IMMUNOLOGY - Roit A. - Mir 2000

Chapter 6. Antibodies and Cellular Receptors for Them

AMINO ACID SEQUENCE VARIATIONS AMONG ANTIBODY MOLECULES CAN BE ISOTYPIC, ALLOTYPIC, AND IDIOTYPIC

Isotypic variation. The genes encoding isotypic antibody variants are normally present in The Genome of all members of a given species. For instance, The Human Genome simultaneously contains the genes for γ1, γ2, γ3, γ4, μ, α1, α2, δ, ε, k, and λ chains, which are therefore classified as isotypes.

Allotypic variation. These variations reflect genetic differences between individuals of the same species, including polymorphisms within a given locus. For example, in humans, the IgG3 variant featuring a phenylalanine residue at position 436 of the γ3 chain—designated G3m(b°)—is not found in all individuals and thus represents an allotype. Allotypes most commonly differ in the constant region of heavy chains.

Idiotypic variation. The existence of different antibody idiotypes is driven by variations in the Amino acid sequences of variable domains, particularly within their hypervariable regions. These very regions determine the Specificity of the antibody's antigen-binding site. Individual (private) idiotypes are typically characteristic of distinct B-Cell clones. However, antibody idiotypes can occasionally be shared (cross-reactive or recurrent) among different B-cell clones.



Last update: 13/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

  • elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
  • editorial organization of content;
  • standardization of terminology in accordance with academic sources;
  • verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.