Natural Born Killers

Don't fear NK cells: They're one of your body's best defenses against disease.

By Joanne Gallo

October 2005

They roam the dark, murky interiors of your body, preying on strangers and outsiders. Deadly predators on a mission, these natural born killers don’t spread destruction randomly—they zero in on the most treacherous invaders that can cause disease and illness. These slayers—a.k.a. natural killer (NK) cells—may sound dangerous at first, but they are actually one of your greatest protectors in the battle for long-lasting health.

Though their reputation is not as widespread as some of their white blood cell partners-in-crime, like those heroic T cells, NK cells have been getting more kudos in recent years from researchers who are uncovering their full disease-fighting potential. They’ve found that NK cells are key in helping to fight cancer and virus-related illnesses like chronic fatigue syndrome, fibromyalgia and hepatitis-C.

“People don’t realize that we’re forming cancer cells every day, and we’re getting infections and viruses left and right,” warns James T. Belanger, naturopathic physician and co-founder of Lexington Natural Health Center in Lexington, Massachusetts. “We’re exposed to toxins in our air and food, and these carcinogens enter our bodies and eventually lead to some cellular damage. The DNA in our cells mutates and the body has to repair itself. If it doesn’t and the carcinogens and their damage accumulates, then it leads to the formation of cancer. We need to have a natural defense against that.”

Enter those multi-tasking NK cells to the rescue, guarding against cancer and chronic fatigue with equal force. “We’re exposed to viruses like monovirus and herpes from an early age, and they remain in our bodies and stay contained by the immune system,” continues Belanger. “Chronic physical and mental stress over time causes these viruses to increase in the body, which can lead to symptoms of chronic fatigue like muscle aches and headaches. Raising natural killer cell activity can help decrease the viral levels in the body and help with these symptoms.”

In Cold Blood

NK cells are a type of lymphocyte, which are white blood cells that identify foreign substances and produce antibodies and cells that specifically target them. Lymphocytes make up 20% to 40% of our white blood cell count, and NK cells represent 5% to 20% of those lymphocytes. The various types of lymphocytes respond to different things: T cells, for example, respond to certain proteins normally found in all cells. If those proteins are lost, as in a cancerous or viral change, then the NK cells will respond. Other white cells are responsible for other things, like fighting bacterial infections or responding to allergens or parasites.

NK cells attach to target viral and cancerous cells and release a deadly burst of chemicals or cytotoxic granules that penetrate the cell wall. Fluids begin to leak in and out, and eventually the cell explodes. (Take that!) But NK cells do not kill indiscriminately: Their intuition allows them to distinguish the good guys from the bad as they spare the normal cells. Plus, NK cells aren’t just mutant destroyers, they’re also immunoregulators, helping to support the entire immune system.

When they encounter pathogens, NK cells “sound the alarm” that mobilizes the coordinated response of other immune system resources into battle. When you’re healthy, they send the “all-clear” message that allows the immune system to rest and respond to the next challenge.

Some people, unfortunately, are simply born at a disadvantage when it comes to immunity, with lesser functioning NK cells. Those with a family history of cancer may inherit low NK cell activity. In fact, with many chronic and degenerative diseases, levels of NK cell function prove to be an important indicator of disease progression and patient prognosis. Studies show that cancer patients with low levels of NK cell activity are at greater risk for reoccurrence or having it spread to the lymph nodes and metastasizing.

Going Cellular

If you’re concerned your NK cell activity is low, have no fear. You can effectively measure your body’s levels—and then take steps to boost their functioning. The standard test for NK cells is a four-hour chromium release assay: A patient’s NK cells are put into a culture with leukemia cells that are labeled with radioactive chromium. If the NK cells are working properly, they will attach to the leukemia cells, poke holes in them and cause them to release chromium into the extra-cellular fluid where it is then measured. If the NK cells aren’t functioning properly, they won’t do much of anything when they attach to the leukemia cells and no chromium is released.

The first step to take if your NK cell activity is low is to evaluate the sources of tension in your life. “Stress has been shown to decrease natural killer cell activity,” reports Belanger. “There is a hormone called cortisol which is released by our bodies when exposed to stress. If we are chronically stressed for a long period, our cortisol levels can be depleted and hardly have any cyclical rhythm anymore. Normally, cortisol is high in the morning and low at night. When people are exposed to chronic stress, it doesn’t go up and down at all; it’s completely flat. There’s one study with breast cancer patients showing that those who have the flat curve have low killer cell activity.”

For that reason, reduced NK cell activity even plays a role in a seemingly unrelated condition like post-traumatic stress disorder.

Helpful stress-reduction techniques include moderate exercise, meditation, massage, aromatherapy—even smiling can reportedly increase NK cell functioning. Belanger also points to the amount of fat a person eats, citing a study where lowering fat content in a patient’s diet caused NK cell activity to increase.

A unique mushroom compound also shows promise for NK cell activity. “Several years ago, I went and tested all these products, from the various mushroom products to different vitamins,” relates Belanger. “I can’t say a lot of them are consistently effective. The one that I found that was consistent is AHCC (Active Hexose Correlated Compound). I’ve seen it work over and over again.” A fermented extract of a hybrid of mushrooms used in traditional Japanese medicine, AHCC has been found by researchers in the US and Japan to up-regulate NK cell function by several hundred percent. In fact, AHCC is used in more than 600 hospitals in Japan to treat cancer, hepatitis and other chronic diseases.

Just think: Right now those NK cells are coursing through your body, ready to wreak havoc on the bad guys. With just a few lifestyle modifications, you can ensure that those natural born killers keep their edge for years to come.

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