So there are two different types of antigens. One of them we call antigen A or glycoprotein A, and the other one we call antigen B or glycoprotein B. And it's the presence or absence of these glycoproteins that determines and differentiates these blood groups from one another. For example, blood type A means our red blood cells contain antigen A and not antigen B. Blood type B means our red blood cell membrane contains antigen B, but not antigen A. Blood type A b means our red blood cells contain both antigen A and antigen B.