Natural killer cells

Definition

Natural killer (NK) cells are a type of lymphocyte in the immune system that play a crucial role in the body's innate defense against tumors and virally infected cells. They are part of the first line of defense, acting quickly to identify and eliminate abnormal cells without the need for prior sensitization to specific antigens. This ability allows them to respond rapidly to a variety of threats, contributing significantly to the innate immune response.

5 Must Know Facts For Your Next Test

1. Natural killer cells recognize stressed, infected, or cancerous cells through a variety of receptors that detect changes in the surface proteins of these abnormal cells.
2. They release cytotoxic granules containing perforin and granzymes, which help to induce apoptosis, or programmed cell death, in target cells.
3. NK cells are activated by various cytokines, particularly interleukin-2 (IL-2) and interleukin-12 (IL-12), enhancing their ability to kill infected or malignant cells.
4. Unlike T cells, NK cells do not require antigen presentation by major histocompatibility complex (MHC) molecules to identify their targets.
5. Natural killer cells also play a role in shaping adaptive immunity by producing cytokines that can influence the activity of other immune cells.

Review Questions

• How do natural killer cells differentiate between healthy cells and those that are infected or cancerous?
  • Natural killer cells differentiate between healthy and abnormal cells by recognizing changes in surface proteins. They have activating and inhibitory receptors that assess whether a cell displays markers indicative of stress or infection. When these activating signals outweigh inhibitory signals, NK cells initiate cytotoxic activity against the abnormal cell, leading to its destruction.
• Discuss the role of cytokines in the activation and function of natural killer cells.
  • Cytokines play a critical role in the activation and function of natural killer cells by enhancing their cytotoxic capabilities. For example, interleukin-2 (IL-2) promotes NK cell proliferation and activation, while interleukin-12 (IL-12) can boost their ability to kill target cells. These signaling molecules enable NK cells to respond effectively during an immune response, allowing them to coordinate with other components of the immune system.
• Evaluate the importance of natural killer cells in both innate and adaptive immunity and their potential therapeutic applications.
  • Natural killer cells are essential for both innate and adaptive immunity due to their rapid response to infected or cancerous cells. They not only eliminate threats but also produce cytokines that can influence T cell responses, thus linking the innate and adaptive immune systems. Their potential therapeutic applications include immunotherapy for cancer, where enhancing NK cell activity could improve patient outcomes by directly targeting tumor cells or by supporting the overall immune response against malignancies.

Related terms

Innate Immunity: A non-specific form of immunity that provides immediate defense against infections through physical barriers and immune cells, including NK cells.

Cytokines: Small proteins released by immune cells that mediate and regulate immunity and inflammation, playing a role in NK cell activation and function.

Lymphocytes: A subset of white blood cells, including B cells, T cells, and NK cells, that are crucial for adaptive and innate immune responses.