The FIVE white blood cells you must know.

White blood cells can be classified as either phagocytes or immunocytes. Of the phagocytes they can be further classified as granulocytes (Basophils, Eosinophils and Neutrophils) as well as monocytes. The immunocytes are the lymphocytes including B and T cells and Natural Killer Cells.

The following is a short blurb on what each does:

Basophils: Are the least common leucocyte, contributing to less than 1% of circulating leucocytes. They have a intensely basophilic (blue) granular appearance. Have IgE attachment sites that lead to histamine release for degranulation.  When migrated into the tissue, basophils mature into Mast Cells.

Eosinophils: Contribute towards 1% of circulating leucocytes. Stain red with eosin. Have a strong role in allergic responses and host defence against parasites. Their production is stimulated by IL-5. Release granules that contain basic proteins and also peroxides.

Neutrophils: Contribute 75% to the circulating leukocytes. Multi lobular nucleus with a granulated appearance. They usually maintain in the circulation. Only present in tissues in large numbers during acute inflammation, killing invading microorganisms via phagocytosis.

Monocytes: In the blood they are known as monocytes, once they migrate into the tissue they mature into macrophages (or histiocytes) . In different tissues they are known as different names.  You may know them by:

  • Kidney: Intraglomerular mesangial cells
  • Brain: Microglia
  • Serosa: Macrophages
  • Lung: Alveolar macrophages
  • Liver: Küpffer cells
  • Spleen: Sinus macrophages, Antigen Presenting Cells (APC)
  • Bone Marrow: macrophages, APC
  • Lymph nodes: macrophages, APC

Lymphocytes: Second most common circulating leukocytes making up nearly 25%. Appear round and have a densely stained nucleus. They include B cells, T cells and also NK cells.

Reference sources:

  1. Young B, Lowe J, Stevens A, Heath J. Blood. Wheater’s Functional Histology. 5th ed. Philadelphia: Elsevier limited; 2006. p. 46–56.
  2. Hoffbrand A, Moss P. White cells: Granulocytes and monocytes.Essential Haematology. 6th ed. Oxford: Wiley-Blackwell; 2011.

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