Neutrophils - Overview

Summary

Neutrophils are the most abundant leukocyte in our bodies. Due to their multi-lobed nuclei, neutrophils are also called polymorphonuclear cells. Neutrophils are seen in acute inflammation, and levels increased in infection, tissue injury, or autoimmune processes. Neutrophils are attracted to inflammation sites by C5a, IL-8, and Leukotriene B4. Neutrophils function in our innate immune response to fight infections by phagocytosing foreign microbes, degranulating to release antimicrobial molecules, or by forming neutrophil extracellular traps (NETs). Although elevated neutrophil counts usually point to infection or inflammation, corticosteroid use can cause elevated neutrophil counts via demargination of resting pools of neutrophils.

Key Points

• Neutrophils
  • Most abundant white blood cell (50-70%) in circulation
  • Contains multilobed nuclei (3-5 lobes)
    • most common polymorphonuclear cell (PMN)
    • hypersegmented nuclei (>6 lobes) characteristic of megaloblastic anemia in Vitamin B9 and B12 Deficiencies
    • Cytoplasm with pale, heterogeneously staining granules 
  • Indicator of acute inflammation 
    • Neutrophil levels increased in infection, tissue injury, or autoimmune processes
    • Majority of neutrophils held in resting pools (liver, lung, spleen)
      • Corticosteroids cause demargination (release into blood)
        • elevated neutrophil counts independent of inflammation
  • Attracted to inflammation sites by
    • C5a
      • Produced in Common Complement Activation
    • Leukotriene B4 (LTB4)
    • Interleukin-8 (IL-8)
    • Platelet-activating factor (PAF), kallikrein also involved
  • Functions
    • Phagocytosis of foreign microbes
    • Degranulation releases antimicrobial contents of Neutrophil Granules
    • Oxidative Burst produces reactive oxygen species
    • Generation of neutrophil extracellular traps (NETs)