In human blood there are two antigens and antibodies. The two antigens are antigen A and antigen B. The two antibodies are antibody A and antibody B.
The antigens are present in the red blood cells and the antibodies in the serum. Regarding the antigen property of the blood all human beings can be classified into 4 groups, those with antigen A (group A), those with antigen B (group B), those with both antigen A and B (group AB) and those with neither antigen (group O).
The antibodies present together with the antigens are found as follows : 1. Antigen A with antibody B 2. Antigen B with antibody A 3. Antigen AB has no antibodies 4. Antigen nil (group O) with antibody A and B.