Kuby Immunology has the following printed in its glossary:
Isotypic determinant is an antigenic determinant within the immunoglobulin constant regions that is characteristic of a species.
I don't understand the last part. Does it mean that the antigenic determinants for a class of antibodies is the same in all members of a species except for minor variations that are represented by allotypic determinants? Does it also mean that an isotype, when introduced from organism 1 to organism 2, will stimulate the production of its corresponding anti-isotype only when Organism 2 belongs to a different species?
1). Yes, exactly. 2). Yes. If organisms 1 and 2 belong to the same species, there will be no anti-isotype Abs.