Immune system

Every day tiny germs like bacteria and viruses meet your body. You never notice most of them because your immune system fights them off. The immune system is not a single place in the body but a whole team of cells and substances that protects you around the clock.

The first wall: skin and mucus

Before a germ can even get into the body it first has to get past barriers. The skin is like a solid wall. In the nose and throat mucus and fine hairs catch many germs, and stomach acid destroys a lot of what you swallow. This defense works all the time, without you doing anything for it.

White blood cells on duty

If a germ does make it into the body, the white blood cells come into play. Some of them surround the invaders and simply eat them up, which is why they are called eater cells. They swim in the blood and in the tissue fluid and patrol through the whole body. At an inflamed wound so many of them gather that the spot turns warm and red.

Antibodies as guided defense

Certain white blood cells produce antibodies. These are small proteins that fit exactly one single germ, like a key fits a lock. An antibody attaches to the germ, makes it harmless, and marks it for the eater cells. For every germ the body needs its own matching antibody.

Memory and vaccination

After you get over an illness the body remembers the germ. Memory cells keep the blueprint for the matching antibody. If the same germ arrives again later, the body reacts much faster. A vaccination uses exactly this: it shows the immune system a harmless part of the germ. Some vaccines only deliver the instructions for that part, and the body makes it itself. So it builds antibodies and memory cells without you getting sick.