Which type of lymphocyte primarily functions in the destruction of infected cells?

• A. Memory B cells
• B. Plasma cells
• C. Active T cytotoxic cells
• D. T helper cells

Answer: (C)

Active T cytotoxic cells are critical components of the adaptive immune response, specifically tasked with identifying and destroying cells that have been infected by viruses or other intracellular pathogens. These cells recognize infected cells through specific surface markers, often linked to the presence of abnormal proteins or antigens displayed on the infected cells' surface. Upon recognition, T cytotoxic cells release molecules that induce apoptosis (programmed cell death) in the infected cells, effectively eliminating the source of infection.

This direct method of cell destruction distinguishes T cytotoxic cells from other lymphocyte types. Memory B cells and plasma cells are primarily involved in the production of antibodies rather than direct cell killing. Memory B cells retain information about previous infections to mount a quicker response upon re-exposure, while plasma cells secrete antibodies that help neutralize pathogens and mark them for destruction. T helper cells play a supportive role in the immune response by assisting other immune cells but do not directly kill infected cells. They activate B cells and enhance the function of T cytotoxic cells among others but do not engage in direct cytotoxicity themselves. Thus, the role of active T cytotoxic cells in directly targeting and destroying infected cells establishes their importance in the immune response to intracellular infections.