Final answer:
B cells that fail to create mu chains die by apoptosis, a process necessary for eliminating cells that cannot mature and produce necessary immunoglobulins, potentially leading to immunodeficiencies such as XLA.
Step-by-step explanation:
B cells that fail to create mu chains die by apoptosis. During B cell development, the production of mu chains is crucial for the formation of the B cell receptor, which is necessary for the further maturation of B cells. Without the mu chains, the B cells cannot proceed to the next stage of development, which leads to a halting of B-cell maturation and differentiation processes.
Impaired B cells that cannot produce immunoglobulin molecules are unable to fight external pathogens effectively, resulting in conditions such as X-Linked Agammaglobulinemia (XLA), where B-cell maturation is interrupted. In individuals with XLA, the lack of functional Btk due to mutations results in the failure of B-cell development at the pre-B-cell stage and these defective cells undergo apoptosis.