Cell mediated immunity is
**Core Concept**
Cell-mediated immunity is a type of immune response that involves the activation of T lymphocytes (T cells) to defend against infections and foreign substances. This process is crucial for eliminating intracellular pathogens, such as viruses and bacteria, and for preventing tumor growth.
**Why the Correct Answer is Right**
Cell-mediated immunity is primarily mediated by T cells, which recognize and respond to antigens presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APCs). Activated T cells can differentiate into various effector cells, including cytotoxic T cells and helper T cells, which orchestrate the immune response. The interaction between T cells and APCs leads to the production of cytokines, which amplify the immune response and recruit other immune cells to the site of infection.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cell-mediated immunity is not solely dependent on the production of antibodies, which is characteristic of humoral immunity.
**Option B:** This option is incorrect because cell-mediated immunity is not primarily mediated by B cells, which are responsible for producing antibodies.
**Option C:** This option is incorrect because cell-mediated immunity is not a type of innate immunity, which provides immediate defense against infections through physical barriers, phagocytosis, and the complement system.
**Clinical Pearl / High-Yield Fact**
Cell-mediated immunity is essential for controlling viral infections, such as HIV and tuberculosis, and for preventing the growth of cancer cells. A weakened cell-mediated immune response can lead to increased susceptibility to infections and cancer.
**Correct Answer: C. Cell-mediated immunity is primarily mediated by T lymphocytes (T cells) to defend against infections and foreign substances.**