Natural killer cell facts for kids

Natural killer cells (often called NK cells) are special cells in your body. They are a type of lymphocyte, which is a kind of white blood cell. NK cells are super important for your innate immune system, which is your body's first line of defense against germs.

NK cells are like quick-response police. They can find and destroy cells infected by viruses or bacteria very fast. They usually act within about three days after an infection starts. NK cells also help fight against tumours, which are abnormal growths of cells.

What makes NK cells unique? They can spot and kill stressed or unhealthy cells without needing special signals like antibodies or major histocompatibility complex (MHC) molecules. This means they can react much faster than other immune cells. Scientists first noticed this "natural" ability in the 1970s. They saw that some cells could kill cancer cells without any prior training. Soon, they realized these were a special type of cell with this amazing power.

How Do NK Cells Work?

NK cells have special sensors on their surface. These sensors are called receptors. There are two main types: "activating" receptors and "inhibitory" receptors. Think of them like switches. When the activating switches are turned on, the NK cell gets ready to attack.

Inside NK cells are tiny packages called granules. These granules hold powerful proteins and enzymes, like granzymes. When an NK cell decides to attack a bad cell, it releases these packages very close to it. One important protein, called perforin, makes holes in the outer layer of the target cell. This creates channels for the enzymes to get inside. Once inside, the enzymes destroy the target cell. This is how NK cells kill cells infected by viruses, bacteria, or even tumor cells.

Why NK Cells Are So Smart

NK cells have a clever way to tell good cells from bad ones. Their "inhibitory" receptors look for special markers called MHC class I molecules on the surface of other cells. Most healthy cells have lots of these MHC class I markers. When an NK cell sees these markers, its inhibitory switch is turned on, and it knows not to attack.

However, some tricky microbes (like viruses) and tumours try to hide from your immune system. They do this by lowering the number of MHC class I molecules on their surface. This makes them invisible to other immune cells, like T-cells. But this is where NK cells become super important!

Because these bad cells have fewer MHC class I markers, they don't turn on the NK cell's inhibitory switch. This means the NK cell's activating switches are free to turn on, and it attacks the hidden threat. Scientists believe NK cells might have developed this ability over time. It's like an evolutionary adaptation to catch cells that try to escape other parts of the immune system.

Images for kids

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  The HLA ligand for KIR

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  Protein structure of NKG2D

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  Protein structure of NKp44

See also

In Spanish: Célula NK para niños