When does genetic rearrangement for the antibody light chains occur during B-cell development?

• A. Before the pre-B cell stage
• B. Not until the cell becomes a mature B cell
• C. When the B cell becomes a plasma cell
• D. As the cell becomes an immature B cell

Answer: (D)

Light chain gene rearrangement happens after the heavy chain has been successfully produced and tested, as the B cell progresses through development. In the bone marrow, developing B cells first rearrange the heavy chain genes; when a productive heavy chain is made, the cell becomes a pre-B cell and then a checkpoint allows light chain rearrangement to begin. The light chain genes (kappa first, then lambda if needed) undergo VJ recombination to produce a functional light chain that can pair with the heavy chain. Once a productive light chain pairs with the heavy chain, the B cell expresses surface immunoglobulin M (IgM) and becomes an immature B cell. This immature stage is when the B cell has a complete B cell receptor and can undergo selection before maturing further.

So, light chain rearrangement is best described as occurring as the cell becomes an immature B cell. It would not occur before the pre-B cell stage (that’s when the heavy chain is first rearranged), nor only at the mature B cell stage or later at the plasma cell stage.