Cellular immunity primarily mediated by?

• A. B lymphocytes and antibodies.
• B. Complement system.
• C. Neutrophils and macrophages.
• D. T lymphocytes and their interactions with infected cells and antigen-presenting cells.

Answer: (D)

Cellular immunity is driven by T lymphocytes. These cells recognize antigens only when they’re displayed by antigen-presenting cells on MHC molecules. Cytotoxic T cells (CD8+) kill infected cells by detecting viral or other intracellular peptides presented on MHC I, while helper T cells (CD4+) coordinate the response by activating cytotoxic T cells, macrophages, and other immune components and by assisting B cells in some contexts. Antigen-presenting cells are essential because they process and present antigens to T cells, enabling their activation and targeted response. This distinguishes cellular immunity from humoral immunity, which is mediated by B lymphocytes and antibodies. While the complement system and phagocytes like neutrophils and macrophages contribute to defense and can support adaptive responses, the primary mediator of cellular immunity is the T cell–driven interaction with infected cells and APCs.