neutrofils

Neutrophils are a type of white blood cell and the most abundant leukocytes in humans, making up a large portion of circulating immune cells. They are granulocytes with a multilobed nucleus and cytoplasmic granules that stain with standard blood stains. Neutrophils are produced in the bone marrow as part of the body's first line of defense against infection and form a key component of the innate immune system.

Functionally, neutrophils act as rapid responders to sites of infection or injury. They migrate from blood vessels to tissues through chemotactic signals, engulf and digest bacteria and fungi via phagocytosis, and destroy pathogens through an oxidative burst that generates reactive oxygen species and antimicrobial compounds. They can release granule contents to kill microbes and, in some circumstances, release networks of DNA and proteins known as neutrophil extracellular traps (NETs) to trap and kill pathogens.

Production, lifespan, and regulation are tightly controlled. Neutrophils originate from myeloid progenitors in the bone marrow and are stimulated by colony-stimulating factors, especially G-CSF. In healthy adults, circulating neutrophil counts typically range around 1.5 to 8.0 x 10^9/L, though exact ranges vary by laboratory. Their circulation is relatively short, with most spending hours in the bloodstream before migrating into tissues, where they may persist for a short time before undergoing programmed cell death.

Clinical relevance includes conditions of abnormal neutrophil numbers or function. Neutropenia, a reduced neutrophil count, increases infection risk and can result from chemotherapy, bone marrow disorders, or severe illness. Neutrophilia, an elevated count, is often seen with acute infections, stress, or inflammatory states. Neutrophil dysfunction can occur in genetic disorders such as chronic granulomatous disease.