Your body's guards
Germs are tiny living things, like some bacteria and viruses, that can make you sick. Your white blood cells are always on the lookout for them.
They ride around in your blood and slip out into your body wherever they are needed. When they find a germ, they get to work.
White blood cells are not really white. They are pale and almost clear. When blood is spun in a special machine, they make a thin, whitish layer, and that is how they got their name.
Different guards, different jobs
There are five main kinds of white blood cells, and each kind has its own job, like players on a team.
Some are germ eaters. They wrap around a germ and swallow it up. They are often the first ones to arrive.
Some make antibodies (AN-tee-bod-eez). Antibodies are like tiny sticky flags that grab on to germs. They mark the germs so other guards can find them and stop them.
Some are helpers that send out messages and tell the other guards where to go.
Guards that remember
Some white blood cells have a super power: they remember. After your body beats a germ, a few memory cells stay behind, sometimes for many years.
If that same germ ever comes back, the memory cells know it right away. They help your body make antibodies fast, often before you even feel sick.
This is how vaccines work. A vaccine shows your white blood cells a harmless copy or piece of a germ, so they can learn what it looks like. Then they are ready if the real germ ever shows up.
Fewer, but mighty
There are far fewer white blood cells than red blood cells. For every white blood cell in your blood, there are hundreds of red ones.
But when you get sick, your body makes more of them, and they rush to where the germs are.
When you have a cold, you might feel little lumps in your neck. These are lymph nodes (LIMF nodes), small bean-shaped stations where white blood cells gather to fight germs. They usually go back to normal when you feel better.
When you feel sick
A fever, a stuffy nose or a sore throat can feel yucky, but they often mean your white blood cells are busy fighting.
Rest, drink plenty of water and let a grown-up take care of you. Resting helps your body put its energy into beating the germs.
If you feel really sick, a grown-up can take you to a doctor.