The following feature is common to both cytotoxic T – cells and NK cells –
**Core Concept**
Cytotoxic T-cells and natural killer (NK) cells are both types of lymphocytes that play crucial roles in the innate and adaptive immune responses. They share a common function of killing infected cells or tumor cells. This is achieved through the release of cytotoxins and the induction of programmed cell death (apoptosis).
**Why the Correct Answer is Right**
Both cytotoxic T-cells and NK cells express killer cell immunoglobulin-like receptors (KIRs) on their surface, which helps them recognize and bind to major histocompatibility complex (MHC) class I molecules on the target cell. This interaction triggers the activation of the perforin-granzyme pathway, leading to the formation of pores in the target cell membrane and the release of cytotoxins, ultimately resulting in cell lysis. Additionally, both cell types can also induce apoptosis through the Fas-Fas ligand pathway.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because cytotoxic T-cells and NK cells have distinct surface markers and functional characteristics. Cytotoxic T-cells require antigen presentation by MHC class I or II molecules for activation, whereas NK cells can recognize and kill target cells without prior antigen exposure.
* **Option B:** This option is incorrect because B-cells are primarily involved in the humoral immune response and produce antibodies, whereas cytotoxic T-cells and NK cells are involved in cell-mediated immunity.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the cytotoxic T-cell and NK cell-mediated killing of target cells is a critical mechanism for controlling viral infections and tumor growth. Understanding the shared features of these cell types can help clinicians appreciate the complex interactions between the immune system and various disease states.
**Correct Answer: C. Expression of KIRs and recognition of MHC class I molecules.**