B-cell effector differentiation: Which type of B cell acts like an antibody factory, secreting immunoglobulins identical in specificity to the original B-cell receptor (BCR) that recognized the antigen?

Introduction / Context:
Upon antigen encounter, B cells can differentiate into two main fates: plasma cells that secrete antibodies and memory B cells that provide rapid responses to future exposures. Understanding this division is central to vaccine design and serology.

Given Data / Assumptions:

• B-cell receptor (BCR) specificity dictates the antibodies produced after differentiation.
• Helper T-cell signals and germinal center reactions enhance affinity and class-switching.
• We are asked to identify the antibody-secreting effector cell.

Concept / Approach:
Plasma cells are terminally differentiated B cells specialized for high-rate antibody secretion. They retain the antigen specificity of the original BCR through identical variable regions, though the constant region may change by class-switch recombination (e.g., IgM to IgG).

Step-by-Step Solution:

Verification / Alternative check:
Serum electrophoresis and ELISPOT assays detect abundant immunoglobulin secretion from plasma cells; histology shows plasma cells in bone marrow and mucosae after immunization.

Why Other Options Are Wrong:

• T cells: provide help or cytotoxicity, not bulk antibody secretion.
• Memory cells: primed for future responses but secrete little antibody at rest.
• Macrophages: phagocytes and antigen-presenting cells, not antibody producers.

Common Pitfalls:
Confusing “memory” with “effector” roles; memory improves speed next time, plasma cells produce antibodies now.

Final Answer:
Plasma cells