Well, the fetus is assumed to be RH positive and that means it contains red blood cells that contain the antigen D. Now, when these antibodies travel through the membrane of the placenta and into the bloodstream of the fetus, they will bind onto the antigen D proteins of the red blood cells of the fetus. And once down, they will destroy, they will lyse the cell. And when the cell breaks, when it licenses, it releases dangerous chemicals into the bloodstream of that fetus. And that can ultimately damage the organs of that fetus, including the brain and other organs. So we can see how as a result of our immune system trying to protect our body, it can actually damage that fetus during the process of pregnancy second time around. So once again to conclude, antigen A and antigen B, the antigens that determine our blood group, are not the only antigens that can be found on the membrane of red blood cells.