Which immune cells are primarily responsible for cell-mediated immunity?

• A. B-cells
• B. Macrophages
• C. T-cells
• D. Natural killer cells

Answer: (C)

Cell-mediated immunity is primarily governed by T-cells, which play a crucial role in the immune response by directly attacking infected cells, cancer cells, and other cells that may pose a threat. T-cells can be subdivided into different types, including cytotoxic T-cells and helper T-cells. Cytotoxic T-cells are responsible for identifying and destroying cells that display foreign antigens, while helper T-cells facilitate and enhance the immune response by activating other immune cells.

In contrast, B-cells primarily function in humoral immunity, producing antibodies that bind to antigens outside of cells. Macrophages are important for phagocytosis and act as antigen-presenting cells, but they do not directly mediate cellular responses like T-cells do. Natural killer cells also play a role in innate immunity by targeting and destroying compromised cells, particularly those infected by viruses or transformed by cancer, but their action is not as specific or adaptive as that of T-cells.

Thus, the primary responsibility for cell-mediated immunity relies on the specialized functions and actions of T-cells, making this choice the correct answer.