What is a distinguishing feature of a pre-B cell?

What is a distinguishing feature of a pre-B cell?

• A. Complete IgM on the surface
• B. Presence of CD21 antigen
• C. μ chains in the cytoplasm
• D. Presence of CD25 antigen

Answer: (C)

In B cell development, the pre-B cell stage is defined by the production of the μ heavy chain and its presence inside the cell, not on the surface. After heavy chain rearrangement, the μ chain is synthesized in the cytoplasm and pairs with surrogate light chains to form the pre-B cell receptor, which sends signals that drive further maturation and switch the cell to rearranging the light chain. This intracellular μ heavy chain reflects that the cell has passed the pro-B stage but hasn’t yet become capable of expressing a complete surface immunoglobulin. That’s why cytoplasmic μ chains are the distinguishing feature of a pre-B cell. By contrast, surface IgM appears later in immature B cells, CD21 marks mature B cells, and CD25 is an activation marker (not specific to the pre-B stage).

In B cell development, the pre-B cell stage is defined by the production of the μ heavy chain and its presence inside the cell, not on the surface. After heavy chain rearrangement, the μ chain is synthesized in the cytoplasm and pairs with surrogate light chains to form the pre-B cell receptor, which sends signals that drive further maturation and switch the cell to rearranging the light chain. This intracellular μ heavy chain reflects that the cell has passed the pro-B stage but hasn’t yet become capable of expressing a complete surface immunoglobulin. That’s why cytoplasmic μ chains are the distinguishing feature of a pre-B cell. By contrast, surface IgM appears later in immature B cells, CD21 marks mature B cells, and CD25 is an activation marker (not specific to the pre-B stage).