Which arm of the immune system involves T lymphocytes and cell-mediated immunity?

• A. Innate immune system
• B. Humoral immunity
• C. Adaptive immune system (T cells)
• D. Complement system

Answer: (C)

Cell-mediated immunity is carried by T lymphocytes, which are central to the adaptive immune response. T cells recognize antigens presented by other cells and act directly to kill infected cells or coordinate other immune cells through signaling molecules. This is different from antibody-driven (humoral) responses that involve B cells producing antibodies to neutralize pathogens in body fluids, and from innate defenses that provide immediate, non-specific protection via barriers, phagocytes, NK cells, and the complement system. So the arm that specifically involves T lymphocytes and their cell-eliminating, cell-signaling activities is the adaptive immune system.