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. And finally, blood type O means we have neither antigen A or antigen B on the red blood cell of the membrane of our red blood cell. Now, the next question is what exactly is the big deal? And what's the relationship between these groups and our immune system?