Most people are familiar with A, B, O, and Rh red cell antigens, as they are the most significant. Completely separate from this “blood group system” there are many other potentially antigenic molecules present on the red cell membrane.

These antigens are mainly significant in regards to blood transfusions.

People generally don’t create antibodies against antigens that they have on their own cells.

If someone receives blood containing an antigen that isn’t present on their own cells, and their body has already created antibodies against this “foregin” antigen, this can cause a hemolytic transfusion reaction (the transfused blood cells will rupture in the recipient), which can be fatal.