system
Given the following post, respond as if you're commenting on Reddit:
human
What is the difference between blood types and why do our bodies only accept the correct type?
gpt
Biologically, ABO blood types are just seen as different combinations of sugars attached to some of the proteins within red blood cell membranes. The reason mismatching is problematic is because your body will initiate an immune response against the donor blood because the blood type is still an antigen. You don't attack your own cells because there is a process during lymphocyte (white blood cells that handle specific immunity) maturation, that will cause any cell that reacts too early (i.e. activates while still in the thymus or bone marrow) to die.

ABO however are not the limit of blood types. Technically there are *hundreds* of different blood groups.