Which lymphocyte is primarily involved in cell-mediated immunity?

• A. B-cells
• B. Helper T-cells
• C. Memory T-cells
• D. Cytotoxic T-cells

Answer: (D)

Cytotoxic T-cells are primarily involved in cell-mediated immunity because they are responsible for directly attacking and destroying infected or cancerous cells. This process is crucial for the body's defense mechanism against pathogens that reside within host cells, such as viruses and some bacteria.

The role of Cytotoxic T-cells involves recognizing antigens presented on the surface of infected cells and inducing apoptosis (programmed cell death) in those cells, effectively eliminating the threat and preventing the spread of infection.

Although other types of lymphocytes, such as Helper T-cells, do play important roles in the immune response by assisting other immune cells and facilitating the production of antibodies, their function is more related to the coordination of the immune response rather than the direct destruction of infected cells. Memory T-cells, on the other hand, serve to provide long-term immunity by remembering past infections but are not actively involved in the immediate response during the initial exposure to pathogens. B-cells are primarily responsible for humoral immunity, producing antibodies that circulate in the blood and target extracellular pathogens.