Which mechanism primarily generates antigen receptor diversity during lymphocyte development?

Which mechanism primarily generates antigen receptor diversity during lymphocyte development?

• A. Somatic hypermutation
• B. V(D)J recombination
• C. Class switch recombination
• D. Germline gene duplication

Answer: (B)

Antigen receptor diversity during lymphocyte development is generated primarily by V(D)J recombination. This process randomly selects and joins variable (V), diversity (D), and joining (J) gene segments to form the variable region of the receptor genes in developing B and T cells. Enzymes like RAG1/2 introduce double-strand breaks, and TdT adds non-templated nucleotides at the junctions, creating junctional diversity. This happens before exposure to antigen, producing a vast pre-immune repertoire. After antigen exposure, somatic hypermutation and class switch recombination modify already-formed receptors or their effector regions, but they are not the primary source of initial diversity. Germline gene duplication is not how individual lymphocytes generate diverse receptors.

Antigen receptor diversity during lymphocyte development is generated primarily by V(D)J recombination. This process randomly selects and joins variable (V), diversity (D), and joining (J) gene segments to form the variable region of the receptor genes in developing B and T cells. Enzymes like RAG1/2 introduce double-strand breaks, and TdT adds non-templated nucleotides at the junctions, creating junctional diversity. This happens before exposure to antigen, producing a vast pre-immune repertoire. After antigen exposure, somatic hypermutation and class switch recombination modify already-formed receptors or their effector regions, but they are not the primary source of initial diversity. Germline gene duplication is not how individual lymphocytes generate diverse receptors.