Neutrophil granulocytes, generally referred to as neutrophils, are the most abundant type of white blood cells in humans and form an essential part of the immune system. They form part of the polymorphonuclear cell family (PMN's) together with basophils and eosinophils.
Their name arrives from staining characteristics on hematoxylin and eosin (H&E) histological or cytological preparations. Whereas basophilic white blood cells stain dark blue and eosinophilic white blood cells stain bright red, neutrophils stain a neutral pink.
Neutrophils are normally found in the blood stream. However, during the beginning (acute) phase of inflammation, particularly as a result of bacterial infection, neutrophils migrate toward the site of inflammation, firstly through the blood vessels, then through interstitial tissue, following chemical signals (such as Interleukin-8 (IL-8), Interferon-gamma (IFN-gamma), and C5a) in a process called chemotaxis. They are the predominant cells in pus, accounting for its whitish/yellowish appearance.
Neutrophils react within an hour of tissue injury and are the hallmark of acute inflammation.
With the eosinophil and the basophil, they form the class of polymorphonuclear cells, named for the nucleus's characteristic multilobulated shape (as compared to lymphocytes and monocytes, the other types of white cells). Neutrophils are the most abundant white blood cells in humans (approximately 10^11 are produced daily) ; they account for approximately 70% of all white blood cells (leukocytes).
The stated normal range for human blood counts varies between laboratories, but a neutrophil count of 2.5-7.5 x 109/L is a standard normal range. People of African and Middle Eastern descent may have lower counts which are still normal.
A report may divide neutrophils into segmented neutrophils and bands.
Neutrophils are much more numerous than the longer-lived monocyte/macrophage phagocytes. The first phagocyte a pathogen (disease-causing microorganism) is likely to encounter is a neutrophil. Some experts 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.
The respiratory burst involves the activation of the enzyme NADPH oxidase, which produces large quantities of superoxide, a reactive oxygen species. Superoxide dismutates, spontaneously or through catalysis via enzymes known as superoxide dismutases (Cu/ZnSOD and MnSOD), to hydrogen peroxide, which is then converted to hypochlorous acid (HOCl, also known as chlorine bleach) by the green heme enzyme myeloperoxidase. It is thought that the bactericidal properties of HOCl are enough to kill bacteria phagocytosed by the neutrophil, but this has not been proven conclusively.
|specific granules (or "secondary granules")||Lactoferrin and Cathelicidin|
|azurophilic granules (or "primary granules")||myeloperoxidase, bactericidal/permeability increasing protein (BPI), Defensins and the serine proteases neutrophil elastase and cathepsin G|
|tertiary granules||cathepsin, gelatinase|
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, and myeloperoxidase 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 causes attacks of fever, arthralgia, peritonitis and - eventually - amyloidosis.
The effect of estrogens on superoxide anion generation by human neutrophil granulocytes: Possible consequences of the antioxidant defense
Aug 01, 2007; Abstract The present study aimed to test whether, beyond the known antioxidant effect of estradiol, such a property is also...