Blood groups and transfusions?

Question

Why does the antigen in the donors blood now agllutinate the recipiants blood...e.g. why can blood group 0 (which produces antibodies a and b) be transfused into people with blood groups A and B without coagulatiion occuring just as blood group AB (although producing no antibodies)can recieve blood from group A(with b antibodies) or B(with a antibodies)

Please read my question before you answer. The last three just continued to explain what was already in my question. Basically why can you not do the reverse in blood transfusions??

Answer 1

You (and the previous answerer) are somewhat confused, which is OK, this is a confusing topic.

Blood group A cells express an "A" protein on the cell surface.
Blood group B cells express a "B" protein on the cell surface.
Blood group AB cells express both an "A" protein and a "B" protein on the cell surface.
Blood group "O" cells have neither A nor B proteins on the cell surface.
Prior to a transfusion, there are no antibodies floating around. If "A" cells are given to an individual who does not naturally express A (i.e. either a "B" or "O" individual), the recipient's immune system will make antibodies against the "A" antigen which will ultimately results in agglutination of the foreign red blood cells that express "A" on the surface. "A" cells must be given to individuals who already express the "A" protein on the cell surface. In these individuals, the immune system is tolerized against the "A" protein and will not mount an antibody response against it.

So "O" is the universal donor because these individuals have neither the "A" or "B" antigens. Essentially, "O" blood is non-immunogenic, having neither of the two major antigens against which an immune response may be mounted.
"AB" is the universal recipient because these individuals already all tolerized against the "A" and "B" antigens.

The Rh blood group works the same way, though there are not "A" and "B" variants. An individual is either "Rh+" or "Rh-".

Understand? If not, send me an email and I can try to explain it a little better. Over the years, I have essentially lost the ability to speak to non-scientists in plain English!

[e-mail]

Answer 2

Type O blood does not have A or B ANTIGENS. Antigens are what trigger an immune response in the recipient of the transplant (e.g. antibodies are produced when antigens are present that are identified as not self.)

Type O blood from a donor therefore would not trigger an immune response in either an A, B, or AB recipient because it lacks antigens A and B. If you transfused type A blood into a recipient with type O, the type A ANTIGENS in the donor blood would trigger the type O recipient to produce A ANTIBODIES. (agglutination)

Answer 3

Blood group A has the anti-B antibodies

Blood group B has the anti-A antibodies

But the O negative blood cells being transfused into them have NEITHER A nor B antigens and so pass for okay for the time being.

Bear in mind that there are other minor antigenic groups which may eventually cause a reaction, but the AB

O (and the Rh) groups are most important.

A person with O blood has anti A and anti B in them, but the transfusion pack of O blood only has O blood cells inside. No anti A or anti B (it's been washed out).

So ... the patient with blood group AB has AB cells, no anti A and no anti B.

When you give them transfusion of group A cells (and no anti B) then they pass as OK

When you give them a transfusion of group B cells (and no anti A) then they pass as OK as well.

But if you gave AB to an A person (with anti-B) you get agglutination. Very bad.

[Edit]

The O blood in the transfusion pack has no A or B antigens. There are no anti-A or anti-B antibodies. If you transfuse this into someone of blood group A or B or AB, their antibodies will not find any antigens on the O blood and therefore will not agglutinate.

The O group person has anti-A and anti-B in their blood. If you transfuse them with group A blood (which has A antigens) it will react with anti-A and agglutinate (cause a transfusion reaction). If you transfuse them with group B blood (which has B antigens) it will react with the anti-B and agglutinate. If you transfuse then with group AB blood (which has A and B antigens) it will react with both sets of antibodies and agglutinate. Thus O can donate to any other ABO blood group but cannot accept anything else but blood group O.

Blood group AB has A and B antigens on the blood cells. There are no antibodies in the transfusion packs or in the patient with blood group AB. There being no antibodies, the patient can receive blood of group A, B, O or AB without reaction. If you try to donate group AB blood to a blood group A person, the B antigens will react and cause agglutination. If you try to donate it to a group B person, the A antigens will react. If you transfuse it into a group O person, they have both sets of antigens and anti-A and anti-B will cause the agglutination/transfusion reaction. Hence AB is a universal acceptor.

And to correct a minor point in vt500ascott's answer, the blood group O, A and B people actually do have the antibodies floating about in their circulations prior to transfusion. We seem to get exposed to the antigens in our food somehow. I'm not sure what foods it is that does it. This does not hold true for the Rhesus blood group and the Rh-ve population remain devoid of anti-D until they are transfused with Rh+ve blood generally.