In the case of the species Homo sapiens, for example, there are a significant number of antigens that are different in every individual.
When antigens from another individual are introduced into another's body, these isoantibodies immediately bind to and destroy them.
When injected into another animal, they trigger an immune response aimed at eliminating them.
The anti-A or anti-B isoantibodies or both (also called isohaemagglutinins) are produced by an individual against the antigens (A or B) on the RBCs of other blood groups.
Anti-A and anti-B antibodies (called isohaemagglutinins), which are not present in human babies, appear in the first years of life.