Neutrofiilide

Neutrofiilide, commonly known as neutrophils in English, are a type of white blood cell belonging to the granulocyte family of the innate immune system. They are the most abundant leukocytes in human blood and are rapidly recruited to sites of infection. Neutrofiilide are produced in the bone marrow from myeloid precursors and are released during acute inflammatory responses.

Morphology and granules: Neutrofiilide are small to medium-sized cells with a multi-lobed nucleus (typically 2–5 lobes) and cytoplasmic granules. They contain two main granule systems: azurophilic (primary) granules with enzymes such as myeloperoxidase and defensins, and specific (secondary) granules with lactoferrin and collagenase. This granule content enables rapid antimicrobial action.

Functions: They circulate for a short time (around 6–10 hours) and migrate rapidly to inflamed tissues in response to chemokines and complement signals. There they perform phagocytosis, generate reactive oxygen species in the respiratory burst, release antimicrobial proteins, and can form neutrofiilide extracellular traps (NETs) to trap and kill pathogens. Lifespan in tissues is typically a day or two before cell death or clearance.

Clinical significance: The total neutrofiilide count and the absolute neutrophil count (ANC) are common blood test metrics. Neutropenia, defined as an ANC below about 1.5 x 10^9/L, increases infection risk and can result from chemotherapy, bone marrow disorders, or autoimmune disease. Neutrophilia, an elevated count, can occur with infection, inflammation, steroids, or smoking. Treatments such as granulocyte colony-stimulating factor (G-CSF) are used to stimulate neutrophil production in certain patients.

Research and topics: Neutrophils are traditionally viewed as first responders to bacterial and fungal infections, but they also participate in tissue homeostasis and chronic inflammatory diseases. Recent work explores neutrophil heterogeneity, aging, and their role in noninfectious conditions.