ABSTRACT
In addition to class and subclass categories, an immunoglobulin (Ig) can be defined by the presence of genetic markers termed allotypes. These markers are different in different individuals and are thus immunogenic when injected into individuals whose Ig lacks the allotype. Like the ABO blood group antigens, they are determinants which segregate within a species (the Ig of some members of the species have them, others do not). Allo-types are normally the result of small amino acid differences in Ig L- or H-chain constant regions. For example, the Km (Inv) marker is an allotype of human k L chains and is the result of a leucine versus valine difference at position 191. The Gm markers are allotypes associated with the IgG H chains. Allotypes are inherited in a strictly Mendelian fashion, and usually have no significance to the function of the antibody molecule, nor are they so immunogenic as to compromise their use in immunotherapy.
