Which cell type is primarily responsible for cell-mediated immunity?

• A. B-Lymphocytes
• B. Platelets
• C. T-Lymphocytes
• D. Erythrocytes

Answer: (C)

Cell-mediated immunity is driven by T lymphocytes. This branch targets cells infected with intracellular pathogens and cancer cells, where antibodies can’t reach. Antigens from inside a cell are presented on its surface by MHC molecules; cytotoxic T cells recognize these with MHC I and destroy the infected cell by releasing perforin and granzymes, halting the pathogen’s ability to replicate. Helper T cells recognize antigens on MHC II presented by antigen-presenting cells and secrete cytokines that boost the overall response, activating more T cells and macrophages to help clear the infection. B lymphocytes, by contrast, are the main players in humoral immunity through antibody production against extracellular invaders. Erythrocytes and platelets don’t play primary roles in immune defense. So the T lymphocytes are the primary drivers of cell-mediated immunity.