I just went for a blood test and came back knowing I have type AB blood. However my blood can only be used by other people who share the same blood type with me but not others, while other people with type O, A, B they can share the blood with me. Why is that so?
In: Chemistry
Your immune system’s way of recognizing “friend vs foe” boils down to basically “known vs unknown”. Your white blood cells generally don’t react to chemicals that they know (because they are supposed to be your body), but react to chemicals they never encountered (because they are likely to be a pathogen). We use the word “antigen” to mean “something that causes immune reaction”.
There is some variation in the way some chemicals in your red blood cells are made. As far as we know, they serve no evolutionary purpose, but there was also never any evolutionary pressure to remove thise variation. The “antigen A” and “antigen B” are just names for chemicals that some people have on their blood cells, and some people don’t. Your cells have both, so if you share your blood with a person that doesn’t have one of them, their immune system will recognize them as a threat and will destroy your blood cells. However if yout get blood from them, there will be no problem, as your immune system will be OK whethere these antigens are there or not. This makes you an universal recipient, while people with type-0 (neither antigen present) are universal donors.
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