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Neutrophils are a type of leukocytes, or white blood cells. They play an important role in the immune system of the body. They are one of the first blood cells to be sent to the site of infection and are largely responsible for the whitish color of pus, as they make up most of it. The immune system uses them as part of the front-line attack to fight any infection or foreign body that enters the body.
They can be divided into two different classes by their developmental stage: segmented neutrophils, or segs, and banded neutrophils, or bands. Segs are fully mature, and bands are almost mature. They contain a nucleus, which is divided into multiple lobes and can be discerned from other blood cells in the lab by staining. Neutrophils are also called neutrophil granulocytes because of their granular appearance.
Along with neutrophils, other types of white blood cells called basophils and eosinophils make up the polymorphonuclear neutrophils (PMNs). This descriptive term comes from the nucleus being lobed. They are produced in the bone marrow and travel in the blood stream.
The immune system is a complicated one, involving multiple mechanisms and cascade systems. White blood cells play a large part in the initial reaction of the body to a pathogen or foreign body. Neutrophils travel through the blood stream constantly, but when an infection or inflammation occurs, they are directed toward the site by cytokines, which are released at the site of infection or injury.
Neutrophils are phagocytic, which means they can ingest pathogens. When this occurs, they form a phagosome into which reactive oxygen species such as superoxide and hydrolytic enzymes are released. This, in turn, should kill the offending bacteria.
Laboratory measurement of white blood cells is used by doctors to diagnose infection and measure the functioning of the immune system. The measurement is expressed as absolute neutrophil count. A significant rise in white cells, especially neutrophils, may indicate an infection in the body.
On the other end of the spectrum, a low level, termed neutropenia, may indicate a suppressed immune system. Common causes of neutropenia include genetic disorders, aplastic anemia and some cancers, such as leukemia. Neutropenia may also happen as a side effect of cancer chemotherapy and other drugs, leaving the patient susceptible to infection. For this reason, patients undergoing cancer therapy must have their white blood cell count routinely monitored.