Natural killer (NK) cells

Definition

Natural killer (NK) cells are a type of lymphocyte that plays a critical role in the body's innate immune response by identifying and destroying infected or cancerous cells. These cells are part of the immune system and are characterized by their ability to recognize stressed cells in the absence of antibodies and MHC, allowing for a rapid immune response.

5 Must Know Facts For Your Next Test

1. NK cells are derived from the common lymphoid progenitor cells in the bone marrow and account for about 5-15% of all circulating lymphocytes in humans.
2. These cells can kill target cells through various mechanisms, including the release of cytotoxic granules containing perforin and granzymes that induce apoptosis in the target cell.
3. NK cells have activating and inhibitory receptors that allow them to differentiate between healthy and abnormal cells, ensuring they attack only those that are harmful.
4. They also produce cytokines, such as interferon-gamma (IFN-γ), which play a role in enhancing the immune response and activating other immune cells.
5. NK cell activity is crucial during the early stages of viral infections and tumor surveillance, providing a first line of defense before the adaptive immune response is fully activated.

Review Questions

• How do natural killer (NK) cells distinguish between healthy and infected or cancerous cells?
  • Natural killer (NK) cells distinguish between healthy and infected or cancerous cells by using a combination of activating and inhibitory receptors. Activating receptors bind to stress-induced ligands on abnormal cells, signaling that these cells should be targeted for destruction. In contrast, inhibitory receptors recognize MHC Class I molecules on healthy cells, which helps prevent NK cell activation against normal tissues. This balance between activation and inhibition is crucial for ensuring that NK cells effectively eliminate threats without harming healthy tissues.
• Discuss the mechanisms by which natural killer (NK) cells kill their target cells and how this differs from the action of cytotoxic T cells.
  • Natural killer (NK) cells kill their target cells primarily through the release of cytotoxic granules that contain perforin and granzymes. Perforin forms pores in the target cell's membrane, allowing granzymes to enter and induce apoptosis. This process does not require prior sensitization to specific antigens, enabling a rapid response to threats. In contrast, cytotoxic T cells require recognition of specific antigens presented by MHC Class I molecules and typically engage in more targeted killing through direct interaction with infected or cancerous cells.
• Evaluate the significance of natural killer (NK) cell function in the context of cancer immunotherapy and emerging treatments.
  • The function of natural killer (NK) cells holds significant promise in cancer immunotherapy due to their innate ability to identify and kill tumor cells without prior sensitization. Therapies aimed at enhancing NK cell activity, such as checkpoint inhibitors or adoptive cell transfer, are being explored to improve patient outcomes in various cancers. By leveraging NK cell responses, these treatments aim to boost the body's natural defenses against tumors, making them a valuable tool in developing effective cancer therapies. Ongoing research continues to investigate how to optimize NK cell responses and overcome challenges such as tumor evasion mechanisms.

Related terms

Innate Immunity: A non-specific defense mechanism that the body is born with, providing immediate protection against pathogens.

Cytotoxic T Cells: A type of T cell that kills cancerous or virus-infected cells through direct contact and the release of cytotoxic substances.

MHC Class I: Major Histocompatibility Complex Class I molecules present on nearly all nucleated cells that display endogenous antigens to cytotoxic T cells and NK cells.