system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does the body respond to someone else's DNA during a blood transfusion?

Do the red blood cells "convert" or do they sort of die off and get replaced? How does the body not really reject the blood like you hear about with transplant surgeries? I am a bit confused. Thanks!
gpt
Red blood cells don't have nuclei. The only way our blood is meaningfully differentiated from another persons in a way the immune system would pick up is via proteins that dot the cells' surface. There are a few different types (A and B and another one called the Rhesus factor are the ones we care about) and they're what determine your blood type. You can only get blood from someone with at least some of the same proteins as you (or no proteins at all which is O type). Usually, other types of blood cells like white blood cells are separated out and not transfused.