To what does the term plasma cell refer?

• A. A differentiated B cell that secretes antibodies
• B. An activated T cell that kills infected cells
• C. An antigen-presenting cell
• D. A macrophage

Answer: (A)

Plasma cells are the antibody-secreting factories of the immune system. They arise when a B lymphocyte encounters its specific antigen and receives help from helper T cells, then proliferates and differentiates. In this state, the cell shifts from presenting as a surface B cell to specializing in producing large amounts of immunoglobulins that circulate in blood and lymph to neutralize pathogens.

These cells are packed with rough endoplasmic reticulum and a prominent Golgi apparatus to support high-rate antibody synthesis. Their primary role is humoral immunity—providing targeted, soluble defenses against extracellular pathogens and toxins. They do not function mainly as cytotoxic effectors (that role belongs to activated T cells) nor as antigen-presenting cells (which include macrophages and dendritic cells). Macrophages, for example, are phagocytes that engulf pathogens rather than secrete antibodies.

So, the term plasma cell refers to a differentiated B cell that secretes antibodies.