The following feature is common to both cytotoxic T cells and NK cells?
**Core Concept**
Cytotoxic T cells (CTLs) and natural killer (NK) cells are both types of lymphocytes that play crucial roles in the immune system's innate and adaptive responses. They share a common mechanism of action, involving the recognition and destruction of infected cells or tumor cells.
**Why the Correct Answer is Right**
Both CTLs and NK cells can recognize and kill target cells through the activation of perforin and granzymes. Perforin forms pores in the target cell membrane, allowing granzymes to enter and induce apoptosis (programmed cell death). This process is mediated by the Fas-FasL pathway, which is a key mechanism of action for both CTLs and NK cells. The expression of Fas ligand (FasL) on the surface of CTLs and NK cells enables them to interact with Fas receptors on target cells, leading to the activation of caspases and apoptosis.
**Why Each Wrong Option is Incorrect**
**Option A:** Cytokine production is a key function of helper T cells and macrophages, but not a primary mechanism of action for CTLs and NK cells.
**Option B:** Antibody-dependent cellular cytotoxicity (ADCC) is a mechanism of action for NK cells, but not a common feature of CTLs.
**Option C:** Complement-dependent cytotoxicity is a mechanism of action for antibodies and the complement system, but not a common feature of CTLs and NK cells.
**Clinical Pearl / High-Yield Fact**
The perforin-granzyme pathway is a key mechanism of action for both CTLs and NK cells, and is essential for the elimination of infected cells and tumor cells. This pathway is also involved in the pathogenesis of autoimmune diseases, such as lupus nephritis.
**Correct Answer:** C.