Blood group antibodies are not stimulated by one's own blood group antigens. However, they are produced due to the cross reactivity of some surface antigens present on some of our own intestinal microflora. read more
AB type of blood indicates the present of antigens A and B both,which are actually some glycoproteins and glycolipids which if bound to its antibodies,generate the immune action and eventually lysing/killing it. read more
Hence people of blood group O, lacking blood-group antigens A and B, will not have become tolerant to them, and will have antibody-producing cells capable of producing antibodies against them, should they encounter them in an incorrect blood transfusion. read more