neutrofilt

Neutrophil, or neutrofilt in Swedish, is a type of white blood cell that forms part of the innate immune system. It is the most abundant leukocyte in humans, accounting for about 40-70% of circulating white cells. Neutrophils are produced in the bone marrow from hematopoietic stem cells through a maturation sequence that ends with segmented neutrophils, which have a distinctive multilobed nucleus and cytoplasmic granules containing antimicrobial substances.

Function and mechanisms: Neutrophils are rapid responders to infection and injury. They phagocytose bacteria and fungi, release proteolytic enzymes and antimicrobial peptides by degranulation, and generate reactive oxygen species via the NADPH oxidase system. They also can form neutrophil extracellular traps (NETs) to trap and kill microorganisms. Their recruitment to tissues is guided by chemokines such as IL-8 and by opsonization through antibodies and complement.

Physiology and life cycle: in blood they circulate for roughly 6-8 hours before migrating into tissues, where they survive about 1-2 days. The bone marrow can upregulate production in response to infection, with granulocyte colony-stimulating factor (G-CSF) increasing neutrophil output.

Clinical relevance and testing: neutrophil counts are a key part of the complete blood count. Neutropenia, a low absolute neutrophil count, increases susceptibility to bacterial and fungal infections and can be congenital or acquired. Neutrophilia, an elevated count, occurs in acute infection, inflammation, stress, or steroid use. Defects in neutrophil function, as in chronic granulomatous disease, can impair microbial killing even when counts are normal.