What Are Natural Killer (NK) Cells? Their Role in the Immune System

Natural Killer (NK) cells are immune cells that destroy infected and cancerous cells. Medi1001 uses NK-cell–based immunotherapy to provide advanced and personalized cancer treatment solutions.

Natural Killer cells (NK cells) are specialized white blood cells that play a vital role in the immune system. They eliminate virus-infected cells, damaged tissues, and malignant cancer cells. As key components of the innate immune system, NK cells act as powerful first responders, protecting the body from a wide range of threats. Medi1001 utilizes the therapeutic potential of NK cells through advanced immunotherapy protocols, offering personalized cancer treatment solutions.

What Are NK Cells?

NK cells belong to the lymphocyte family, alongside B-cells and T-cells. Unlike other immune cells, NK cells do not require prior exposure to a pathogen to kill it, which is why they are called "natural" killers.

Unless a rare genetic disorder (classical NKD) prevents the bone marrow from producing them, every healthy individual has NK cells.

What Do NK Cells Do?

NK cells detect and eliminate cells that pose a danger, including:

• Virus-infected cells
• Malignant or mutated cancer cells
• Damaged or abnormal tissues

Beyond their killing function, NK cells also release cytokines—messenger molecules that activate other immune cells and coordinate immune responses.

How NK Cells Work in the Immune System

NK cells scan the body and analyze surface markers to determine whether a cell is healthy or harmful.

Inhibition

Healthy cells express MHC-1, a marker indicating the cell is "self". If NK cells bind to MHC-1, their killing mechanism turns OFF.

Activation

NK cells kill when:

• The target lacks MHC-1
• MHC-1 levels are reduced
• Cancer or infected cells produce activating signals

Destruction Mechanism

To kill a harmful cell, NK cells release:

• Perforin → creates pores in the cell membrane
• Granzymes → enter the cell and trigger programmed cell death

Activated NK cells also release cytokines to alert additional immune cells.

Where Are NK Cells Found?

NK cells develop in the bone marrow and then migrate to:

• Lymph nodes
• Spleen
• Tonsils
• Thymus

Mature NK cells circulate in the bloodstream and reside in organs such as the liver and lungs.

They account for 5-10% of the lymphocytes in human blood, with over 2 billion NK cells present in an adult at any time.

Conditions Associated With NK Cells

Abnormal NK function increases susceptibility to infections and cancer. NK cells are also involved in:

• Autoimmune diseases
• Asthma
• Inflammatory bowel disease (IBD)

NK Cell Deficiencies

Two genetic immunodeficiencies directly affect NK cells:

Classical NKD

Less than 1% of circulating lymphocytes are NK cells.

Functional NKD

NK cells exist but do not function properly.

Both conditions increase vulnerability to:

• HPV
• Herpesvirus
• CMV
• EBV
• Varicella-zoster virus

Medi1001 Perspective

Medi1001 integrates NK-cell biology into advanced immunotherapy, offering:

• Personalized immune-boosting treatments
• Cellular therapy options
• Tailored cancer immunotherapy programs

These approaches support the body's natural ability to recognize and eliminate cancer cells.