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What is The Immune System? (4-6)

This is the grade 4-6 (ages 9-11) version of this lesson. There is also a grades 7+ version on the site.

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The body has an amazing defense system called the immune system

The immune system protects us against harmful germs. 

The immune system is made up of different parts that work together to protect the body. 

Keeping Germs Out


The skin provides a large physical barrier that keeps most germs out of the body. Germs can only get through if there is a break in the skin, like a cut or a scrape. 

Nose, mouth, and eyes 

Germs can get inside the body through our nose, mouth, and eyes. Our immune system protects these openings with mucous. Mucous is a sticky lining that traps germs that try to get through these openings. We sometimes call mucous spit or snot. Saliva and tears also help kill germs trying to get in through your mouth and eyes.

Fighting Germs on the Inside

Even though our skin is a barrier, sometimes, germs still manage to get inside the body. 

When that happens, our immune system sends out messages that warn about the germ being in our body. 

This warning starts up the next set of defenses in the body, which involves our white blood cells.


White Blood Cells Explained 

White blood cells are the body’s disease-fighting cells.

There are different types of white blood cells. They all work to protect the body. Each different type of white blood cell has a different job in keeping you healthy. 

Some white blood cells constantly patrol the body and seek out and fight off any germs they see. 

Other more specialized white blood cells jump into action if an infection starts. Some of these more specialized white blood cells produce special protein molecules called antibodies. 

Antibodies stick to germs and flag them for other white blood cells to destroy. 

These white blood cells can’t work quickly enough to stop you from getting sick with the infection. But by fighting off the germs they can help you get well again.
Our white blood cells start fighting off germs as soon as they enter our body, but sometimes this takes time. That’s why it usually takes about 3 to 5 days and sometimes longer to feel better after getting an infection. 

Sometimes your body needs help fighting off infections. This is why your doctor will sometimes give you medicine.


The really good thing about our immune system is that after fighting off the infection, the body remembers the germ and how to fight it. This is why people usually only get sick once with the same germ. Chickenpox or measles are good examples. You might not be familiar with chickenpox or measles because you have protection from them from vaccines. This protection is called immunity. Immunity can come from a previous infection or from a vaccine. 


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 This was just one of the lessons in our Germs, The Body's Defense System, & How Vaccines Help section. There are over 500 lessons on Kids Boost Immunity just like this one on a variety of subjects. Each lesson includes a quiz and every time a student scores 80% or higher on a quiz, we will donate life-saving vaccines to UNICEF Canada. Sign up now!

To see other sample lessons, click here.

  Aug 25, 2023