What is the primary target of cell-mediated immunity?

• A. Extracellular pathogens
• B. Intracellular pathogens
• C. Bacteria in body fluids
• D. Allergies

Answer: (B)

Cell-mediated immunity primarily targets intracellular pathogens, which include viruses and some bacteria that reside within host cells. This immune response is facilitated mainly by T lymphocytes, particularly cytotoxic T cells, which are adept at identifying and destroying infected cells.

When an intracellular pathogen infects a cell, it often alters the proteins produced by that cell. These changes can be detected by cytotoxic T cells, which recognize specific antigens presented on the cell surface via Major Histocompatibility Complex (MHC) molecules. Upon recognizing an infected cell, cytotoxic T cells can initiate a response that leads to the destruction of the compromised cell, thereby eliminating the intracellular threat.

This mechanism is crucial because it addresses pathogens that have evaded detection by antibodies and remain hidden within cells, making them inaccessible to humoral (antibody-mediated) responses that primarily target extracellular pathogens. By effectively carrying out cell-mediated immunity, the immune system can control and eliminate infections that would otherwise persist and potentially cause widespread harm.