Blood group Antigen and Antibodies

Antigen – An antigen is a substance on the red cell membrane (carbohydrate/protein) which can stimulate the immune system to produce an antibody. Blood group of an individual is determined by the antigens expressed on the red cells. A high-incidence antigen is found on the red cells of most of the population. When an antigen is absent on the red cells of the majority of people it is called a low incidence antigen.

Antibody – Antibody is produced by the immune system in response to a foreign antigen when the body comes in contact with an antigen it does not recognize.

Clinical Significance

An antibody which can react at 37°C (body temperature) resulting in destruction of red cells bearing the corresponding antigen and ultimately causing hemolysis is called a clinically significant antibody.

Responder/Non-Responder – Routine transfusion practice includes only ABO and D antigen typing of the donors. So, when a patient is transfused, the differences in the red cell antigen makeup can cause immune response and the patient can produce antibodies against the antigens which they lack.  Responders are people who produce antibodies when they are transfused with blood which has the antigens that they lack. This includes about 3-5% of the general population. Non-responders do not produce an immune response even when transfused with blood which has the antigens that they lack.  

Repeated exposure to foreign red cells with multiple transfusions in clinical cases including thalassemia, sickle cell anemia and pregnancy can increase the chance of an individual in producing antibodies. When a patient with multiple antibodies or a patient with naturally occurring antibodies to a high incidence antigen requires blood transfusion, it becomes difficult to provide matched blood. Since only A, B, O and D antigens are routinely typed, blood cannot be provided immediately. Screening the available donor units in the blood center for those antigens should be done and it is a labour intensive and long standing process.

Blood group antigens are distributed unevenly among different population based on the ethnicity.  For example prevalence of Bombay (Oh) phenotype is 1 in 1000 in India and 1 in 1,00,000 in Europe. 

Bombay phenotype, P null, -D-/-D- , In(a+b-), Co(a-b-), CdE/CdE (ryry) and I-i- are the various rare blood group phenotypes reported in India. Extended phenotyping of donor blood is pivotal in creating a donor panel and in identifying rare phenotypes present in the local population.

Kasturba Hospital, Blood Centre has screened for clinically significant blood group antigens among regular blood donors and formed a registry for rare phenotypes. The centre keeps updating the registry as applicable.  

Currently the rare blood phenotypes present in the registry are listed below. This list will be updated regularly.

• Bombay phenotype, 
• Lu(a-b-)
• RzRz 
• R2Rz 
• r”r
• R1Rz
• R2R2
• r’r 
• [R2R2, Jkb-, M-, Le(a-b-)],
• [R2R2, Jka-, Fy b-], 
• [R2R2, Fy b-, P1-, N-, S-], 
• [R1R1, Fy a-, Jka-, s-, P1- ],
• [R1R1, Fy a-, Jka-, P1-, N-, S-, Le(a-b-)], 
• [R1R1, Fy a-, Jk(b-), s-, P1-],
• [R1R1, Fy a-, Jk b-, M-, P1-],
• [rr, Fy b-, Jka-, P1-, N-],
• [rr, Fy a-, Jkb-, P1-, S-]
• [rr, Fy a-, Jka-, s-, N-]
• [rr, M-, S-]
• [r’r, Fy a-, Jkb-, M-, S- P1- ]
• [r’r, Fy b-, Jkb-, S-]
• [R0r, Fy a-, Jkb-, N-, S- P1-]
• [R0r, Fy b-, Jkb-, M-, S- ]
• [R1r, H-, Fy a-, Jka-, N-, S- P1-]
• [R1R2, H-, Fy b-, Jka-, M-, S-]
• [R1R2, H-, Le(a-b-)]