White blood cells, also known as leukocytes, are nucleated cells of the bloodstream and their primary functions are defense mechanisms. There are five primary types of white blood cells: the neutrophils, lymphocytes, monocytes, eosinophils and basophils. All but the lymphocytes are considered phagocytic scavengers, which means they engulf and destroy invading microorganisms and remove unwanted or dead cells. The lymphocytes also have a defense mechanism function in which they are integral in the production of antibodies.
Neutrophils
Neutrophils are the most predominant of the white blood cells in human blood, accounting for about 60 percent of white blood cells in a normal person. The mature neutrophil have a multi-lobed nucleus and a cytoplasm containing faint pink granules. They are anti-bacterial cells that not only phagocytize microorganisms but also produce an enzyme that destroys bacterial cells. Increases in neutrophils are seen in bacterial infections. Certain types of leukemias can alter the amount of white blood cells present in blood.
Lymphocytes
Lymphocytes are smaller white blood cells that have a single nucleus that takes up most of the cell and a cytoplasm that lacks granules. In the normal adult, lymphocytes make up 30 percent to 35 percent of circulating white blood cells. Lymphocytes originate in the lymph nodes while other white blood cells originate in the bone marrow. The lymphocytes are involved in the production of antibodies and regulate immune responses. Increases of lymphocytes are seen in acute viral infections such as mononucleosis, mumps and German measles among others.
Monocytes
The monocytes, like the lymphocytes, are mononuclear white blood cells that lack cytoplasmic granules. They are the largest of the white blood cells and can appear in a variety of shapes. They make up 4 percent to 6 percent of the circulating white blood cells. According to David King at the Southern Illinois University School of Medicine, monocytes act as macrophages, engulfing foreign microorganisms, dead or worn-out cells, and other tissue debris. Increases in monocytes can be seen in cases of mononucleosis and chronic inflammation.
Eosinophils
Like neutrophils, eosinophils are multi-lobed granulocytic white blood cells. They are characterized by the large red granules found in the cytoplasm. They make up only about 3 percent of white blood cells. Increases in eosinophils are seen with allergic reactions and parasitic infections.
Basophils
This white blood cell constitutes only about 0.5 percent of all circulating white blood cells. The appearance of the basophil shows a multi-lobed nucleus with deep purple to black staining granules. They are involved in the process of triggering inflammation. Increases in peripheral basophils are associated with chronic myelogenous leukemia.
References
- "Clinical Laboratory Science: The Basics and Routine Techniques"; Jean Jorgenson Linne; 1999
- Southern Illinois University: Blood Cells
