Missense mutations in PIEZO1, which encodes the Piezo1 mechanosensor protein, define Er red blood cell antigens.

Despite the identification of the high-incidence red cell antigen Era nearly 40 years ago, the molecular background of this antigen, together with the other 2 members of the Er blood group collection, has yet to be elucidated. Whole exome and Sanger sequencing of individuals with serologically defined Er alloantibodies identified several missense mutations within the PIEZO1 gene, encoding amino acid substitutions within the extracellular domain of the Piezo1 mechanosensor ion channel. Confirmation of Piezo1 as the carrier molecule for the Er blood group antigens was demonstrated using immunoprecipitation, CRISPR/Cas9-mediated gene knockout, and expression studies in an erythroblast cell line. We report the molecular bases of 5 Er blood group antigens: the recognized Era, Erb, and Er3 antigens and 2 novel high-incidence Er antigens, described here as Er4 and Er5, establishing a new blood group system. Anti-Er4 and anti-Er5 are implicated in severe hemolytic disease of the fetus and newborn. Demonstration of Piezo1, present at just a few hundred copies on the surface of the red blood cell, as the site of a new blood group system highlights the potential antigenicity of even low-abundance membrane proteins and contributes to our understanding of the in vivo characteristics of this important and widely studied protein in transfusion biology and beyond.

Immunoglobulin isotype compositions of ABO specific antibodies are dependent on the individual patient blood group and blood group specificity: Results from a healthy donor cohort.

Antibodies specific for the blood group ABO system antigens are of clinical significance and immunological interest. Routine clinical methods typically employ direct or indirect haemagglutination methods to measure IgM and IgG, respectively. We have developed a simple, single tube method to quantify IgM, IgG, and IgA specific for A and B antigens in order to improve accuracy and reproducibility, and to investigate the relationships between ABO group antibody type, and antibody level. Plasma samples from 300 healthy blood donors were studied. Levels of IgM and IgG binding to reagent group A and B red cells were measure by agglutination (HA) and multi-colour flow cytometry (MC-FC). IgA was also measured by MC-FC. Our FC method was found to be significantly more reproducible than HA for the measurement of blood group A and B specific antibodies. We found statistically significant correlations between antibodies measured by GC-HA and MC-FC, but sufficient differences to indicate that these methods are not equivalent. By MC-FC, IgM, IgG and IgA levels and isotope profiles were found to be dependent on both the donor ABO type and the specificity of the antibody. This study demonstrated heterogeneity in the immunoglobulin class profiles of ABO-blood group specific antibodies within the healthy population. Differences in isotype profiles of ABO-blood group specific antibodies may indicate fundamental differences in the immune mechanisms that generate these antibodies. This is likely to be relevant to the clinical situations where management or diagnosis depend on ABO-specific antibody detection and measurement.