White blood cell

White blood cells, also called leukocytes or immune cells, are important for keeping our bodies healthy. They help protect us from infectious disease and things that don’t belong in our bodies. White blood cells are bigger than red blood cells and have a special part called a nucleus.

There are different kinds of white blood cells. Some of them are lymphocytes, monocytes, and granulocytes. Granulocytes include neutrophils, eosinophils, and basophils. All white blood cells start from special cells in our bone marrow called hematopoietic stem cells.

The number of white blood cells in our blood can help doctors learn about our health. If there are more white blood cells than usual, it often means the body is fighting an infection. Even though there are fewer white blood cells than red blood cells, they are very important for keeping us safe and well.

Etymology

The name "white blood cell" comes from how blood looks after it is spun in a machine. When blood is spun, white cells form a thin, white layer called the buffy coat. This layer sits between the red blood cells and the liquid part of blood, called plasma. The scientific name for these cells is leukocyte, from Greek words meaning "white" and "cell".

Types

White blood cells, also called leukocytes, are bigger than red blood cells and come in several types. They can be grouped by their looks into granulocytes (which have granules) and agranulocytes (which do not). Another way to group them is by their family into myeloid cells and lymphoid cells. The five main types of white blood cells are neutrophils, eosinophils, basophils, lymphocytes, and monocytes.

Neutrophils are the most common type and help fight infections. Eosinophils mainly fight infections and are important in allergic reactions. Basophils are involved in allergic responses and release chemicals to help the body react to injuries. Lymphocytes include B cells, which make antibodies, and T cells, which help coordinate the immune response and fight infected cells. Monocytes are the largest white blood cells and help clean up dead cells and fight infections.

Type	Appearance		Approx. % in adults See also: Blood values	Diameter (μm)	Main targets	Nucleus	Granules	Lifetime
	(micrograph)	(illustration)
Neutrophil			62%	12–15	Bacteria Fungi	Multilobed	Fine, faintly pink (H&E stain)	6 hours – few days (days in spleen and other tissue)
Eosinophil			2.3%	12–15 (slightly bigger than neutrophils)	Larger parasites Modulate allergic inflammatory responses	Bi-lobed	Full of pink-orange (H&E stain)	8–12 days (circulate for 4–5 hours)
Basophil			0.4%	12–15 (slightly smaller than neutrophils)	Release histamine for inflammatory responses	Bi-lobed or tri-lobed	Large blue	A few hours to a few days
Lymphocyte			30%	Small lymphocytes 7–8 Large lymphocytes 12–15	B cells: releases antibodies and assists activation of T cells T cells: CD4+ T helper cells: activate and regulate T and B cells CD8+ cytotoxic T cells: virus-infected and tumor cells. Gamma delta T cells: bridge between innate and adaptive immune responses; phagocytosis Regulatory T cells: Returns the functioning of the immune system to normal operation after infection; prevents autoimmunity Natural killer cells: virus-infected and tumor cells.	Deeply staining, eccentric	NK-cells and cytotoxic (CD8+) T-cells	Years for memory cells, weeks for all else.
Monocyte			5.3%	15–30	Monocytes migrate from the bloodstream to other tissues and differentiate into tissue resident macrophages, Kupffer cells in the liver.	Kidney shaped	None	Hours to days

Fixed leucocytes

Some white blood cells move to different parts of the body and stay there forever. For example, in the liver, they become special cells called Kupffer cells that help keep the body safe. These cells still work for the immune system, even though they no longer move around in the blood.

Other types of fixed white blood cells include Histiocytes, Dendritic cells, Mast cells, and Microglia. Each type has its own important job in keeping the body healthy.

Disorders

White blood cell disorders can be divided into two main groups.

One group is based on the number of white blood cells. Too many white blood cells, called proliferative disorders, can happen when the body is fighting an infection or due to other health problems. Too few white blood cells, called leukopenias, can make it harder for the body to fight off germs.

The other group is based on how well the white blood cells work, even if their numbers are normal. Sometimes, white blood cells can develop cancers, which are called leukemias and lymphomas. These conditions can be serious and need special care from doctors.

Counting and reference ranges

A complete blood cell count is a test that checks how many white blood cells are in your blood. It also counts each type of white blood cell. This helps doctors know if your immune system is healthy. In healthy adults, there are usually between 4,000 and 11,000 white blood cells in each cubic millimeter of blood. Doctors also check the numbers of each kind of white blood cell to make sure they are balanced.