Final answer:
Upon successful rearrangement of light chain genes, the small pre-B cell becomes an immature B cell, signifying a critical phase in B cell development and antibody production.
Step-by-step explanation:
When rearrangement of the light chain genes stops, the small pre-B cell becomes an immature B cell. This is a critical step in B cell development that involves the maturation of germ-line B cells through a process called V(D)J recombination, where DNA recombinase selectively excises V (variable) and J (joining) segments from the light chain gene. These segments are then spliced together to create a unique variable region that is capable of binding different antigens.
B cell maturation depends on successful gene rearrangement. If this process is disrupted, such as in agammaglobulinemia (XLA) where Btk is defective, B cells cannot mature past the pre-B cell stage. However, when successful, maturity leads to the production of antibodies, each with a unique antigen-binding capability due to the vast possible combinations of VJ arrangements. Once activated, these B cells proliferate and differentiate into plasma cells, which are essentially antibody-secreting factories.