that GP.Mur is the only prevalent Miltenberger subtype in Taiwan. The current anti-'Mi(a)' screening method used in Taiwan, although neither sensitive nor specific, is still a suitable practice. Although St(a) antigen has a high prevalence in Taiwan, routine screening for anti-St(a) is not warranted based on current evidence.

Clinically significant anti M antibodies--a report of two cases.

INTRODUCTION: Most anti-M antibodies are not active at 37°C and are thus of no clinical significance. Occasionally these antibodies have a wide thermal range and can lead to hemolytic transfusion reactions or hemolytic disease of the new born. PATIENT AND METHODS: We describe two cases of anti-M antibodies, both of which were clinically significant. RESULTS: The first case was detected due to crossmatch incompatibility and the second presented as a blood group discrepancy. CONCLUSION: When the antibody is active at 37°C, M antigen negative red cell units should be issued.

Prevalence and specificity of red-blood-cell antibodies in a multiethnic South and East Asian patient population and influence of using novel MUT+Mur+ kodecytes on its detection.

BACKGROUND AND OBJECTIVES: Appropriate screening for irregular red-cell antibodies is essential for ensuring transfusion compatibility and for antenatal management of mothers at risk of haemolytic disease of the foetus and newborn. Screening for all relevant antibodies is, however, limited by screening cells that do not express antigens present in the patient and donor population. Technology to artificially incorporate antigens into red cells is currently available and may be an option for customizing screening cells. MATERIALS AND METHODS: We sought to identify retrospectively the changing patterns of alloantibody prevalence in our multiethnic population on change of screening cells. Antibody screening records of 143 501 patients tested from 2004 to 2010 were retrieved and divided into two groups: period-1 (2004-2008) and period-2 (2009-2010). During period-1, standard screening cells were used while in period-2, MUT+Mur+ KODE(™) transformed red cells (kodecytes) were used. RESULTS: Four per cent of samples tested during period-2 were positive on antibody screening compared to 3·2% in period-1. Specific antibodies, excluding anti-D, were identified in 1·66% and 1·52% of patients in period-2 and -1, respectively. When confined to antibodies of clinical significance only, period-2 showed higher alloantibody prevalence of 1·16% as compared to 0·66% in period-1. Antibodies to glycophorin variants of MNS (vMNS) were more commonly detected while antibodies to Lewis antigens declined during period-2. CONCLUSION: Antibodies to vMNS antigens are common in South and East Asian populations and are often missed when using standard screening cells. Use of specifically engineered screening cells to express red-cell antigens artificially is beneficial in detecting the diverse alloantibodies present in our population.

Sixty years of antibodies to MNS system hybrid glycophorins: what have we learned?

The MNS system was the second blood group system discovered and at least 16 of the 46 antigens in the MNS system result from genetic recombination, producing a hybrid glycophorin. The incidence of these hybrid glycophorins is highest in East Asian populations. MNS system antigens defined by hybrid glycophorins are immunogenic with alloimmune IgG responses developing after transfusion or pregnancy; with reports originating from Asia, Europe, the Americas, and Australia. This demonstrates the global nature of problems associated with these antibodies. Since the initial report that production of anti-Mi(a) was a cause of hemolytic disease of the fetus and newborn (HDFN), antibodies to antigens defined by hybrid glycophorins have been reported in 27 cases of HDFN (1 fatal) and 8 cases of hemolytic transfusion reaction (HTR) (1 fatal). In at least 40% of these clinical cases, the disease was reported as severe. Hyporegenerative fetal anemia is a common feature of the reported HDFN cases. In all published cases, the causative antibodies were identified by reference laboratory investigative tests following clinical presentation. The failure to detect these antibodies by routine testing highlights the need for consideration of the medical importance of these antibodies when defining antibody screening practices and reagents. The aim of this review is to raise awareness of severe disease caused by antibodies to MNS antigens defined by hybrid glycophorins and, thus, to improve diagnosis and patient management.

MNS blood group system: a review.

The MNS blood group system is second only to the Rh blood group system in its complexity. Many alloantibodies to antigens in the MNS system are not generally clinically significant although antibodies to low-prevalence and high-prevalence MNS antigens have caused hemolytic disease of the fetus and newborn. The MNS antigens are carried on glycophorin A (GPA), glycophorin B (GPB), or hybrids thereof, which arise from single-nucleotide substitution, unequal crossing over, or gene conversion between the glycophorin genes. Antigens in the MNS system are fully developed at birth. This review summarizes aspects of the MNS system, including the molecular basis of some antigens in the MNS blood group system. Readers are referred to existing excellent reviews for background information. Throughout this document, information given without references can be found in the reviews listed previously, and the reader is referred to these reviews for references to original reports.

Characterization of human blood group scFv antibodies derived from a V gene phage-display library.

We previously reported the initial characterization of five human single-chain Fv (scFv) antibody fragments specific for the blood group antigens B, D(Rh), E(Rh), Kpb and HI. The scFvs were isolated from a phage-antibody library constructed from the variable region genes of two non-immunized donors. In this paper we report the specificity, affinity and kinetics of antigen binding of these scFv fragments. All five scFvs agglutinated the appropriate red cell phenotype following the addition of a monoclonal antibody which recognizes a peptide tag incorporated into the scFv. The anti-B and anti-HI scFv molecules, which recognize high density carbohydrate antigens, spontaneously polymerized and agglutinated red cells directly. None of the antibody fragments showed cross-reactivity with other red cell antigens, with the exception of the anti-E which reacted weakly with E-negative cells. Specific scFv binding was confirmed by ELISA, flow cytometry and radioactive labelling. The anti-D scFv recognized 17,600 sites on cDE/cDE red cells with an association constant (Ka), of 5.2 x 10(7) M-1 and a rate constant for dissociation (koff) of 1.9 x 10(-2) s-1. The anti-E scFv recognized 29,800 and 39,800 sites on cDE/cDE red cells in two experiments with Kas of 8.4 x 10(6) and 4.4 x 10(7) M-1. The koff for this antibody was 2.7 x 10(-2) s-1. The results demonstrate that scFv antibody fragments specific for cell surface antigens and possessing affinities typical of the primary immune response can be obtained from a phage-display library.