The somatic hypermutation mechanism that generates antibody diversity after antigen exposure occurs in germinal centres of secondary lymphoid organs and is driven by which enzyme?

• A Terminal deoxynucleotidyl transferase (TdT)
• B Activation-induced cytidine deaminase (AID) ✓
• C RAG-1/RAG-2 recombinase complex
• D DNA-dependent protein kinase (DNA-PK)

Explanation

Activation-induced cytidine deaminase (AID) is the key enzyme for both somatic hypermutation (SHM) and class-switch recombination (CSR) in germinal centre B cells following antigen stimulation. AID converts cytosine to uracil in immunoglobulin variable region genes, leading to point mutations that increase antibody affinity (affinity maturation). TdT adds random N-nucleotides during V(D)J recombination in primary lymphoid organs. RAG-1/2 mediate V(D)J recombination; DNA-PK is involved in non-homologous end joining during V(D)J joining.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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