I read in my biology textbook that an antigen is any foreign microbe that enters the blood. Antibodies are produced by the body to fight against the antigens. But blood group AB has antigens A and B but no antibodies. Then how does the body fight against the antigens?

Question

anonymous · Answer

The antibodies are coated on the cell to let white cells recognise friend from foe.
Also antigen doesnt have to be in the blood

anonymous · Answer

Your textbook isn't explaining it completely. An antigen is any small piece of a  protein, carbohydrate, lipid, or nucleic acid that B-cells (a kind of white blood cell) can recognize as foreign. The antigens on foreign microbes are bits of molecules in their cell membrane or cell wall. B cells make proteins called antibodies that bind the antigens. B-cells don't care about the microbe; they just make antibodies that bind the antigen. Since the antigens are part of the microbe though, the antibodies stick to them.
     Our bodies go thru a time before we are born when all the B-cells that can attack our own cells are killed. The B-cells that can bind to the A, B, and O antigens in your blood are killed then. BUT, if you get a blood transfusion after you are born, and the blood is a different type, that means it has antigens your body can recognize. Your B cells attack the foreign blood.