- Blood group, also known as blood type, is a group of types of blood based on the presence and absence of blood group antigens in the surface (membrane) of the RBCs, and antibodies on the plasma.
- Karl Landsteiner, on the basis of blood transfusion results, proposed that blood of different persons has some biochemical differences.
- He confirmed the presence of two types of proteins in human blood –
- Antigens – Glycoprotein present on the plasma membrane of RBCs. There are two types of antigens – A , B.
- Antibody – It is a protein present in the blood plasma. There are two types of antibodies – a , b.
Incompatibility and agglutination
- Both antigen A and antibody a are incompatible and antigen B and antibody b are incompatible to each other.
- So when incompatible blood comes together, it results in clumping of RBCs which is referred as agglutination.
- Only antigen A and antibody b can exist together and so can antigen B and antibody a.
- Antigen A and B can occur together if they lack their antibodies.
- Similarly, antibodies a and b can exist together if they lack their antigens.
Types of Blood Groups
| Blood Group | Antigen present | Antibody present | Can donate blood to | Can receive blood from |
| A | A | b | A and AB | A and O |
| B | B | a | B and AB | B and O |
| AB | A and B | None | AB | All (Universal recipient) |
| O | None | a and b | All (Universal donor) | O |
Rh Factor
- Rh factor is an antigen protein present on the surface of RBC in human beings.
- It was first discovered by Landsteiner and Weiner on the plasma membrane of RBC of Rhesus monkey, so called as Rh factor.
- A person is said to be Rh+ if its RBCs contain Rh antigen and Rh– if he has no Rh antigen on his RBCs.