Leukocytes are commonly known as white blood cells. They are formed in the bone marrow, and are vital to the functioning of the immune system. There are five types of leukocyte, and each one has a different purpose in fighting illness.
A blood differential is a diagnostic test that measures and compares the amounts of each type of leukocyte. Doctors can gain insight into the cause of a patient's symptoms based on which leukocyte levels are elevated or depleted, according to the University of Maryland Medical Center.
Neutrophils
White blood cells that contain granules within the cell are referred to as "granulocytes." Neutrophils are a type of granulocyte.
In a normal blood sample, neutrophils make up 65 percent of the total white blood cell count. They are responsible for cellular defense. The granules within neutrophils produce powerful enzymes that can destroy bacteria, according to Mosby's Anatomy and Physiology 5th Edition.
Neutrophils can migrate outside of the blood vessels to fight infection in other body tissues. When cells are damaged by infection or inflammation, those cells release chemicals that attract neutrophils to the infected area. Neutrophils are short-lived, having a life cycle of from several hours up to 3 days.
Eosinophils
Eosinophils are also granulocytes. They make up 2 to 3 percent of a normal white blood cell count. They are prominent in the lining of the respiratory and digestive systems. Eosinophils release substances that counteract inflammation due to allergic reactions. They also perform cellular defense functions against larger disease-causing microorganisms, such as parasites and protozoa. Mosby states that eosinophils typically have a lifespan of 10 to 12 days.
Basophils
Basophils are the third type of granular leukocyte. They account for only 0.5 to 1 percent of the normal white blood cell count, making them the least numerous leukocyte. Basophils release inflammatory chemicals called histamines, as well as the anticoagulant, heparin. Basophils live about as long as neutrophils, up to 3 days.
Lymphocytes
Lymphocytes are the smallest leukocytes, but the second most numerous. They are agranulocytes, meaning they do not contain granules. Lymphocytes perform important immune functions by directly attacking cells that are infected or cancerous, or producing antibodies to fight infection. Lymphocytes can live for years, but some only last a few days.
Monocytes
The largest leukocytes are monocytes. Like the lymphocytes, they are agranulocytes. Being the largest leukocyte, they are capable of attacking and engulfing large bacterial cells, cancer cells, cellular debris and cells infected by viruses. They are also very motile, and can migrate beyond the blood vessels to attack infection in other tissues. Monocytes have a life span of several months.
References
- University of Maryland Medical Center: Blood Differential Overview
- Mayo Clinic: High White Blood Cell Count
- Anatomy and Physiology, 5th Edition; Gary A. Thibodeau, Kevin T. Patton; 2003
