Neutrophil granulocyte
From Free net encyclopedia
Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of white blood cells and form an integral part of the immune system. Image:Segmented neutrophils.jpg
Contents |
Role in blood
Neutrophil granulocytes have an average volume of 330 femtoliters (fl) and a diameter of 12-15 micrometers (µm) in peripheral blood smears.
Together with the eosinophil and the basophil they form the class of polymorphonuclear cells (PMNs), as their nucleus has a characteristic, multilobulated shape—as opposed to the other types of white cells, namely lymphocytes and monocytes. Neutrophils are the most abundant white blood cells; they account for 70% of all white blood cells (leukocytes), although there are ethnic differences.
The average halflife of a non-activated neutrophil in the circulation is about 4-10 hours, wherafter they marginate (stick to the blood vessel wall) and migrate into tissues, where they survive for 1-2 days.
Function
Neutrophils are active phagocytes, capable of ingesting microorganisms or particles. However, they can only execute one phagocytic event, expending all of their glucose reserves in an extremely vigorous "respiratory burst".
The respiratory burst involves the activation of an NADPH oxidase enzyme, which produces large quantities of superoxide, a reactive oxygen species, which generally kills the ingested organism.
Being highly motile, neutrophils quickly congregate at a focus of infection, attracted by cytokines expressed by activated endothelium, mast cells and macrophages.
Neutrophils are much more numerous than the longer-lived monocyte/macrophages. The first phagocyte a pathogen (disease-causing microorganism) is likely to encounter is a neutrophil. Some authorities feel that the short lifetime of neutrophils is an evolutionary adaptation to minimize propagation of those pathogens that parasitize phagocytes. The more time such parasites spend outside a host cell, the more likely they will be destroyed by some component of the body's defenses. However, because neutrophil antimicrobial products can also damage host tissues, other authorities feel that their short life is an adaptation to limit damage to the host during inflammation.
Role in disease
Low neutrophil counts are termed "neutropenia". This can be congenital (genetic disorder) or due to acquired factors. It can also be a side-effect of medication, most prominently chemotherapy. Neutropenia predisposes heavily for infection.
Functional disorders of neutrophils are often hereditary. They are disorders of phagocytosis or deficiencies in the respiratory burst (as in chronic granulomatous disease, a rare immune deficiency).
In alpha 1-antitrypsin deficiency, the important neutrophil enzyme elastase is not adequately inhibited by alpha 1-antitrypsin, leading to excessive tissue damage in the presence of inflammation - most prominently pulmonary emphysema.
In Familial Mediterranean fever (FMF), a mutation in the pyrin (or marenostrin) gene, which is expressed mainly in neutrophil granulocytes, leads to a constitutionally active acute phase response and causing attacks of fever, arthralgia, peritonitis and - eventually - amyloidosis.
See also
External links
- Crawling Neutrophil Chasing a Bacterium video from a 1950s 16-mm movie by the late David Rogers at Vanderbilt University (requires Apple QuickTime)
| Immune system - edit |
|---|
| Humoral immune system | Cellular immune system | Lymphatic system | White blood cells | Antibodies | Antigen (MHC) | Complement system | Inflammation | Clotting factors |
de:Neutrophiler Granulozyt fr:Granulocyte neutrophile he:נויטרופיל ja:好中球 lt:Neutrofilas pl:Neutrofil ru:Нейтрофильные гранулоциты tr:Nötrofil