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.