B cells are primarily responsible for which aspect of immunity?

• A. Antibody-mediated immunity
• B. Cell-mediated immunity
• C. Oxygen transport
• D. Phagocytosis

Answer: (A)

B cells drive antibody-mediated (humoral) immunity. When a B cell encounters its specific antigen and receives help from helper T cells, it turns into a plasma cell that secretes antibodies into body fluids. These antibodies bind to pathogens or toxins, neutralize them, prevent them from entering cells, and flag them for destruction by other parts of the immune system through processes like opsonization and complement activation. This is distinct from cell-mediated immunity, which is orchestrated by T cells and focuses on infected cells and other intracellular threats. Phagocytosis is carried out by phagocytes like macrophages and neutrophils, and oxygen transport is a function of red blood cells, not immune lymphocytes.