How does the ABO blood group system work?
Group A means you only have the Group A antigen on your red blood cells and will recognize others such as Group B as foreign. Same goes for group B but opposite. Group AB is uniques because it has A and B antigens so therefore there is no possible blood type that would be recognized as foreign to the body. Thats why Group AB is the universal recipient (lucky bastards). Group O is the universal donor, they have no A or B antigens on the RBC and will elicit an immune response against anything that is not O Then you have to factor in the Rh Factor which is what makes your blood positive or negative.
