Overview

Proportion of leukocytes≈ 40–75%

Normal count2.0–7.5 × 10⁹/L

Diameter≈ 12–15 µm

LifespanHours in blood; ≈ 1–2 days in tissues

Neutrophils are ≈ 12–15 µm across, with a nucleus of 3–5 lobes joined by thin strands of chromatin and a pale cytoplasm filled with fine, faintly lilac granules (staining with neither acidic nor basic dyes — hence "neutral"). In females a small "drumstick" appendage (the inactive X chromosome, Barr body) may be seen on a few cells. Immature band forms have an unsegmented, horseshoe-shaped nucleus.

They are made in the bone marrow over ≈ 10–14 days, which keeps a large reserve of mature cells ready for release. In the blood they survive only hours (half-life roughly 7–10 h) before entering tissues, where they live 1–2 days and die by apoptosis — being cleared by macrophages, a key step in the resolution of inflammation. Pus consists largely of dead neutrophils and liquefied tissue.

Recruited within minutes to hours by CXCL8, C5a and leukotriene B4, neutrophils phagocytose bacteria and fungi coated with opsonins (IgG via Fcγ receptors, C3b/iC3b via complement receptors). The phagosome fuses with granules and activates NADPH oxidase — the respiratory (oxidative) burst — producing superoxide and hydrogen peroxide, which myeloperoxidase converts to hypochlorous acid (bleach). Granule proteases, defensins and lactoferrin complete the killing. Activated neutrophils can also expel neutrophil extracellular traps (NETs) — webs of chromatin studded with granule proteins that trap microbes.

Location: Bone marrow (storage pool), blood (circulating and marginated pools in roughly equal parts) and inflamed tissues.

Parts & subdivisions

Primary (azurophilic) granules
Lysosome-like: myeloperoxidase, elastase, cathepsin G, defensins, bactericidal/permeability-increasing protein. Appear first at the promyelocyte stage.
Secondary (specific) granules
Lactoferrin, lysozyme, collagenase, membrane components of NADPH oxidase; appear at the myelocyte stage.
Tertiary (gelatinase) granules and secretory vesicles
Gelatinase (MMP-9) for migration through basement membrane; vesicles carrying receptors and integrins to the surface.
Multilobed nucleus
3–5 lobes; flexibility helps squeeze between endothelial cells. Bands (unsegmented) are immature.

Anatomy

Histology: Lobed nucleus, pale granular cytoplasm. Reactive changes: left shift (bands and earlier forms), toxic granulation, Döhle bodies and cytoplasmic vacuoles in sepsis.

Function

Rapid migration to sites of infection and tissue injury.
Phagocytosis and intracellular killing of bacteria and fungi (oxygen-dependent and oxygen-independent).
Release of NETs and antimicrobial granule proteins.
Amplification of inflammation through cytokines and lipid mediators.

Physiology: Production is driven by G-CSF; glucocorticoids raise the count by releasing marrow reserves and causing demargination. Normal count 2.0–7.5 × 10⁹/L.

Clinical significance

Neutrophilia and neutropenia

Neutrophilia: bacterial infection, inflammation, necrosis (myocardial infarction), corticosteroids, pregnancy, smoking, myeloproliferative disease. Neutropenia: chemotherapy, drugs causing agranulocytosis (carbimazole, clozapine, sulfasalazine), viral infection, B12/folate deficiency, autoimmune and benign ethnic neutropenia.

Hypersegmented neutrophils

Neutrophils with ≥ 6 lobes (or > 5% with 5 lobes) are an early sign of megaloblastic anaemia (vitamin B12 or folate deficiency).

Chronic granulomatous disease

Inherited defect of NADPH oxidase (commonly X-linked CYBB): neutrophils ingest but cannot kill catalase-positive organisms (Staphylococcus aureus, Aspergillus, Serratia, Burkholderia, Nocardia), causing recurrent abscesses and granulomas. Diagnosed by an abnormal dihydrorhodamine (DHR) flow-cytometry test (formerly the nitroblue tetrazolium test).

Compiled from standard anatomy and physiology references — see the Lymphatic & Immune System sources. For education only; not medical advice.