Final answer:
A B cell ceases to produce its unique light chain upon differentiating into a plasma cell, following antigen activation and clonal expansion. Plasma cells are dedicated to secreting large amounts of antibodies before they become terminally differentiated and die. Memory B cells, on the other hand, survive to grant quicker, more robust secondary responses.
Step-by-step explanation:
A B cell stops creating its original light chain when it differentiates into a plasma cell. The process begins with the germ-line B cell undergoing V(D)J recombination facilitated by DNA recombinase, which randomly combines various V and J segments. This results in a vast diversity of light chains that can then be part of the B cell receptor (BCR). Upon encountering an antigen, the B cell binds to this antigen using its specific BCR, and this event triggers the activation and differentiation of the B cell.
The activated B cell then undergoes clonal expansion, and the daughter cells differentiate into plasma cells which produce large quantities of antibodies. These antibodies are secreted, have the same variable regions as the original BCR, and have the same antigen specificity. The plasma cells, now terminally differentiated, eventually die after a period of prolific antibody production.
Memory B cells also arise from the clonal expansion of an activated B cell, but they persist in the body and provide a faster and stronger secondary response upon re-encounter with the same antigen. During maturation in the bone marrow, an enormous diversity of B cell clones is generated, providing the capacity to recognize literally trillions of different antigens.