Basophil

Basophils, or basophil granulocytes, are rare granulocytes. If you had 10,000 white blood cells, only 1–30 of them would be basophils.

Basophil
3D rendering of a basophil
Basophil among red blood cells
System	Immune system

Drawing of a basophil granulocyte. See animation at [1]

Basophils contain large cytoplasmic granules. When stained, the granules hide the cell nucleus from sight. However, when unstained, the nucleus is visible and it usually has two lobes.

The mast cell, another granulocyte, is similar in appearance and function. Both cell types store histamine, a chemical that is secreted by the cells when stimulated. However, they come from different cell lines. Mast cells usually do not circulate in the blood stream, but instead stay in connective tissue. Like all circulating granulocytes, basophils go from the blood into a tissue when needed.

The name comes from the fact that these leukocytes are basophilic, i.e., they are stained by basic dyes, as shown in the illustrations.

How they work is not well understood. Basophils have protein receptors on their cell membrane which binds IgE, an immunoglobulin involved in macroparasite defence and allergy. They are found in unusually high numbers at sites of ectoparasite infection, for example, by ticks.

Basophil Media

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  Reference ranges for blood tests of white blood cells, comparing basophil amount (shown in violet) with other cells.

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  Alternate stain of a basophil