Isoantibodies
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Isoantibodies, formerly called alloantibodies, are antibodies produced by an individual against isoantigens produced by members of the same species. 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.
One common example is the isohaemagglutinins, which are responsible for blood transfusion reactions.[1] This may subjectively differ from the term 'natural' antibodies, or simply 'antibodies', as the former seem to arise from genetic control without apparent antigenic stimulation whereas the latter arise due to antigenic stimulation.
A protein or other substance, such as histocompatibility or red blood cell antigens, that is present in only some members of a species and therefore able to stimulate isoantibody production in other members of the same species who lack it. When injected into another animal, they trigger an immune response aimed at eliminating them. Therefore, it can be thought of as an antigen that is present in some members of the same species, but is not common to all members of that species. If an alloantigen is presented to a member of the same species that does not have the alloantigen, it will be recognized as foreign. They are the products of polymorphic genes.[2]