Neutrophils: The Predominant White Blood Cell (50–70%)—Production, Infection Defense, and Inflammatory Role

Neutrophils are the most abundant leukocytes (50–70% of circulating WBCs), produced in bone marrow from myeloid precursors. They circulate ~10–14 hours (marginated pool extends functional lifespan).

Antimicrobial Mechanisms

• Phagocytosis: Engulf bacteria/fungi; fuse with granules → phagolysosome.
• Degranulation: Release elastase, cathepsin G, myeloperoxidase (MPO), defensins.
• NETosis: Neutrophil extracellular traps (DNA + antimicrobial proteins) ensnare pathogens.
• Reactive oxygen species (ROS): Respiratory burst (NADPH oxidase) kills ingested microbes.

Inflammatory Role

• Chemotaxis toward IL-8, LTB4, C5a, fMLP.
• Release cytokines (TNF-α, IL-1β) amplifying inflammation.
• Increase vascular permeability, recruit monocytes/macrophages.

Clinical Relevance

• Neutropenia (<1500/µL): Infection risk (bacterial/fungal); causes: chemo, autoimmune, congenital, drugs.
• Neutrophilia: Stress, infection, inflammation, corticosteroids, myeloproliferative neoplasms.
• Functional defects: CGD (NADPH oxidase deficiency), LAD (adhesion deficiency).