Natural Killer Cells

Definition

Natural killer (NK) cells are a type of lymphocyte that play a crucial role in the innate immune response by identifying and destroying virus-infected cells and tumor cells. They are essential for early defense against viral infections, functioning without the need for prior sensitization to antigens, which distinguishes them from other immune cells.

5 Must Know Facts For Your Next Test

1. Natural killer cells can recognize infected or abnormal cells without prior exposure to specific antigens, allowing them to respond rapidly to viral infections.
2. NK cells are activated by various cytokines, such as interleukin-2 (IL-2), which enhances their cytotoxic function and proliferation.
3. They have unique receptors known as activating and inhibitory receptors that help determine whether a target cell is healthy or stressed/infected.
4. Natural killer cells release cytotoxic granules containing perforin and granzymes to induce apoptosis in target cells.
5. Dysfunction or impairment of NK cell activity can lead to increased susceptibility to viral infections and can contribute to the progression of cancers.

Review Questions

• How do natural killer cells contribute to the early immune response against viral infections?
  • Natural killer cells contribute significantly to the early immune response by rapidly identifying and destroying virus-infected cells. They are activated quickly upon detecting stress signals from these infected cells. By releasing cytotoxic granules, NK cells can induce apoptosis in their targets, effectively limiting the spread of the virus before the adaptive immune response has fully developed.
• Discuss the mechanisms by which natural killer cells distinguish between healthy and infected or abnormal cells.
  • Natural killer cells utilize a combination of activating and inhibitory receptors to differentiate between healthy and infected or abnormal cells. In normal conditions, healthy cells present MHC class I molecules, which engage inhibitory receptors on NK cells, preventing activation. However, in infected or transformed cells, there is often a downregulation of MHC class I expression or the presence of stress-induced ligands that activate NK cell receptors, prompting an attack on these compromised cells.
• Evaluate the implications of natural killer cell dysfunction in the context of viral infections and cancer development.
  • Dysfunction in natural killer cell activity can have significant implications for both viral infections and cancer. In cases where NK cell function is impaired, individuals may experience heightened vulnerability to viral infections due to insufficient clearance of infected cells. Furthermore, inadequate NK cell responses can allow tumors to evade immune surveillance, promoting cancer development and progression. Thus, understanding NK cell dynamics is critical for developing therapeutic strategies aimed at enhancing their function in both infectious diseases and cancer treatment.

Related terms

Cytotoxic T Cells: A subset of T lymphocytes that directly kill virus-infected cells and cancer cells, requiring specific recognition of antigens presented by major histocompatibility complex (MHC) molecules.

Interferons: A group of signaling proteins produced by host cells in response to viral infections that help inhibit viral replication and activate immune cells, including NK cells.

Apoptosis: A form of programmed cell death that is a natural process for eliminating damaged or infected cells; NK cells can induce apoptosis in their targets through various mechanisms.