Which of the following is a distinguishing feature of B cells?

• A. Act as helper cells
• B. Active in phagocytosis
• C. Presence of surface antibody
• D. Able to kill target cells without prior exposure

Answer: (C)

Presence of surface antibody is what sets B cells apart. B cells carry membrane-bound immunoglobulin that acts as their receptor, allowing them to recognize specific antigens directly and become activated. This surface antibody is the defining feature because it enables the humoral immune response, with B cells expanding and differentiating into plasma cells that secrete antibodies. Other described roles belong to different cells: helper functions are typical of helper T cells, phagocytosis is done by macrophages and neutrophils, and killing of target cells without prior exposure is a function of cytotoxic T cells or NK cells.