Which statement correctly distinguishes T cell receptor diversity from B cell receptor diversity?

• A. TCR diversity arises from VDJ recombination and pairing; BCR diversity includes VDJ recombination plus somatic hypermutation and class switching
• B. BCR diversity arises from VDJ recombination; TCR diversity from somatic hypermutation
• C. Both rely entirely on clonal expansion
• D. TCR diversity is created by antigen-dependent affinity maturation only

Answer: (A)

The key idea is how receptor diversity is produced differently in T cells and B cells. T cell receptors gain their vast repertoire mainly through gene rearrangement (VDJ recombination) of TCR segments and by pairing of the alpha and beta chains, creating many unique receptor specificities before encountering antigen. In contrast, B cell receptors (antibodies) start with VDJ recombination for heavy and light chains, but can further diversify after antigen exposure through somatic hypermutation in the variable regions and by class switch recombination in the constant region. This combination of mechanisms gives antibodies not only a wide range of specificities but also varying effector functions. TCRs do not undergo somatic hypermutation or class switching, so their diversity does not include those processes.