The difference between people who get flu every year and people who have never had flu is the strength of their immune system.
The immune system protects our body from various diseases. The diseases are not only a common cold and flu but also cancers. Because of the immune system, we don’t get cancer. In our body cancer cells are born every day. The number of cancer cells is said to be a few thousands. Immune cells patrol all over the body and every time they find cancer cells, they kill the cancer cells so that we don’t get cancer. Among the immune cells, Natural Killer cells (NK cells) are important. NK cells kill all external enemies.
But the immune system possibly weakens gradually. One of the reason is aging. The activeness of NK cells is peak at the age of 20 and it becomes a half at the age of 70. So it is pretty natural that we tend to have cancer with age.
There is an unusual reason that immune cells become weak. Immune cells which are supposed to protect our body take a rest without doing their jobs!
Immune cells wait in lymph nodes located at important parts of the body and patrol all the body through blood vessels regularly. Once immune cells find a foreign substance, they attack and kill the foreign substance. (Fig. 3)
If the activity of the immune cells is decreased by some cause, the immune cells keep resting in the lymph nodes and don’t go to patrol. That is considered as one of the biggest causes of the lowering of the immune strength.
What should we do to boost up the immune strength once lowered?