The Immune System – Tutorial #3
Natural Killer cells (NK cells) are a cancer cell’s worst nightmare. It’s pretty clear from their name that natural killer cells mean business. They are the special agents of the immune system that have the unique assignment of killing “self” cells that have become traitors (cancer cells) and conspirators (cells that harbor viruses).
NK cells are constantly on surveillance. Several billion NK cells patrol your body continually in search of virus-infected cells or new cancer cells. Both virus and cancer cells display antigens (identity markers) on their surface that say to NK cells “not-self.” Antigens cause the immune system to react and attack.
In the early stages of a tumor’s growth the “not-self” tumor antigen may not be as robust as the antigens on the surface of a true foreign invader such as bacteria. The “bumps” or protein shapes on the surface of newly formed cancer cells may be very similar to that of all the other cells in your body, but a healthy natural killer cell is not fooled.
When fighting cancer, NK cells are drawn to areas where cancer is present. Once a cancer cell is detected the NK cell slides up next to it seeking membrane-to-membrane contact. By simply touching its target – the “kiss of death” – a lethal chain reaction begins and it’s game over for the tumor cells.
The natural killer cells release enzymes that open holes in the tumor cells membrane. The cancer cell simply leaks to death.
A cancer cell (top) with a hole in the cell’s membrane. NK cell (bottom right)
Since natural killer cells wander the body outside the bloodstream, many cancer researchers think it’s fairly common that cancer cells form in the body all of the time, but the NK cells dispatch them before they can cause any trouble.
When the immune system is suppressed tumors develop to the danger point. Research has shown that NK cells can control both local tumor growth and metastasis. They have the ability to act on their own, spontaneously and immediately, and kill cells that are displaying a “not-self” marker. This is true even if the cell also has “self” markers on its surface. The immune systems’ natural killer cells seem to make cancer cells a specialty.