When an organ is replaced with someone else’s, the body needs immunosuppressants because of the foreign object now in the body. Why is the same not true for a blood transfusion?

Question

Basically title! I was wondering about this. Thanks!

In: 144

Answer 1

Some patients with reduced immune system needs Irradiated blood bags (red blood cells/platelets).
The minimum dose of radiation for the blood bag is (here in Germany) at least 25 gray.

Due to the production of the blood bag, a few white blood cells can still permeate the filter (from the whole blood bag) into the final product.

If you transfuse this blood bag to an patient with a low or incompetent immune system a “graft-versus-host-disease” can occur.

Answer 2

Blood Bank Scientist here.

Because in all but the most dire of emergency situations, we crossmatch blood for compatibility which helps to minimize the chances that the recipient will have a clinically significant immune response. We take a sample of patient plasma which contains their antibodies, mix it with the cells we intend to donate, then we look for a reaction usually using a card with a special gel in it. The gel allows cells that don’t have antibodies stuck to them, to pass, while holding antibody bound cells in place. When we look at the gel if we see all the cells at the bottom of the well the blood is deemed compatible, if we see cells anywhere else in the gel, it’s incompatible and we start looking into why, which is a whole different topic that goes beyond ELI5.

WRSaunders mentioned in another comment that red cells don’t live very long, while this is true, this doesn’t prevent an immune response. It’s still critically important that the blood we give out is compatible, the wrong blood can kill you in a matter of hours. What this does mean however is that we don’t have to consider the long term ramifications of the immune system constantly attacking because of small incompatibilities, organs are crossmatched to a much more stringent standard than blood but getting a 100% match is impossible. This isn’t a problem when you only need the donation for a short time until your body recovers it’s own cells, but if you need the donation over the long term to live, you need to get those low level immune responses in check or they’ll slowly degrade that organ.