>>11923270Blood type is determined by the presence of antigens on your red blood cells. A healthy immune system will only generate leukocytes(Immune system response cells) tolerant to the antigens of its own body, called self-antigens. Consider the antigens on your red blood cells as self antigens.
An example
Type A blood has Type A self-antigens present on the blood cell. An individual with type A blood will not produce immune cells that recognize that Type A self antigen, so there is no immune response against it.
If someone with Type B blood were to receive type A blood in a transfusion, their immune system would not be tolerant to the type A antigens and so would create an immune response against those blood cells, to damaging effect.
Type A has type A antigens
Type B has type B antigens
Type AB has type A and type B antigens
Type O has no type A or type B.
You can see how someone with type AB is a "universal recipient" since their immune system tolerates all blood types (Notwithstanding + or -, but it works the same way) and type O is called "universal donor" because their blood doesn't cause an immune response in anybody.
Does that help? I really shouldn't spoonfeed you, you should go get a degree in biology if this kind of thing is genuinely interesting to you.
