Antibodies and Memory Cells: The Body's Targeted Defence

0:00When germs get into your body, how does your immune system target them?

0:05Every germ carries molecules called antigens on its surface, and each kind of germ has its own antigen shape.

0:13White blood cells called lymphocytes respond by making antibodies.

0:19An antibody is a Y-shaped protein. The tips of its two arms fit one antigen shape.

0:26It fits its antigen like a key in a lock, and sticks to the germ.

0:31But this antibody does not fit a different germ, whose antigens have another shape.

0:37So one antibody does not work against every germ. Each kind of germ needs its own antibody.

0:44With two arms, an antibody can hold two germs at once, so antibodies clump germs together.

0:52Then phagocytes, another kind of white blood cell, engulf the clump and digest the germs.

0:59After the infection, some lymphocytes stay in the body as memory cells.

1:06This graph shows the level of antibodies in the blood over time.

1:10The first time you meet a germ, antibodies take several days to build up, so you may feel ill.

1:17If the same germ comes back, memory cells make the matching antibodies faster, and far more of them.

1:25So the germs are usually destroyed before you feel ill. This is called immunity.

1:32Each antibody fits one antigen like a key in a lock, and memory cells make the response to the same germ faster and bigger.