Which process underlies the generation of antibody diversity by rearranging gene segments?

Which process underlies the generation of antibody diversity by rearranging gene segments?

• A. Clonal expansion
• B. Somatic hypermutation
• C. Class switching
• D. V(D)J recombination

Answer: (D)

Antibody diversity comes from rearranging the gene segments that encode the variable regions of immunoglobulins. In developing B cells, the variable regions for the heavy and light chains are created by joining different V, D, and J segments (heavy chain uses V-D-J; light chain uses V-J). This V(D)J recombination is executed by RAG enzymes at recombination signal sequences, generating many possible combinations and further increasing diversity at the junctions. This rearrangement happens before the antibody is expressed and lays the foundation for a vast repertoire of antigen specificities. Clonal expansion, by contrast, just amplifies B cells that have already been activated, increasing the number of cells with a given specificity rather than creating new specificities. Somatic hypermutation introduces point mutations in the already rearranged variable regions after activation to improve affinity, but it does not rearrange the gene segments. Class switching changes the constant region of the heavy chain and alters effector function without changing the antigen-binding site.

Antibody diversity comes from rearranging the gene segments that encode the variable regions of immunoglobulins. In developing B cells, the variable regions for the heavy and light chains are created by joining different V, D, and J segments (heavy chain uses V-D-J; light chain uses V-J). This V(D)J recombination is executed by RAG enzymes at recombination signal sequences, generating many possible combinations and further increasing diversity at the junctions. This rearrangement happens before the antibody is expressed and lays the foundation for a vast repertoire of antigen specificities.

Clonal expansion, by contrast, just amplifies B cells that have already been activated, increasing the number of cells with a given specificity rather than creating new specificities. Somatic hypermutation introduces point mutations in the already rearranged variable regions after activation to improve affinity, but it does not rearrange the gene segments. Class switching changes the constant region of the heavy chain and alters effector function without changing the antigen-binding site.