https://doi.org/10.1351/goldbook.12861
Antigen, present in some but not all individuals of a particular species, that arises from polymorphisms at the major histocompatibility complex (MHC) loci and stimulates intense reactions to allograft tissues from other individuals of the same species that do not produce it.
Note: The human ABO blood group system antigens and Rhesus (Rh) factor are important examples of alloantigens.