Neutrophils

• Neutrophils are a type of Granulocyte (PMN)

They are phagocytic

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.

• 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.

destruction of bacteria by neutrophils.

 Neutrophils are distributed within the body in several discrete and highly dynamic compartments or pools (Figure 18-2). In the marrow, mitotically active myeloid progenitors mature over a period of 7 to 10 days to give rise to large numbers of neutrophils. Under steady-state conditions, most of these newly formed neutrophils die without ever being released into the blood, constituting a storage pool that can be called upon during times of increased need. Upon release from the marrow, neutrophils enter the circulating pool, the only pool that is measured clinically. On average, neutrophils circulate for less than 24 hours before migrating into tissues, where they may survive for up to 3 days. At any given time, roughly half of the neutrophils in the blood are adherent to vessel walls; these cells are referred to as the marginal pool. Finally, some circulating neutrophils are sequestered in the spleen. Normally, <5% of the neutrophils in the body are in the circulating pool, which turns over quickly. As a result, stimuli that alter the release of neutrophils from the marrow, neutrophil margination, or the migration of neutrophils into tissues can have rapid and sometimes profound effects on the peripheral blood neutrophil count.