Our Immune System How it Works

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What is the Immune System?

The immune system is complex and very important for our survival, yet many people don't understand it and only vaguely know of its existence. As a result, they sometimes completely ignore it.

Here are three definitions for the Immune System:

The immune system, then, is our body's first line of defence against disease, infection, germs, bacteria, and viruses.

How Does the Immune System Work?

When something foreign in the body is detected, the immune system goes to work. Several types of cells work together to recognize anything that doesn't belong in the body. These cells help to produce what are known as antibodies 2.

Antibodies, which are very helpful in keeping you well, have several jobs:

Three Types of Immunity

You are born with innate (or natural) immunity which is a type of general, overall protection, simply because you are a human being. There are germs that affect other species but don't harm us. 4 Dogs and cats, for instance, get diseases that humans don't get, and vice versa.

Innate immunity includes the skin and mucous membranes that line the nose, throat, and gastrointestinal tract. They are there early on — to prevent diseases from even getting into your body. The skin, for instance, will begin the healing process as soon as it is cut — and immune cells on the skin will attack any germs that try to invade.

By contrast to innate immunity, adaptive (or active) immunity develops throughout our lives. This occurs as we are either exposed to diseases or we are immunized through vaccination.

Passive immunity is borrowed and lasts for a short time — antibodies in a mother's breast milk, for instance, will give a baby temporary immunity to any diseases the mother has been exposed to.

It may seem as though some people never seem to get sick while others are always getting sick. That is because everyone's immune system is different — and can change as we get older. Older people may become immune to more germs as the immune system comes into contact with more and more of them throughout the years. But some viruses evolve and change from year to year, making our immunity to last year's flu no longer useful for this year's flu.

Disorders of the Immune System

Disorders of the immune system fall into several categories:

Can Exercise Help your Immune System?

The good news is that there is some research to indicate that regular, moderate exercise helps the immune system because of the physiological changes which occur during exercise. It is believed that during exercise cells that promote immunity circulate through the system more rapidly. After exercising, the body returns to normal within a few hours. However, it is possible that a regular exercise routine may extend periods of immunity.

"Dr. David Nieman, an exercise immunologist at Appalachian State University, is one of the country’s most respected authorities in this area. One of his studies showed that people who walked at 70 to 75 percent of their VO2max for 40 minutes per day reported half as many sick days because of colds or sore throats compared to people who didn't exercise." 5

The bad news is that there is some evidence that too much exercise may negatively affect immunity. "One study found that 90 minutes or more of high-intensity exercise (marathons, endurance races) makes a person more susceptible to illness for up to 72 hours after working out. Researchers think that during high-intensity exercise, the body produces two hormones, cortisol and adrenaline, that ... temporarily weaken the immune system." 6

Should you Exercise when your Immune System is Compromised?

Most doctors, including Dr. David Nieman (quoted in the previous section), recommend the following regarding exercising when you don't feel well:

Generally speaking, the advice from doctors is that exercise is usually acceptable "if your symptoms are all "above the neck." As soon as you have signs of respiratory distress, exercising is probably not a good idea.Some physicians have also suggested that engaging in moderate exercise before getting a flu shot could improve your body’s response to the vaccine and enhance your immunity to the flu.

Three different studies conclude:

Taking Care of your Immune System

Harvard Medical School recommends five ways to take care of your immune system. They are:

If you travel, consider these safety tips:


Most of us are guilty of taking our immune system for granted. When we come down with a cold or the flu, we feel as though our immune system has let us down. But, in truth, it's working hard for us, trying to fight off the virus that is attacking our body and wants to take over.

Those of us who suffer from allergies are perhaps more likely to be frustrated with our immune system as it over-works to fight against whatever it believes should not be in our body,yet is actually not a danger to us.

If you are healthy, your immune system will most likely be healthy. Exercise will "keep it in shape," just as exercise helps other systems in your body as well.

Other articles that may interest you:

I am a BCRPA-certified fitness instructor in Vancouver, BC. I teach four classes at the West End Community Centre in Vancouver, BC, mostly designed for the older adult. The Inevitable Disclaimer: Everything published here expresses only my opinion, based on my training and research. What you do with the information is entirely your own responsibility. I am not liable for any injury you suffer that seems to be related to anything you read here. Always consult your doctor before beginning an exercise program. For other articles, return to the table of contents.

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  1. These three dots behave exactly like a footnote. Click on them and you will get more information about the topic. 

  2. This gets pretty technical. Antibodies are Y -shaped protein molecules which are produced by B cells as a primary immune defense. Each molecule has a unique binding site that can combine with the site of a foreign antigen, such as on a virus or bacterium. That will disable the antigen and signal help from other immune defenses. 

  3. This is also how immunizations prevent certain diseases. An immunization introduces the body to an antigen. It doesn't make someone sick, but it does allow the body to produce antibodies that will then protect the person from future attack by the germ or substance that produces that particular disease. 

  4. For example, the viruses that cause leukemia in cats or distemper in dogs don't affect humans. 

  5. from this website 

  6. from this website 

  7. from this website 

  8. from this research. If this link doesn't work, go to PubMed and seek number 7883401. 

  9. from this research. If this link doesn't work, go to PubMed and seek number 1470018.