Polymorphonuclear Leukocytes (PMNs): Neutrophil Function and Clinical Significance

PMNs = Neutrophils (most abundant leukocyte, 60–70% of circulating WBCs). Multi-lobed nucleus (2–5 lobes), cytoplasmic granules.

Key Functions

• Phagocytosis: Engulf bacteria/fungi; oxidative burst (NADPH oxidase → ROS), granular enzymes (MPO, elastase, cathepsin G) → microbial killing.
• NETosis: Neutrophil extracellular traps (DNA + antimicrobial proteins) trap/kill pathogens.
• Chemotaxis: Rapid migration to infection sites (IL-8, LTB4, C5a, fMLP gradients).
• Inflammation modulation: Cytokines (TNF-α, IL-1β, IL-8), lipid mediators.
• Adaptive immunity bridge: Antigen presentation, T-cell recruitment, B-cell help.

Clinical Counts (Absolute Neutrophil Count = ANC)

• Normal: 1.5–8.0 ×10³/µL (varies by lab/ethnicity).
• Neutrophilia (>8k): Infection, inflammation, stress, steroids, myeloproliferative neoplasms.
• Neutropenia (<1.5k): Chemo, autoimmune, congenital, drugs, B12/folate deficiency, sepsis (consumption).
• Benign ethnic neutropenia: Common in African, Middle Eastern descent; no infection risk.

Emergency

ANC <0.5k (severe neutropenia) + fever = medical emergency (febrile neutropenia).