White blood cells definition

White blood cell definition: also called leukocytes or leucocytes or white corpuscles, a cellular component of the blood that lacks hemoglobin, has a nucleus, is capable of motility, and defends the body against infection.

All white blood cells are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells. The production of leukocytes increases in response to any tissue damage, this is part of the normal inflammatory response. Its purpose is to limit the damage, remove the causative factor and restore tissue.

White blood cells differ in their structure, which determines the differences in their functions and roles in the body. 

White blood cells are divided into 2 groups:

Granulocytes are white blood cells that help the immune system fight off infection.

Agranulocytes are white blood cells that have no distinct granules in their cytoplasm.

The total number of white blood cells in the body of a healthy adult is approximately 7,000 cells per microliter of blood with the majority of lymphocytes and neutrophils in them.


Changes in the level of leukocytes and leukocyte formula are important signs that are used in the diagnosis of many diseases:

  • an increase in the level of leukocytes compared to the norm is called leukocytosis. A significant increase in the number of leukocytes (more than 50-100 thousand x 1012/l), as a rule, indicates a malignant tumor of the bone marrow and requires urgent medical attention,
  • a decrease (leukopenia) is much less common and most often indicates a viral infection, but it may be a sign of more dangerous diseases, such as AIDS or aplastic anemia.


White blood cells types:

  • neutrophils.
  • lymphocytes.
  • eosinophils.
  • monocytes.
  • basophils.