What are T cells primarily responsible for?

• A. Antibody production
• B. Cell-mediated immunity and activating B cells
• C. Oxygen transport
• D. Phagocytosis

Answer: (B)

T cells coordinate the adaptive immune response, driving the cell-mediated arm and helping B cells produce antibodies. They recognize antigens presented by APCs on MHC molecules, with helper T cells releasing cytokines that activate B cells to become plasma cells that secrete antibodies, while cytotoxic T cells directly kill infected or abnormal cells. This combination—cell-mediated immunity plus activating B cells—best captures what T cells do. Antibody production is carried out by B cells, not T cells, so that part isn’t correct. Oxygen transport is the job of red blood cells, and phagocytosis is performed by phagocytes such as macrophages and neutrophils.