Blood groups
Blood is divided into different groups based on the type of antigen present in the cells. The blood group antigen are glycolipids or glycoproteins having a molecular weight of 20,000 to 30,000 present on the surface of the erythrocytes.
The antigens are highly specific and the specificity of the antigens appears to depend upon carbohydrate portion of the molecule. Based on the antigenic type present on the surface of the RBCs cell membrane blood can be grouped into different groups or types.
Landsteiner (1900) was the first to identify four blood groups, A, B, AB and O in human beings.
About 70 blood groups have been identified in man, but the ABO, Rh, MNS, P and Lewis groups are best known. Among these five, ABO and Rh systems are widely used for blood grouping in human beings.
O-A-B blood groups
- There are two related antigens namely type A and type B are present on the surfaces of the RBCs among most of the population. These antigens are inherited and an individual may have either one or both nor do neither of them are present in their cells.
- The genes on two adjacent chromosomes, one gene on each chromosome determine the O-A- B blood groups. There may be any one type of the three types O, A, B and six possible combinations of genes are known. Type O is always functionless as there are no antigens present.
- The antigens (type A and type B) present on the surface of the RBCs are known as Agglutinogens and the plasma antibodies that cause agglutination are known as Agglutinins.
- Based on the presence or absence of agglutinogens in the RBCs blood is grouped.
- Group A – when only type A antigen is present
- Group B – when only type B antigen is present
- Group AB – when type A and B antigens are present
- Group O – when neither A nor B are present.
| Blood Group | Antigens on RBCs | Antibodies in Sera | Genotypes |
| A | A | Anti-B | AA or AO |
| B | B | Anti-A | BB or BO |
| AB | A and B | Neither | AB |
| O | Neither | Anti-A and anti-B | OO |
- During blood transfusion, if the blood between recipient and donor are mismatched, there will be reaction of antigen (agglutinogen) with the antibody (agglutinin) causing clumping or agglutination of the erythrocytes. These agglutinated RBCs are carried by the leukocytes to the RE system where they are lysed releasing Hb. Sometimes, mismatching of recipient and donor’s blood leads to immediate hemolysis of the RBC’s in the circulating blood, caused by the complement system.
- AB group of blood is designated as universal recipient
- O group of blood is commonly referred as universal donor
Antigen antibody reaction
Generally, antibodies present in the donor’s plasma, which would be active against the recipient’s red cells, do not produce such a reaction because of the rapid dilution in the recipient’s circulation.
Serious problem of antigen-antibody reaction result from antibodies present in the recipients plasma reacting with the donor’s RBCs. This agglutination of the donor’s erythrocytes may produce systemic thrombosis in the blood vessels.
Blood typing
Determination of the blood groups of the recipient and donor prior to transfusion is done by matching. RBCs are diluted with saline and one portion is mixed with anti A antibody and the other with anti B antibody. The mixture is observed under the microscope.
If the RBCs have become clumped antigen antibody reaction is said to have taken place which indicates mismatching.
Rh system
Rh antigens are transmembrane proteins with loops exposed at the surface of red blood cells. They are named after the rhesus monkey in which they were first discovered.
They are used for the transport of carbon dioxide and/or ammonia across the plasma membrane. In Rh system, spontaneous agglutinins do not occur. There are six Rh antigens (Rh factors) C, D, E, c, d and e. Of these six types D is widely prevalent and is considered to be more antigenic than others. The presence of D antigen indicates Rh +.
In this system there is no immediate reaction when blood transfusion is effected between Rh+ and Rh– individuals. When Rh– individual receives Rh+ blood, the development of antibody or agglutinin occurs only after 2 to 4 weeks.
Hence, the transfusion reaction is usually delayed and mild. If the same person has subsequent blood transfusion with the same antigen, there will be enhanced antigen – antibody reaction.
Erythroblastosis fetalis
It is a disease of the fetus and newborn infants characterized by progressive agglutination and phagocytosis of RBC’s. The mother is Rh–, father Rh+, the baby inherits Rh+ from the father. Usually the Rh– mother develops anti-Rh agglutinins only when the Rh + child develops by inheriting the Rh+ factor from its father.
The child’s Rh+ antigen enters the maternal system and causes development of Rh+ antibodies. Placental diffusion of this antibody causes hemolytic conditions in the subsequent Rh+ new born infants. This disease condition is characterised by varying degrees of anaemia and jaundice in the newborn infants depending upon antibody reaction by the mother. This condition can be prevented by passively immunising the mother against Rh+ factor.
Blood groups in animals
- In animals, the antigens representing the blood group are not strongly antigenic and occurrence of the natural antibody in their blood is rare. However, naturally occurring antibodies to some red cell antigens can be found in normal animals that lack the respective antigens.
- In domestic animals, the initial transfusion of whole blood will not result in serious problem. However, subsequent transfusions with the similar isoantigen can cause enhanced antigen-antibody response, which may produce the clinical symptoms like muscular trembling, salivation, dyspnea, and hemoglobinuria.
- In dogs, the blood groups are known as DEA system. They include 1.1, 1.2, and 3-8. DEAs 1.1 and 1.2 are present in 60% of the canine populations and these dogs are considered as A positive and the others in which DEA 1.1 and 1.2 blood groups are not present as A negative. The A negative dogs do have antibodies against A positive blood.
- In horses eight blood groups A, C, D, K, P, O, T and U has been identified. Hemolytic icterus occurs in newborn foals due to their erythrocytic destruction by the isoantibodies from the colostrum. This condition is very common in blood containing antibody for A or C.
- In cattlemore than sixty erythrocyte antigenic factors, which are divided into 11 groups. They are designated as A, B, C, F- v, J, L, M, N, S, Z and R’-S. Anti- J is the naturally occurring antibody.
- In sheep, there are seven antigenic groups A, B, C, D, M, R–O and X-Z of which anti- R is the naturally occurring antibody of the R – O antigen.
- In the goats, five blood group antigens have been identified, A, B, C, M and J.
- In pigs, thirteen blood group systems, A, B, C, E, F, G, H, I, J, K, L, M and N have been identified . `A’ antigen possesses naturally occurring antibody.
- In cats, three blood groups have been identified A, B and AB. Type A is most common and they have antibodies against A isoantigens. Type AB is very rare in occurrence.
Significance of blood groups in animals
- To identify monozygotic twins from dizygotic twins.
- Some blood group systems correlate with economic traits, eg: milk fat, milk yield. Hence, useful for selection of animals for breeding.
- To solve parentage problem if there is any dispute.
Precautions for blood transfusion in animals
The blood with anti-isoantibody A in pig, J in cattle, R in sheep and A or C in horse should be avoided for blood transfusion.