Natural Killer (NK) Cells 1

Natural Killer (NK) Cells

Definition

Natural Killer (NK) cells are a type of cytotoxic lymphocyte that plays a crucial role in the innate immune system. They are part of the body’s first line of defense against infections and tumors, capable of recognizing and destroying infected or malignant cells without prior sensitization to specific antigens.

Key Characteristics

Innate Immune Function:

• NK cells are classified as innate lymphoid cells and represent about 5-20% of circulating lymphocytes in humans. They respond rapidly to viral infections and tumor transformations, acting without the need for prior exposure to the pathogen or cancer cell.

Mechanism of Action:

• NK cells can identify stressed, infected, or transformed cells through a balance of activating and inhibitory receptors. They recognize changes in the expression of molecules on target cells, such as reduced levels of MHC class I molecules, which often occurs in cancerous cells.
• Upon activation, NK cells kill target cells through several mechanisms:
  • Cytotoxic Granule Release: They release granules containing perforin and granzymes that induce apoptosis (programmed cell death) in target cells.
  • Cytokine Production: NK cells produce various cytokines (e.g., interferon-gamma) that enhance the immune response by activating other immune cells like macrophages and T-cells.

Role in Cancer Immunity:

• NK cells are essential for immunological surveillance against tumors. They can recognize and eliminate cancer cells, including those that have downregulated MHC class I molecules to evade detection by T-cells. This ability makes them a significant focus in cancer immunotherapy.

Clinical Applications:

• Due to their potent cytotoxic capabilities, NK cells are being explored for therapeutic applications, including:
  • Adoptive Cell Therapy: Infusing patients with activated or expanded NK cells to enhance anti-tumor responses.
  • Combination Therapies: Using NK cell therapies alongside other treatments like chemotherapy or monoclonal antibodies to improve efficacy against cancer.

Conclusion

Natural Killer (NK) cells are vital components of the innate immune system, providing rapid responses to viral infections and malignancies. Their unique ability to recognize and kill abnormal cells without prior sensitization positions them as promising candidates for immunotherapeutic strategies in cancer treatment.

References

1. NCBI. (2023). Human natural killer cells: form, function, and development. Retrieved from NCBI.
2. Wikipedia contributors. (2023). Natural killer cell. In Wikipedia, The Free Encyclopedia. Retrieved from Wikipedia.
3. Stem Cell for Life. (n.d.). NK Cell. Retrieved from Stem Cell for Life.
4. Nature Reviews Immunology. (2023). Roles of natural killer cells in immunity to cancer, and applications to immunotherapy. Retrieved from Nature.