Which immune response fights infections inside cells?

• A. Humoral immunity
• B. Antibody production
• C. Inflammatory response
• D. Cell-mediated immunity

Answer: (D)

Cell-mediated immunity is the part of the immune system that targets pathogens hiding inside our own cells. Antibodies travel in the blood and body fluids, so they’re great at neutralizing pathogens outside cells, but they can’t reach pathogens that are inside infected cells. T cells step in here: cytotoxic T cells recognize infected cells presenting viral or intracellular bacterial antigens on MHC class I molecules and directly kill those cells to stop the pathogen from spreading. Helper T cells guide and enhance this response, and natural killer cells provide early, rapid killing before the specific T-cell response develops. In contrast, antibodies (humoral immunity) and the inflammatory response aren’t specialized to eliminate infections already inside cells, which is why cell-mediated immunity is the best match for this scenario.