Which blood cells fight infection?

White blood cells are made in the bone marrow and make up only about 1% of blood volume. A healthy adult normally has about 4,000 to 11,000 of them in each microlitre of blood. There are five main types: neutrophils, the most common, which engulf bacteria; lymphocytes, including B cells that make antibodies and T cells that attack infected cells; monocytes, which become germ-eating macrophages; eosinophils, which target parasites; and basophils, which release chemicals during allergic reactions. When you have an infection, your body often makes more white blood cells, which is why doctors check a white cell count. Pus is largely made of dead neutrophils that have fought bacteria.