Antibody
Antibody is a protein your body makes to find and stick to germs so they stop making you sick.
Think of it this way
A key fits one lock and no other. Each antibody has a shape that matches one germ and nothing else. When the antibody finds its germ, it sticks to the outside like a lid snapping onto a jar. Once the germ is covered, your immune cells can find it and clear it away.
Explaining antibody by grade level
When a germ gets in your body, your blood makes tiny helpers. These helpers are called antibodies. Each one fits one kind of germ, like a key fits a lock. The helper sticks to the germ so your body can get rid of it.