It has no antigen hence named as blood group O.Whereas blood group A and B produces antigen A and B resp which are nothing but slightly different form of immuno sugars (N-acetyl-D-galactosamine and galactose) present on the membrane of RBC.Also remember that if an antigen is present in the RBC the corresponding antibody will be absent in the blood plasma and vice versa. read more
The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. In human blood transfusions it is the most important of the 36 different blood type (or group) classification systems currently recognized. read more