Natural Killer Cells What are they and why are they so important in the fight against cancer?

Christel Payseng
6 min readFeb 9, 2024

Natural killer cells (NK cells) are a type of white blood cell that play a crucial role in your immune system by targeting and eliminating infected cells and cancer cells.

Unlike other immune cells, NK cells do not require prior exposure to a specific pathogen to recognize and destroy threats. They are part of a group of white blood cells known as lymphocytes, which also include B-cells and T-cells.

NK cells are referred to as “natural” killers because they possess the innate ability to identify and eliminate potential threats without prior priming.

Natural killer cells (NK cells) are like superheroes in your body’s defense system. They target and destroy cells that have turned bad, such as those infected with viruses or cancer cells. By doing this, NK cells stop these harmful cells from spreading and causing more trouble.

Think of NK cells as the frontline soldiers of your immune system. They’re part of what’s called the innate immune system, which is your body’s first line of defense against all kinds of threats. This defense system includes physical barriers like skin and mucous membranes that block germs from getting in. NK cells are like special forces, stepping in to destroy any threats that manage to sneak past these barriers.

But NK cells don’t just fight on their own; they’re also great communicators. They release special proteins called cytokines that tell other immune cells to join the battle against harmful cells and germs. So, in short, NK cells are essential warriors in keeping you healthy by finding and destroying dangerous cells before they can cause harm.

How do NK cells work in the immune system?

Natural killer cells patrol your body, checking cells for signs of health or disease. If they find a cell that seems harmful, they release chemicals to destroy it. Whether they kill a cell depends on the signals they get from it.

These cells have receptors on their surface that can either activate or stop them from killing a target.

Inhibition Natural killer cells don’t attack cells with markers showing they’re healthy and belong in your body. The most common marker they recognize as “self” is called MHC-1. When MHC-1 on a cell binds to an NK cell’s inhibitory receptor, it stops the NK cell from killing. Instead, the NK cell moves on to check another cell.

Activation of NK Cells

Natural killer cells become active to destroy cells they don’t recognize as part of the body. These include:

Cells emitting activating signals: Cancer cells and infected cells sometimes release chemicals that trigger NK cells to attack. Cells lacking or having reduced MHC-1: NK cells target cells that don’t have MHC-1. Sometimes, a cell has MHC-1, but it’s decreased.

This can happen during a viral infection, for instance. NK cells use perforin and granzymes to kill a target cell. Perforin creates a gap in the target cell, allowing granzymes to enter and kill it.

Activated NK cells also release cytokines, which signal other white blood cells to help eliminate the threat.

Where are natural killer cells located?

NK cells begin to form in the soft tissue inside certain bones called bone marrow. As they grow, some NK cells stay in the bone marrow, while others move to different parts of your lymphatic system, like:

  • Lymph nodes
  • Spleen
  • Tonsils
  • Thymus

When they’re fully developed, your body releases NK cells into your bloodstream. Mature NK cells are also found in lymph tissue and related organs, such as the liver and lungs.

There are about 5% to 10% of a specific type of white blood cells, called lymphocytes, in your blood that are natural killer cells. They typically last for about two weeks.

Adults usually have over 2 billion natural killer cells in their bodies at any given time.


Not having enough natural killer (NK) cells can make you more prone to infections and cancer. Studies suggest that NK cells might also be involved in other health issues, such as:

Autoimmune diseases: Problems with NK cell function might contribute to autoimmune diseases, where the immune system mistakenly attacks healthy cells instead of harmful ones.

Asthma: NK cells are part of the body’s response to inflammation in asthma. They can either increase or decrease inflammation, depending on different factors.

Inflammatory bowel disease (IBD): NK cells are involved in the body’s response to bacterial infections in the gut, which is linked to conditions like inflammatory bowel disease.

Natural Killer Cells & Ovarian Cancer

In ovarian cancer, NK cells have been shown to infiltrate the tumor microenvironment, where they interact with cancer cells. However, the effectiveness of NK cell-mediated killing of ovarian cancer cells can be influenced by various factors, including the presence of inhibitory signals from the tumor cells themselves or from other immune cells within the tumor.

Strategies employed to enhance anti-cancer Natural Killer surveillance in the clinic.

Research suggests that enhancing NK cell activity may hold promise for improving the treatment of ovarian cancer. Strategies aimed at boosting NK cell function, such as immunotherapy or targeted therapies, are being explored as potential therapeutic approaches in ovarian cancer treatment.

Furthermore, understanding the mechanisms underlying the interaction between NK cells and ovarian cancer cells may provide valuable insights into the development of novel treatment strategies that harness the power of the immune system to combat this disease more effectively.

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Christel Payseng

Writer, PR Media, Literature Hobbyists, Digital Marketer