antibody

An antibody is a tiny Y-shaped protein your body builds to grab hold of one specific intruder. The two tips of the Y are exquisitely shaped to clamp onto a particular target — a piece of a virus, a bacterium, a speck of pollen — the way a key fits one lock and no other. That target is called the antigen, and a single antibody ignores everything except its own.

Once it latches on, the antibody acts like a flag and a handcuff at the same time. It can smother a virus so it can't break into your cells, clump invaders together into a sticky useless wad, or tag them so the immune system's clean-up crews know exactly what to swallow. Your body can make an astonishing variety of them — billions of different shapes — ready for almost anything it might meet.

Here's the part that protects you for life: after an infection, a few cells keep the winning recipe on file. Meet that same germ again and your body churns out matching antibodies fast, often before you ever feel sick. That memory is exactly what vaccines train. Antibodies are also why a blood transfusion has to match: your plasma carries antibodies aimed at the blood-group markers — the antigens — that your own red cells happen to lack, so the wrong blood gets attacked. A common myth is that antibodies kill germs directly; mostly they don't. They mark and disarm, then hand the target over to the rest of the immune system.