Natural killer cells

Definition

Natural killer (NK) cells are a type of lymphocyte that plays a crucial role in the innate immune response by identifying and destroying infected or cancerous cells. They are part of the body's first line of defense, acting quickly to eliminate threats without the need for prior sensitization, and are particularly important in responding to parasitic infections and their associated immunopathologies.

5 Must Know Facts For Your Next Test

1. Natural killer cells can recognize stressed cells in the absence of antibodies and MHC, allowing them to act quickly in eliminating infected or tumor cells.
2. They release cytotoxic granules containing perforin and granzymes, which facilitate the destruction of target cells by inducing apoptosis.
3. NK cells are influenced by various cytokines, such as IL-12, IL-15, and type I interferons, which enhance their activity and proliferation during immune responses.
4. In parasitic infections, NK cells contribute to both direct killing of infected host cells and the regulation of other immune responses through their cytokine production.
5. While primarily involved in innate immunity, NK cells can also have roles in shaping adaptive immunity by interacting with dendritic cells and influencing T cell responses.

Review Questions

• How do natural killer cells contribute to the innate immune response against parasitic infections?
  • Natural killer cells contribute to the innate immune response by directly identifying and destroying parasitized or infected host cells. They can recognize stressed or infected cells without needing prior exposure to specific antigens, allowing for a rapid response. This capability is vital when dealing with parasitic infections, as NK cells can eliminate infected cells early on before adaptive immunity is fully activated.
• Discuss the role of cytokines in the activation and function of natural killer cells during a parasitic infection.
  • Cytokines play a significant role in the activation and function of natural killer cells during parasitic infections. Cytokines such as IL-12 and IL-15 enhance NK cell proliferation, activation, and cytotoxicity. Additionally, these signaling molecules help NK cells communicate with other immune components, facilitating a coordinated response to eliminate parasites effectively while also regulating inflammation.
• Evaluate the balance between the protective effects of natural killer cells and their potential contribution to immunopathology in parasitic infections.
  • Natural killer cells have protective effects by swiftly targeting and destroying infected or abnormal cells, which helps control parasitic infections. However, an overactive NK cell response can lead to tissue damage and contribute to immunopathology. The excessive release of pro-inflammatory cytokines and cytotoxic substances may result in collateral damage to healthy tissues, highlighting the importance of regulation in their activity during infections to balance protection with potential harm.

Related terms

Cytokines: Signaling molecules that mediate and regulate immunity, inflammation, and hematopoiesis; they play a key role in the activation and function of NK cells.

Antigen-presenting cells: Cells that display antigens to T cells and are essential for initiating adaptive immune responses, though NK cells can act independently of these processes.

Apoptosis: A programmed cell death mechanism that NK cells can induce in target cells, helping to eliminate infected or abnormal cells without causing inflammation.