The Er blood group system consists of five human

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

surface

antigens In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

, Er^a, Er^b, Er3, Er4 and Er5. The incidences of Er^a and Er3 are each greater than 99% of the human population, while the incidence of Er^b is less than 0.01%. Er4 and Er5 are found at a high frequency in the general population. Individuals with

antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

against Er3 may develop

acute hemolytic transfusion reaction An acute hemolytic transfusion reaction (AHTR), also called immediate hemolytic transfusion reaction, is a life-threatening reaction to receiving a blood transfusion. AHTRs occur within 24 hours of the transfusion and can be triggered by a few milli ...

upon transfusion with an incompatible unit, while Er^a and Er^b are unlikely to be clinically significant. The clinical significance of antibodies against Er4 and Er5 is poorly understood due to a lack of data, but two cases of severe

hemolytic disease of the fetus and newborn Hemolytic disease of the newborn, also known as hemolytic disease of the fetus and newborn, HDN, HDFN, or erythroblastosis foetalis, is an alloimmune condition that develops in a fetus at or around birth, when the IgG molecules (one of the five ...

have been reported in women with these antibodies. Expression of the Er blood group antigens is controlled by the gene ''

PIEZO1 Piezo1 is a mechanosensitive ion channel protein that in humans is encoded by the gene ''PIEZO1''. Piezo1 and its close homolog PIEZO2, Piezo2 were cloned in 2010, using an siRNA-based screen for mechanosensitive ion channels. Structure and fun ...

''. Er^a was first identified in 1982 and Er^b was identified in 1988. Er was recognized as a blood group collection by the

International Society of Blood Transfusion The International Society of Blood Transfusion (ISBT) is a scientific society founded in 1935, which promotes the study of blood transfusion and spreads reliable information about the ways in which blood transfusion medicine and science can bes ...

in 1990 and promoted to a blood group in 2022.

References

Blood antigen systems Transfusion medicine {{Immunology-stub