During affinity maturation in germinal centres, B cells undergo somatic hypermutation of their variable region genes. Which enzyme is primarily responsible for initiating this process?
- A Terminal deoxynucleotidyl transferase (TdT)
- B Activation-induced cytidine deaminase (AID) ✓
- C RAG1/RAG2 recombinase complex
- D DNA-dependent protein kinase (DNA-PKcs)
Explanation
Activation-induced cytidine deaminase (AID) converts cytosine to uracil in single-stranded DNA of immunoglobulin variable region genes during B cell activation in germinal centres. This initiates a mutational process that introduces point mutations, increasing or decreasing antigen-binding affinity. B cells with increased affinity receive survival signals (positive selection), while low-affinity cells undergo apoptosis. AID also mediates class-switch recombination. RAG1/RAG2 is responsible for V(D)J recombination during B cell development (not affinity maturation), and TdT adds N-nucleotides during V(D)J joining.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.