Idiotype-anti-idiotype network theory was proposed to explain immune regulation. In this context, the idiotype refers to:
- A The constant region of the heavy chain determining immunoglobulin class
- B The allotypic determinants encoded by polymorphic Ig heavy chain genes
- C The light chain variable region shared across multiple antibody clones
- D The unique antigen-binding site (hypervariable region) of an immunoglobulin molecule ✓
Explanation
The idiotype of an immunoglobulin refers to the unique antigenic determinants (idiotopes) located in the variable region — specifically the hypervariable complementarity-determining regions (CDRs) that form the antigen-binding site. According to Jerne's network theory, anti-idiotype antibodies (Ab2) recognize these unique binding-site determinants and can either suppress or stimulate the original B cell clone expressing that idiotype. This network regulates immune responses and forms the basis for anti-idiotype vaccine strategies. The constant region (Fc) encodes isotype/class, while allotypes are inherited polymorphisms in constant regions.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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