Certain receptors on immune cells grab onto antibodies attached to germs, helping the cells swallow them up so they can be broken down and shown to other immune cells.

One type of receptor (FcγRI) grabs onto single antibodies really tightly, while other receptors only grab well when many antibodies are stuck together on a germ.

One type of receptor (FcγRIIB) can also swallow antibody-tagged germs, but it doesn’t turn on the immune system as strongly — it needs 30 times more germs to get the same effect as the activating receptors.

When antibodies tag a germ, immune cells that show antigens to killer T cells do a much better job of it than if the germ was just floating around without tags.