An antigen that incites antibody production in members of the same species.
An antigen that forms a natural component of an individual’s tissues. Thus the antigens of the HL-A system are isoantigens, as are the agglutinogens of the different ‘blood groups.
A substance present in certain individuals that stimulates antibody production in other members of the same species but not in the donor (e.g., blood group isoantigens that are harmless to the donor but may produce severe antibody response in a recipient of a different blood group or type).