Discussion
Pick the correctly matched pairs.
P. Immature B cells - Terminal deoxynucleotidyl transferase
Q. Activated B cells - Class switching
R. Pre B cells - Surrogate light chain
S. Mature B cells - Recombination activating gene 1
Answer: B
The correctly matched pairs are Q and R.
Q is correct: once activated by antigen and T-cell help, B cells undergo class switching (for example from IgM to IgG, IgA or IgE) in germinal centres. R is correct: pre-B cells pair their newly rearranged μ heavy chain with the surrogate light chain (VpreB and λ5) to form the pre-B cell receptor.
P is wrong because terminal deoxynucleotidyl transferase adds N-nucleotides during heavy-chain rearrangement in pro-B cells, and is switched off by the immature stage. S is wrong because the recombination activating genes RAG1 and RAG2 work in developing B cells and are turned off in mature B cells. So pairs containing P or S are excluded.
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