White blood cells, or leukocytes, are a part of the immune system. They help our bodies fight infection. White blood cells circulate in the blood so they can be transported to an area that has developed an infection. In normal adult bodies there are 4,000 to 10,000 (average 7,000) white blood cells per microliter of blood. If the number of white blood cells in your blood increases, it is a sign of an infection somewhere in the body.
There are six main types of white blood cells:
- Neutrophils, which make up 58 percent of the blood
- Eosinophils, which make up 2 percent
- Basophils, which makes up 1 percent
- Bands, which makes up 3 percent
- Monocytes, which makes up 4 percent
- Lymphocytes, which makes up 4 percent
Most white blood cells are formed in the bone marrow. The neutrophil, eosinophil and basophil type of white blood cells are also called granulocytes. They have granules that contain digestive enzymes. If a granulocyte is released into the blood, it remains for an average of four to eight hours. Then, it goes into the tissues of the body, where it can last for an average of four to five days. If a severe infection is present, these times are often shorter.