system
Given the following post, respond as if you're commenting on Reddit:
human
What happens when someone gets a blood transfusion of the wrong blood type?
gpt
The donor cells have antigens on them (either A, B, or AB, plus the Rh factor if present) that cause the recipient's body to treat them as foreign.  This results in the recipient's own antibodies (anti-A, anti-B, or anti-Rh) to attack the donor blood cells.  The cells are hemolyzed (they get broken open), causing the reaction listed by other posts, namely kidney failure.

Yay for phlebotomy!