- Neutrophils are a type of Granulocyte (PMN) which serve in the initial wave of immune attack during a microbial infection. As such, the presence of Neutrophils in a tissue indicates on going Acute Inflammation.
- Neutrophils are short-lived immune cells that are never present in normal, healthy tissues. Instead, these cells circulate inactive in the blood where they compose between 40-60% of circulating leukocytes. They are rapidly recruited, within hours, to sites of inflammation where they quickly phagocytose cellular debris and any present pathogens. Internalized debris and microbes are destroyed by exposure to a variety toxic materials such as degradative enzymes and reactive oxygen species. Neutrophilic inflammation is often accompanied by significant host tissue damage as neutrophil-derived toxic materials often leak into the surrounding tissue.
- Neutrophils are derived from Hematopoietic Stem Cells within the bone marrow. Refer to Hematopoiesis for a description of neutrophil development.
- Neutrophils possess highly lobulated nuclei, characteristically with four to five separate lobes, justifying their classification as PMNs (PolyMorphoNuclear leukocytes). In addition, the Neutrophil cytoplasm possesses a variety of visible granules which represent lysosomes containing a variety of toxic and inflammatory mediators, justifying their classification as granulocytes.