Neutrophil
Most abundant white blood cell, key in innate immunity.
Neutrophils are a type of phagocytic white blood cell and part of innate immunity. They form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in different animals; in humans they participate in processes such as sterile inflammation, tissue repair, and cancer, and exhibit coordinated collective behavior. They are also known as neutrocytes, heterophils or polymorphonuclear leukocytes.
- field
- Immunology, Hematology
- known_for
- First responders in acute inflammation; predominant cells in pus; phagocytic activity against bacteria
- normal_range
- 2.5–7.5 × 10^9/L in human blood
- average_diameter
- 12–15 μm (adhered); 8.85 μm (in suspension)
Lore & Background
Neutrophils are formed from stem cells in the bone marrow and differentiated into subpopulations of neutrophil-killers and neutrophil-cagers. Neutrophils may be subdivided into segmented neutrophils and banded neutrophils (or bands). They form part of the polymorphonuclear cells family (PMNs) together with basophils and eosinophils. The name neutrophil derives 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. Normally, neutrophils contain a nucleus divided into 2–5 lobes.
Reader's Guide
Neutrophils are a cornerstone of the acute inflammatory response. During the beginning phase of inflammation, particularly due to bacterial infection, environmental exposure, and some cancers, neutrophils are among the first responders to migrate toward the site of inflammation. They migrate through blood vessels and interstitial space following chemical signals such as interleukin-8 (IL-8), C5a, fMLP, leukotriene B4, and hydrogen peroxide in a process called chemotaxis. They are the predominant cells in pus, accounting for its whitish-to-yellowish appearance. Neutrophils are recruited to the site of injury within minutes following trauma and are the hallmark of acute inflammation. They not only play a central role in combating infection but also contribute to pain in the acute period by releasing pro-inflammatory cytokines and other mediators that sensitize nociceptors. However, due to some pathogens being indigestible, they may not resolve certain infections without assistance from other immune cells. Their short lifespan is hypothesized to be an evolutionary adaptation that minimizes propagation of pathogens that parasitize phagocytes and limits host tissue damage during inflammation.
Did You Know?
- Neutrophils make up approximately 50–70% of all white blood cells in humans.
- The capacity of neutrophils to engulf bacteria is reduced when simple sugars like glucose, fructose, sucrose, honey, and orange juice are ingested, while fasting strengthens this capacity.
- Up to 17% of female human neutrophil nuclei have a drumstick-shaped appendage containing the inactivated X chromosome.
- Neutrophils preferentially engulf and kill beta-1,6-glucan targets compared to beta-1,3-glucan targets.
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