Why Can Blood types AB receive blood from everyone?

Question

Why can blood types AB positive receive blood from any other blood type but no other blood type can receive blood from every other blood type.

Answer 1

If you are only considering the ABO blood group system then Group AB can receive blood from group A or B or O since group AB has no antibodies in the plasma (against A or B) to react with the antigens on the donor red blood cells.

Group O can  donate blood to group A or B or AB since on the red blood cells of group O there are no antigens for the antibodies in the recipient plasma to react to.

However, another important blood group is the Rhesus factor which has to be taken into account

Answer 2

Blood types are a special case in immunology in that you make antibodies against whatever A or B antigens you don't possess.

A person with type A blood naturally makes anti-B antibodies.

A persone with type B blood naturally makes anti-A antibodies.

Type O individuals, because they lack both A and B antigens, produce both anti A and anti B antibodies.

AB individuals, because they possess both A and B antigens, make no antibodies against A or B.

So, type AB people can be transfused regardless of the ABO type of the donor.

Answer 3

Blood typing is based on proteins that the red blood cells have in their membranes.  A person can have neither A nor B, in which case they are considered type O.  The two types of proteins that the cells can have are called (obviously) A and B.  If a person with neither type of protein receives blood from a person with either or both of the proteins, the recipient's body will reject it, because his/her immune system will "see" the proteins, identify them as 'non-self' and attack the cell with them.

A person with AB blood already has both proteins, so can receive blood from someone with type O, type A, type B or type AB blood.  That's why s/he is called the universal receptor.  However, s/he can only donate blood to someone who also has AB blood.

Alternatively, a person with type O blood can only receive blood from someone with type O, but can donate it to any type - so, is the universal donor.