system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does giving someone a transfusion of my blood to someone not give them my immunity?

I keep up with all my vaccines and even have Hep A and B covered due to working in a hospital. But I was curious as to the reason I could not pass on my immunity to another via a blood transfusion. Is it simply because the blood cells are incapable of passing on what they have learned to the new host body?
gpt
The problem here is the white blood cells, or WBCs. They have a nasty tendancy to attack everything they don't recognize. When you get a transfusion, the blood is taken from the donor and put into the recipient's body - meaning they'll start going berserk and attacking everything in sight until subdued. Riot time! It doesn't really matter in small quantities, as the recipient's WBCs will quickly overpower the donor's WBCs. But in the case that you are giving a lot of blood or the recipient has a weak immune system (aka is *immunocompromised*), the donor's WBCs will wreck havoc for a while. Not good. 

To prevent this, there are a few means for getting rid of the WBCs. You can use a filter / centrifuge to physically get rid of them, or you can irradiate the blood to kill the WBCs off. This is possible because only WBCs have nuclei (DNA) that can be damaged by the irradiation. Red blood cells (RBCs) and platelets (plts) do not, and so are unaffected. Since we are generally doing transfusion for the RBCs this works out pretty well.

And of course, no WBCs means no immunity, so nothing gets transferred in the end.