The ABO blood group system was discovered by Karl Land Steiner in 1901.
Red blood cells or erythrocytes are present in the blood and contain certain proteins on their surface. These proteins are called antigens. The plasma which is the liquid part contains antibodies which will attack certain antigens if they are present. There are various types of red blood cell antigens - the ABO and rhesus types are the most important. By the time a person is six months old, he naturally will have developed antibodies against the antigens his red blood cells lack.
ABO Blood Group System
A blood group individuals will have type A antigens on the surface of red blood cells and anti-B antibodies in plasma. There are about 20 different subgroups of which A1 and A2 subtypes are the most common.
B blood group individuals will have type B antigens on the surface of red blood cells and anti-A antibodies in your plasma.
AB blood group are those who will have type A and type B antigens on the surface of red blood cells and no antibodies to A or B antigens in plasma.
O blood group are those who will have neither type A or type B antigens on the surface of red blood cells but will have anti-A and anti-B antibodies in plasma.