Isotype

Isotypic determinants are constant-region determinants that collectively define each heavy-chain class and subclass and

(a) Isotypic determinants

(a) Isotypic determinants

Isotypic Determinants

Mouse IgG1

Mouse IgM

Mouse IgG1

Mouse IgM

(b) Allotypic determinants

(b) Allotypic determinants

Isotypic Determinant

Mouse IgG1 (strain A)

Mouse IgG1 (strain B)

Mouse IgG1 (strain A)

Mouse IgG1 (strain B)

(c) Idiotypic determinants

Idiotopes

Idiotopes

(c) Idiotypic determinants

Idiotopes

Idiotopes

Idiotypic Determinant

Mouse IgG1 against antigen a

Mouse IgG1 against antigen b

FIGURE 4-17

Mouse IgG1 against antigen a

Mouse IgG1 against antigen b

FIGURE 4-17

Antigenic determinants of immunoglobulins. For each type of determinant, the general location of determinants within the antibody molecule is shown (left) and two examples are illustrated (center and right). (a) Isotypic determinants are constant-region determinants that distinguish each Ig class and subclass within a species. (b) Allotypic determinants are subtle amino acid differences encoded by different alleles of isotype genes. Allotypic differences can be detected by comparing the same antibody class among different inbred strains. (c) Idiotypic determinants are generated by the conformation of the amino acid sequences of the heavy- and light-chain variable regions specific for each antigen. Each individual determinant is called an idiotope, and the sum of the individual idiotopes is the idiotype.

each light-chain type and subtype within a species (see Figure 4-17a). Each isotype is encoded by a separate constant-region gene, and all members of a species carry the same constant-region genes (which may include multiple alleles). Within a species, each normal individual will express all isotypes in the serum. Different species inherit different constant-region genes and therefore express different isotypes. Therefore, when an antibody from one species is injected into another species, the isotypic determinants will be recognized as foreign, inducing an antibody response to the isotypic determinants on the foreign antibody. Anti-isotype antibody is routinely used for research purposes to determine the class or subclass of serum antibody produced during an immune response or to characterize the class of membrane-bound antibody present on B cells.

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