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 recognize and eliminate infected cells or produce chemical signals that activate other immune cells. This process is crucial for combating intracellular pathogens and tumor cells.
**Why the Correct Answer is Right**
The correct answer is based on the understanding that cell-mediated immunity is primarily mediated by T cells, which recognize antigens presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APCs). Activated T cells can then differentiate into various effector cells, such as cytotoxic T cells (CD8+ T cells) and helper T cells (CD4+ T cells), which play distinct roles in eliminating infected cells or activating other immune cells. The activation of T cells is a key event in cell-mediated immunity, allowing for the coordinated response to intracellular pathogens and tumor cells.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because cell-mediated immunity is not primarily mediated by antibodies, which are the hallmark of humoral immunity.
* **Option B:** This option is incorrect because cell-mediated immunity is not limited to the activation of B cells, although B cells do play a role in presenting antigens to T cells.
* **Option C:** This option is incorrect because cell-mediated immunity is not solely dependent on the complement system, which is a part of the innate immune response.
**Clinical Pearl / High-Yield Fact**
Cell-mediated immunity is critical for controlling chronic infections, such as HIV, and tumor growth, making it an essential aspect of the immune response to be understood in clinical practice.
**Correct Answer:** C