Well, let's begin with blood type A. So, in an individual that has blood type A, what that means is on chromosome nine of that individual, they have a gene that codes for antigen A. And that means all the red blood cells will contain this particular glycoprotein antigen A. Now the immune system, because these are self antigens, that means the immune system will not produce any antibodies against the antigen A glycoprotein. But because the red blood cells of blood type A individual do not have antigen B proteins, what that means our immune system will begin producing antibodies against that particular antigen B. And so if that individual with blood type A ever receives blood type B, for example, the red blood cells of the blood type B individual will be destroyed as a result of the presence of those antibodies against antigen B.