Natural killer cells

Definition

Natural killer (NK) cells are a type of lymphocyte in the innate immune system that play a crucial role in the body’s defense against tumors and virally infected cells. They act quickly to identify and eliminate these threats without the need for prior sensitization, which makes them essential for immediate immune responses. Their ability to recognize stressed cells in the absence of antibodies or major histocompatibility complex (MHC) molecules highlights their unique function in immune surveillance and responses to cellular abnormalities.

5 Must Know Facts For Your Next Test

1. Natural killer cells can recognize and kill target cells that lack MHC class I expression, a common feature of tumor cells and virus-infected cells.
2. They release cytotoxic granules containing perforin and granzymes that induce apoptosis in the target cells.
3. NK cells also produce cytokines, such as interferon-gamma (IFN-γ), which enhance the immune response and activate other immune cells.
4. They develop from common lymphoid progenitors in the bone marrow and are found throughout peripheral blood and tissues.
5. Natural killer cells are regulated by activating and inhibitory receptors that ensure they distinguish between healthy and abnormal cells effectively.

Review Questions

• How do natural killer cells contribute to the innate immune response compared to other lymphocytes?
  • Natural killer cells provide an immediate response to infections and tumors, unlike other lymphocytes like B and T cells that require specific antigen recognition and time for activation. NK cells can recognize stressed or abnormal cells without prior sensitization, making them vital for early defense mechanisms. Their cytotoxic functions allow them to kill target cells directly, contributing significantly to the innate immune system's rapid response to threats.
• Discuss the role of natural killer cells in tumor immune evasion and how cancer can manipulate these cells.
  • Tumor cells often develop mechanisms to evade detection by natural killer cells, such as downregulating MHC class I molecules or expressing ligands for inhibitory receptors on NK cells. This helps them escape immune surveillance. In some cases, tumors can create an immunosuppressive microenvironment that affects NK cell function. Understanding these interactions is crucial for developing therapies aimed at enhancing NK cell responses against tumors.
• Evaluate the potential therapeutic applications of enhancing natural killer cell activity in cancer treatment.
  • Enhancing natural killer cell activity presents promising therapeutic strategies for cancer treatment. Techniques such as adoptive cell transfer, where activated NK cells are infused into patients, aim to boost anti-tumor responses. Additionally, immunotherapies that block inhibitory pathways or use cytokines to activate NK cells have shown potential in improving patient outcomes. Research continues to explore combination therapies that leverage NK cell functions alongside other immune modalities for more effective cancer management.

Related terms

Cytotoxic T Cells: A subset of T cells that directly kill infected or cancerous cells by recognizing specific antigens presented by MHC class I molecules.

Innate Immunity:

The first line of defense against pathogens that is non-specific and includes physical barriers, immune cells like NK cells, and various proteins.

MHC Class I:

Molecules expressed on the surface of all nucleated cells that present endogenous antigens to cytotoxic T cells, playing a key role in immune recognition.