How does your immune system work ?
Your immune system uses a huge army of defender cells - different types of white blood cell. Some of these cells, called macrophages, constantly patrol your body, destroying germs as soon as they enter. This is your natural immunity. But if an infection begins to take hold, your body fights back with an even more powerful defence of T- and B-cells. They give you acquired immunity, so that the same germ can never make you as ill again.
What are T and B cells ?
T- and B-cells are highly specialised defender cells - different groups of cells are tailored to different germs. When your body is infected with a particular germ, only the T- and B-cells that recognise it will respond. These selected cells then quickly multiply, creating an army of identical cells to fight the infection. Special types of T- and B-cells 'remember' the invader, making you immune to a second attack